JP5632199B2 - Method for producing silica composite particles - Google Patents

Description

  The present invention relates to a method for producing silica composite particles in which silica is composited with inorganic particles. More preferably, the present invention relates to the case where the inorganic particles are regenerated particles produced by dehydrating and heat-treating an object to be treated mainly using paper sludge.

  Conventionally, inorganic particles such as calcium carbonate, clay, and talc have been used as fillers and pigments for papermaking. However, in recent years, silica composite particles in which silica is combined with these inorganic particles have been developed. Yes.

  Specifically, for example, Patent Document 1 discloses a method for producing inorganic fine particles / silica composite particles, which is intended to improve paper bulkiness, whiteness, opacity, and prevention of paper strength reduction. This document describes the production of the inorganic fine particles / silica composite particles: “The inorganic fine particles are added to and dispersed in an alkali silicate aqueous solution to prepare a slurry, and then the temperature of the liquid is kept in the range of 60 to 100 ° C. while stirring with heating. Sulfuric acid is added to form a silica sol, and the pH of the final reaction solution is adjusted to the range of 8-11 ”.

  Further, the present applicant has disclosed a method for producing silica-coated regenerated particles that use regenerated particles in particular as inorganic particles. For example, in Patent Document 2, “in the deinking process of the used paper processing process for producing used paper pulp” Using the deinked floss discharged as the main raw material, through the dehydration process, the drying process, the firing process and the pulverization process, regenerated particles made into aggregates in the firing process are obtained, and the regenerated particles are suspended in an aqueous alkali silicate solution. And a mineral acid is added, and the periphery of the regenerated particles is coated with silica to obtain silica-coated regenerated particles.

  Silica composite particles obtained by these production methods are attracting attention because they have improved properties as fillers and pigments for papermaking, which were insufficient with conventional inorganic particles. In particular, according to the method using the regenerated particles disclosed by the present applicant, the problem of paper sludge disposal is solved at the same time, which leads to the solution of important problems related to environmental problems in the paper industry.

  However, all of the conventional methods for producing silica composite particles are so-called “batch type” in which the production of silica composite particles is repeated every predetermined amount, and not “continuous type” in which silica composite particles are produced continuously. When the silica composite particles are continuously produced, the production efficiency is naturally improved. However, for example, it becomes difficult to control the average particle size and particle size distribution of the silica composite particles, and the silica composite particles do not become homogeneous. . In other words, if it is simply produced continuously, the silica composite particles are not suitable for use as a paper filler or pigment. In addition, when the silica composite particles are continuously produced, the scale cannot be removed, and thus the problem may be further increased.

Japanese Patent No. 3898007 Japanese Patent No. 4087431

  The main problem to be solved by the present invention is that silica composite particles capable of continuously producing silica composite particles having a particle size, degree of wear, homogeneity, and oil absorption suitable for use as a filler or pigment for papermaking It is in providing the manufacturing method of.

The present invention that has solved this problem is as follows.
[Invention of Claim 1]
A method for producing silica composite particles in which silica is combined with the inorganic particles from inorganic particles, an aqueous alkali silicate solution, and a mineral acid,
While supplying the inorganic particles and the alkali silicate to the preceding tank, the slurry in which the inorganic particles in the preceding tank are dispersed flows from the preceding tank directly or through another tank to the subsequent tank,
In addition to adding the mineral acid to the slurry in the subsequent tank, the mineral acid is also added to the slurry in the preceding tank, and at least the polyacrylic acid sodium carbonate is used as the main agent in the slurry in the preceding tank. A silica composite particle is continuously produced by adding a dispersant.
A method for producing silica composite particles.

[Invention of Claim 2]
The total amount of the mineral acid, the amount of slurry passing through the trailing tank is pH7.0~8.5 to and the amount of mineral acid to the preceding added and 18-48 volume% of the total amount To
The method for producing silica composite particles according to claim 1.

[Invention of Claim 3]
The dispersant is added in a mass ratio of 1: 2 to 1: 4 in the preceding tank and the subsequent tank, and the total added amount is 0.05 with respect to 100 parts by mass of the inorganic particles in terms of solid content. To be added to 2.00 parts by mass,
The manufacturing method of the silica composite particle of Claim 1 or Claim 2.

[Invention of Claim 4]
As the inorganic particles,
Recycled particles having an average particle diameter of 1.4 μm or more obtained by dehydrating and heat-treating an object whose main raw material is papermaking sludge and a ratio of the particle diameter of 1 μm or less of 5% or more are used,
The manufacturing method of the silica composite particle of any one of Claims 1-3.

  As in the invention according to claim 1, the slurry in which the inorganic particles and the alkali silicate are supplied to the preceding tank, and the inorganic particles in the preceding tank are dispersed is directly from the preceding tank or through the other tanks. In addition to adding mineral acid to the slurry in the subsequent tank, the mineral acid is also added to the slurry in the preceding tank, and at least the polyacrylic acid soda is the main agent in the slurry in the preceding tank. By adding the dispersant, the generation of scale in the tank is efficiently suppressed, and the silica composite particles having a particle size, wear degree, homogeneity, and oil absorption suitable for use as a filler or pigment for papermaking Can be manufactured continuously.

  Further, as in the invention according to claim 2, the total addition amount of the mineral acid is set to an amount such that the slurry passed through the subsequent tank has a pH of 7.0 to 8.5, and the total amount of the mineral acid to be added in advance is totaled. By making it 18 to 48% of the addition amount, silica can be sufficiently combined on the surface of the inorganic particles, and the particle size distribution of the obtained silica composite particles can be sharpened.

  Furthermore, as in the invention according to claim 3, the dispersant is inorganic so that the added mass ratio of the preceding tank and the succeeding tank is 1: 2 to 1: 4, and the total addition amount is in terms of solid content. By adding 0.05 to 2.00 parts by mass with respect to 100 parts by mass of the particles, generation of scale can be surely prevented throughout the entire process. Silica composite particles more suitable as a pigment can be continuously produced.

  In addition, as in the invention according to claim 4, the ratio of the average particle size obtained by dehydrating and heat-treating an object whose main raw material is papermaking sludge as the inorganic particles is 1.4 μm or more and the particle size is 1 μm or less. By using regenerated particles having a particle size of 5% or more, the effect that the particle size distribution of the obtained silica composite particles can be sharpened on the small diameter side is surely exhibited.

It is a schematic diagram of a silica composite facility.

Next, the form for implementing this invention is demonstrated.
The manufacturing method of the silica composite particle of this form uses inorganic particles, alkali silicate aqueous solution, mineral acid and a dispersant as main raw materials, and combines silica with inorganic particles to form silica composite particles.

  The kind of inorganic particles that can be used as a raw material is not particularly limited. For example, known inorganic particles such as light calcium carbonate, heavy calcium carbonate, clay, talc, kaolin, calcined kaolin, titanium dioxide, aluminum hydroxide, Preferably, calcium carbonate, clay and talc, which are preferably used as fillers and pigments for papermaking, can be used.

  However, since the problem of paper sludge disposal and the like can be solved at the same time, it is more preferable to use regenerated particles made mainly from paper sludge. Therefore, in the following, after describing a method for combining silica with inorganic particles, a preferred embodiment of a method for producing regenerated particles will be described.

[Composite method of silica]
In the composite (manufacturing) method of silica of this embodiment, as shown in FIG. 1, first, inorganic particles S and alkali silicate K are supplied to the first tank 70A, which is the preceding tank, The slurry HA in which the inorganic particles S are dispersed is transferred from the first tank 70A to the second tank 70B, from the second tank 70B to the third tank 70C which is a subsequent tank, and from the third tank 70C to the second tank 70C. It shall flow to 4 tank 70D. In addition to adding the mineral acid R2 to the slurry HC in the third tank 30C, the mineral acid R1 is also added in advance to the slurry HA in the first tank 70A. Furthermore, dispersants B1 and B2 mainly composed of polyacrylic acid soda are added to the slurry HA in the first tank 70A as the preceding tank and the slurry HC in the third tank 70C as the succeeding tank, so that the silica composite particles Continuously manufacturing,
In this embodiment, the slurry HA in which the inorganic particles S are dispersed flows from the first tank 70A as the preceding tank to the third tank 70C as the subsequent tank through the second tank 70B as the other tank. Although other tanks are made into two tanks, three tanks or a plurality of more tanks, conversely, other tanks are not provided, but directly from the first tank 70A as the preceding tank. It can also flow into the third tank 70C. Further, a dispersant mainly composed of polyacrylic acid soda is added only to the slurry HA in the first tank 70A as the preceding tank, and not added to the slurry HC in the third tank 70C as the subsequent tank. Also, it can be added to the slurry HB in the second tank 70B and the slurry HD in the fourth tank 70D. Details will be described below.

<< First tank >>
In this embodiment, although not shown, the inorganic particles S and the alkali silicate K can be separately supplied to the first tank 70A, and stirred and mixed in the first tank 70A to form a slurry. However, as in the illustrated example, inorganic particles S, alkali silicate K (or an aqueous solution thereof), and water as appropriate are supplied to the mixing tank 90S preceding the first tank 70A, and stirring and mixing are performed in the mixing tank 90S. Then, it is preferable to supply the first tank 70A. As described above, when the inorganic particles S and the alkali silicate K are stirred and mixed in advance and then supplied to the first tank 70A, the inorganic particles S are more uniformly dispersed, so that the homogeneity of the manufactured silica composite particles is improved. .

  In this regard, normally, the dispersibility of the inorganic particles S can be enhanced by increasing the stirring strength of the slurry HA in the first tank 70A or by increasing the stirring time. However, in this embodiment, when the dispersibility of the inorganic particles S is increased by increasing the stirring strength or increasing the stirring time, the silica sol produced in the first tank 70A is suitable as described later. There is a possibility that it will not be. Therefore, it is preferable to increase the dispersibility of the inorganic particles S by stirring and mixing the inorganic particles S and the alkali silicate K in advance.

  In addition, although stirring and mixing of this inorganic particle S etc. can also be considered using an in-line mixer, it is more preferable to use mixing tank 90S like this form from a viewpoint of prevention of a scale.

(Alkali silicate)
The type of alkali silicate is not particularly limited. For example, sodium silicate (Na ₂ O.nSiO ₂ .nH ₂ O) such as sodium silicate glass (water glass), which is a liquid, powdered anhydride, or flaky sodium orthosilicate. ), Potassium silicate aqueous solution for general industrial use, potassium silicate (K ₂ O.nSiO ₂ ) such as high-purity potassium silicate used as a fluorescent material binder for cathode ray tubes, and the like can be used. However, it is preferable to use No. 3 water glass, which is a sodium silicate solution, because it is easily available and inexpensive.

The alkali silicate can be supplied as an aqueous solution, for example, and the silicic acid (SiO ₂ ) concentration of the aqueous alkali silicate solution is preferably 6 to 18 g / L, more preferably 8 to 16 g / L. It is particularly preferably 10 to 14 g / L.

  When the silicic acid concentration is less than 6 g / L, there is a possibility that the silica sol is not sufficiently generated in the third tank 70C, and silica is not complexed with some inorganic particles S, and the homogeneity of the produced silica complex particles is May be reduced. In this regard, when the production of the silica composite particles is performed batchwise as in the prior art, the amount of silicic acid can be ensured by increasing the mixing ratio of the aqueous alkali silicate solution. However, the manufacturing method according to the present embodiment is a continuous type in which silica composite particles are continuously manufactured, and the slurry HA mixed with alkali silicate is changed from the first tank 70A to the second tank 70B as needed. Flow from the tank 70B to the third tank 70C, and from the third tank 70C to the fourth tank 70D, and each separate reaction proceeds in each tank 70A, 70B, 70C, 70D. Therefore, a large increase in only one raw material may lead to a decrease in homogeneity of the silica composite particles to be produced, which is not preferable.

  On the other hand, when the silicic acid concentration exceeds 18 g / L, white carbon is generated instead of silica sol in the third tank 70C, and part of the inorganic particles S may be covered with white carbon in the fourth tank 70D. is there. If the inorganic particles S are coated with white carbon, for example, the properties of the inorganic particles S are not exhibited, and in particular, when the inorganic particles S are regenerated particles, the porous properties and optical properties of the regenerated particles are reduced. The characteristics and the like are not exhibited, and the advantage of using the regenerated particles is lost.

(Inorganic particles)
The kind of the inorganic particles S is as described above.
The inorganic particles S preferably have an average particle size of 1.4 to 3.2 μm, more preferably 1.7 to 3.0 μm, and particularly preferably 2.0 to 2.8 μm. .

  When the average particle diameter of the inorganic particles S is less than 1.4 μm, the small-diameter inorganic particles S in the second tank 70B are glued also by the manufacturing method of the present embodiment (the meaning of this “glue” will be described later). May be insufficient, and the particle size distribution of the silica composite particles to be produced may be broad on the small diameter side. On the other hand, if the average particle size of the inorganic particles S exceeds 3.2 μm, the average particle size of the silica composite particles to be produced becomes too large, which may be unsuitable for use as a filler or pigment for papermaking. .

  The volume average particle size of the inorganic particles S is determined by measuring the particle size distribution with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation), and the cumulative volume with respect to the volume of all particles. Is determined as the particle diameter (d50) when the ratio is 50%. In preparing the measurement sample, the inorganic particles S are added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed by ultrasonic waves for 1 minute.

  In the inorganic particles S, the mass ratio of the small-sized inorganic particles S having a particle diameter of 1 μm or less is preferably 5 to 20%, more preferably 5 to 15%, and particularly preferably 5 to 10%. preferable.

  When the mass ratio of the small-diameter inorganic particles S having a particle diameter of 1 μm or less is less than 5%, that is, when the small-diameter inorganic particles S are originally small, the gluing function of the small-diameter inorganic particles S by the manufacturing method of this embodiment is effective. It may not be demonstrated. On the other hand, when the mass ratio of the small-diameter inorganic particles S having a particle diameter of 1 μm or less exceeds 20%, the paste of the small-diameter inorganic particles S is insufficient even by the manufacturing method of this embodiment, The particle size distribution may be broad on the small diameter side.

  The mass ratio of the inorganic particles S having a particle size of 1 μm or less is determined by measuring the particle size distribution with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation). As a cumulative volume of particles having a particle diameter of 1 μm or less. In preparing the measurement sample, the inorganic particles S are added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed by ultrasonic waves for 1 minute.

  The concentration of the inorganic particles S in the slurry HA before adding the mineral acid R1 and the dispersant B1 is preferably 95 to 125 g / L, more preferably 100 to 120 g / L. It is particularly preferably 115 g / L.

  When the concentration of the inorganic particles S is less than 95 g / L, the productivity is poor, and there is a possibility that the gist of the present embodiment aiming at improving the productivity as a continuous type is diminished. On the other hand, when the concentration of the inorganic particles S exceeds 125 g / L, the viscosity of the slurries HA, HB, HC, and HD in the tanks 70A, 70B, 70C, and 70D may increase and the dispersibility of the inorganic particles S may decrease. There is a possibility that the homogeneity of the produced silica composite particles may be lowered. In particular, when the inorganic particles S are regenerated particles, the regenerated particles are extremely porous, so that the viscosity of the slurry HA, HB, HC, HD is more likely to increase, and the homogeneity of the silica composite particles to be produced May be more reduced.

(Shimizu)
In this embodiment, separately from the mixed liquid of inorganic particles S and alkali silicate K, fresh water W is heated through an inline mixer 90W or the like, preferably with steam J or the like, and supplied to the first tank 70A. By supplying the fresh water W, the concentration and temperature of the inorganic particles S of the slurry HA in the first tank 70A can be adjusted.

(Mineral acid)
The mineral acid R1 is added in advance to the slurry HA in the first tank 70A. This mineral acid R1 is added separately from the mineral acid R2 added to the slurry HC in the third tank 70C, and the technical meaning is different from the addition of the mineral acid R2.

  That is, it is the same in that the silica sol is generated by adding the mineral acids R1 and R2 in both the first tank (preceding tank) 70A and the third tank (following tank) 70C. However, the silica sol generated in the third tank 70C is a silica sol for combining with the inorganic particles S in the fourth tank 70D. On the other hand, the silica sol generated in the first tank 70A has the so-called small-diameter inorganic particles S for adhering the small-diameter inorganic particles S to the other inorganic particles S in the second tank 70B. This is a silica sol for gluing (gluing function). Therefore, the characteristics required for each silica sol are different, and the addition conditions of the mineral acids R1 and R2 are also different. That is, the mineral acid R1 and the mineral acid R2 are added separately in a plurality of stages in order to uniformly disperse the mineral acids R1, R2 in the slurry HA, HB, HC, HD. Is different.

  In addition, regarding the addition of the mineral acid R1, the expression “preceding” is used, but this does not mean an auxiliary addition to the mineral acid R2, but prior to the composite of the silica by the addition of the mineral acid R2, the inorganic particles S It means to add in advance to make the particle diameter uniform.

  The kind of mineral acid R1 is not particularly limited, and for example, a dilute solution of mineral acid such as dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and the like can be used. However, it is preferable to use dilute sulfuric acid as the mineral acid R1 from the viewpoints of price and handling properties.

  The concentration of the mineral acid R1 is preferably 0.50 to 4.00 mol / L (1 to 8N (normality)), and more preferably 1.00 to 3.00 mol / L (2 to 6N). It is preferably 1.75 to 2.25 mol / L (3.5 to 4.5 N).

  If the concentration of the mineral acid R1 is less than 0.50 mol / L, the proportion of silica sol that does not grow to a sufficient length increases, so that the function of gluing the small-diameter inorganic particles S may not be sufficiently exhibited in the second tank 70B. There is a possibility that the particle size distribution of the produced silica composite particles becomes broad on the small diameter side. In particular, the production method of the present embodiment is a continuous method for continuously producing silica composite particles, and the slurry HA to which the mineral acid R1 has been added flows from the first tank 70A to the second tank 70B as needed. Therefore, it is not suitable for making the silica sol grow to a sufficient length by lengthening the reaction time.

  On the other hand, when the concentration of the mineral acid R1 exceeds 4.00 mol / L, the dispersibility of the mineral acid R1 is deteriorated, so that the length of the generated silica sol becomes nonuniform, and the particle diameter of the silica composite particles to be produced Distribution may be broad. Specifically, if there is a silica sol that does not grow to a sufficient length, the paste of the small-diameter inorganic particles S in the second tank 70B becomes insufficient, and the particle size distribution of the manufactured silica composite particles There is a possibility of broadening on the small diameter side. On the other hand, if there is a silica sol grown to a length longer than necessary, this silica sol may cause the gluing effect of the average diameter inorganic particles S and the large diameter inorganic particles S in the second tank 70B. There is a possibility that the particle size distribution of the produced silica composite particles becomes broad on the large diameter side.

  In this respect, the silica sol grown to an unnecessarily long length can be shortened by vigorous stirring, but if vigorously stirred, it may be shortened to other silica sols. The shortening of the other silica sol is the same as the increase in the proportion of silica sol that does not grow to a sufficient length, and accordingly, the paste of the small-diameter inorganic particles S in the second tank 70B becomes insufficient. There is a possibility that the particle size distribution of the produced silica composite particles becomes broad on the small diameter side.

  Further, when the concentration of the mineral acid R1 is higher, the silica sol is generated earlier. When the dispersibility of the mineral acid R1 is poor, the silica sol is generated earlier in the portion having a high concentration in the slurry HA. There is a possibility that the gluing of the small-diameter inorganic particles S will start in the first tank 70A. Therefore, when the concentration of the mineral acid R1 exceeds 4.00 mol / L, the silica sol is generated in the first tank 70A, and the small-diameter inorganic particles S are glued in the second tank 70B. The purpose of this embodiment, which attempts to sharpen the particle size distribution, may be reduced.

  Here, in order to make the progress of the reaction more uniform, the mineral acid R1 can be added not from one place as in the illustrated example, but from two places, three places or more. However, in this embodiment, the inorganic particles S are dispersed in the slurry HA prior to the addition of the mineral acid R1, and the inorganic particles S suppress the generation rate of the silica sol, so that the apparatus structure is not complicated. From this point of view, the addition position of the mineral acid R1 may be one.

Silica is generally roughly classified into silicic anhydride (SiO ₂ ) and hydrated (hydrous) silicic acid (SiO ₂ .nH ₂ O), and the silica sol produced in this embodiment is mainly hydrous silicic acid sol. It is thought that. However, this is not to deny that other silicate sols are produced. Silica sol is generally considered to be in the form of particles having a particle diameter of 10 to 20 nm, but these particles exist in a chained state. Therefore, in this specification, the length of this chain is expressed as the length of the silica sol.

  The addition amount of the mineral acid R1 is not particularly limited, but the slurry that has passed through the third tank 70C, that is, the fourth tank 70D is adjusted by adjusting the total addition amount with the mineral acid R2 added in the third tank 70C. The amount of the slurry HD is preferably pH 7.0 to 8.5, more preferably pH 7.5 to 8.5, and pH 7.8 to 8.2. Is particularly preferred.

  If the total addition amount of the mineral acid R1 and the mineral acid R2 is an amount whose pH is lower than 7.0, white carbon is generated in the third tank 70C instead of silica sol, and inorganic particles are generated in the fourth tank 70D. S may be covered with white carbon. If the inorganic particles S are coated with white carbon, the properties of the inorganic particles S will not be exhibited. In particular, when the inorganic particles S are regenerated particles, the porous properties and optical properties of the regenerated particles are exhibited. And the advantage of using regenerated particles is lost. Further, when the total addition amount of the mineral acid R1 and the mineral acid R2 is an amount where the pH is less than 7.0, when the inorganic particles S are regenerated particles, calcium as a constituent component of the regenerated particles is converted to calcium sulfate. It is easy to change, for example, the volume average particle diameter of the silica composite particle manufactured may fall too much, or a shape may become non-uniform | heterogenous. If the volume average particle diameter of the silica composite particles is excessively decreased or the shape becomes nonuniform, for example, when used as a paper filler, it may lead to a decrease in yield, generation of paper dust, a decrease in opacity, etc. there is a possibility.

  On the other hand, if the total addition amount of the mineral acid R1 and the mineral acid R2 is an amount where the pH exceeds 8.5, the third tank 70C is usually used depending on the addition ratio of the mineral acid R1 and the mineral acid R2. In the fourth tank 70D, there is a possibility that the composite of silica with the inorganic particles S becomes insufficient in the fourth tank 70D.

  On the other hand, in relation to limiting the total amount of mineral acid R1 and mineral acid R2 to the above pH range, the amount of mineral acid R1 is preferably 18 to 48% by volume of the total amount added. It is more preferable to set it to -43 volume%, and it is especially preferable to set it as 28-38 volume%.

  When the addition amount of the mineral acid R1 is less than 18% by volume of the total addition amount, the silica sol is not sufficiently generated in the first tank 70A, and the function of gluing the small-diameter inorganic particles S is sufficiently exhibited in the second tank 70B. There is a possibility that the particle size distribution of the silica composite particles produced may be broad on the small diameter side.

  On the other hand, when the addition amount of the mineral acid R1 exceeds 48% by volume of the total addition amount, the silica sol is not sufficiently generated in the third tank 70C, and the composite of silica with the inorganic particles S is sufficiently generated in the fourth tank 70D. May not be done. When the composite of silica is insufficient, particularly when the inorganic particles S are regenerated particles, for example, the degree of wire wear becomes high, and the properties as a paper filler or pigment may be inferior.

  The addition rate of the mineral acid R1 is not particularly limited, and the total addition amount of the mineral acid R1 and the mineral acid R2 (the pH of the slurry HD in the fourth tank 70D), the addition ratio of the mineral acid R1, It can be appropriately determined from the passage time of slurry HA, which will be described later.

(Dispersant)
To the slurry HA in the first tank 70A, together with the mineral acid R1, a dispersant B1 mainly composed of polyacrylic acid soda is added. The addition of the dispersant B1 prevents the generation of scale due to the addition of the mineral acid R1. In addition, when the mineral acid R2 is also added to the slurry HC in the third tank (following tank) 70C as in the present embodiment, in the third tank 70C, more than in the first tank 70A. A large amount of scale is generated. However, in the first tank 70A, it is necessary to generate a silica sol for gluing the small-diameter inorganic particles S. In this generation, generation of scale becomes a big problem. Therefore, it is necessary to add the dispersant to at least the slurry HA in the first tank 70A, and it is more preferable if it is added to the slurry HC in the third tank 70C. Further, the dispersant can be added to, for example, the slurry HB in the second tank 70B and the slurry HD in the fourth tank 70D, and further added to the mixing tank 90S preceding the first tank 70A. You can also. In addition, in this form, a main ingredient means the component which occupies 50 mass% or more.

  The type of dispersant B1 mainly composed of polyacrylic acid soda is not particularly limited, and examples include Aron T540 (manufactured by Toa Gosei), Poise 520 (manufactured by Kao), SN Dispersant 5040 (manufactured by San Nopco), and the like. it can. However, it is preferable to use a dispersant mainly composed of polycarboxylic acid soda, and it is more preferable to use a dispersant mainly composed of polycarboxylic acid soda having a strong anionic property and many carboxylic acid groups. Examples of the dispersant mainly composed of polycarboxylic acid soda having many carboxylic acid groups include Poise 520 (manufactured by Kao), SN Dispersant 5040 (manufactured by San Nopco), and the like.

  Dispersing agents B1 and B2 have a total addition amount of 100 parts by mass of inorganic particles (S) in terms of solid content so that the addition mass ratio of the preceding tank and the subsequent tank is 1: 2 to 1: 4. It is preferable to add so that it may become 0.05-2.00 mass parts. Moreover, it is preferable that especially addition amount of dispersing agent B1 shall be 0.013-0.66 mass part with respect to 100 mass parts of inorganic particles (S) in conversion of solid content, and 0.04-0.40. It is more preferable to set it as a mass part, and it is especially preferable to set it as 0.07-0.20 mass part. When the added amount of the dispersant B1 is less than 0.013 parts by mass, the cationic groups contained in the inorganic particles S and the acrylic acid groups such as carboxylic acid groups are aggregated to increase the viscosity of the slurry HA, HB, HC, HD. Therefore, there is a possibility that a scale is generated on the inner wall surface of each tank 70A, 70B, 70C, 70D. Further, the aggregation of the inorganic particles S and the dispersant B1 may cause the particle size distribution of the finally obtained silica composite particles to become broad on the large diameter side.

  On the other hand, when the added amount of the dispersant B1 exceeds 0.66 parts by mass, the electrolyte concentration in the slurry HA, HB, HC, HD increases and the slurry HA, HB, HC, HD increases in viscosity. A scale may generate | occur | produce on the inner wall face of each tank 70A, 70B, 70C, 70D. In addition, when the obtained silica composite particles are used as a filler for papermaking, the yield may decrease due to the electrolyte present in excess.

(Stirring)
In order to further improve the homogeneity of the silica composite particles to be produced, it is preferable to stir the slurry HA in the first tank 70A. The strength of the stirring is not particularly limited, but the stirring is preferably performed so that the Reynolds number (Re) of the slurry HA is 4000 to 16000, and the stirring is performed so as to be 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

  When stirring so that the Reynolds number is less than 4000, the length of the generated silica sol becomes non-uniform, and the particle size distribution of the manufactured silica composite particles may become broad. Specifically, if there is a silica sol that does not grow to a sufficient length, the paste of the small-diameter inorganic particles S in the second tank 70B becomes insufficient, and the particle size distribution of the manufactured silica composite particles There is a possibility of broadening on the small diameter side. On the other hand, if there is a silica sol grown to a length longer than necessary, this silica sol may cause the gluing effect of the average diameter inorganic particles S and the large diameter inorganic particles S in the second tank 70B. There is a possibility that the particle size distribution of the produced silica composite particles becomes broad on the large diameter side.

  In addition, when the concentration of the mineral acid R1 is higher, the silica sol is generated earlier. When the Reynolds number is less than 4000, the mineral acid R1 has poor dispersibility and is early in the high concentration portion of the slurry HA. There is a possibility that the silica sol is generated and the silica sol starts to paste the small-diameter inorganic particles S in the first tank 70A. Accordingly, when stirring is performed so that the Reynolds number is less than 4000, the generation of silica sol is performed in the first tank 70A, and the small-diameter inorganic particles S are glued in the second tank 70B. There is a possibility that the gist of the present embodiment which attempts to sharpen the diameter distribution is diminished. Furthermore, if stirring is performed so that the Reynolds number is less than 4000, the dispersant B1 is not sufficiently dispersed, and there is a possibility that a scale is partially generated.

  On the other hand, when the stirring is performed so that the Reynolds number exceeds 16000, the silica sol grown to a sufficient length is shortened, and a state similar to an increase in the proportion of silica sol that does not grow to a sufficient length is obtained. Therefore, the paste of the small-diameter inorganic particles S in the second tank 70B is insufficient, and the particle size distribution of the manufactured silica composite particles may be broad on the small-diameter side.

Here, the Reynolds number (Re) is a dimensionless number indicating the nature of the flow of the slurry HA in the first tank 70A, and is represented by the following equation (1).
Re = ρvd / μ (1)
In the formula (1), “ρ” is the density (g / cm ³ ) of the slurry HA, “v” is the flow velocity (cm / s) of the slurry HA, and “d” is the diameter (cm) of the first tank 70A. ), “Μ” is the viscosity coefficient (Ns / cm ³ ) of the slurry HA.

  The method for adjusting the Reynolds number to the above range is not particularly limited. For example, as can be seen from the above formula (1), the Reynolds number can also be adjusted by changing the diameter of the first tank 70A. However, since the diameter is usually determined from the viewpoint of processing efficiency and cannot be changed for adjusting the Reynolds number, the stirring means 80A provided with stirring blades and the like in the illustrated example is provided in the first tank 70A. It is preferable to adjust the Reynolds number by providing and stirring the slurry HA by the stirring means 80A.

  In adjusting the Reynolds number using the stirring means 80A in this way, for example, the stirring blades can be reversed as appropriate, and in order to enhance the stirring effect of the stirring means 80A, the first tank 70A A baffle plate can be attached to the inner wall.

(Passing time)
In relation to setting the Reynolds number of the slurry HA in the first tank 70A to 4000 to 16000, the passage time of the slurry HA in the first tank 70A is preferably 2 to 20 minutes, and 4 to 18 More preferably, the time is more preferably 8 to 12 minutes.

  If the passage time of the slurry HA is less than 2 minutes, the proportion of silica sol that does not grow to a sufficient length increases, so that the small-diameter inorganic particles S may not be sufficiently glued in the second tank 70B, and are produced. There is a possibility that the particle size distribution of the silica composite particles becomes broad on the small diameter side.

  In this regard, when the passage time is less than 2 minutes, even if the concentration of the mineral acid R1 is increased, the improvement in the stirring strength is limited as described above, so the silica sol only grows unevenly. It is difficult to reduce the proportion of silica sol that does not grow to a sufficient length.

  On the other hand, even if the passage time of the slurry HA exceeds 20 minutes, the treatment efficiency is lowered, and it is not useful for the generation and growth of silica sol. On the other hand, when the passage time of the slurry HA exceeds 20 minutes, the pasting of the small-diameter inorganic particles S may start in the first tank 70A and the progress of the reaction may not be uniform. The particle size distribution may not be sharp.

  Here, the passage time of the slurry HA is a calculated time from the addition of the mineral acid R1 to the outflow from the first tank 70A, and does not include the time before the mineral acid R1 is added.

(temperature)
The temperature of the slurry HA in the first tank 70A is not particularly limited, but is preferably 50 to 100 ° C, more preferably 70 to 100 ° C, and particularly preferably 90 to 100 ° C.

  The temperature of the slurry HA affects the generation / growth, strength, etc. of the silica sol. When the temperature of the slurry HA is lower than 50 ° C., the generation / growth of the silica sol becomes slow, and the ratio of the silica sol that does not grow to a sufficient length There is a possibility of increase. As a result, the small-sized inorganic particles S may not be sufficiently glued in the second tank 70B, and the particle size distribution of the manufactured silica composite particles may be broad.

  In this respect, the manufacturing method of the present embodiment is a continuous type in which silica composite particles are continuously manufactured, and the slurry HA flows from the first tank 70A to the second tank 70B as needed. Therefore, it is not suitable for increasing the reaction time to grow the silica sol to a sufficient length. Further, if the silica sol does not grow to a sufficient length in the first tank 70A, white carbon may be generated instead of silica in the second tank 70B having a long passage time. Not only the pasting of the particles S does not proceed, but also a part of the inorganic particles S may be covered with white carbon. If the inorganic particles S are covered with white carbon in the second tank 70B, the silica composite in the fourth tank 70D may not sufficiently advance. In particular, when the inorganic particles S are regenerated particles, the porous characteristics and optical characteristics of the regenerated particles are not exhibited, and the advantage of using the regenerated particles is lost.

  On the other hand, if the temperature of the slurry HA exceeds 100 ° C., it becomes necessary to use an autoclave or the like, which complicates the equipment. Further, if the temperature of the slurry HA exceeds 100 ° C., the heat energy is wasted and the liquid level fluctuates due to the boiling of the slurry HA. Therefore, even if the dispersant B1 is added, the inner wall surface of the first tank 70A There is a possibility that scale will adhere to the surface. In addition, since the concentration of the slurry HA increases due to evaporation of moisture, the viscosity increases, which may result in poor stirring due to thickening.

  In adjusting the temperature of the slurry HA, for example, a heating facility may be provided in the first tank 70A and the slurry HA in the first tank 70A may be directly heated. It is preferable that the fresh water W is heated by steam J or the like and supplied into the first tank 70A. In this embodiment, since uniform dispersion of various raw materials is aimed at, according to the method of heating and supplying the fresh water W, the whole slurry HA is necessarily heated uniformly.

  Although not shown, since the dispersibility of the inorganic particles S is improved when the temperature of the slurry is increased, it is also a preferable mode to warm the alkali silicate K (solution).

As the steam J, a known heat source can be used, but by using raw steam (for example, 13 kg / m ² , 120 ° C.) in the factory, energy can be effectively used.

  Here, the temperature of the slurry HA is the temperature of the slurry HA existing in the center of the bottom surface of the first tank 70A.

(Slurry transfer)
The method of flowing (moving) the slurry HA in the first tank 70A to the second tank 70B is not particularly limited. For example, a pipe communicating with the first tank 70A and the second tank 70B is provided, The slurry HA can be moved through this pipe.

  However, it is preferable that the slurry HA in the first tank 70A is overflowed and moved into the second tank 70B as in the illustrated example. In the illustrated example, a partition wall 71A that does not reach the bottom surface is provided in the first tank 70A, and various materials (inorganic particles S, alkali silicate K, mineral acid R1, dispersion dispersed in the first tank 70A) are provided. The agent B1, fresh water W) descends in the first tank 70A as the slurry HA, dives through the partition wall 71A, rises, overflows, and is moved to the second tank 70B. According to the form in which the slurry HA is moved through the pipe, there is a possibility that the problem of scale, unintended growth of the silica sol, pasting of the small-diameter inorganic particles S, etc. may proceed, but according to the form of the illustrated example, such possibility is reduced. .

《Second tank》
In this embodiment, the slurry HB in the second tank 70B is only the one in which the slurry HA in the first tank 70A has flowed (moved), and newly inorganic particles S, alkali silicate K, mineral acid. No dispersant or the like is added.

  In the second tank 70B, the small-diameter inorganic particles S are glued to the other inorganic particles S by the silica sol generated and grown in the first tank 70A. The distribution becomes sharp on the small diameter side.

  Although this second tank 70B can be omitted, from the viewpoint of aligning the progress of the reaction such as the generation of silica sol and the pasting of the small-diameter inorganic particles S, the second tank 70B is not used as in this embodiment. It is preferable to provide it.

(Stirring)
In this embodiment, in order to advance the gluing of the small-diameter inorganic particles S uniformly, it is preferable to stir the slurry HB as in the first tank 70A. The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HB is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

  When stirring is performed so that the Reynolds number is less than 4000, the pasting of the small-diameter inorganic particles S proceeds non-uniformly, and the particle size distribution of the manufactured silica composite particles may be broad on the small-diameter side.

  On the other hand, if the stirring is performed so that the Reynolds number exceeds 16000, the silica sol grown to a sufficient length is shortened, and the proportion of the silica sol that is not a sufficient length increases. There is a possibility that the pasting of S becomes insufficient, and the particle size distribution of the produced silica composite particles becomes broad on the small diameter side. In addition, when stirring is performed so that the Reynolds number exceeds 16000, normal inorganic particles S and small-diameter inorganic particles S once glued to large-diameter inorganic particles S may be redispersed. There is a possibility that the particle size distribution of the silica composite particles is broad on the small diameter side.

Here, the Reynolds number is a dimensionless number indicating the nature of the flow of the slurry HB in the second tank 70B, and is represented by the above-described equation (1).
However, in the second tank 70B, “ρ” is the density of the slurry HB (g / cm ³ ), “v” is the flow velocity (cm / s) of the slurry HB, and “d” is the diameter of the second tank 70B ( cm), “μ” is the viscosity coefficient (Ns / cm ³ ) of the slurry HB.

  The method for adjusting the Reynolds number to the above range is not particularly limited. For example, as can be seen from the above formula (1), the Reynolds number can be adjusted by changing the diameter of the second tank 70B. However, since the diameter is usually determined from the viewpoint of the processing efficiency and the passage time ratio between the first tank 70A and the second tank 70B and cannot be changed for Reynolds number adjustment, As described above, it is preferable to adjust the Reynolds number by providing stirring means 80B provided with stirring blades and the like in the second tank 70B, and stirring the slurry HB with the stirring means 80B.

  The stirring means 80B may be the same as the stirring means 80A in the first tank 70A, but the size and shape are appropriately different according to the capacity and shape of the second tank 70B. Is preferred.

  In adjusting the Reynolds number using the stirring means 80B, for example, the stirring blades can be appropriately reversed, and in order to enhance the stirring effect by the stirring means 80B, the inner wall of the second tank 70B is obstructed. You can also attach a plate.

(Passing time)
In the first tank 70A, the slurry HA is agitated so that the Reynolds number is 4000 to 16000 while flowing so that the passage time is 2 to 20 minutes. The passing time of the slurry HB is preferably adjusted to be 20 to 50 minutes, more preferably adjusted to be 25 to 45 minutes, and particularly preferably adjusted to be 30 to 40 minutes. .

  When the passing time of the slurry HB is less than 20 minutes, the pasting of the small-diameter inorganic particles S does not sufficiently proceed, and the particle size distribution of the manufactured silica composite particles may be broad on the small-diameter side. On the other hand, even if the passage time of the slurry HB exceeds 50 minutes, the slurry HA is stirred in the first tank 70A so that the Reynolds number is 4000 to 16000, and the passage time is 2 to 20 minutes. In the relationship with the silica sol produced and grown as a product, the pasting of the further small-diameter inorganic particles S does not proceed, and the processing efficiency may decrease.

  Here, the passage time of the slurry HB is a calculated time from when the slurry HB (HA) flows into the second tank 70B until it flows out into the third tank 70C.

(temperature)
Although the temperature of the slurry HB in the 2nd tank 70B is not specifically limited, Preferably it is 50-100 degreeC, More preferably, it is 70-100 degreeC, Most preferably, it is 90-100 degreeC.

  The temperature of the slurry HB affects the viscosity of the slurry HB. When the temperature of the slurry HB is below 50 ° C., the dispersibility of the small-diameter inorganic particles S deteriorates. This may be insufficient, and the particle size distribution of the produced silica composite particles may be broad on the small diameter side. In this regard, if the stirring strength is increased to improve the dispersibility, the normal inorganic particles S and the small-diameter inorganic particles S glued to the large-diameter inorganic particles S may be redispersed.

  On the other hand, if the temperature of the slurry HB exceeds 100 ° C., an autoclave or the like must be used, so that the equipment becomes complicated. Further, when the temperature of the slurry HB exceeds 100 ° C., the heat energy is wasted and the liquid level fluctuates due to the boiling of the slurry HB, so that the dispersant B1 is added to the slurry HA in the first tank 70A. Even so, the scale may adhere to the inner wall surface of the second tank 70B. In addition, since the concentration of the slurry HB is increased by evaporation of moisture, the viscosity is increased, and there is a possibility of poor stirring due to this thickening.

  Here, the temperature of the slurry HB is the temperature of the slurry HB present in the center of the bottom surface of the second tank 70B.

  In adjusting the temperature of the slurry HB, for example, a heating facility may be provided in the second tank 70B, and the slurry HB in the second tank 70B may be directly heated. However, if the first tank 70A and the second tank 70B are made of a heat-insulating material, it is usually sufficient to adjust the temperature of the slurry HA in the first tank 70A. There is no need to do it.

  Although not shown, the temperature of the second tank 70B can be adjusted by supplying fresh water heated by steam or the like to the slurry HB, as in the case of the first tank 70A.

(Slurry transfer)
The method of flowing (moving) the slurry HB in the second tank 70B to the third tank 70C is not particularly limited. For example, a pipe communicating with the second tank 70B and the third tank 70C is provided. The slurry HB can be moved through this pipe.

  However, as in the illustrated example, it is preferable that the slurry HB in the second tank 70B is overflowed and moved into the third tank 70C, as in the first tank 70A. In the illustrated example, a partition wall 71B that does not reach the bottom surface is provided in the second tank 70B, and the slurry HB (HA) supplied into the second tank 70B descends in the second tank 70B, and the partition wall After diving 71B, it rises, overflows and is moved to the third tank 70C.

  In this respect, according to the form in which the slurry HB is moved through the pipe, there is a possibility of a problem of scale and unintended dispersion of the small-diameter inorganic particles S, but according to the form of the illustrated example, such a possibility is reduced.

《Third tank》
Dispersant B2 mainly composed of mineral acid R2 and polyacrylic acid soda is added to slurry HC in third tank 70C. Addition of the mineral acid R2 produces a silica sol as in the first tank 70A. However, the silica sol is a silica sol for compounding with the inorganic particles S in the fourth tank 70D. In order to paste the small-diameter inorganic particles S to the other inorganic particles S in the second tank 70B, the first sol The technical meaning is different from that of the silica sol produced in the tank 70A. Therefore, as will be described below, the characteristics required for the silica sol are different, and as a result, the conditions for adding the mineral acid R2 are different. Moreover, generation | occurrence | production of the scale in the 3rd tank 70C is reliably prevented by addition of the dispersing agent B2.

(Mineral acid)
The kind of the mineral acid R2 is not particularly limited, and for example, a dilute solution of mineral acid such as dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and the like can be used. The mineral acid R2 may be the same type as the mineral acid R1 used in the first tank 70A or may be a different type. However, from the viewpoint of the stability of the treatment, the same kind as that of the mineral acid R1 is preferable, and from the viewpoint of price, handling property, etc., it is preferable to use dilute sulfuric acid as the mineral acid R2.

  The concentration of the mineral acid R2 is preferably 0.50 to 4.00 mol / L (1 to 8N (normality)), more preferably 1.00 to 3.00 mol / L (2 to 6N), and particularly preferably 1 .75 to 2.25 mol / L (3.5 to 4.5 N).

  When the concentration of the mineral acid R2 is less than 0.50 mol / L, the silica sol is not sufficiently generated, and thus there is a possibility that the composite of silica with the inorganic particles S in the fourth tank 70D may be insufficient. The silica composite particles may become heterogeneous. In particular, the manufacturing method of the present embodiment is a continuous type in which silica composite particles are continuously manufactured, and the slurry HC to which the mineral acid R2 is added flows from the third tank 70C to the fourth tank 70D as needed. Therefore, it is not suitable for increasing the reaction time to produce silica sol.

  On the other hand, when the concentration of the mineral acid R2 exceeds 4.00 mol / L, the dispersibility of the mineral acid R2 is deteriorated, so that the generation of the silica sol becomes non-uniform and the homogeneity of the produced silica composite particles may be lowered. There is sex. Further, when the concentration of the mineral acid R2 is higher, the silica sol is generated earlier. When the dispersibility of the mineral acid R2 is poor, the silica sol is generated earlier at the portion where the concentration in the slurry HC is higher. In the third tank 70C, there is a possibility that the composite of silica with the inorganic particles S proceeds. Therefore, when the concentration of the mineral acid R2 exceeds 4.00 mol / L, the generation of silica sol is performed in the third tank 70C, and the composite of silica with the inorganic particles S is performed in the fourth tank 70D. The purpose of this embodiment, which attempts to sharpen the particle size distribution, may be reduced.

  Here, in order to further align the progress of the reaction, the mineral acid R2 can be added from two, three, or more than one place as shown in the illustrated example. However, in this embodiment, prior to the addition of the mineral acid R2, the inorganic particles S are dispersed in the slurry HC, and the inorganic particles S have a small diameter in the first tank 70A and the second tank 70B. The particle size distribution is made uniform by pasting of the inorganic particles S. Therefore, since the inorganic sol S can make the generation rate of the silica sol more uniform, the addition location of the mineral acid R2 can be made one. In addition, when mineral acid R2 is added from several places, naturally an apparatus structure will become complicated.

  The addition amount of the mineral acid R2 is not particularly limited, but the slurry HD in the fourth tank 70D has a pH of 7. by adjusting the total addition amount with the mineral acid R1 added in the first tank 70A as described above. The amount of 0 to 8.5 is preferable, the amount of pH 7.5 to 8.5 is more preferable, and the amount of pH 7.8 to 8.2 is particularly preferable.

  And in relation to restricting the total addition amount of the mineral acid R1 and the mineral acid R2 to the above pH range, the amount of the mineral acid R2 is preferably 52 to 82% by volume of the total addition amount, 57 It is more preferable to set it to -77 volume%, and it is especially preferable to set it as 62-72 volume%.

  When the addition ratio of the mineral acid R2 is less than 52% by volume, the silica sol is not sufficiently generated in the third tank 70C, and there is a possibility that the composite of silica with the inorganic particles S in the fourth tank 70D becomes insufficient. The silica composite particles to be produced may not be suitable for use as a paper filler or pigment. In particular, when the inorganic particles S are regenerated particles, if the composite of silica is insufficient, there is a possibility that the degree of wire wear will be high, and the regenerated particles are extremely porous. Peeling is likely to occur, and the silica may be peeled off by a shearing force applied during papermaking.

  On the other hand, when the addition ratio of the mineral acid R2 exceeds 82% by volume, the addition ratio of the mineral acid R1 in the first tank 70A decreases, and there is a possibility that the silica sol is not sufficiently generated and grown in the first tank 70A. There may be insufficient gluing of the small-diameter inorganic particles S in the second tank 70B.

(Dispersant)
In this embodiment, a dispersant B2 containing polyacrylic acid soda as a main agent is added to the slurry HC in the third tank 70C together with the mineral acid R2. Since the scale is easily generated when the mineral acid is added, the mineral acid is preferably added to the slurry HC in the third tank 70C rather than the slurry HB in the second tank 70B. Of course, a mineral acid can be added to both slurries HB and HC.

  The type of dispersant B2 mainly composed of polyacrylic acid soda is not particularly limited, and examples include Aron T540 (manufactured by Toa Gosei), Poise 520 (manufactured by Kao), SN Dispersant 5040 (manufactured by San Nopco), and the like. it can. However, it is preferable to use a dispersant mainly composed of polycarboxylic acid soda, and it is more preferable to use a dispersant mainly composed of polycarboxylic acid soda having a strong anionic property and many carboxylic acid groups. Examples of the dispersant mainly composed of polycarboxylic acid soda having many carboxylic acid groups include Poise 520 (manufactured by Kao), SN Dispersant 5040 (manufactured by San Nopco), and the like. The meaning of the main agent is as described above.

  The dispersant B2 may be the same type as the dispersant B1 used in the first tank 70A or may be a different type. However, from the viewpoint of processing stability, the same type as that of the dispersant B1 is preferable.

  The addition mass ratio of the dispersant B2 and the total addition amount with the dispersant B1 are as described above, but in terms of solid content, 0.027 to 1.34 mass with respect to 100 mass parts of the inorganic particles (S). Part is preferable, 0.08 to 0.80 part by mass is more preferable, and 0.14 to 0.40 part by mass is particularly preferable. When the addition amount of the dispersant B2 is less than 0.027 parts by mass, the scale preventing effect in the third tank 70C and the fourth tank 70D may not be sufficiently exhibited.

  On the other hand, when the addition amount of the dispersant B2 exceeds 0.40 parts by mass, the electrolyte concentration in the slurry HC and HD increases, and the slurry HC and HD increase in viscosity, and the third tank 70C and the fourth tank Scale may occur on the inner wall surface of the tank 70D. In addition, when the obtained silica composite particles are used as a filler for papermaking, the yield may decrease due to the electrolyte present in excess. In addition, generation | occurrence | production of the scale in this process affects the production | generation of the silica sol in the 3rd tank 70C, As a result, there exists a possibility that the composite of the silica with respect to the inorganic particle S in the 4th tank 70D may not be made uniform.

(Stirring)
In this embodiment, the slurry HC in the third tank 70C is agitated in the same manner as in the first tank 70A and the second tank 70B in order to further increase the homogeneity of the silica composite particles to be produced. It is preferable to do this.

  The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HC is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

Here, the Reynolds number is a dimensionless number indicating the nature of the flow of the slurry HC in the third tank 70C, and is represented by the above-described formula (1).
However, in the third tank 70C, “ρ” is the density (g / cm ³ ) of the slurry HC, “v” is the flow rate (cm / s) of the slurry HC, and “d” is the diameter of the third tank 70C ( cm), “μ” is the viscosity coefficient (Ns / cm ³ ) of the slurry HC.

  When stirring so that the Reynolds number is less than 4000, the generated silica sol becomes non-uniform, and the homogeneity of the finally obtained silica composite particles may be lowered. In addition, since the silica sol is generated in a shorter time as the concentration of the mineral acid R2 is higher, if the Reynolds number is less than 4000, the composite of silica may start partially in the third tank 70C. There is. Therefore, the purpose of this embodiment is to improve the homogeneity of the silica by generating the silica sol in the third tank 70C and combining the silica in the fourth tank 70D so as to align the progress of the reaction. May be killed. Furthermore, if stirring is performed so that the Reynolds number is less than 4000, the dispersant B2 may not be sufficiently dispersed, and partial scale generation may not be prevented.

  On the other hand, when stirring is performed so that the Reynolds number exceeds 16000, there is a possibility that the normal inorganic particles S or the small inorganic particles S glued to the large inorganic particles S may be redispersed. There is a possibility that the particle size distribution of the particles becomes broad on the small diameter side.

  In this embodiment, the method for adjusting the Reynolds number to the above range is not particularly limited. For example, as can be seen from the above formula (1), the Reynolds number can also be adjusted by changing the diameter of the third tank 70C. However, the diameter is usually determined from the viewpoint of the processing efficiency and the passage time ratio with the other tanks 70A, 70B, 70D, and cannot be changed for Reynolds number adjustment. Therefore, it is preferable to adjust the Reynolds number by providing the stirring means 80C provided with stirring blades and the like in the third tank 70C as in the illustrated example, and stirring the slurry HC by the stirring means 80C.

  The stirring means 80C can be the same as the stirring means 80A in the first tank 70A, but the size and shape are appropriately different according to the capacity and shape of the third tank 70C. Is preferred.

  In adjusting the Reynolds number using the stirring means 80C, for example, the stirring blades can be appropriately reversed, and the inner wall of the third tank 70C is obstructed in order to enhance the stirring effect of the stirring means 80C. You can also attach a plate.

(Passing time)
In relation to setting the Reynolds number of the slurry HC in the third tank 70C within the range of 4000 to 16000, the passing time of the slurry HC in the third tank 70C is adjusted to be 2 to 20 minutes. It is more preferable to adjust so that it may become 4-18 minutes, and it is especially preferable to adjust so that it may become 8-12 minutes.

  Here, the passage time of the slurry HC is a calculated time until the slurry HC flows out from the third tank 70C after the mineral acid R2 is added. In this embodiment, the slurry HC continuously flows from the second tank 70B into the third tank 70C, and the addition of the mineral acid R2 is also continuously performed. It is the same as the time from when (HB) flows in until it flows out.

  When the passing time of the slurry HA is less than 2 minutes, the silica sol is not uniformly generated, and thus the silica composite in the fourth tank 70D may be non-uniform. May be reduced.

  In addition, when the passage time is less than 2 minutes, even if the concentration of the mineral acid R2 is increased, the upper limit of the stirring strength is limited as described above, so that the generation of the silica sol may be uneven. .

  On the other hand, even if the passing time of the slurry HC exceeds 20 minutes, the processing efficiency is reduced, and it may not be useful for the generation of silica sol. On the contrary, when the passage time of the slurry HC exceeds 20 minutes, the composite of silica starts in the third tank 70C, and there is a possibility that the progress of the reaction is not uniform. As a result, the homogeneity of the silica composite particles produced may be reduced.

  In this embodiment, the addition rate of the mineral acid R2 is not particularly limited, and the total addition amount of the mineral acid R1 and the mineral acid R2 (pH of the slurry HD in the fourth tank 70D), the mineral acid R2 It can be appropriately determined from the addition ratio, the passage time of the slurry HC, and the like.

(temperature)
In this embodiment, the temperature of the slurry HC in the third tank 70C is not particularly limited, but is preferably 50 to 100 ° C, more preferably 70 to 100 ° C, and particularly preferably 80 to 100 ° C.

  The temperature of the slurry HC affects the generation and strength of the silica sol. If the temperature of the slurry HC is below 50 ° C., the generation of the silica sol tends to be slow and the strength tends to decrease. There is a possibility that the silica composite at 70D becomes insufficient, the homogeneity of the silica composite particles produced decreases, and is not suitable for use as a paper filler or pigment. On the other hand, when the temperature of the slurry HC is lower than 50 ° C., the viscosity of the slurry HC is increased, so that dispersibility is deteriorated. In this respect, the homogeneity of the silica composite particles produced may be lowered. Furthermore, the manufacturing method of the present embodiment is a continuous type in which silica composite particles are continuously manufactured, and the slurry HC flows from the third tank 70C to the fourth tank 70D at any time. It is not preferable to make the silica sol long enough to produce a sufficient amount of silica sol.

  On the other hand, if the temperature of the slurry HC exceeds 100 ° C., an autoclave or the like must be used, so that the equipment becomes complicated. Further, if the temperature of the slurry HC exceeds 100 ° C., the heat energy is wasted and the liquid level fluctuates due to the boiling of the slurry HC. Therefore, even if the dispersants B1 and B2 are added, the third tank 70C Scale may adhere to the inner wall. In addition, since the concentration of the slurry HC increases due to evaporation of moisture, the viscosity may increase, resulting in poor agitation due to thickening.

  Here, the temperature of the slurry HC is the temperature of the slurry HC present at the center of the bottom surface of the third tank 70C.

  In this embodiment, the temperature of the slurry HC can be adjusted by, for example, providing a heating facility in the third tank 70C and directly heating the slurry HC in the third tank 70C. However, if the first tank 70A, the second tank 70B, and the third tank 70C are formed of a heat-insulating material, the temperature of the slurry HA in the first tank 70A is usually only adjusted. The temperature of the slurry HC in the third tank 70C is in the above range, and there is no need to adjust the temperature.

  Although not shown, the temperature of the third tank 70C can also be adjusted by supplying fresh water heated by steam or the like to the slurry HC, as in the case of the first tank 70A.

(Slurry transfer)
In this embodiment, the method of flowing (moving) the slurry HC in the third tank 70C to the fourth tank 70D is not particularly limited. For example, the slurry HC communicates with the third tank 70C and the fourth tank 70D. A pipe is provided, and the slurry HC can be moved through the pipe.

  However, as in the first tank 70A and the second tank 70B, it is preferable that the slurry HC in the third tank 70C is overflowed and moved into the fourth tank 70D. In the illustrated example, a partition wall 71C that does not reach the bottom surface is provided in the third tank 70C, and the slurry HC (HB) supplied into the third tank 70C descends in the third tank 70C, After diving through the partition wall 71C, it rises, overflows and is moved to the fourth tank 70D.

  In this respect, according to the form in which the slurry HC is moved through the pipe, there is a possibility of scale problems, unintentional composite of silica with inorganic particles S, and redispersion of small-diameter inorganic particles S. According to the form to be made, this possibility can be reduced.

《Fourth tank》
In this embodiment, the slurry HD in the fourth tank 70D is only the one in which the slurry HC in the third tank 70C has flowed (moved), and newly contains inorganic particles S, alkali silicate K, mineral acid. No dispersant or the like is added.

  In this embodiment, silica is composited with the inorganic particles S by the silica sol generated in the third tank 70C to form silica composite particles.

(Agitation strength)
In the present embodiment, it is preferable to stir the slurry HD in the same manner as in the other tanks 70A, 70B, and 70C in order to advance the composite of silica uniformly. The strength of the stirring is not particularly limited, but stirring is preferably performed so that the Reynolds number (Re) of the slurry HD is 4000 to 16000, and stirring is preferably performed to 6000 to 14000. Is more preferable, and it is particularly preferable to stir so as to be 8000 to 12000.

Here, the Reynolds number is a dimensionless number indicating the nature of the flow of the slurry HD in the fourth tank 70D, and is represented by the above-described formula (1).
However, in the fourth tank 70D, “ρ” is the density of the slurry HD (g / cm ³ ), “v” is the flow velocity (cm / s) of the slurry HD, and “d” is the diameter of the fourth tank 70D ( cm), “μ” is the viscosity coefficient (Ns / cm ³ ) of the slurry HD.

  When stirring so that the Reynolds number is less than 4000, the composite of silica becomes non-uniform, and the homogeneity of the finally obtained silica composite particles may be lowered.

  On the other hand, when stirring is performed so that the Reynolds number exceeds 16000, the composite of silica is inhibited, and re-dispersion of the small-diameter inorganic particles S occurs, so that the particle size distribution of the manufactured silica composite particles becomes broad on the small-diameter side. There is a possibility.

  In this embodiment, the method for adjusting the Reynolds number to the above range is not particularly limited. For example, as can be seen from the above formula (1), the Reynolds number can also be adjusted by changing the diameter of the fourth tank 70D. However, the diameter is usually determined from the viewpoint of processing efficiency and the passage time ratio with the other tanks 70A, 70B, 70C, and cannot be changed for adjusting the Reynolds number. It is preferable to adjust the Reynolds number by providing stirring means 80D provided with blades and the like in the fourth tank 70D and stirring the slurry HD by the stirring means 80D.

  The stirring means 80D can be the same as the stirring means 80A in the first tank 70A, but the size and shape are appropriately different according to the capacity and shape of the fourth tank 70D. Is preferred.

  In adjusting the Reynolds number using the stirring means 80D, for example, the stirring blades can be appropriately reversed, and the inner wall of the fourth tank 70D is obstructed to enhance the stirring effect by the stirring means 80D. You can also attach a plate.

(Passing time)
In this embodiment, the total addition amount of the mineral acid R1 and the mineral acid R2 is limited to the aforementioned pH range, and the amount of the mineral acid R2 is 52 to 82% by volume of the total addition amount. The passage time of the slurry HD in the tank 70D of No. 4 is preferably adjusted to be 20 to 50 minutes, more preferably adjusted to be 25 to 45 minutes, and adjusted to be 30 to 40 minutes. It is particularly preferable to do this.

  Here, the passage time of the slurry HD is a calculated time from when the slurry HD (HC) flows into the fourth tank 70D to when it flows out.

  When the passing time of the slurry HD is less than 20 minutes, the silica composite does not proceed sufficiently, and thus the silica composite particles to be produced may be inhomogeneous, which is suitable for use as a paper filler or pigment. There is a possibility that it will not be. In particular, when the inorganic particles S are regenerated particles, if the composite of silica is insufficient, there is a possibility that the degree of wire wear will be high, and the regenerated particles are extremely porous. Peeling is likely to occur, and the silica may be peeled off by a shearing force applied during papermaking.

  On the other hand, even if the passing time of the slurry HD exceeds 50 minutes, the total addition amount of the mineral acid R1 and the mineral acid R2 is limited to the aforementioned pH range, and the amount of the mineral acid R2 is 52 to 82 volume of the total addition amount In the relationship with the silica sol produced as a percentage, the composite of silica does not progress, and the processing efficiency may decrease.

(temperature)
In this embodiment, the temperature of the slurry HD in the fourth tank 70D is not particularly limited, but is preferably 50 to 100 ° C, more preferably 60 to 100 ° C, and particularly preferably 70 to 100 ° C.

  The temperature of the slurry HD affects the viscosity of the slurry HD, and when the temperature of the slurry HD is lower than 50 ° C., the dispersibility of the silica sol deteriorates in particular, so that the composite of the silica (sol) does not proceed sufficiently. There is a possibility that the homogeneity of the silica composite particles to be produced is lowered and the silica composite particles are not suitable for use as a filler or pigment for papermaking. In particular, when the inorganic particles S are regenerated particles, if the composite of silica is insufficient, there is a possibility that the degree of wire wear will be high, and the regenerated particles are extremely porous. Peeling is likely to occur, and the silica may be peeled off by a shearing force applied during papermaking. In addition, when it is going to improve dispersibility by raising stirring intensity | strength, the normal small-diameter inorganic particle S may re-disperse.

  On the other hand, when the temperature of the slurry HD exceeds 100 ° C., an autoclave or the like must be used, so that the equipment becomes complicated. Further, if the temperature of the slurry HD exceeds 100 ° C., the heat energy is wasted and the liquid level fluctuates due to the boiling of the slurry HD, so even if the dispersants B1 and B2 are added, the fourth tank A scale may adhere to the inner wall surface of 70D. In addition, since the concentration of the slurry HD increases due to the evaporation of moisture, the viscosity may increase, resulting in poor stirring due to increased viscosity.

  The temperature of the slurry HD is preferably 5 to 10 ° C. higher than the temperature of the slurry HC in the third tank 70C. The treatment in the third tank 70C is generation of silica sol, while the treatment in the fourth tank 70D is a composite of silica with the inorganic particles S. From the viewpoint of this combination, it is preferable to lower the flow rate of the slurry HD in the fourth tank 70D, and the viscosity of the slurry HD is increased by relatively increasing the temperature of the slurry HD in relation to lowering the flow rate of the slurry HD. Is lowered. Thereby, the Reynolds number of the slurry HD can be maintained in the above-mentioned range.

  Here, the temperature of the slurry HD is the temperature of the slurry HD present in the center of the bottom surface of the fourth tank 70D.

  In this embodiment, the temperature of the slurry HD can be adjusted by, for example, providing a heating facility in the fourth tank 70D and directly heating the slurry HD in the fourth tank 70D. However, if each tank 70A, 70B, 70C, 70D is formed of a heat insulating material, it is usually sufficient to adjust the temperature of the slurry HA in the first tank 70A, and it is necessary to adjust the temperature in this embodiment. Will disappear.

  Although not shown, the temperature of the fourth tank 70D can also be adjusted by supplying fresh water heated by steam or the like to the slurry HD, as in the case of the first tank 70A.

(Slurry transfer)
In this embodiment, the method of moving the slurry HD in the fourth tank 70D from the fourth tank 70D to other equipment such as a dehydrator is not particularly limited. The equipment can be communicated with a pipe or the like, and the slurry HD can be moved through the pipe.

  However, similar to the movement from the first tank 70A to the second tank 70B, from the second tank 70B to the third tank 70C, and from the third tank 70C to the fourth tank 70D, the fourth tank It is preferable that the slurry HD in 70D is overflowed and moved to another facility. In the illustrated example, a partition wall 71D that does not reach the bottom surface is provided in the fourth tank 70D, and the slurry HD (HC) supplied into the fourth tank 70D descends in the fourth tank 70D, After diving through the partition wall 71D, it rises, overflows and is moved to another facility.

  In this regard, according to the form in which the slurry HD is moved through the pipe, there is a possibility of scale problems, unintentional dispersion of small-diameter inorganic particles S, separation of the composite silica, etc. , This possibility can be reduced.

<Other processes>
The slurry HD that has flowed out of the fourth tank 70D is suitably controlled in terms of average particle size, particle size distribution, degree of wear, and the like. Therefore, according to the above production method, it is suitable for use as a filler or pigment for papermaking. Thus, it is possible to obtain continuous silica composite particles.

  Further, the slurry HD can be made into a wet cake by, for example, filtration, washing with water, dehydration and the like. This wet cake is, for example, air-dried or heat-dried into dry fine particles, and then, using a pulverizer such as a dry pulverizer or a wet pulverizer, the particle size is adjusted to obtain silica composite particles having an arbitrary particle size. It can be.

  In the above description, the processing (reaction) in each of the tanks 70A, 70B, 70C, and 70D has been described as different. However, these descriptions are intended processing, meaning that no other reaction or the like occurs at all. Not what you want. For example, in the first tank 70A, the purpose is to produce a silica sol, but this does not mean that the small-diameter inorganic particles S should not be glued at all. In addition, an appropriate step can be added to the above steps as long as the object of the present invention is not impaired.

  In the illustrated example above, the slurry HC in the third tank 70C is more than the slurry HA in the first tank 70A, and the slurry HB in the second tank 70B is in the fourth tank 70D. The slurry HD has a smaller capacity, but this is merely a drawing and does not limit the capacity of each of the slurries HA, HB, HC, and HD. Therefore, for example, the capacities of the slurry HA and the slurry HC, the slurry HB and the slurry HD can be the same, or the capacities of the latter 70C and 70D can be increased. The capacities of these slurries HA, HB, HC, and HD can be appropriately determined according to the passage times of the respective tanks 70A, 70B, 70C, and 70D.

  However, from the viewpoint of simplifying the device structure, the passage time of the first tank 70A and the third tank 70C and the passage time of the second tank 70B and the fourth tank 70D are the same. In this case, the same capacity, preferably the same shape may be used.

  In the illustrated example, the tanks 70A, 70B, 70C, and 70D are integrally formed. However, they can be formed separately.

<Silica composite particles>
The silica composite particles of the present embodiment are obtained by fixing particulate silica to the surface of the inorganic particles S, and the particle diameter of the fixed silica is usually 10 to 20 nm. The particle diameter of the silica can be adjusted by adjusting, for example, the stirring intensity and temperature of the slurry HA, HB, HC, HD.

  The particle diameter of silica means the diameter when the silica is spherical, and means the average value of the major and minor diameters when the silica is not spherical, and can be measured using, for example, a scanning electron microscope or a transmission electron microscope. it can.

(Abrasion degree)
The silica composite particles of the present embodiment have a wire wear degree measured using a plastic wire wear meter (manufactured by Nippon Filcon, 3 hours, slurry concentration 2 mass%), preferably 15 to 100 mg, more preferably 25 to 90 mg, Especially preferably, it is 35-70 mg.

(Particle size)
The silica composite particles obtained by the above production method have a volume average particle diameter of preferably 3.0 to 5.0 μm, more preferably 3.4 to 4.3 μm, and particularly preferably 3.8 to 4.3 μm. It is. When the volume average particle diameter of the silica composite particles is less than 3.0 μm, the effect of the silica composite is not sufficiently exhibited. For example, when used as a filler for papermaking, the effect of improving oil absorption and opacity is sufficient. It may not be a thing. On the other hand, if the volume average particle diameter of the silica composite particles exceeds 5.0 μm, when used as a filler for papermaking, it may lead to a decrease in tensile strength or a decrease in tear strength, etc. There is a possibility that the equipment will be polluted.

  The volume average particle size is measured with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200” manufactured by Shimadzu Corporation), and the cumulative volume with respect to the volume of all particles is 50%. It is calculated | required as particle diameter (d50) when becoming. In preparing a measurement sample, silica composite particles are added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed with an ultrasonic wave for 1 minute.

  Moreover, the silica composite particle manufactured by the manufacturing method of this form has the ratio of the small particle | grains whose particle diameter is 1 micrometer or less, Preferably it is 0-2%, More preferably, it is 0-1.5%, Most preferably, it is 0-1. 0.0%. On the other hand, the ratio of large particles having a particle size of 10 μm or more is preferably 4 to 16%, more preferably 6 to 14%, and particularly preferably 8 to 12%.

  The mass ratio of the silica composite particles S having a particle size of 1 μm or less is measured by measuring the particle size distribution with a laser particle size distribution measuring device (laser analysis type particle size distribution measuring device “SALD-2200 type” manufactured by Shimadzu Corporation). It is determined as the cumulative volume of particles having a particle diameter of 1 μm or less relative to the volume. In preparing the measurement sample, the inorganic particles S are added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed by ultrasonic waves for 1 minute.

(Oil absorption)
The silica composite particles of this embodiment preferably have an oil absorption of 50 to 180 ml / 100 g.
When the oil absorption amount of the silica composite particles is 50 to 180 ml / 100 g, when used as a filler for papermaking, the silica composite particles absorb the vehicle component of the ink impregnated in the paper layer, the organic solvent, etc. Problems such as printing opacity, ink drying, and bleeding are improved. On the other hand, when the oil absorption amount of the silica composite particles is less than 50 ml / 100 g, the improvement effect may be insufficient, or the silica composite particles may inhibit the ink absorbability and drying properties. In this regard, when the silica composite is mixed with an adhesive to form a coating liquid, the silica composite particles absorb the adhesive in the coating liquid, and the true density is reduced. It will not be unevenly distributed in the construction layer. However, when the oil absorption is less than 50 mL / 100 g, this effect becomes insufficient, and the silica composite particles may settle and be unevenly distributed due to the difference between the true specific gravity of the silica composite particles and the specific gravity of the coating liquid.

  On the other hand, if the oil absorption amount of the silica composite particles exceeds 180 ml / 100 g, the ink absorbability is excessively improved, and there is a possibility that ink sinks or color developability deteriorates. In addition, when silica composite particles with an oil absorption amount exceeding 180 ml / 100 g are mixed with an adhesive and used as a coating liquid, after coating, a large amount of paint absorbed by the silica particles is released and shrinks during drying. The coating layer may crack or the smoothness of the coating layer surface may be lost.

  The amount of oil absorption of the silica composite particles can be adjusted, for example, by adjusting the temperature, passage time, pH, viscosity, etc. of the slurry HA, HB, HC, HD in the silica composite process.

The oil absorption amount of the silica composite particles is a value calculated by a kneading method described in JIS K 5101-13-2. That is, 2-5 g of silica composite particles (sample) dried at 105-110 ° C. for 2 hours are placed on a glass plate, and refined linseed oil (oxidized 4 or less) is dropped from the buret into the center of the sample little by little. Knead together. This dripping and kneading operation is repeated, and when the whole is first assembled into a single rod, the end point is obtained. The amount (ml) of refined linseed oil dropped at this point is obtained, and the oil absorption amount is calculated by the following equation.
Oil absorption (ml / 100) = (linseed oil amount (ml) × 100) / sample (g)

(Ratio of silica component)
In the silica composite particles of this embodiment, the ratio of the silica component is preferably 10.0 to 50.0% by mass, more preferably 41.0 to 49.0% by mass, and particularly preferably 42.0 to 48.0% by mass. %. When the ratio of the silica component is less than 10.0% by mass, there is a possibility that the composite of silica is not sufficiently performed, and when used as a filler or pigment for papermaking, there is an effect of improving the oil absorption and opacity. It may become insufficient. On the other hand, if the proportion of the silica component exceeds 50.0% by mass, silica may be overcombined, and when used as a paper filler or pigment, the oil absorption and opacity are improved. The effect may be insufficient.

(Component composition)
When the regenerated particles are used as the inorganic particles S, the component composition of the silica composite particles obtained by the above production method is calcium: silicon: aluminum = 30-80: 10-50: 7-20 in terms of oxide. The mass ratio is preferably In addition, this component structure is the value which carried out the elemental analysis by the acceleration voltage (15 KV) using the X-ray microanalyzer by Horiba, and converted the component into the oxide.

<Application>
The silica composite particles of the present embodiment have high whiteness, and particularly when regenerated particles are used as the inorganic particles S, the hardness is low. Therefore, it is suitable for use as a filler or pigment for papermaking, and for example, wear troubles such as a paper machine or a coating machine can be avoided. In addition, when regenerated particles are used as the inorganic particles S, the surface of the regenerated particles that are porous is composited with silica, so that the specific surface area becomes extremely wide, and when used as a filler or pigment for papermaking Can be expected to improve oil absorption and opacity. Furthermore, when the regenerated particles are used as the inorganic particles S, the interfiber bonding is moderately inhibited by the cationicity of the regenerated particles and the anionicity of the silica. Therefore, when used as a filler for papermaking, it is bulky. Can be expected to improve.

  When the silica composite particles of this embodiment are used as a papermaking filler or pigment, they can be used alone or in combination with other fillers or pigments. Examples of other fillers and pigments include inorganic particles such as calcium carbonate, clay, talc, silica, titanium dioxide, and satin white, vinyl chloride resin, polystyrene resin, urea formalin resin, melamine resin, and styrene / butadiene copolymer. The organic particle etc. which are manufactured from synthetic resins, such as system resin, can be illustrated.

  Further, if necessary, for example, polyacrylamide polymer, polyvinyl alcohol polymer, starch such as cationized starch, urea / formalin resin, melamine / formalin resin, vegetable gum, aqueous cellulose derivative and other paper strength Yield improver such as enhancer, acrylamide / aminomethylacrylamide copolymer salt, cationized starch, polyethyleneimine, polyethylene oxide, acrylamide / sodium acrylate copolymer, quaternary ammonium salt, rosin, starch, carboxyl Size agents such as methyl cellulose (CMC), polyvinyl alcohol (PVA), alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), neutral rosin, aluminum sulfate (sulfate band), water resistance, UV protection agent, fading Inhibitors, dyes, pigments It may be used in combination auxiliaries such as colorants.

  When using the silica composite particle of this form as a filler for paper manufacture, it can be used so that the mass ratio with respect to the total filler may be, for example, 5 to 100%, and preferably 10 to 100%. Such a composition is effective in securing bulkiness and cushioning properties. However, in this case, in order to prevent the silica composite particles from being crushed as the density is increased by the flattening treatment, the paper has an ash content of 10 to 20%, preferably 15 to 20%. Thus, it is preferable to adjust.

  When the silica composite particles of this embodiment are used as a filler for papermaking, for example, the wet cake may be dispersed again in water to form a filler slurry, and the filler slurry may be internally added to the pulp slurry. Additives such as a paper strength enhancer, a sizing agent, a yield improver and the like are added to the pulp slurry with the filler internally added to make paper, thereby obtaining a silica composite particle-containing paper.

Although the basic weight of this silica composite particle internal paper is not specifically limited, For example, it can be set as 36-200 g / m < ² >.

  On the other hand, the silica composite particles of the present embodiment can be used, for example, as a pigment for producing coated paper (for making paper). When used as a pigment, for example, after appropriately mixing with another pigment, for example, a dispersant such as sodium silicate, sodium hexametaphosphate, sodium polyacrylate is added to form a slurry, and an adhesive or other additive is added to the slurry. A coated paper can be produced by mixing a coating agent to prepare a coating liquid and coating the coating liquid on a paper substrate made of medium-quality paper or high-quality paper.

  When using the silica composite particles of this embodiment as a pigment for producing coated paper, the average particle diameter of the silica composite particles is 0.5 to 2.0 μm from the viewpoint of improving workability in the coating machine and preventing defects. Is preferable, and it is more preferable that it is 0.5-1.5 micrometers. This average particle diameter can be adjusted, for example, by adjusting the average particle diameter of the inorganic particles S and the average particle diameter of the silica composite particles themselves.

  The adhesive used together with the silica composite particles in the coating liquid is not particularly limited, and examples thereof include conjugated diene copolymer latex such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, acrylate ester and methacrylic ester. Acrylic polymer latexes such as acid ester polymers or copolymers, vinyl polymer latexes such as ethylene-vinyl acetate copolymers, and these various polymer latexes with functional group-containing monomers such as carboxyl groups Modified alkali partially soluble or insoluble polymer latex can be used.

  The coating solution further includes, for example, positive starch, oxidized starch, oxygen-modified starch, thermochemically modified starch, etherified starch, esterified starch, cold water-soluble starch, carboxymethylcellulose, hydroxymethylcellulose, etc. Water-soluble synthetic adhesives such as celluloses, polyvinyl alcohol, and olefin-maleic anhydride resins can be added.

  Moreover, various additives, such as an antifoamer, a water-proofing agent, a fluidity modifier, a coloring agent, and a fluorescent brightening agent, can be added as needed.

  The coating liquid containing the silica composite particles is also known as an ordinary coating liquid, for example, an air knife coater, blade coater, gate roll coater, rod coater, bar coater, cast coater, gravure coater, curtain coater, etc. It can coat on a paper base material using a coating machine (coater).

  A coated paper coated with a coating liquid containing silica composite particles is the same as a normal coated paper for the purpose of imparting printability such as smoothness and gloss after drying of the coating liquid. In addition, the paper can be passed through a calendar flattening means for pressure finishing. As the calendar, a known calendar, for example, a super calendar, a gloss calendar, a soft compact calendar, or the like can be used.

  The silica composite particles of the present embodiment can be used as additives for rubber, plastics, paints, inks, etc., in addition to papermaking fillers and pigments.

[Production method of regenerated particles]
Next, a method for producing regenerated particles that can be used as the inorganic particles S will be described. Although the regenerated particles can be produced by the method described in the above-mentioned Patent Document 2, since a more suitable regenerated particle production method has been developed thereafter, the following will describe the improvements of this production method. To do.

  Regenerated particles are generally produced by burning papermaking sludge. However, the organic matter contained in paper sludge varies in a variety of ways depending on the source, papermaking varieties in the paper mill, periodic repairs, production fluctuations, etc. As a result, the quality, particularly properties, of the finally obtained combustion product (regenerated particles) are not constant, and the whiteness of the combustion product is not uniform.

  Therefore, the present inventors have adjusted the calorific value fluctuation of papermaking sludge within a predetermined range, and as a result of repeated studies on means for obtaining regenerated particles with stable quality without causing fluctuations in combustion temperature and fluctuations in combustion time. In the production of regenerated particles by dehydrating and heat-treating the material to be processed using paper sludge as the main raw material as appropriate, the heat treatment is dried in this drying step and the drying step for drying the material to be treated. A first heat treatment step of heat-treating the processed object, a second heat treatment step of heat-treating the object heat-treated in the first heat treatment step at a temperature exceeding the first heat treatment temperature, and the second heat treatment step. The reprocessed particles having a uniform quality can be obtained by dividing into at least four steps including a third heat treatment step of heat-treating the workpiece heat-treated in the heat treatment step at a temperature exceeding the second heat treatment temperature. stable It was found to be able to elephants.

  At the same time, it has also been found that it is preferable that “the above drying is performed by allowing the dehydrated object to be entrained in a hot air stream”. When the “method of drying the dehydrated material in a hot air stream” (hereinafter simply referred to as “air current drying method”) is used, the material to be processed is unraveled as it is dried. Thus, the regenerated particles with uniform quality can be more stably produced.

  In this respect, it is difficult to unravel the workpiece uniformly until it is suitable for the subsequent heat treatment prior to drying. In addition, if the material to be processed is unraveled prior to drying, it is necessary to increase the dewatering rate. However, if the dewatering rate is increased, the material to be processed is highly compressed, and the drying efficiency of the material to be processed is partially increased. There is a risk of lowering, and there is a risk of non-uniform drying treatment and thus non-uniform product. On the other hand, if the object to be processed is unwound after drying, the object to be processed in a non-uniform state is dried, so that drying is not performed uniformly and heat treatment is not performed uniformly. As a result, it becomes impossible to stably produce regenerated particles with uniform quality.

On the other hand, in this embodiment, the advantage of dividing the subsequent heat treatment into a plurality of steps is as follows.
Papermaking sludge contains various organic substances (organic components). Among these organic substances, acrylic organic substances having a calorific value peak around 220 ° C. derived from paper, cellulose having a calorific value peak around 320 ° C., 420 ° C. It contains a styrenic organic component having a peak in calorific value in the vicinity and has a calorific value of, for example, 1000 to 2000 cal / g, although the fluctuation range is large depending on the type and amount of starting materials such as waste paper. In the conventional method for producing regenerated particles, measures have been taken to remove these organic components by burning (oxidizing) them together with other organic components in the combustion step (oxidation step). However, the inventors of the present invention indicate that each of the above organic substances is a substance having a high calorific value with a peak calorific value in the vicinity of the above temperature, and is ignited when an organic component thermally decomposed at 200 to 300 ° C. is combusted.・ Overheating occurs, combustion control becomes difficult, and it is found that not only a decrease in whiteness but also the production of a hard substance composed of gehlenite and anorthite is generated. First, in the first heat treatment step, a predetermined high calorific value is generated. It has been found that by removing the components (acrylic organic substance and cellulose) from the object to be treated by heat treatment, overcombustion can be suppressed and generation of a hard substance can be suppressed.

  Further, the advantage of providing the first heat treatment step and the second heat treatment step separately is imparted by the fine fibers in the object to be treated, latex that is an organic polymer, or printing. In order to burn the ink components and the like efficiently, a method of dehydrating and drying the water content to less than 40% and heat-treating at a high temperature has been adopted. However, in the manufacturing method of the present embodiment, as described above, the organic matter that is thermally decomposed and evaporated by evaporation at 200 to 300 ° C. in the object to be processed is gasified in the first heat treatment step. Can stably carry out heat treatment, and over-burning and pulverization of the object to be treated are suppressed. In addition, the first heat treatment step and the second heat treatment step are separated, and the acrylic organic matter and cellulose contained in the treatment object are pyrolyzed and gasified in the first heat treatment step, and the treatment object is formed in the second heat treatment step. By pyrolyzing the contained styrenic organic matter, the contribution of the obtained regenerated particles to stabilizing the quality and improving the whiteness is large, and the regenerated particles can be obtained uniformly and stably. In this way, in the third heat treatment step, the organic matter including carbon remaining in the object to be treated can be efficiently heat treated and removed, and the generation of hard substances caused by overcombustion can be suppressed. . Further, since the ignition temperature of the pyrolysis gas of cellulose is lower than the pyrolysis temperature of styrene, it is preferable that the cellulose is pyrolyzed and removed in the first heat treatment step, and styrene is pyrolyzed in the second heat treatment step. There is also an advantage that the first heat treatment step and the second heat treatment step are separately provided.

By the way, in this embodiment, it is preferable to use a kiln furnace in each heat treatment step except the drying step. The reason for this is as follows.
Conventionally used heat treatment furnaces can be broadly classified into four types: stalker furnaces (fixed bed), fluidized bed furnaces, cyclone furnaces, and kiln furnaces. As a result of repeated examinations of the manufacturing process, the following matters became clear.

  In the stalker furnace (fixed bed), it is difficult to adjust the degree of combustion of papermaking sludge such as deinking floss, and the regenerated particles are non-uniform. Causes dust to fall. Since air is blown up from below the object to be processed through the grate and burned, calcium carbonate or the like becomes fly ash and is sent to the exhaust gas facility together with the exhaust gas, which causes a problem in yield reduction. Since the stalker (stepped shape) is heat-treated while passing the object to be processed with a predetermined width, the stirring is insufficient and the heat treatment varies in the width direction.

  Since the fluidized bed furnace uses a particulate fluid medium such as silica sand in the furnace, there is a problem that silica sand or the like is mixed into the object to be processed, resulting in a deterioration in quality or a problem that uniform stirring cannot be performed. . After the cinnabar sand is mixed with the fluidized bed and heat treated, the sago sand and the material to be treated are separated and the sago sand etc. is returned to the furnace and only the material to be treated is taken out. Separation is difficult due to the particle size. Since the object to be treated is heat-treated in a floating state with dredged sand or the like, it is difficult to adjust the degree of heat treatment, resulting in variations in quality. The object to be processed is pulverized by friction and collision with high-hardness silica sand and the like and becomes fly ash, which is discharged out of the system and the yield decreases.

  In the cyclone furnace, since the object to be processed passes through the furnace in an instant, the organic matter in the object to be processed cannot be sufficiently heat-treated, leading to a decrease in whiteness. In addition, because of the air blowing, fine particles are not separated by the cyclone, and the yield is reduced because the fine particles are transferred to the exhaust gas treatment process together with the exhaust gas.

  As a result of intensive studies on the above problems, an internal heat or external heat kiln furnace was selected as a suitable heat treatment means in the heat treatment step excluding the drying step of this embodiment.

《Example of this regenerated particle》
The regenerated particles obtained by the method for producing regenerated particles according to the present embodiment have a ratio of calcium, silica, and aluminum of 30 to 82: 9 to 35: 9 to 35 in terms of oxides in elemental analysis of fine particles using an X-ray microanalyzer. It is preferable that the mass ratio is preferably 40 to 82: 9 to 30: 9 to 30, more preferably 60 to 82: 9 to 20: 9 to 20. When the ratio of calcium, silica and aluminum is 30 to 82: 9 to 35: 9 to 35 in terms of oxide, the specific gravity is light and excessive aqueous solution absorption is suppressed, so that dehydration is good. It is.

  As a method for adjusting the mass ratio of calcium, silica, and aluminum, the main component is to adjust the raw material composition of the object to be processed, but the first heat treatment step, the second heat treatment step, and the third heat treatment step. In addition, coating floss and preparation process floss with a clear origin can be added by spraying or the like, or by adding incinerator scrubber lime. For example, neutral papermaking wastewater sludge and coated paper production sludge are used to adjust calcium, and newspaper paper is made by adding a large amount of white carbon as an opacity improver to adjust silica. Wastewater sludge can be used, and for adjustment of aluminum, papermaking wastewater sludge using acidic papermaking type sulfuric acid band, and wastewater sludge in high quality papermaking process where a large amount of clay is used can be used.

  By the way, waste paper, which can be said to be the raw material of processed materials, has increased the use of calcium carbonate as a filler / pigment with the increase in the amount of coated paper with good-looking printing due to the progress of neutral papermaking and visualization in recent years. This leads to an increase in the content of calcium carbonate in the paper sludge, resulting in an increase in the production of gehlenite and anorthite, so that the content of gehlenite and anorthite, so-called hard substances contained in the regenerated particles is reduced as much as possible. The need to let it grow. Therefore, the above-mentioned method for producing regenerated particles capable of reducing the content of the hard substance is extremely useful, and the regenerated particles of this embodiment produced by this production method have a total content of gehlenite and anorthite of 1. It is 5 mass% or less, Preferably it is 1.0 mass% or less, More preferably, it is 0.5 mass% or less.

Here, the total content of gehlenite and anorthite is a value measured by the following method.
(Measuring method)
It is measured by an X-ray diffraction method (manufactured by Rigaku Denki, RAD2X). Measurement conditions are: Cu-Kα-curved monochromator: 40 KV-40 mA, divergence slit: 1 mm, SS: 1 mm, RS: 0.3 mm, scanning speed: 0.8 degrees / minute, scanning range: 2 theta = 7 to 85 Degree, sampling: 0.02 degree.

  The regenerated particles obtained as described above have a high whiteness of 75 to 85%, preferably 80 to 85%, and little variation in whiteness. Therefore, when silica composite particles in which silica is combined with the regenerated particles are internally added to the base material of the ink jet recording paper, the whiteness is lower than in the case of using conventionally known regenerated particles or commercially available calcium carbonate. Get higher.

  In addition, since the regenerated particles have a characteristic that the average particle size is larger than the average particle size (1 to 2 μm) of the known calcium carbonate and the regenerated particles are fixed between fibers, silica composite particles in which silica is combined However, by satisfying the various conditions described above, the same characteristics are obtained, and the bulkiness is improved. In addition, since the aluminum content of the regenerated particles is cationic, the fixing property to the fiber (anion-on property) is strong, and the bulkiness and strength can be improved by reducing the blending amount as compared with calcium carbonate.

  Next, the operational effects of the present invention will be clarified by giving production examples according to the present invention. Of course, the present invention is not limited to these examples. Further, “parts” and “%” shown below are based on the absolute dry mass unless otherwise specified.

  With respect to the inorganic particles, silica was compounded under the conditions shown in Tables 1 and 2 using the production facility of FIG. The component analysis results of the produced silica composite particles are shown in Table 3.

In the above production examples, various conditions and components are as follows. The conditions not described below are the same as described above.
(Regenerated particles)
After dewatering the papermaking sludge, regenerated particles were produced by the production method described above, which is an improvement of the production method described in Patent Document 2.

(Amount of dispersant added)
It is the addition amount (mass part) with respect to 100 mass parts of inorganic particles (solid content conversion).

((Wire) wear degree)
It is the value measured at a slurry concentration of 2% by mass using a plastic wire wear meter (manufactured by Nippon Filcon, 3 hours).

(Homogeneity)
The variation ratio was measured for the whiteness and average particle diameter of each silica composite particle, and the case where the variation was small was defined as “homogeneous”.

(Comprehensive evaluation)
The overall evaluation was performed based on the particle size (particle size distribution) and oil absorption.
5: The volume average particle diameter is in the range of 3.42 to 4.26 μm, the content of the particle diameter of 1 μm or less is 1.0% or less, the content of the particle diameter of 10 μm or more is 10% or less, and the wear degree is 50 mg or less. When the oil absorption is 80 ml / 100 g or more 4: According to the overall evaluation 5, when the content of the particle diameter of 1 μm or less exceeds 1.0% or the wear degree is less than 80 mg 3: Overall evaluation According to 5, the volume average particle diameter is outside the range of 3.42 to 4.26 μm, and the content ratio of the particle diameter of 1 μm or less exceeds 1.0%, or the content ratio of the particle diameter of 10 μm or more exceeds 10%. When it is in the range 2: In the evaluation criteria of the overall evaluation 5, any of the three items of the volume average particle size, the content rate of the particle size of 1 μm or less, the content rate of the particle size of 10 μm or more, the degree of wear, and the oil absorption amount are out of the range. When there is 1: In evaluation criteria of overall evaluation 5 When any of the four items of the volume average particle size, the content of the particle size of 1 μm or less, the content of the particle size of 10 μm or more, the degree of wear, and the oil absorption amount are out of the range.

(Discussion)
In any of the production examples, the average particle size and particle size distribution were suitable, the degree of wear was kept low, and the homogeneity and the oil absorption amount were sufficient. However, in this production example, there was a relative tendency as follows.
In Production Example 2, the particle size distribution was slightly broad.
In Production Example 4, the number of small-diameter particles was slightly larger and the particle size distribution was slightly broader.
In Production Example 5, the number of large-sized particles was slightly larger and the particle size distribution was slightly broader.
In Production Example 6, the degree of wear was slightly high, and the particle size distribution was slightly broad.
Production Example 7 had a small amount of small-diameter particles.
In Production Example 8, the number of small-diameter particles was slightly larger and the particle size distribution was slightly broader.
In Production Example 9, the degree of wear was slightly high.
In Production Example 10, the number of small-diameter particles was slightly larger and the particle size distribution was slightly broader.
In Production Example 11, the number of large-sized particles was slightly larger and the particle size distribution was slightly broader. In addition, the degree of wear was slightly high.
In Production Example 12, the number of small-diameter particles was slightly larger, and the particle size distribution was slightly broader.
In Production Example 13, the number of small-diameter particles was slightly larger, and the particle size distribution was slightly broader.
In Production Example 25, the average particle size was slightly small.
In Production Example 26, the average particle size was slightly small and the oil absorption amount was slightly low.

Next, a test example for clarifying the relationship between the addition of a dispersant and the generation of scale will be shown.
For the inorganic particles, the production equipment of FIG. 1 was used, and the tank to which the dispersant was added was changed as shown in Table 4 to compound silica. The results are also shown in Table 4. As the inorganic particles, regenerated particles similar to those in Example 1 were used after dewatering the papermaking sludge. As the dispersant, a polycarboxylic acid-based dispersant (Poise 520 / Kao) was used. Moreover, the addition amount of a dispersing agent shall be 0.13 mass part in conversion of solid content with respect to 100 mass parts of reproduction | regeneration particles in a 1st tank, and with respect to 100 mass parts of reproduction | regeneration particles in a 3rd tank. Thus, it was 0.27 parts by mass in terms of solid content.

  The amount of the scale was visually evaluated and classified into four levels: “large”, “normal”, “small”, and “none”.

  The present invention can be applied as a method for producing silica composite particles in which silica is combined with inorganic particles, particularly as a method for producing silica composite particles suitable for use as a filler or pigment for papermaking.

  70A ... first tank, 70B ... second tank, 70C ... third tank, 70D ... fourth tank, 80A-D ... stirring means, B1, B2 ... dispersant, HA-HD ... slurry, K ... Silicate alkali, R1, R2 ... mineral acid, S ... inorganic particles, W ... fresh water.

Claims (4)

A method for producing silica composite particles in which silica is combined with the inorganic particles from inorganic particles, an aqueous alkali silicate solution, and a mineral acid,
While supplying the inorganic particles and the alkali silicate to the preceding tank, the slurry in which the inorganic particles in the preceding tank are dispersed flows from the preceding tank directly or through another tank to the subsequent tank,
In addition to adding the mineral acid to the slurry in the subsequent tank, the mineral acid is also added to the slurry in the preceding tank, and at least the polyacrylic acid sodium carbonate is used as the main agent in the slurry in the preceding tank. A silica composite particle is continuously produced by adding a dispersant.
A method for producing silica composite particles. The total amount of the mineral acid, the amount of slurry passing through the trailing tank is pH7.0~8.5 to and the amount of mineral acid to the preceding added and 18-48 volume% of the total amount To
The method for producing silica composite particles according to claim 1. The dispersant is added in a mass ratio of 1: 2 to 1: 4 in the preceding tank and the subsequent tank, and the total added amount is 0.05 with respect to 100 parts by mass of the inorganic particles in terms of solid content. To be added to 2.00 parts by mass,
The manufacturing method of the silica composite particle of Claim 1 or Claim 2. As the inorganic particles,
Recycled particles having an average particle diameter of 1.4 μm or more obtained by dehydrating and heat-treating an object whose main raw material is papermaking sludge and a ratio of the particle diameter of 1 μm or less of 5% or more are used,
The manufacturing method of the silica composite particle of any one of Claims 1-3.

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