JP2012188468A - Method for producing composite particle, composite particle, composite particle-internally added paper, and coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a composite particle capable of obtaining composite particles with narrow particle size distribution, and in addition, to provide the composite particle obtained by such a method, composite particle-internally added paper to which the composite particles are internally added, and coated paper which includes the composite particles in the coating layer thereof.SOLUTION: The method for producing a composite particle capable of obtaining the composite particles by compounding inorganic particles includes: a suspension step of obtaining a suspension of the inorganic particles by suspending at least two kinds of particles as the inorganic particles in an aqueous solution of an alkaline silicate; and an aggregation step of agglutinating the inorganic particles by adding a mineral acid to the suspension and precipitating silica on the surfaces of the inorganic particles. Preferably, the inorganic particle has a median diameter of 0.5-2 μm and a mode diameter smaller than the median diameter.

Description

  The present invention relates to a method for producing composite particles, composite particles, composite particle-added paper, and coated paper.

  In recent years, paper such as newsprint tends to be lightened from the viewpoint of resource problems and cost reduction. However, when the weight of the paper is reduced, there is a disadvantage that the white paper opacity and the opacity after printing (hereinafter, both opacity are also simply referred to as “opacity”) are reduced. As a countermeasure, it is common practice to add various particles to paper as a filler or to apply it as a pigment to increase opacity.

  As the particles, kaolin, talc, titanium dioxide, hydrated silicic acid (white carbon), urea-formalin polymer fine particles and the like are usually used. In addition, attempts have been made to combine particles in order to increase the functionality of each particle. For example, the applicant has developed composite particles in which regenerated particles obtained by recycling are coated with silica (see Japanese Patent Application Laid-Open No. 2008-81390). Also, bulky paper (see Japanese Patent Application Laid-Open No. 2003-49389) using composite inorganic particles in which silica is coated on inorganic fine particles as a filler, or a light calcium carbonate-silica composite in which light calcium carbonate is coated with silica (special feature). No. 2005-219945) has been proposed.

  However, in the production of the composite particles, it is difficult to obtain uniform composite particles having a desired particle diameter due to unevenness in precipitation when silica is deposited on the core particle surface. When such composite particles are used as fillers, the yield decreases due to the presence of particles having a small particle size, while the paper strength is weakened due to the presence of particles having a large particle size, resulting in a decrease in printability and the like.

JP 2008-81390 A JP 2003-49389 A JP 2005-219945 A

  This invention is made | formed based on the above situations, and it aims at providing the manufacturing method of the composite particle which can obtain the composite particle with a narrow particle size distribution. In addition, another object of the present invention is to provide composite particles obtained by such a production method, composite particle-containing paper with the composite particles added therein, and coated paper containing the composite particles in a coating layer. .

The invention made to solve the above problems is
A method for producing composite particles obtained by combining inorganic particles,
A suspension step of suspending at least two kinds of particles as the inorganic particles in an alkali silicate aqueous solution to obtain a suspension of inorganic particles;
And adding a mineral acid to the suspension to precipitate silica on the surface of the inorganic particles, thereby aggregating the inorganic particles.

  The median diameter of the inorganic particles (the entire inorganic particles) is preferably 0.5 μm or more and 2 μm or less, and the mode diameter is preferably smaller than the median diameter. In this case, the particle size distribution of the inorganic particles used in the method for producing composite particles contains a large number of particles having a relatively small particle size. When inorganic particles having such a particle size distribution are coated with silica, those having a small particle size among inorganic particles are aggregated together with the precipitation of silica on the surface, while those having a large particle size are silica particles. Precipitation is the main and aggregation tends to be difficult to proceed. Therefore, according to the method for producing composite particles, composite particles having a narrow particle size distribution can be obtained. That is, according to the method for producing composite particles, composite particles suitable as a filler or pigment used for papermaking can be efficiently obtained.

  The inorganic particles preferably include a particle A having a median diameter of 1 μm to 3 μm and a particle B having a median diameter of 0.2 μm to less than 1 μm. By using the particle A and the particle B as the inorganic particles, the inorganic particles are easily brought into the above-described particle size distribution state. Therefore, according to the method for producing composite particles, composite particles having a narrow particle size distribution can be easily obtained.

  The particle A may be at least one selected from the group consisting of regenerated particles obtained from paper sludge as a main raw material and subjected to dehydration, heat treatment and pulverization steps, and heavy calcium carbonate particles. The regenerated particles and heavy calcium carbonate particles have a wide particle size distribution and are irregular. Therefore, according to the method for producing composite particles, it is possible to effectively utilize the difference in silica precipitation due to the above-described difference in particle size, and thus the difference in cohesiveness, so that it is easy to obtain composite particles having a narrow particle size distribution. Become. Furthermore, according to the manufacturing method, the point that the heavy calcium carbonate particles have a large number of knife edges on the surface and the whiteness of the regenerated particles are not sufficient can be improved by coating the surface with silica. The range of utilization of these inorganic particles can be expanded.

  The particles B are preferably titanium dioxide particles. According to the method for producing composite particles, by using titanium dioxide particles as particles B having a small particle diameter, for example, when using the obtained composite particles as a filler, titanium dioxide particles having a low yield are usually contained in paper. The opacity can be increased.

  The composite particles of the present invention are obtained by the above production method. Since the composite particle has a narrow particle size distribution width, it has high yield when used as a filler, and can improve the printability of the resulting paper. Moreover, since the said composite particle is equipped with the 1 or several inorganic particle used as a nucleus, and the precipitated silica, it is amorphous and porous. Therefore, according to the composite particles, since the light scattering ability and the oil absorption ability are high, it is possible to increase the white paper opacity and the opacity after printing.

  In the composite particles, the median diameter is 3 μm or more and 10 μm or less, and the ratio of particles having a particle diameter of 2 μm or less is preferably 20% or less. In addition to the median diameter being in the above range, the composite particles have a particle ratio of 2 μm or less with a particle size of 2 μm or less, which is difficult to stay in paper, so that the yield can be further improved.

  The composite particle internal paper of the present invention is one in which the composite particles are internally added. According to the composite particle internal paper, since the composite particles are internally added, the yield of the composite particles as the filler is high, the opacity can be increased, and the printability is excellent.

  The coated paper of the present invention is a coated paper having a base paper and one or more coating layers formed on at least one surface of the base paper, wherein the coating layer is the composite It is characterized by containing particles. According to the coated paper, since the composite particles are used as a pigment in the coating layer, the opacity and printability are excellent.

  The median diameter, mode diameter, and particle diameter in the present invention are based on volume. Specifically, the number of measurements: Avg / 2, using a Nikkiso Microtrack particle size distribution measuring device (model number: MT-3300). Measurement time: 10 seconds, distribution display: volume, particle size classification: standard, calculation mode MT-3300II, measurement upper limit 2000 μm, measurement lower limit 0.021 μm.

  As described above, according to the method for producing composite particles of the present invention, composite particles having a narrow particle size distribution can be obtained. Therefore, according to the composite particles of the present invention, the yield is high when used as a filler, and the opacity of paper and post-printing opacity can be increased when used as a filler or a pigment in coated paper. Further, according to the composite particle-containing paper and coated paper, since the composite particles are used as a filler or a pigment, the yield and opacity improvement effects are high, and the printability is excellent.

  Hereinafter, embodiments of the method for producing composite particles, composite particles, composite particle-containing paper and coated paper of the present invention will be described in detail.

<Method for producing composite particles>
The method for producing the composite particles of the present invention comprises:
(1) A suspension step of suspending at least two kinds of particles as inorganic particles in an aqueous alkali silicate solution to obtain a suspension of inorganic particles;
(2) adding a mineral acid to the suspension and precipitating silica on the surface of the inorganic particles to agglomerate the inorganic particles.

<(1) Suspension process>
In this step, at least two kinds of particles as inorganic particles are suspended in an aqueous alkali silicate solution to obtain a suspension. The aqueous alkali silicate solution is not particularly limited, but a sodium silicate solution (No. 3 water glass) is preferable because it is easily available.

The concentration of the alkali silicate solution is preferably 3 to 10% by mass in terms of the silicic acid content in the aqueous solution (in terms of SiO ₂ ). If the amount exceeds 10% by mass, the formed composite particles are coated with the white carbon to be produced, and the amorphous form and optical characteristics of the calcium carbonate in the core may not be exhibited. On the other hand, if the amount is less than 3% by mass, the silica component in the composite particles is lowered, so that it is difficult to form composite particles coated with silica.

  Moreover, as solid content concentration of this suspension, 3-35 mass% is preferable. By adjusting this concentration within the above range, it becomes easy to control the particle size, particle size distribution, silica content and the like of the obtained composite particles to a desired range.

  As the inorganic particles, it is preferable to use inorganic particles having a median diameter of 0.5 μm to 2 μm and a mode diameter smaller than the median diameter.

  The inorganic particles used in the method for producing the composite particles have a median diameter in the above range and a mode diameter smaller than the median diameter, and therefore have a particle size distribution containing a large number of relatively small particles. When inorganic particles having such a particle size distribution are coated with silica in the subsequent agglomeration step, the inorganic particles having a small particle size are aggregated with a plurality of particles as silica is deposited on the surface. In the case of a large particle, precipitation of silica is the main and aggregation tends to be difficult to proceed. Therefore, according to the method for producing composite particles, composite particles having a narrow particle size distribution can be obtained. That is, according to the method for producing composite particles, composite particles suitable as a filler or pigment used for papermaking can be efficiently obtained.

  In addition, when the mode diameter is larger than the median diameter in the inorganic particles to be used, relatively large particles also aggregate from the initial stage, and uniform aggregation due to the difference in particle diameter is not exhibited. Therefore, in this case, since the particle size of the obtained composite particles is increased as a whole, there is a case where a sharp particle size distribution cannot be obtained.

  The lower limit of the median diameter of the inorganic particles is preferably 0.5 μm, and more preferably 0.65 μm. On the other hand, the upper limit of the median diameter is preferably 2 μm, and more preferably 1 μm. When the median diameter of the inorganic particles is less than the above lower limit, composite particles having a sufficient particle size may not be obtained. On the contrary, when the median diameter exceeds the above upper limit, the particle diameter of the obtained composite particles becomes too large. For example, when used as a filler, there is a possibility that inconveniences such as a decrease in paper strength may occur.

  The mode diameter of the inorganic particles is preferably smaller than the median diameter, but is more preferably 0.1 μm or more and more preferably 0.15 μm or more and 0.3 μm or less than the median diameter. By setting the difference between the mode diameter and the median diameter in such a range, the agglomeration of relatively small particles and the non-aggregation of relatively large particles are adjusted in a well-balanced manner, and the particle size distribution of the resulting composite particles can be further increased. Can be sharp. When this difference is less than 0.1 μm, uniform aggregation due to the particle size difference is not sufficiently exhibited, and composite particles having a sharp particle size distribution may not be obtained. On the contrary, when this difference is larger than 0.3 μm, the small particles hardly aggregate to a sufficient particle size, and as a result, the particle size distribution may not be sharp as well.

  Moreover, as a specific minimum of the mode diameter of the said inorganic particle, 0.2 micrometer is preferable and 0.5 micrometer is more preferable. When the mode diameter of the inorganic particles is less than the above lower limit, a large amount of small particles may cause a sufficient particle size not to be obtained even if aggregation proceeds.

  Inorganic particles having such a particle diameter can be easily obtained by mixing a plurality of kinds of particles having different median diameters. Specifically, the inorganic particles preferably include particles A having a median diameter of 1 μm to 3 μm and particles B having a median diameter of 0.2 μm to less than 1 μm. By using the particle A and the particle B as the inorganic particles, the inorganic particles are easily brought into the above-described particle size distribution state.

<Particle A>
The preferred median diameter of the particles A is 1 μm or more and 3 μm or less, and more preferably 1.2 μm or more and 2 μm or less. By setting the median diameter of the particles A within the above range, efficient aggregation can be promoted using the particles A as nuclei in the aggregation process. When the median diameter of the particle A exceeds the above upper limit, the particle diameter of the obtained composite particle becomes too large. Conversely, when the median diameter of the particle A is less than the lower limit, it is difficult to obtain composite particles having a sufficient particle diameter.

  The type of the particle A is not particularly limited, and for example, heavy calcium carbonate particles, light calcium carbonate particles, regenerated particles, kaolin, talc, hydrated silicon, white carbon, and the like can be used. It is good to be at least one selected from the group consisting of particles and heavy calcium carbonate particles.

  The regenerated particles and heavy calcium carbonate particles have a wide particle size distribution and are irregular. Therefore, according to the method for producing composite particles, it is possible to effectively utilize the difference in silica precipitation due to the above-described difference in particle size, and thus the difference in cohesiveness, so that it is easy to obtain composite particles having a narrow particle size distribution. Become. In addition, the regenerated particles having an irregular shape and the heavy calcium carbonate possessed can enhance the strength of the composite particles obtained by fixing the particles B in the recessed portions on the surface in the aggregation step. Furthermore, according to the manufacturing method, the point that the heavy calcium carbonate particles have a large number of knife edges on the surface and the whiteness of the regenerated particles are not sufficient can be improved by coating the surface with silica. The range of utilization of these inorganic particles can be expanded.

<Heavy calcium carbonate particles>
This heavy calcium carbonate can be prepared by a method of pulverizing and classifying natural limestone, and commercially available heavy calcium carbonate available as a powder can be pulverized and classified as necessary. . Examples of the pulverization here include pulverization using a dry pulverizer such as a roll mill, jet mill, dry ball mill, and impact pulverizer, wet pulverization such as a wet ball mill, a vibration mill, a stirring tank mill, a flow tube mill, and a coball mill. The pulverization by a machine is mentioned, and these pulverizers can be used in appropriate combination.

  Examples of the classification method include, for example, sieving such as resonant vibration sieve, low head screen, electromagnetic screen, etc., dry classification such as micron separator, cyclone, etc., wet classification such as decanter type centrifuge, liquid cyclone, drug classifier, etc. These classifiers can be used in appropriate combination.

  As this heavy calcium carbonate, what is obtained from the hard limestone which received the thermal metamorphosis by the magma activity called common name (Marble) is preferable. Almost all of the limestone that is the raw material for heavy calcium carbonate produced in Japan belongs to this type. Heavy calcium carbonate particles produced using this Marble-type rough have irregular shapes, and since there are many knife edges on the particle surface, the wear on the plastic wire is large, and the plastic wire is used. It is said that it is unsuitable as a filler for neutral papermaking. However, according to the manufacturing method, it is considered that the irregular shape and the presence of the knife edge are conversely increasing the sharpness of the composite particles obtained by aggregation.

<Regenerated particles>
The regenerated particles are obtained by using papermaking sludge as a main raw material, followed by dehydration, heat treatment and pulverization steps. The regenerated particles obtained through such steps are suppressed from over-combustion and can suppress thickening during slurrying. Further, since the regenerated particles have an indefinite shape and a porous shape, it is possible to fix titanium dioxide particles having a relatively small particle size to the pores or the like during aggregation as described above. A preferable method for producing the regenerated particles will be described in detail later.

<Particle B>
A preferable median diameter of the particle B is 0.2 μm or more and less than 1 μm, and more preferably 0.3 μm or more and 0.7 μm or less. Moreover, it is preferable that the median diameter of the particle B is 1/5 or more and 1/2 or less of the median diameter of the particle A. By setting the median diameter of the particle B within the above range, the particle B can be efficiently aggregated using the particle A as a nucleus during aggregation.

  When the median diameter of the particle B is less than the above lower limit, aggregation does not proceed efficiently, making it difficult to obtain composite particles having a sufficient particle size and a sharp particle size distribution. On the contrary, when the median diameter of the particle B exceeds the upper limit, the particle size of the obtained composite particle tends to be too large and the particle size distribution tends to be broad.

  The blending ratio of the particles B is preferably 20 parts by mass or more and 70 parts by mass or less with respect to the entire inorganic particles. Further, the mass ratio of the particles A and the particles B is preferably in the range of 80:20 to 30:70. By setting such a blending ratio, an appropriate amount of particles having a relatively small particle size can be present while widening the particle size distribution of the entire inorganic particles. That is, with such a blending ratio, composite particles having a desired size and a narrow particle size distribution can be efficiently obtained. In addition, by blending the particle B, which is a relatively small particle, in the above range, the light refraction and reflection by the particle interface can be fully utilized, and the blank paper opacity and the like of the resulting composite particle can be increased. This effect is more prominent when, for example, titanium dioxide particles having a high refractive index are used as the particles B.

  The type of the particle B is not particularly limited, and for example, titanium dioxide particles, kaolin, talc, hydrated silicon, white carbon and the like can be used. Among these, titanium dioxide particles are preferable.

<Titanium dioxide particles>
Titanium dioxide particles have a high refractive index and excellent light scattering ability. Therefore, by using the titanium dioxide particles as the particles B, when the obtained composite particles are used as a filler, the titanium dioxide particles having a low yield can be kept in the paper and the opacity can be increased.

  The titanium dioxide particles are not particularly limited, and those known for papermaking can be used. As the crystal form of the titanium dioxide particles, any of anatase type, rutile type, brookite type and the like can be used, but it is preferable to use rutile type or anatase type.

  In addition, it is preferable to grind these inorganic particles beforehand so that it may become a desired particle size. As a pulverization method, pulverization can be performed by a dry pulverizer or a wet pulverizer, and pulverization can be performed by providing a plurality of stages of dry pulverizers and wet pulverizers or by appropriately combining them. In view of grinding efficiency, it is more preferable to make the particles smaller by means such as dry grinding before wet grinding.

  Examples of the dry pulverizer include a roll crusher, a roller mill, a stamp mill, an edge runner, a cutter mill, a rod mill and the like as pulverizers that pulverize several millimeters to tens of μm. A roller mill, a jet mill, a dry ball mill, an impact pulverizer, or the like can be used as a pulverizer for pulverizing to several μm or less.

  As the wet pulverizer, a wet ball mill, a vibration mill, a stirring tank mill, a flow tube mill, a coball mill, or the like can be used. In the wet pulverization, water is added to the inorganic particles to form a slurry. At this time, a dispersant may be added to uniformly disperse the particles. By adding a dispersant, the increase in viscosity can be prevented even when the slurry is concentrated. Sodium polyacrylate, sodium lignin sulfonate, phosphate, olefin, and maleic anhydride used as a dispersant can be prevented. It is preferable to use one or more of polymers, sodium citrate, sodium succinate and the like as necessary. In addition, an increase in viscosity due to wet grinding can be prevented, and grinding efficiency and handling properties can be improved.

<(2) Aggregation step>
In this step, mineral acid is added to the suspension, and silica is deposited on the surface of the inorganic particles to coat them, thereby aggregating at least a part of the inorganic particles.
In the production method, the inorganic particles in the suspension obtained in the suspension step are aggregated by using a flocculant and the like, and then the aggregation is performed by precipitation of silica. It is preferable that silica is directly deposited and agglomerated in order to obtain composite particles having a sharp particle size distribution. As described above, the reason why the composite particles obtained when silica is directly deposited has a sharp particle size distribution is not clear, but by allowing inorganic particles having various particle sizes to be present in the suspension, It is considered that silica is preferentially precipitated in particles having a small volume (surface area) among the particles, and the difference in cohesiveness, which is an effect of the present invention, is effectively exhibited.

  Examples of the mineral acid include diluted solutions of mineral acids such as dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid, but dilute sulfuric acid is preferred in terms of price and handling. Further, the concentration when adding dilute sulfuric acid is preferably 0.2 to 4.0 mol%. Addition of an excessive concentration of mineral acid may cause alteration of the resulting composite particles.

  Moreover, since silica precipitates in a short time, so that there is much mineral acid addition amount, it is preferable to adjust an addition rate according to those conditions. In addition, the addition within 5 minutes makes the structure of the uniform reaction system insufficient.

  The reaction temperature in this aggregation step is preferably 60 ° C. or higher and 100 ° C. or lower. As a result of intensive studies by the present inventors, the reaction temperature with the inorganic particles used in the present invention affects the silica formation, the crystal growth rate, and the mechanical strength of the formed composite particles. When the reaction temperature is less than 60 ° C., the silica formation / growth rate is slow, the coverage of the formed composite particles is inferior, the coating is easily peeled off, and the coating is easily broken by the shearing force applied when making the filler-added paper. On the other hand, if the temperature exceeds 100 ° C., the reaction process becomes complicated because an autoclave must be used because it is an aqueous reaction. The optimum reaction temperature is 65 to 95 ° C.

  In this agglomeration step, silica sol is produced by adding a mineral acid as described above, and composite particles are obtained by adjusting the suspension to neutral to weakly alkaline, preferably pH in the range of 8-11. Can do. At this time, the mineral acid may be added in such a range that the temperature of the suspension is 60 ° C. or more and 100 ° C. or less and the silica content in the composite particles is 2% by mass or more and 30% by mass or less. By controlling the temperature and the amount of mineral acid added, more preferably, the retention time of the agglomeration step is 30 to 120 minutes, more preferably 45 to 100 minutes. On the other hand, agglomeration of a plurality of particles is progressing, whereas for inorganic particles having a large particle size, the coating is such that the silica particles are deposited on the surface, particularly the tip portion where precipitation is likely to occur, and agglomeration with other particles occurs. By not occurring, the above-mentioned composite particles having a narrow particle size distribution can be obtained efficiently. If the holding time is less than 30 minutes, the aggregation of inorganic particles having a small particle size (particle B or the like) becomes insufficient, and if it exceeds 120 minutes, excessive silica coating occurs, resulting in composite particles having an excessive particle size. There is a case.

<Composite particle>
The composite particles of the present invention are obtained by the above production method. Since the composite particle has a narrow particle size distribution width, it has high yield when used as a filler, and can improve the printability of the resulting paper. Moreover, since the said composite particle is equipped with the 1 or several inorganic particle used as a nucleus, and the precipitated silica, it is amorphous and porous. Therefore, according to the composite particles, since the light scattering ability and the oil absorption ability are high, it is possible to increase the white paper opacity and the opacity after printing.
Especially for regenerated particles with originally porous structure or inorganic fine particles combining heavy calcium carbonate with complex shape and knife edge and titanium dioxide with high whiteness and opacity but low yield due to its fineness The combination of depositing silica can efficiently obtain composite particles having a narrow particle size distribution, which is an object of the present invention.

  The median diameter of the composite particles is preferably 3 μm to 10 μm, and more preferably 4 μm to 7 μm. By setting the median diameter of the composite particles in such a range, opacity and the like when used as a filler or pigment can be efficiently increased. When the median diameter of the composite particles is less than the above lower limit, the yield may not be sufficiently improved when used as a filler, and the opacity improving ability is not sufficient. On the other hand, when this median diameter exceeds the above upper limit, when used as a filler, the strength between pulp fibers may be reduced, resulting in reduced paper strength or increased wire wear, and a large particle size. Thus, the uniform dispersibility in the slurry or coating liquid may be reduced, and the opacity and opacity after printing may be reduced.

  The proportion of the composite particles having a particle size of 2 μm or less is preferably 20% or less, and more preferably 10% or more and 18% or less. According to the composite particles, since the ratio of particles having a particle diameter of 2 μm or less that hardly stays in the paper is suppressed, the yield can be improved. In particular, according to the composite particles, as a preferable example, even when titanium dioxide particles having a normal yield are used as the particles B, the small particle size in the composite particles thus obtained is reduced, and titanium dioxide is obtained. Various performances of particles can be effectively utilized.

  As a content rate of the silica in the said composite particle, 2 to 30 mass% is preferable, and 10 to 25 mass% is more preferable. By setting the silica content in such a range, for inorganic particles with a small particle size, the amount of silica deposited on the surface is sufficient so that a plurality of particles flexibly aggregate, and the inorganic particles with a large particle size On the other hand, the silica stays on the surface, particularly the tip portion such as a knife edge that is likely to be precipitated, and the coating does not cause agglomeration with other particles. Therefore, according to the composite particles, by covering inorganic particles with a wide particle size distribution with silica having such a mass ratio, it becomes easy to control the aggregate state with a narrow particle size distribution, and as a result, the yield of the composite particles is improved. , Oil absorption and opacity can be increased, and wire wear can be reduced.

  When the silica content is less than the above lower limit, the inorganic particles cannot be sufficiently aggregated, and the particle size distribution of the resulting composite particles is difficult to narrow, and as a result, the yield when used as a filler may not be improved. is there. On the contrary, when the silica content exceeds the above upper limit, the aggregation of inorganic particles having a relatively large particle size can easily proceed. As a result, in the resulting composite particles, the number of particles having a large particle size increases, similarly, the particle size distribution is not easily narrowed, the ability to improve opacity is not sufficient, and the number of particles having a large particle size is large. There is a risk that paper dust is likely to be generated.

<Application, quality, etc.>
The composite particles can be suitably used alone or mixed with pigments such as ordinary calcium carbonate, kaolin clay, talc, titanium dioxide, and plastic pigment as an internal filler or a coating pigment in papermaking. .

  When the composite particles are used as an internal additive or a coating pigment, for example, the composite particles are preferably contained in an amount of 5 to 100% by mass with respect to the total amount of the normal internal additive or coating pigment. Can be used by adding 10 to 100% by mass.

  The composite particles preferably include heavy calcium carbonate or regenerated particles that have been subjected to wet milling derived from minerals, so that those having a wide particle size distribution are agglomerated by the silica sol of fine particles and into particles of a relatively large particle size. Due to silica sol adhesion, the hardness of the particles is relatively low, and the particle size distribution width is narrow. Therefore, when the composite particles are used as a filler or pigment for papermaking, it is possible to avoid wear-out troubles such as a paper machine or a coating machine. In addition, the composite particles have a specific surface area that is increased by the fact that, for example, the surface of high-density heavy calcium carbonate or the like is originally coated with silica, and this is used as a filler for internal addition or a pigment for coating. Then, a paper with high whiteness and opacity and high filler yield can be obtained.

  The oil absorption of the composite particles is preferably 30 mL / 100 g or more and 100 mL / 100 g or less, more preferably 50 mL / 100 g or more and 90 mL / 100 g or less. When composite particles having such an oil absorption are used as an internal filler, the composite particles absorb ink vehicle or organic solvent impregnated in the paper layer in the paper layer, and the printing opacity of the paper is reduced. By suppressing the reduction and absorbing the ink vehicle, the organic solvent, and the like, the ink drying property and the effect of preventing blurring can be remarkably exhibited. When the oil absorption is less than 30 mL / 100 g, the above effect is not sufficient, and the composite particles may tend to inhibit the ink absorption and drying properties. On the other hand, if the oil absorption exceeds 100 mL / 100 g, there is a case where the ink sinks and the so-called color developability is inferior due to high ink absorbability.

  The composite particles can be used as fillers for rubber, plastics, paints, inks, etc. in addition to papermaking. By using the composite particle as a filler, high whiteness and concealment can be imparted.

<Composite particle paper>
The composite particle internal paper of the present invention is one in which the composite particles are internally added. According to the composite particle internal paper, since the composite particles are internally added, the yield of the composite particles as the filler is high, and the opacity and printing opacity can be increased. Can reduce wear.

  A method for producing a composite particle-added paper using the composite particles of the present invention as an internal filler is the same as a normal method for producing a filler-added paper. For example, the composite particles are mixed with other fillers in the above ratio. The obtained slurry is added to a pulp raw material slurry, and further, a paper slurry obtained by adding additives such as a paper strength enhancer, a sizing agent, and a yield improver, if necessary, is obtained by papermaking. The filler addition rate with respect to the pulp raw material (solid content) is 1 to 50% by mass, preferably 3 to 30% by mass.

  As additives to be added to the paper slurry, known ones can be used, for example, starch, vegetable gum, aqueous cellulose derivative, polyacrylamide, etc. as paper strength enhancer, rosin, starch, CMC (carboxyl methyl cellulose), polyvinyl alcohol, alkyl ketene dimer, ASA (alkenyl succinic anhydride), neutral rosin, etc., and yield improvers include polyacrylamide and copolymers thereof, quaternary ammonium salts, etc. be able to. You may add coloring materials, such as dye and a pigment, to a data slurry further as needed.

These additives are added to and mixed with the paper stock slurry, and paper making is performed with a known paper machine to produce composite particle-containing paper. The basis weight of the composite particle-containing paper is not particularly limited, but is usually about 10 to 300 g / m ² .

<Coated paper>
The coated paper of the present invention is a coated paper having a base paper and one or more coating layers formed on at least one surface of the base paper, wherein the coating layer is the composite It is characterized by containing particles. According to the coated paper, since the composite particles are used as a pigment in the coating layer, the opacity and post-printing opacity are excellent.

  The method of producing a coated paper using the composite particles of the present invention is the same as the method of producing a normal coated paper. For example, the composite particles of the present invention are mixed with other pigments at the above ratio, and a dispersant is added. The slurry obtained by addition is mixed with an adhesive or other additives to prepare a coating material, which is obtained by coating on a paper material such as medium-quality paper or high-quality paper.

  Also when manufacturing coated paper using the said composite particle, the range of 30-100 mL / 100g of the oil absorption degree of the said composite particle is preferable. This is because when mixed with an adhesive, the composite particles absorb the adhesive in the coating solution, and the true density is reduced, so that sedimentation is suppressed, and the composite particles are biased in the coating layer. This is because the effect of being uniformly dispersed in the coating layer appears remarkably. When the oil absorption is 30 mL / 100 g or less, the above effect is insufficient, and the composite particles settle out due to the difference between the true specific gravity of the composite particles and the specific gravity of the coating liquid, and are not uniform in the coating layer. Since it will be in a dispersed state, it is not preferable. On the other hand, when the oil absorption exceeds 100 mL / 100 g, when blended as a coating pigment in the coating layer, a binder such as latex or starch is absorbed and the coating layer strength is lowered.

  In addition, when heavy calcium carbonate is used as the inorganic particles, the surface of the heavy calcium carbonate is coated with silica, so that the shape of the heavy calcium carbonate having an angular shape is rounded, It is possible to reduce wear due to calcium, such as blades, coating rolls, and equipment for discharging coating liquid. Furthermore, even when recycled as waste paper or waste paper, it is possible to reduce wear of wires and equipment due to inorganic particles remaining in the obtained recycled pulp.

  As the adhesive contained in the coating liquid, known ones can be used, for example, conjugated diene copolymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic acid ester, and the like. // Acrylic polymer latex such as a polymer or copolymer of methacrylic acid ester, vinyl polymer latex such as ethylene-vinyl acetate copolymer, or a functional group such as a carboxyl group containing these various polymer latexes An alkali partially soluble or alkali insoluble polymer latex modified with a monomer is used.

  In addition to the above synthetic adhesives, for example, cationized starch, oxidized starch, oxygen-modified starch, thermochemically-modified starch, etherified starch, esterified starch, starch such as cold water-soluble starch, carboxymethylcellulose, hydroxy Celluloses such as methylcellulose, water-soluble synthetic adhesives such as polyvinyl alcohol and olefin-maleic anhydride resin can be appropriately selected and used in combination. Moreover, various additives, such as an antifoamer, a water resistance agent, a fluidity modifier, a coloring agent, and a fluorescent brightening agent, are added to the pigment slurry and paint as necessary. Examples of the dispersant include sodium silicate, sodium hexametaphosphate, and sodium polyacrylate.

As a coating method of the coating liquid, it can be performed by a known coating machine (coater) such as an air knife, a blade, a gate roll, a rod, a bar, a cast, a gravure, or a curtain depending on the coating amount. The coating amount is usually about several to several tens g / m ^{2 in} terms of dry mass per side.

  The coated paper obtained after drying is generally subjected to pressure finishing by passing it through a calendar for the purpose of imparting printability (for example, high smoothness and high gloss). As the calendar device in this case, for example, various calenders such as a super calender, a gloss calender, a soft compact calender or the like, or a combination of a drum and an elastic roll, can be appropriately used in on-machine or off-machine specifications.

<Method for producing regenerated particles>
Here, a method for producing regenerated particles that can be suitably used in the present invention will be described in detail in the order of raw materials and steps of dehydration, heat treatment, and pulverization. In addition, it is preferable to have a mixing | blending / slurry process between a heat treatment process and a grinding | pulverization process, and also other processes can be provided as needed.

(material)
As the raw material for the regenerated particles, papermaking sludge is used as the main raw material, and among the papermaking sludge, deinking floss is preferably used. The deinking floss refers to what is separated from the pulp fiber in the deinking process for removing ink adhering to the used paper in the used paper processing process for producing the used paper pulp. In the used paper pulp manufacturing process in papermaking, for the purpose of continuously producing used paper pulp of stable quality, the used paper is selected and selected, and used paper of a certain quality is used. For this reason, the types, ratios, and amounts of inorganic substances brought into the used paper pulp manufacturing process are basically constant. Moreover, even if the waste paper contains plastics such as vinyl and film that cause fluctuations in unburned materials, these foreign matters are removed at the stage before the deinking process for obtaining the deinking floss. Accordingly, deinking floss is a raw material for producing regenerated particles with extremely stable quality as compared with papermaking sludge generated in other processes such as a factory drainage process and a papermaking raw material preparation process.

(Dehydration process)
The dehydration step is a step of removing moisture of a raw material such as deinking floss up to a predetermined ratio. For example, deinking floss separated from pulp fibers in a deinking process for producing waste paper pulp is subjected to various operations and dehydrated by a known dewatering facility.

  Examples of the dehydration step include the following steps. First, water is separated from the deinking floss by a screen as one dehydrating means and dehydrated. The deinking floss dehydrated to 70% to 90% in this screen is sent to another dehydrating means such as a screw press, and further dehydrated to a predetermined moisture content.

  The raw material after dehydration (deinking floss) is 60% or less, preferably 30% or more and less than 50%, more preferably 30% or more and 45% or less, and particularly preferably more than 30% and 40% or less.

  If the water content of the raw material after dehydration exceeds 60%, the processing temperature in the heat treatment process will be lowered, the energy loss for heating will be great, and the raw material will be unevenly burned, making it difficult to promote uniform combustion. Become. Further, the exhaust gas discharged has a large amount of moisture, which has the disadvantage that the efficiency of the recombustion treatment in the dioxin countermeasures is reduced and the load of the exhaust gas treatment equipment is increased. On the other hand, if the moisture content of the raw material after dehydration is as low as less than 30%, it is contrary to the reduction of dehydration energy.

  As described above, if the raw material (deinking floss) is dehydrated in a multi-stage process and abrupt dehydration is avoided, the outflow of inorganic substances can be suppressed and the deinking floss flocs do not become too hard. In the dehydration treatment, an auxiliary agent for improving the dehydration efficiency such as an aggregating agent for aggregating the deinking floss may be added, but it is preferable to use an aggregating agent that does not contain iron. When iron is contained, the whiteness of the regenerated particles may be reduced due to oxidation of iron.

  It is preferable in terms of production efficiency that the equipment for the dehydration process is adjacent to the equipment of other processes of the regenerated particles, but the equipment is provided in advance adjacent to the waste paper pulp manufacturing process and transports the dehydrated equipment. It is also possible to transport to a metering feeder by a transport means such as a truck or a belt conveyor, and to supply the heat treatment process from this metering feeder.

  The raw material after dehydration is a particle having an average particle diameter of 40 mm or less, preferably an average particle diameter of 3 mm to 30 mm, more preferably an average particle diameter of 5 mm to 20 mm by a pulverizer (or pulverizer) before being supplied to the heat treatment step. It is preferable to arrange the diameters, and it is preferable to arrange the particle diameters so that the ratio of the particle diameters of 50 mm or less is 70% by mass or more. If the average particle size is less than 3 mm, overcombustion tends to occur. Conversely, when the average particle diameter exceeds 40 mm, it becomes difficult to uniformly burn the raw material core.

  The average particle diameter and the ratio of the particle diameter in the dehydration step are values measured using a sample solution sufficiently dispersed by a stirring type disperser. In addition, the particle diameter in each heat processing process mentioned later is the value measured with the metal plate sieve based on JIS-Z8801-2: 2000.

(Heat treatment process)
The heat treatment step includes a first heat treatment step in which drying for further moisture removal of the dehydrated raw material and a first combustion at a relatively low temperature are performed in series, and the heat treatment product obtained in the first heat treatment step is again used. And a second heat treatment step for heat treatment (combustion) at a higher temperature than the first heat treatment step. By passing through the two-stage heat treatment step in which the temperature is raised in this way, over-combustion of the raw material can be suppressed, and thickening when the obtained regenerated particles are slurried can be suppressed. In addition, by performing the heat treatment at a relatively low temperature, it is possible to similarly suppress over-combustion of the raw material and suppress thickening when the obtained regenerated particles are slurried. Specifically, the upper limit of the heat treatment temperature is preferably 780 ° C, more preferably 750 ° C.

(First heat treatment step)
The raw material that has undergone the dehydration step is heat-treated as a first heat treatment step using, for example, an internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis.

  In this internal heat kiln furnace, hot air generated in the hot air generation furnace is sent from the outlet side so as to counter-flow with the raw material flow. An exhaust gas chamber is provided on one side of the internal heat kiln furnace, and an exhaust chamber is provided on the other side. Hot air is blown from the other side of the internal heat kiln furnace through the discharge chamber, and is charged from the other side to dry and burn the raw material sequentially transferred to the other side as the internal heat kiln furnace rotates. To do.

  In this way, in the first heat treatment step, the raw material is dried and burned gently from the supply port to the discharge port by drying and burning in the internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. Can control the degree of combustion of raw materials with various properties such as agglomeration, hard and soft, and stable grain alignment. Can do. In addition, drying can be divided into separate steps and dried by, for example, a blow-up type dryer.

  The heat treatment temperature in the first heat treatment step (for example, the outlet temperature (hot air temperature) of the internal heat kiln furnace) is 300 ° C. or higher and lower than 600 ° C., preferably 400 ° C. or higher and lower than 550 ° C., more preferably 400 ° C. or higher and 500 ° C. or lower. Is preferred. In the first heat treatment step, it is preferable to heat-treat at a temperature in the above range for the purpose of slowly burning the combustible organic matter and suppressing the formation of residual carbon that is difficult to burn. When the temperature is excessively low, the organic matter is not sufficiently combusted. On the other hand, when the temperature is excessively high, overcombustion occurs, and calcium oxide is easily generated by decomposition of calcium carbonate. In addition, when the temperature is 600 ° C. or higher, drying / combustion proceeds locally faster than the alignment of dehydrated materials having various properties such as hard and soft, so that the particle surface and the interior of the particle are not. It becomes difficult to reduce the difference in the flammability and make it uniform.

  In the first heat treatment step, an easily combusted organic substance contained in the raw material is slowly burned, and in order to suppress the formation of residual carbon, the heat treatment is performed for 30 minutes to 90 minutes in the residence (heat treatment) time under the above conditions. Is preferred. If the heat treatment time is less than 30 minutes, sufficient combustion is not performed and the ratio of remaining carbon increases. On the other hand, when the heat treatment time exceeds 90 minutes, thermal decomposition of calcium carbonate occurs due to excessive combustion of the dehydrated product, and the obtained regenerated particles become extremely hard. In terms of organic combustion and production efficiency, heat treatment is preferably performed with a residence time of 40 minutes to 80 minutes. In order to ensure constant quality, it is preferable to perform heat treatment combustion with a residence time of 50 minutes to 70 minutes.

(Second heat treatment step)
The raw material which passed through the 1st heat treatment process is heat-processed using the external heat kiln furnace which has the external heat jacket which a main body turns sideways and rotates around a central axis as a 2nd heat treatment process. In this way, through the first and second heat treatment steps, the organic component in the raw material is burned and removed, and the inorganic substance can be discharged as a heat treatment product.

  In the second heat treatment step, in order to burn the residual organic matter that could not be burned in the first heat treatment step, for example, residual carbon, the heat treatment adjusted to a particle size smaller than the particle size of the raw material supplied in the first heat treatment step. It is preferable to use a product. The grain alignment of the heat-treated product after the first heat treatment step is preferably adjusted so as to be an average particle diameter of 10 mm or less, more preferably adjusted so as to be an average particle diameter of 1 to 8 mm, and an average particle diameter of 1 to It is particularly preferable to adjust to 5 mm. If the average particle diameter at the inlet of the external heat kiln in the second heat treatment step is less than 1 mm, there is a risk of overcombustion. If the average particle diameter exceeds 10 mm, the remaining carbon is difficult to burn, and combustion may not proceed to the core. There is a possibility that the whiteness of the regenerated particles may decrease.

  As the external heat source of the external heat kiln furnace, an electric heating type heat source that is easy to control the temperature in the external heat kiln furnace and easy to control the longitudinal temperature is suitable. Is preferred. By using electricity as an external heat source, the temperature in the furnace can be finely and uniformly controlled, and the degree of combustion of the heat-treated product having various properties such as formation of aggregates, hard and soft, Grain alignment can be performed stably. In addition, by providing a plurality of electric heaters in the flow direction of the furnace, the electric furnace can arbitrarily provide a temperature gradient, and the temperature of the heat-treated product can be maintained at a constant temperature for a certain period of time. Residual organic content in the heat-treated product after one heat treatment step, especially residual carbon, can be brought to zero as much as possible without causing decomposition of calcium carbonate in the second heat treatment step, for example, low wire wear compared to heavy calcium carbonate And high whiteness regenerated particles can be obtained.

  The heat treatment temperature in the second heat treatment step is preferably 550 ° C to 780 ° C, more preferably 600 ° C to 750 ° C. In the second heat treatment step, as described above, since it is necessary to burn the residual organic matter that has not been burned in the first heat treatment step, particularly the residual carbon, it is preferable to perform the heat treatment at a higher temperature than the first heat treatment step. If the heat treatment temperature is less than 550 ° C., there is a possibility that the residual organic matter cannot be burned sufficiently. If the heat treatment temperature exceeds 780 ° C., decarboxylation of calcium carbonate in the heat treatment proceeds and the particles become hard. There is a fear.

  The residence (heat treatment) time in the external heat kiln furnace as the second heat treatment step is preferably 60 minutes or more, more preferably 60 minutes to 240 minutes, particularly preferably 90 minutes to 150 minutes, and most preferably 120 minutes to 150 minutes. Minutes are desirable for complete combustion of the remaining carbon. In particular, the remaining carbon must be burnt slowly at a high temperature that does not cause the decomposition of calcium carbonate as much as possible. If the residence time is less than 60 minutes, the remaining carbon is burnt in a short time, If the residence time exceeds 240 minutes, the calcium carbonate may be decomposed. In addition, in the stable production of the heat-treated product, it is preferable that the residence time is 60 minutes or more, and in order to prevent overcombustion and secure productivity, the residence time is 240 minutes or less.

  The average particle diameter of the heat-treated product discharged from the external heat kiln furnace as the second heat treatment step is preferably adjusted to 10 mm or less, preferably 1 mm to 8 mm, more preferably 1 mm to 4 mm. This adjustment can be performed, for example, by passing the heat-treated product between two rotating rolls having a certain clearance.

  The heat-treated product that has undergone the second heat treatment step is preferably an agglomerate, for example, cooled by a cooler, sorted by a particle size sorter such as a vibration sieve, and temporarily stored in a combustion product silo. Then, after adjusting to the target particle diameter in the blending / slurry step and the pulverization step, the particles are used as reclaimed particles for application destinations such as fillers.

  In addition, although the case where the deinking floss was used as a raw material was illustrated above, the deinking floss was used as a raw material, and the raw material was appropriately mixed with other papermaking sludge such as paper sludge in the papermaking process. You can also.

(Formulation / slurry process)
The blending / slurrying step is a step of blending an acid and / or salt into the heat-treated product discharged from the second heat treatment step and suspending the heat-treated product in water to make a slurry.

  This heat-treated product is preferably pulverized after being suspended in water by using a mixer or the like in order to achieve effective pulverization in the subsequent pulverization step. In this case, the lower limit of the slurry concentration (mass ratio of the heat-treated product added to the whole slurry) is preferably 15%, and more preferably 20%. Further, the upper limit of the slurry concentration is preferably 50%, and more preferably 40%. When the slurry concentration is less than the above lower limit, when the finally obtained particles are made into a solid state, production efficiency decreases, for example, enormous energy is generated. On the other hand, if the slurry concentration exceeds the above upper limit, effective pulverization may be difficult in the subsequent pulverization step, and solidification and solidification may easily occur.

  The acid and / or salt can precipitate a calcium salt in the presence of calcium ions. According to the acid and / or salt, it reacts with calcium ions dissolved in the slurry due to calcium oxide and metakaolin generated by overcombustion, and precipitates calcium salt, thereby coexisting with calcium ions in the slurry. The reaction with silicate ions and aluminate ions can be suppressed, and the generation of a cured substance can be suppressed. As a result, by using this acid and / or salt, solidification and solidification of the slurry can be suppressed.

(Crushing process)
The pulverization step is a step in which regenerated particles are obtained by pulverizing the slurry obtained in the above-described step to obtain fine particles. In this pulverization step, a known pulverizer or the like can be used. Through this pulverization step, the resulting regenerated particles can be suitably used as a pigment for coating and a filler for internal addition by finely pulverizing the slurry to a necessary particle size.

(Other processes)
In the method for producing regenerated particles, a raw material aggregation process, a granulation process, a classification process between the processes, a carbonation process for carbonizing the slurry, and the like may be provided.

(Carbonation process)
The obtained slurry of regenerated particles is as alkaline as pH of 12 or more as it is, and may react with other chemicals in a coating liquid adjusting step in the application of coating pigments, for example, and may cause quality deterioration. Therefore, in order to return the calcium oxide in the heat-treated product or the regenerated particles to calcium carbonate and reduce the pH, the carbon dioxide in the exhaust gas discharged in the first heat treatment combustion step or the second heat treatment step is used, for example, 7 It is preferable to adjust the pH to ˜9.

  The carbonation step may be performed between the blending / slurry step and the pulverization step, simultaneously with the pulverization step, or after the pulverization step. The carbon dioxide blowing may be a blending / slurrying step as a blending of carbonic acid instead of or in addition to blending with other acids and / or salts.

  During carbonation, a gas blowing port is provided at the bottom of the reaction tank, and a pH meter for measuring the pH in the tank is provided, and batch processing is performed on the slurry in the tank until the pH of the slurry falls below a predetermined value. This can be done by blowing gas. Further, a gas blowing port is provided at a portion where a gear such as a VF pump is engaged, and pulverization and gas blowing can be simultaneously performed on the slurry.

As carbon dioxide for carbonation, carbon dioxide can be separated from exhaust gas using a carbon dioxide separator such as a PSA separator in the CO ₂ separation step. Moreover, exhaust gas can be used directly, or commercially available carbon dioxide gas can be used and used together.

  The blowing rate of carbon dioxide can be constant or variable, and in the case of being variable, it can be appropriately adjusted according to the transition of pH.

  In this embodiment, in order to further stabilize the quality of the regenerated particles, it is preferable to classify the particle diameter of the object to be processed uniformly in each process, and feed back coarse and fine particles to the previous process. By doing so, quality can be further stabilized.

  In addition, it is preferable to granulate the deinked floss (dehydrated product) that has been subjected to dehydration treatment in the previous stage of the drying step, and it is more preferable to perform classification to make the particle size of the granulated product uniform. The quality can be further stabilized by feeding back coarse and fine granulated particles to the previous process. In granulation, known granulation equipment can be used, but equipment such as a rotary type, a stirring type, and an extrusion type is suitable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

  In addition, each measured value in a present Example is a value measured with the following method.

[Change in median diameter (μm), mode diameter (μm), ratio of particles having a particle diameter of 2 μm or less (volume%), and peak height]
Using a laser diffraction particle size distribution analyzer [Microtrack / Nikkiso Co., Ltd.] (model number: MT-3300), number of measurements: Avg / 2 (average of two measurements), measurement time: 10 seconds, distribution display: volume, Particle size classification: Measured under conditions of standard, calculation mode MT-3300II, measurement upper limit 2000 μm, measurement lower limit 0.021 μm. In the preparation of the measurement sample, particles were added to a 0.1% sodium hexametaphosphate aqueous solution and dispersed with an ultrasonic wave for 1 minute.

  The change in peak height is the comparison between the peak in the particle size distribution of the entire inorganic particles (the frequency ratio (volume%) of particles occupying the mode in the particle size distribution) and the peak (volume%) of the resulting composite particles. did. A composite particle having a higher peak was increased, and a composite particle having a lower peak was decreased. It can be said that the particle size distribution is sharp when the peak height is increased.

[Silica coverage (mass%)]
Using an X-ray microanalyzer manufactured by HORIBA, the elemental analysis is performed at an acceleration voltage (15 KV), the content ratio of clay, calcium carbonate, talc, etc. is estimated from the contained components, and the silica component after silica coating is contained From the rate, the silica coverage (mass%) was calculated.

[Whiteness (%)]
The whiteness of the particles was measured based on the Tappi-534 pm-76 method.

[Oil absorption (mL / 100g)]
It measured according to the kneading method described in JIS-K5101. That is, 2 g to 5 g of a sample dried at 105 ° C. to 110 ° C. for 2 hours is taken on a glass plate, and refined linseed oil (having an acid value of 4 or less) is dropped from the burette to the center of the sample little by little and kneaded with a spatula each time. The kneading operation was repeated, and the dripping amount of the refined linseed oil was determined with the end point when the whole was first assembled into one rod shape, and the oil absorption was calculated by the following formula (1).
Oil absorption (mL / 100g)
= [Look of linseed oil (mL) x 100] / paper (g) (1)

[Basis weight (g / m ² )]
It measured based on "Paper and board-Basis weight measuring method" described in JIS-P8142.

[Ash yield (%)]
The calculation was performed by dividing the ash content (measured in accordance with JIS-P8251) of the composite particle-added paper obtained by hand-drawing with the ash content in the paper material used for hand-drawing.

[Blank Opacity (%)]
It measured based on the method of JIS-P8149.

[Opacity after printing (%)]
J. et al. In accordance with TAPPI 45, newspaper offset printing ink (black) was used, and solid printing was performed by changing the amount of ink with an RI printing tester (manufactured by Meisei Seisakusho). From the ratio of the back surface reflectance after printing to the back surface reflectance before printing (opposite side of the printing surface) when the printing surface reflectance is 9%, the printing opacity (Y) is calculated using the following formula (2). did. In addition, the spectral whiteness meter (made by Suga Test Instruments) was used for the reflectance measurement.
Y = {(back surface reflectance after printing) / (unprinted back surface reflectance)} × 100 (2)

[Wire wear degree (mg / h): Metal wear resistance]
The wire wear properties of the composite particles shown in Table 1 were measured in order to evaluate the metal wear properties of the internally added paper and the coated paper.
The wire abrasion property is determined by testing the dispersion of the obtained inorganic particles having a solid content concentration of 10% while circulating the pump using a wire abrasion tester (manufactured by Nippon Filcon Co., Ltd.) (weight = 650 g, wire = Abrasion degree test was performed using plastic wire / SS-40 (made by Nippon Filcon Co., Ltd., test time = 3 hours), and the weight (mg / h) of the reduced wire was used as the wire wear degree (mg / h). It shows that wire abrasion property is so large that a numerical value is large.

[Coating suitability]
The coating liquid was applied to the substrate, and the occurrence of defects was determined by the number of defects detected by the reflective defect detector installed in the coating machine.
A: 0 to 1 in a flow 10,000 m ○: 2 to 4 in a flow 10,000 m Δ: 5 to 7 in a flow 10,000 m ×: 8 or more in a flow 10,000 m

[Production of regenerated particles]
A deinking floss was used as a raw material, and the dehydration step was performed so that the moisture content was 45 mass%, the average particle size was 10 mm, and the proportion of particles of 50 mm or less was 90 mass%. This dehydrated product was washed with shower water, and the first heat treatment step and then the second heat treatment step were performed under the following conditions to obtain a heat treatment product.
First heat treatment process conditions Combustion type: Internal heat kiln Combustion temperature: 500 ° C
Oxygen concentration: 10%
Residence time: 50 minutes Second heat treatment process conditions Combustion type: Combined use of external and internal heat kilns Average particle diameter at inlet: 5 mm
Combustion temperature: 700 ° C
Oxygen concentration: 14%
Residence time: 140 minutes Average particle diameter at outlet: 5 mm
To 100 parts by mass of the obtained heat-treated product, 0.3 parts by mass of calcium sulfate dihydrate is added as a blending / slurry step, and the additive is suspended in water to obtain a concentration (total slurry). A mass of 35% by mass of a heat-treated product with respect to mass was obtained and pulverized with a pulverizer. This pulverized product was classified to obtain regenerated particles having a median diameter of 2.0 μm.

Example 1 Production of Composite Particle 1 As inorganic particles, 50 parts by mass of heavy calcium carbonate (CaCO ₃ ) particles having a median diameter of 1.6 μm and 50 parts by mass of titanium dioxide (TiO ₂ ) particles having a median diameter of 0.5 μm. 200 g of this inorganic particle mixed slurry (concentration: 10% by mass) was prepared. To this mixed slurry, 60 g of an aqueous sodium silicate solution was added, and a suspension treatment (slurry) was prepared by carrying out a dispersion treatment at a rotational speed of 3,000 rpm for 20 minutes using a homomixer. Next, this slurry was put into a 1 L four-necked flask equipped with a stirrer, a temperature sensor, and a reflux condenser, and heated to 75 ° C. in an oil bath while stirring. Next, while maintaining the slurry in the container at 75 ° C., 150 mL of 1N sulfuric acid was added dropwise over 1 hour at a dropping rate of 2.5 mL / min using a metering pump to obtain composite particles 1. The pH of the reaction solution at this time was 8.8. Furthermore, no. The wet cake of composite particles 1 was obtained by filtering, washing with water using 2 filter papers, and filtering again.

<Examples 2 to 9 and Comparative Examples 1 to 4> Production of Composite Particles 2 to 9 and Composite Particles i to iv As inorganic particles, the types and median diameters shown in Table 1 are used. Except having carried out, it carried out similarly to Example 1, and performed Examples 2-9 and Comparative Examples 1-4, and obtained the composite particles 2-9 and the composite particles i-iv. Each inorganic particle was used after being pulverized by a pulverizer so as to have a desired median diameter.

  Table 1 shows the evaluation results of the obtained composite particles.

<Example 10> Manufacture of internal paper The composite particle 1 was slurried with a coreless mixer to prepare a slurry having a solid content concentration of 10%. A pulp slurry containing 10 parts by mass of NBKP (freeness = CSF 520 mL) and 90 parts by mass of LBKP (freeness = CSF 480 mL) was mixed with 15 parts by mass of the slurry, 0.5 parts by mass of a sulfuric acid band, and 0. 7 parts by weight, 1.0 part by weight of a neutral rosin sizing agent, and 0.1 part by weight of a yield improver were added to prepare a paper material having a solid content concentration of 0.9%. The paper stock was hand-made, a pulp sheet was prepared with a paper machine, dried, and then passed through a lab super calender to obtain an internal paper of Example 10.

<Examples 11 to 18 and Comparative Examples 5 to 8>
Each of the internal papers was obtained in the same manner as in Example 10 except that the composite particles shown in Table 2 were used instead of the composite particles 1.

  Table 2 shows the evaluation results of the obtained internal papers.

<Example 19> Production of coated paper 20 parts by mass of composite particle 1 as a pigment, 11 parts by mass of SBR latex (PA4098: Japan A & L), 2 parts by mass of starch (star coat: Nippon Food Processing Co., Ltd.) and a dispersant ( Aron A-6028: Toa Gosei Chemical Co., Ltd.) 0.3 parts by mass was mixed with water and slurried with a Coreless mixer to prepare a coating liquid having a solid content of 50% by mass.

The coating liquid was coated on one side by roll test coater so that the basis weight 64 g / drying one side of quality base paper of m ² weight 12 g / m ^2, then dried and further testing supercalendered (linear pressure 160 kg / cm × 2 times) to obtain a coated paper.

<Examples 20 to 21 and Comparative Examples 9 to 12>
Except having used each composite particle shown in Table 3 instead of the composite particle 1, operation similar to Example 19 was performed and the coated paper of Examples 20-21 and Comparative Examples 9-12 was obtained.

  Table 3 shows the evaluation results of the obtained coated papers.

  From the results of Tables 2 and 3, the composite particle-containing paper with the composite particles of the present invention internally added and the coated paper coated with the composite particles of the present invention have excellent opacity and post-print opacity. I understand that. In addition, the results of Table 2 show that the composite particles of the present invention have a high yield.

The composite particles obtained by the production method of the present invention can be suitably used as an internal filler in papermaking or a pigment in a coating solution.

Claims (8)

A method for producing composite particles obtained by combining inorganic particles,
A suspension step of suspending at least two kinds of particles as the inorganic particles in an alkali silicate aqueous solution to obtain a suspension of inorganic particles;
A method of producing composite particles, comprising: adding a mineral acid to the suspension, and precipitating silica on the surface of the inorganic particles to aggregate the inorganic particles.   The method for producing composite particles according to claim 1, wherein the median diameter of the inorganic particles is 0.5 μm or more and 2 μm or less, and the mode diameter is smaller than the median diameter. The inorganic particles are
Particles A having a median diameter of 1 μm to 3 μm;
The method for producing composite particles according to claim 1, comprising particles B having a median diameter of 0.2 μm or more and less than 1 μm. The particle A is
Paper sludge is the main raw material, and is at least one selected from the group consisting of regenerated particles obtained through dehydration, heat treatment and pulverization processes, and heavy calcium carbonate particles,
The method for producing composite particles according to claim 3, wherein the particles B are titanium dioxide particles.   The composite particle obtained by the manufacturing method of the composite particle of any one of Claim 1 to 4.   The composite particle according to claim 5, wherein the median diameter is 3 μm or more and 10 μm or less, and the ratio of particles having a particle diameter of 2 μm or less is 20% or less.   A composite particle-added paper in which the composite particle according to claim 5 or 6 is internally added. A coated paper having a base paper and one or more coating layers formed on at least one surface of the base paper,
A coated paper, wherein the coated layer contains the composite particles according to claim 5 or 6.