JP2012121752A - Composite particle, composite particle internally added paper, and coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite particles having high yield, ability to improve opacity, and whiteness, and to provide composite particle internally added paper and coated paper that use the composite particles and have outstanding opacity.SOLUTION: Regenerated particles whose main raw material is paper making sludge and which are obtained by passing through dehydration, heat treatment, and pulverization process, and titanium dioxide particles are aggregated by flocculant to result in composite particles. In the composite particle internally added paper, the composite particles are internally added. Teh coated paper has a base paper and one or a plurality of coating layers formed on at least one face of the base paper. The coating layer includes the composite particle.

Description

  The present invention relates to composite particles containing regenerated particles and titanium dioxide particles, composite particle-added paper, and coated paper.

  In order to improve opacity, whiteness, printability, and the like, various fillers suitable for improving these functions are internally added to the paper. As the filler, titanium dioxide, calcium carbonate, kaolin, talc, hydrated silicic acid (white carbon), urea-formalin polymer fine particles and the like are used. Among these, titanium dioxide is effective in improving opacity because it has a high refractive index and excellent light scattering ability. However, the titanium dioxide particles are expensive, have a low oil absorption capacity, and have a disadvantage that the yield during papermaking is low due to the small particle diameter.

  Under such circumstances, various methods have been proposed to improve the yield of titanium dioxide particles as a filler. As this method, calcium carbonate particles and titanium oxide particles are aggregated using a specific aggregating agent (cationic polymer, amphoteric polymer, acrylic acid monomer, etc.) to obtain aggregated particles (Japanese Patent Application Laid-Open No. 2004-18336). And JP-A-6-93204). However, according to such a method of aggregating the two kinds of particles, since the binding between the calcium carbonate particles and the titanium oxide particles by the aggregating agent is not strong, this aggregation state is not maintained during papermaking. A sufficient yield improvement effect cannot be obtained, and as a result, the opacity of the obtained paper cannot be effectively improved.

  On the other hand, the reuse of inorganic substances in paper sludge discharged from various processes in a paper mill as so-called recycled particles for paper making fillers has become an important issue related to environmental problems in the paper industry. As a method for producing such regenerated particles, paper sludge is used as a main raw material, and dehydration, heat treatment and pulverization steps are generally performed in this order. Such regenerated particles have been improved in various ways, but because the raw material is waste, the quality including the particle size is not constant, and the whiteness is not sufficient.

  Thus, as a technique for improving the quality of fillers such as regenerated particles, attempts have been made to combine the particles with silica (see Japanese Patent Application Laid-Open Nos. 2008-81390 and 2003-49389). By covering the regenerated particles with silica in this manner, the yield and whiteness are improved, but there is room for improvement in order to make the regenerated particles have the same quality as other fillers.

JP 2004-18336 A JP-A-6-93204 JP 2008-81390 A JP 2003-49389 A

  The present invention has been made based on the above-mentioned circumstances, and uses regenerated particles and titanium dioxide particles, composite particles having high yield, opacity improving ability and whiteness, and using these composite particles, and excellent Another object of the present invention is to provide a composite particle internal paper and coated paper having high opacity and the like.

The invention made to solve the above problems is
Paper sludge as the main raw material, regenerated particles obtained through dehydration, heat treatment and pulverization process,
It is a composite particle formed by agglomerating titanium dioxide particles with a flocculant.

  The composite particles are formed by agglomerating regenerated particles and titanium dioxide particles having a relatively large particle diameter, and thus the titanium dioxide particles are in an aggregated state so as to cover the surface of the regenerated particles. Therefore, according to the composite particle, the particle diameter is relatively large despite using titanium dioxide particles, and excellent yield and opacity improving ability can be exhibited. In particular, in the composite particles, not only a flocculating effect by a flocculating agent, but also a part of titanium dioxide particles having a small particle size penetrates into the pores (recesses) of the porous regenerated particles during aggregation. By doing so, a strong aggregated state is formed. For this reason, according to the regenerated particles, this agglomerated state is maintained even during papermaking and the like, and an excellent yield can be exhibited. In addition, since the composite particles are in a state in which the titanium dioxide particles having high whiteness cover the regenerated particles, the whiteness is high even though the regenerated particles are used.

  It is preferable that at least a part of the surface of the composite particle is coated with silica. According to the composite particles, since at least a part of the surface is coated with silica as described above, the two types of particles are more firmly fixed, and this aggregation state can be more reliably ensured even in the papermaking process. This can be maintained, and the yield can be further improved. In addition, the composite particles can exhibit a high oil absorption by the excellent oil absorption ability of the porous silica covering at least a part of the surface, and the printing opacity can be increased.

  The silica coverage is preferably 5% by mass or more and 30% by mass or less. According to the composite particles, by setting the silica coverage within the above range, the aggregation state of the two types of particles can be sufficiently maintained even during papermaking, and as a result, the yield can be further improved. In addition to being able to achieve this, it is possible to achieve both excellent white paper opacity and printing opacity due to the balance between silica and other particles.

  The composite particles preferably have an average particle size of 2 μm or more and 15 μm or less. When the composite particles have an average particle diameter in the above range, when used as a filler, the composite particles can exhibit better yield while suppressing a decrease in paper strength.

  The regenerated particles may have an average particle size (primary particle size) of 1 μm or more and 10 μm or less, and the titanium dioxide particles may have an average particle size (primary particle size) of 0.2 μm or more and 1 μm or less. According to the composite particle, by using two types of particles having a particle size in the above range, the above-mentioned regenerated particles having a relatively large particle size are used as nuclei, and a plurality of small dioxide particles having a small particle size so as to cover the surface. It is easy to form an aggregated state of titanium particles. Therefore, the composite particles can sufficiently exhibit the excellent light scattering ability of the titanium dioxide particles, and can further increase both opacity and whiteness.

  The composite particle internal paper of the present invention contains the above composite particles. According to the composite particle-added paper, since composite particles having the above performance are internally added, the yield of the composite particles as the filler is high, and the white paper opacity and the printing opacity can be increased.

  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 particle. It is characterized by containing. Since the coated paper contains the composite particles as a pigment in the coating layer, the coated paper is excellent in blank paper opacity and post-printing opacity.

Here, the average particle diameter refers to a volume average particle diameter in the measured particle size distribution by laser diffraction scattering method (D _50).

  As described above, the composite particles of the present invention have high yield, opacity improving ability, and whiteness. Therefore, composite particle-added paper and coated paper using this composite particle can exhibit excellent opacity and the like.

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

<Composite particle>
The composite particle of the present invention is a composite particle obtained by agglomerating a regenerated particle obtained from papermaking sludge as a main raw material through a dehydration, heat treatment and pulverization step and a titanium dioxide particle with a flocculant.

  The composite particles are formed by agglomerating regenerated particles and titanium dioxide particles having a relatively large particle diameter, and thus the titanium dioxide particles are in an aggregated state so as to cover the surface of the regenerated particles. Therefore, according to the composite particle, the particle diameter is relatively large despite using titanium dioxide particles, and excellent yield and opacity improving ability can be exhibited. In particular, in the composite particles, not only the flocculating effect by the flocculating agent, but also a part of the titanium dioxide particles having a small particle size is firmly adhered to the pores of the porous regenerated particles during the aggregation. An agglomerated state is formed. For this reason, according to the regenerated particles, this agglomerated state is maintained even during papermaking, and the agglomerated state is not easily broken, so that an excellent yield can be exhibited. In addition, since the composite particles are in a state in which the titanium dioxide particles having high whiteness cover the regenerated particles, the whiteness is high even though the regenerated particles are used.

  The average particle size of the composite particles is preferably 2 μm or more and 15 μm or less, and more preferably 4 μm or more and 10 μm or less. Since the composite particles have an average particle diameter in the above range, when used as a filler, the composite particles can exhibit better yield performance while suppressing a decrease in paper strength. Moreover, the uniform dispersibility, such as when contained in a coating liquid and used as a pigment, can be improved. Therefore, the opacity when used as a filler or pigment can be efficiently increased.

  When the average particle size 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 average particle diameter exceeds the upper limit, when used as a filler, as a result of reducing the strength between the pulp fibers, the paper strength may be reduced, and because the particle size is large, slurry or coating Uniform dispersibility in the liquid may be reduced, and opacity and opacity after printing may be reduced.

  The content ratio (mass ratio) of the regenerated particles and titanium dioxide particles is preferably 30:70 to 90:10, and more preferably 50:50 to 90:10. By setting the content ratio of both particles in such a range, titanium dioxide particles having a small particle diameter can be efficiently aggregated on the surface with the regenerated particles as nuclei. Therefore, according to the composite particle, it is possible to exhibit a better yield by increasing the particle size as an aggregate while utilizing the excellent light scattering ability of the titanium dioxide particles. Moreover, according to the said composite particle, whiteness can be raised more by efficiently coat | covering the reproduction | regeneration particle | grains which are not high whiteness with titanium dioxide.

<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.

  The average particle size (primary particle size) of the regenerated particles is preferably 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 5 μm or less. By setting the average particle diameter of the regenerated particles in the above range, aggregation of the regenerated particles having a small particle diameter progresses, whereas the effect of the aggregation of particles having a large particle diameter from the tendency of the agglomeration to hardly proceed is obtained. Can be easily controlled within a desired range, and the yield in papermaking can be further increased.

  When the average particle diameter of the regenerated particles is less than the above lower limit, aggregation may not proceed to a sufficient particle size even with a flocculant, and the yield may not be sufficiently increased. Conversely, when the average particle size of the regenerated particles exceeds the above upper limit, the particle size of the resulting aggregate may be too large, and as a result, the paper strength may be reduced.

<Titanium dioxide particles>
Titanium dioxide particles have a high refractive index and an excellent light scattering ability, and therefore can increase the white paper opacity.

  The titanium dioxide particles used for the composite particles preferably have an average particle size (primary particle size) of 0.2 μm or more and 1 μm or less, and more preferably 0.3 μm or more and 0.8 μm or less. The average particle size of the titanium dioxide particles relative to the average particle size of the regenerated particles is preferably 0.05 times or more and 0.4 times or less.

  By setting the average particle diameter of the titanium dioxide particles in such a range, a plurality of titanium dioxide particles having a small particle diameter are aggregated so as to cover the surface with the regenerated particles having a relatively large particle diameter as a core. Easy to form a state. Therefore, the composite particles can sufficiently enhance both the opacity and the whiteness by sufficiently exhibiting the excellent light scattering ability of the titanium dioxide particles. When the average particle diameter of the titanium dioxide particles is less than the above lower limit, aggregation is unlikely to proceed and it may be difficult to obtain composite particles having a sufficient particle diameter. On the other hand, when the average particle diameter of the titanium dioxide particles exceeds the above upper limit, the cohesiveness is low and the yield may be lowered due to difficulty in entering the pores (recessed parts) of the regenerated particles.

  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.

<Flocculant>
The flocculant aggregates the regenerated particles and the titanium dioxide particles. The aggregating agent is not particularly limited as long as it can entangle and aggregate a plurality of particles by the polymer chain, and a polymer compound such as a cationic polymer, an anionic polymer, or a nonionic polymer. Can be used. However, according to the knowledge of the present inventors, it is preferable to use a cationic polymer in order to use a slurry containing regenerated particles and titanium dioxide particles and coat the surface of the regenerated particles with titanium dioxide particles as a core. It is more preferable to use a cationic synthetic polymer. By using a cationic polymer as the aggregating agent, the aggregating agent is preferentially attached to the negatively charged regenerated particle surface, and the titanium dioxide particles can be effectively attached to the surface, Aggregation of relatively large cationized regenerated particles can be suppressed, and the resulting composite particles can be prevented from becoming large. Moreover, the cationic charge density and suitable molecular weight of this flocculant can be easily adjusted by using a cationic synthetic polymer.

  As a lower limit of the mass average molecular weight of the flocculant, particles having a small particle diameter progress in aggregation, while particles having an originally large particle diameter sufficiently exhibit the effect that aggregation does not proceed easily, that is, the effect of narrowing the particle size distribution. Therefore, 4 million is preferable, 6 million is more preferable, and 7 million is particularly preferable. On the other hand, the upper limit of the mass average molecular weight is preferably 20 million, more preferably 12 million, and particularly preferably 10 million. By setting the molecular weight of the aggregating agent within the above range, regenerated particles having a small particle diameter can be aggregated, while regenerated particles having an originally large particle diameter can exhibit cohesiveness in which aggregation does not easily proceed. In particular, for regenerated particles having an average particle size as described above, a composite particle (aggregate) having a desired particle size can be efficiently obtained by using an aggregating agent having a molecular weight in such a range. be able to. The mass average molecular weight is a numerical value measured using a gel permeation chromatography method (GPC method).

  When the mass average molecular weight of the flocculant is less than the above lower limit, sufficient aggregating ability cannot be exhibited, and the particles are not agglomerated, so that the yield may not be improved. Conversely, if this average molecular weight exceeds the above upper limit, the agglomeration ability is too strong, the occurrence of partial agglomeration, the viscosity of the slurry is increased, the paper workability is reduced, the paper strength of the resulting paper is It may decrease.

  The upper limit of the cation charge density of the flocculant is preferably 30 meq / g, more preferably 20 meq / g, and particularly preferably 15 meq / g. On the other hand, the lower limit of the cation charge density is preferably 0.1 meq / g, more preferably 1 meq / g, and particularly preferably 2 meq / g. By setting the cation charge density of the aggregating agent in the above range, in the broad particle size distribution of the regenerated particles, the particles having a small particle diameter proceed to agglomerate, whereas the particles having an originally large particle diameter are less likely to proceed to agglomerate. Excellent cohesiveness can be exhibited. In addition, when using a some component as an aggregating agent, the cation charge density as the whole aggregating agent is said.

In the present invention, the cationic charge density is a value measured by the following method. After adjusting the sample to an aqueous solution of pH 4.0, the anion demand was measured by titration using a 1/1000 normal aqueous potassium potassium sulfate solution with a particle charge measuring device (Muteck PCD-03) based on the streaming potential method. To do. The cationic charge density per 1 g of sample is calculated by the following formula (1).
Cationic charge density = A / B (1)
A: Anion requirement (μeq / l) of the flocculant aqueous solution adjusted to pH 4.0
B: Solid content concentration of the flocculant aqueous solution (g / l)

  When the cation charge density of the flocculant exceeds the above upper limit, in addition to the regenerated particles, the titanium dioxide particles also have a cation charge, and aggregation may not easily occur due to repulsion due to the charge. Conversely, when the cation charge density of the flocculant is less than the above lower limit, the effect of being able to electrically agglomerate negatively charged regenerated particles (particularly regenerated particles having a small particle size) should be sufficiently exhibited. May not be possible, resulting in a broad particle size distribution.

  Cationic synthetic polymers that can be suitably used as flocculants include homopolymers of (meth) acrylate-based cationic monomers or copolymers with nonionic monomers, and Mannich modification of polyacrylamide. Products, poly (dimethyldiallylammonium chloride), dialkylamine-epichlorohydrin condensate, alkylene dichloride-polyalkylene polyamine condensate, polyethyleneimine, dicyandiamide-formalin condensate, polyvinylamidine, chitosan, polyalkylene polyamine, and the like. These can be used alone or in combination of two or more.

  Among these, a copolymer of a (meth) acrylate cationic monomer and a nonionic monomer is preferable from the viewpoint of aggregation and slurry thickening suppression, and a (meth) acrylate cationic monomer is preferable. A copolymer of a monomer and a nonionic monomer and a mixture of a polyalkylene polyamine are particularly preferred.

  Examples of (meth) acrylate-based cationic monomers include (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloyloxy-2-hydroxypropyltrimethylammonium chloride, and the like. Can do. Among these (meth) acrylate cationic monomers, it is preferable to use a (meth) acrylic monomer from the viewpoints of agglomeration with respect to regenerated particles and titanium dioxide particles and suppression of thickening of the slurry. ) Acryloyloxyethyltrimethylammonium chloride is more preferred, and acryloyloxyethyltrimethylammonium chloride is particularly preferred.

  Nonionic monomers used for copolymerization with (meth) acrylate cationic monomers include acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, N, N-dimethylacrylamide, Examples thereof include acrylonitrile, diacetone acrylamide, and 2-hydroxyethyl (meth) acrylate. Among these, acrylamide is preferably used because it is easy to obtain a cationic synthetic polymer having a desired molecular weight and charge density.

<Silica>
In the composite particles, at least a part of the surface is preferably coated with silica. According to such composite particles, since at least a part of the surface is coated with silica, the above two types of particles are more firmly fixed, and this agglomerated state is more reliably maintained even in the papermaking process. And the yield can be further improved. In addition, the composite particles can exhibit a high oil absorption by the excellent oil absorption ability of the porous silica covering at least a part of the surface, and the printing opacity can be increased.

  The silica is not particularly limited, and a known silica can be used. As will be described later, by depositing and coating silica in an aqueous solution, it is possible to efficiently coat the aggregate and to exhibit a superior oil absorption ability because it can be coated in a porous state. Can do.

  The silica coverage is preferably 5% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less. By making the silica coverage in such a range, it is possible to sufficiently maintain the aggregation state of the two types of particles even during papermaking, and as a result, in addition to being able to further increase the yield, silica and It is possible to achieve both excellent white paper opacity and printing opacity due to the balance with other particles. This silica coverage can be calculated from the content of the silica component after silica coating by conducting elemental analysis of the particles, estimating the content ratio of clay, calcium carbonate, talc and the like from the constituent components contained. The silica coverage refers to the ratio of the mass of silica to the total mass of the composite particles.

  When the silica coverage is less than the above lower limit, this silica does not sufficiently function as a binder for the two kinds of particles, and the agglomerated state is divided during papermaking, and the yield may not be improved. Moreover, the sufficient oil absorption improvement effect by silica may not be exhibited. On the other hand, when the silica coverage exceeds the above upper limit, the silica coating amount becomes too large, so that the light scattering function of the titanium dioxide particles is not sufficiently exhibited, and the blank paper opacity may be lowered.

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

  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 have high whiteness as described above. The specific whiteness of the composite particles is preferably 80% or more, and more preferably 85% or more. The whiteness is a value measured according to the Tappi-534 pm-76 method.

  The oil absorption of the composite particles is preferably 30 mL / 100 g or more and 150 mL / 100 g or less, more preferably 60 mL / 100 g or more and 100 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 150 mL / 100 g, there is a case where the ink sinks and the so-called color developability is inferior because the ink absorbability is high.

  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.

<Method for producing composite particles>
Although it does not specifically limit as the manufacturing method of the said composite particle, For example,
(1) A method having an aggregating step of aggregating regenerated particles and titanium dioxide particles with an aggregating agent, and (2) a silica coating step of coating silica on at least a part of the agglomerate surface as necessary. Can do. Hereinafter, each step will be described in detail.

<(1) Aggregation step>
This aggregating step can be performed, for example, by adding an aggregating agent to a particle slurry in which regenerated particles and titanium dioxide particles are dispersed in water. The two particles may be dispersed in water by dispersing the two types of particles in water at the same time, or by dispersing titanium dioxide particles in a regenerated particle slurry in which regenerated particles are dispersed in water, and vice versa. There may be.

  When a cationic flocculant is used as the flocculant, a regenerated particle and titanium dioxide particle slurry in which regenerated particles and titanium dioxide particles (or titanium dioxide particle slurry in which titanium dioxide particles are dispersed in water) are dispersed in water. A cationic flocculant may be added therein. By this method, the effect of using the cationic flocculant without consuming the effect of the flocculant in the previous particle is different from the means of adding other particles in the subsequent step after adding the cationic flocculant to the single particle. (The cationic flocculant preferentially adheres to the surface of the negatively charged regenerative particles, and the titanium dioxide particles can effectively adhere to the surface, while the relatively large regenerated particles that are cationized The effect of suppressing the agglomeration and suppressing the resulting composite particles from becoming large) can be sufficiently exhibited.

  The solid content concentration of both particles (total of regenerated particles and titanium dioxide particles) in the particle slurry is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, and more preferably 15% by mass or more. 25 mass% or less is especially preferable. By making the concentration of the particle slurry in the above range, the efficiency of particle aggregation can be improved.

  When the concentration of the particle slurry is less than the lower limit, the particles may not aggregate to a suitable particle size even by the addition of a flocculant. On the other hand, when the concentration of the particle slurry exceeds the above upper limit, the viscosity is too high and workability may be deteriorated, or the particle size distribution of the composite particles may be widened to reduce the yield.

  The addition amount of the flocculant is preferably 200 ppm or more and 3,000 ppm or less, more preferably 1,000 ppm or more and 2500 ppm or less in terms of solid content, based on the total solid content of the regenerated particles and titanium dioxide particles. In the broad particle size distribution of regenerated particles, for example, in the broad particle size distribution of 500 ppm to 2,000 ppm, agglomeration of particles having a small particle diameter progresses, whereas a particle having an originally large particle diameter effectively exhibits the effect that aggregation does not easily proceed. Therefore, it is particularly preferable.

  When the addition amount of the flocculant is less than the above lower limit, sufficient aggregation cannot be exhibited, and the yield improvement effect may not be exhibited. On the contrary, if the addition amount of the flocculant exceeds the above upper limit, the viscosity of the slurry may be significantly increased, or tertiary and quaternary aggregation may occur, and the paper strength of the obtained paper may be reduced.

<(2) Silica coating step>
In this silica coating step, silica is coated on the surface of the aggregate obtained in the above step. As a method for coating this silica, an alkali silicate aqueous solution and a mineral acid are added to the aggregate slurry in this order, and the surface of the aggregate is coated with silica, or the aggregate slurry is added to the alkali silicate aqueous solution and mixed. Then, a method of adding a mineral acid to coat silica can be exemplified.

  Although the said alkali silicate aqueous solution is not specifically limited, A sodium silicate solution (No. 3 water glass) is desirable at the point which is easy to acquire. 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 SiO2). The composite particles in which the aggregate formed when the content exceeds 10% by mass is coated with silica are not silica-coated composite particles, but are coated with white carbon, and the regenerated particles that form the core (aggregate) and titanium dioxide There is a risk that the optical characteristics may not be exhibited at all. On the other hand, if it is less than 3% by mass, the silica component in the resulting composite particles may be lowered.

  Examples of the mineral acid include dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and other mineral acid dilutions, but they are price, handling, calcium elution prevention from regenerated particles, and corrosion prevention of equipment / equipment. For this reason, dilute sulfuric acid is most preferable. Further, the concentration when adding dilute sulfuric acid is preferably 0.2 to 4.0 molar. 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, there is a possibility that the addition within 5 minutes may result in an insufficient uniform reaction system configuration.

  The reaction temperature in this step is preferably in the range of 60 to 100 ° C. As a result of the present inventors' extensive studies, the reaction temperature between the regenerated particles and the aggregates of titanium dioxide particles used in the present invention and the silica is determined by the formation of silica, the crystal growth rate, and the dynamics of the formed silica-coated composite particles Affects strength. If the reaction temperature is less than 60 ° C, the silica formation / growth rate is slow, the coverage of the formed silica-coated composite particles is inferior, the coating is easily peeled off, and the coating breaks due to the shearing force applied when making the filler-added paper. Cheap. Moreover, when it exceeds 100 degreeC, since it is a water-system reaction, since an autoclave must be used, a reaction process will become complicated.

  In addition, the reaction holding time (mineral acid addition time) in this step is preferably 20 minutes or longer and 3 hours or shorter, and more preferably 30 minutes or longer and 2 hours or shorter. When the reaction holding time is less than the above lower limit, sufficient silica coating may not be performed. On the other hand, when the reaction holding time exceeds the above upper limit, the silica coating amount is too large, and the particle size of the composite particles becomes too large. As a result, the paper strength and opacity may be lowered.

  Moreover, when performing silica coating of the aggregate of regenerated particles and titanium dioxide particles, for example, the aggregate is added to and dispersed in an alkali silicate aqueous solution to prepare a slurry. The slurry concentration is preferably 3 to 35% by mass. By adjusting the slurry concentration, the particle size of the silica-coated composite particles to be formed can be controlled, and at the same time, the composition ratio of the aggregate and silica can be determined.

  As a preferable silica coating step, an aggregate of both particles is added and dispersed in an aqueous alkali silicate solution to prepare an aggregate slurry. Thereafter, while stirring the slurry, the liquid temperature is maintained in the range of 60 to 100 ° C., and a mineral acid is added to form a silica sol. Silica-coated composite particles can be obtained by adjusting the pH of the mixed solution (mixed solution of agglomerates, alkali silicate and mineral acid) to neutral to weakly alkaline, and preferably the mixed solution to a pH of 8 to 11. .

<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 white paper opacity and the printing opacity can be increased.

  The method for producing a composite particle-added paper using the composite particles of the present invention as an internal filler is the same as the method for producing an ordinary filler-added paper. For example, the composite particles and, if necessary, other fillers and It is obtained by adding a slurry mixed with a pulp raw material slurry and making a paper slurry containing additives such as a paper strength enhancer, a sizing agent, and a yield improver, if necessary, and 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 pulp raw material slurry, known ones can be used. For example, starch, vegetable gum, aqueous cellulose derivative, polyacrylamide and the like are used as a paper strength enhancer, and 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.

By making the paper stock slurry with a known paper machine, composite particle-containing paper can be produced. The basis weight of the composite paper-added 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 white paper opacity and the opacity after printing are excellent.

  The method for producing coated paper using the composite particles of the present invention is the same as the method for producing ordinary coated paper. For example, the composite particles of the present invention are mixed with other pigments as necessary, and a dispersing agent is used. It is obtained by mixing the slurry obtained by adding an adhesive and other additives to prepare a coating material, and coating the slurry on a paper material such as medium-quality paper or high-quality paper.

  Also when manufacturing coated paper using the said composite particle, the oil absorption degree of the said composite particle has the preferable range of 30-150 mL / 100g. 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 contrary, when the oil absorption exceeds 150 mL / 100 g, when blended as a coating pigment in the coating layer, a binder such as latex or starch is absorbed, resulting in a disadvantage that the coating layer strength is lowered.

  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 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 a combination of a drum and an elastic roll can be used as appropriate in an on-machine or off-machine specification.

<Method for producing regenerated particles>
Here, the method for producing regenerated particles suitable for the composite particles of 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, the deinking floss is a raw material for producing regenerated particles having 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.

  When the moisture content of the raw material after dehydration exceeds 60%, the processing temperature in the heat treatment process is lowered, energy loss for heating increases, and uneven combustion of the raw material is likely to occur, 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 to transport the dehydrated material. 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 increased in this way, it is possible to suppress overburning of the raw material and to suppress thickening when the obtained regenerated particles are slurried. 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 in a portion where the gears such as a VF pump mesh with each other, 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 in the previous stage of the drying process, and it is more preferable to classify the granulated product to make the particle size 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 a synthesis example and an Example demonstrate 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.

[Average particle size (μm)]
A volume average particle diameter (D ₅₀ : μm) was measured using a laser diffraction particle size distribution measuring device [Microtrack / Nikkiso Co., Ltd.] (model number: MT-3300). 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.

[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 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 (2).
Oil absorption (mL / 100g)
= [Look of Linseed Oil (mL) x 100] / Paper (g) (2)

[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 (3). 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 (3)

[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 volume average particle size of 1.0 μm, 2.0 μm, 3.4 μm, 5.0 μm and 10.0 μm, respectively.

<Example 1>
60 parts by mass of regenerated particles having an average particle diameter of 3.4 μm obtained by the above method and 40 parts by mass of titanium dioxide particles having an average particle diameter of 0.5 μm are dispersed in water, and 17.4% by mass (solid content concentration). Particle slurry was obtained. To this particle slurry, 1,750 ppm of a cationic flocculant (“Himoloc FR-740” manufactured by Hymo Co., Ltd.) was added to obtain an aggregate slurry.

  The aggregate slurry is adjusted to a solid content concentration of 10%, 60 g of sodium silicate aqueous solution (5% by mass) is added to 200 g of the slurry, and dispersion treatment is performed for 20 minutes at 3,000 rpm using a homomixer. A slurry containing sodium silicate was prepared. 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 85 ° C. in an oil bath while stirring. Next, while maintaining the slurry in the container at 85 ° C., 150 mL of 1N sulfuric acid was dropped over 100 minutes at a dropping rate of 2.5 mL / min using a metering pump, and the composite particles 1 coated with silica were separated. A composite particle slurry containing was obtained.

  The obtained composite particles 1 had a silica coverage of 21% by mass, an average particle size of 6.4 μm, a whiteness of 94.0%, and an oil absorption of 62 mL / 100 g.

<Examples 2 to 17 and Comparative Examples 1 to 3>
Examples 2 to 17 and Comparative Example were the same as Example 1 except that the regenerated particles, titanium dioxide particles, the mixing ratio (mass ratio), the flocculant, and the silica coating conditions described in Table 1 were used. 1-3 were performed, and composite particles 1-17 and i-iii were obtained.

  In Examples 7, 9 and 17, the silica coating after aggregation was not performed. In Comparative Example 1, only the regenerated particles were aggregated and then coated with silica. In Comparative Example 2, light calcium carbonate particles having an average particle diameter of 3.0 μm were used instead of the regenerated particles. In Comparative Example 3, only the regenerated particles and the titanium dioxide particles were mixed, and neither aggregation nor silica coating was performed.

The flocculants in Table 1 used are as follows.
Cationic flocculant: “Himoloc FR-740” manufactured by Hymo Corporation
Copolymer of acrylamide and acryloyloxyethyltrimethylammonium chloride and polyalkylene polyamine mixture Weight average molecular weight: 8.5 million Cationic charge density: 8.0 meq / g
Anionic flocculant: “Himolock FA230” manufactured by Hymo
Copolymer of sodium acrylate and acrylamide Mass average molecular weight: 14 million Cationic charge density: -4 meq / g

  Table 1 shows the silica coverage, average particle diameter, whiteness, and oil absorption of each composite particle obtained.

<Example 18>
Using the obtained composite particles 1, a slurry having a solid content concentration of 10% was prepared. 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, 0. 7 parts by mass, 1.0 part by mass of a neutral rosin sizing agent, and 0.1 part by mass of a yield improver were added to prepare a paper material having a solid content concentration of 0.9% by mass. The paper stock was hand-made, a pulp sheet was prepared with a paper machine, dried, and then passed through a lab super calendar to obtain a composite particle-containing paper of Example 18 having a rice basis weight of 64.7 g / m ² .

<Examples 19 to 34 and Comparative Examples 4 to 6>
Except that the composite particles used were those shown in Table 2, the same operations as in Example 18 were performed to obtain each composite particle-added paper of Examples 19 to 34 and Comparative Examples 4 to 6.

  Table 2 shows the basis weight, ash yield, blank paper opacity, and post-print opacity of each composite particle-containing paper obtained.

<Example 35>
As pigments, 20 parts by mass of composite particles 1, 40 parts by mass of calcium carbonate particles (Hydrocurve # 90: Omiya) and 20 parts by mass of kaolin (HF-90: Huber), SBR latex (PA4098: Japan A & L) 11 Part by weight, 2 parts by weight of starch (star coat: Nippon Food Processing Co., Ltd.) and 0.3 parts by weight of a dispersant (Aron A-6028: Toa Gosei Chemical Industry) are mixed in water, slurried with a Coreless mixer, and a solid content of 50 A mass% coating solution was prepared.

The coating liquid was coated by a roll test coater each side as one side of fine base paper having a basis weight of 41.5 g / m ² a dry weight 6.8 g / m ^2, then dried and further testing supercalendered ( A linear pressure of 160 kg / cm × 2 passes through) to obtain a coated paper.

<Examples 36 and 37 and Comparative Examples 7 and 8>
Each composite particle shown in Table 3 was used in place of the composite particle 1, and the same operation as in Example 35 was performed except that the coating amount in Table 3 was used, and Examples 36 and 37 and Comparative Examples 7 and 8 Each coated paper was obtained.

  Table 3 shows the opacity and printing opacity of each coated paper obtained.

  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. Moreover, it turns out that the composite particle of this invention has high yield property and whiteness from the result of Table 2.

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

Claims (7)

Paper sludge as the main raw material, regenerated particles obtained through dehydration, heat treatment and pulverization process,
Composite particles obtained by agglomerating titanium dioxide particles with an aggregating agent.   The composite particle according to claim 1, wherein at least a part of the surface is coated with silica.   The composite particle according to claim 2, wherein the silica coverage is 5% by mass or more and 30% by mass or less.   The composite particle according to claim 1, wherein the average particle diameter is 2 μm or more and 15 μm or less. The average particle diameter of the regenerated particles is 1 μm or more and 10 μm or less,
The composite particle according to any one of claims 1 to 4, wherein an average particle diameter of the titanium dioxide particles is 0.2 µm or more and 1 µm or less.   A composite particle-containing paper to which the composite particle according to any one of claims 1 to 5 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 any one of claims 1 to 5.