JP2012255230A - Printing paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide printing paper which employs a regenerated particle and a titanium dioxide particle as a raw material for a filler contained in the paper, and has high opacity and whiteness.SOLUTION: The printing paper containing the filler comprises composite particles as the filler, which are formed by aggregating the regenerated particles obtained by using paper sludge as a main raw material and passing the sludge through dehydration and heat treatment and a pulverization step, and the titanium dioxide particles, with the use of an aggregating agent; and has a printing opacity of 90% or more but 96% or less. It is preferable that at least one part of a surface of the composite particle is covered with silica. In addition, a content of silica in the composite particle is preferably 5 mass% or more but 30 mass% or less. An average particle diameter (primary particle diameter) of the regenerated particles is preferably 1 μm or larger but 10 μm or smaller, and an average particle diameter (primary particle diameter) of the titanium dioxide particles is preferably 0.2 μm or larger but 1 μm or smaller.

Description

  The present invention relates to printing paper.

  In recent years, printing paper such as newsprint tends to be lightened from the viewpoint of resource problems and cost reduction. However, when the printing paper is reduced in weight, there is a disadvantage that blank paper opacity and opacity after printing (hereinafter, both opacity are also simply referred to as “opacity”) are reduced. As a countermeasure, it is common practice to increase the opacity by adding various fillers 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 in order 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 improving 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). Thus, by covering the regenerated particles with silica, the yield and whiteness are improved, but the regenerated particles have not reached the same quality as other fillers. Therefore, there is room for improvement in printing paper using recycled particles or titanium dioxide particles as a filler.

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 an object thereof is to provide a printing paper having high opacity and whiteness by using recycled particles and titanium dioxide particles as raw materials for the internally added filler. .

The invention made to solve the above problems is
Printing paper with internal fillers,
As the filler, a composite particle in which papermaking sludge is used as a main raw material, and regenerated particles and titanium dioxide particles obtained through dehydration, heat treatment and pulverization steps are aggregated with a flocculant,
The printing opacity is 90% or more and 96% or less.

  The composite particles internally added to the printing paper are formed by agglomerating regenerated particles having a relatively large particle size and generally titanium dioxide particles having a small particle size, so that the surface of the regenerated particles is covered with titanium dioxide. The particles are in an aggregated state. That is, the composite particles have a relatively large particle diameter despite the use of titanium dioxide particles, and can exhibit excellent yield and opacity improving ability. In particular, in the above composite particles, not only the flocculation effect by the flocculating agent, but also a part of the 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 said composite particle, this aggregation state is maintained also at the time of papermaking etc., and the outstanding yield can be exhibited. Moreover, since the said composite particle is in the state which the titanium dioxide particle with high whiteness covers the reproduction | regeneration particle | grains, it is high in whiteness in spite of using reproduction | regeneration particle | grains. Accordingly, the printing paper can increase both opacity and whiteness.

  In addition, since the composite particles are obtained by aggregating the two kinds of particles with a flocculant, the particle size distribution may be sharp compared to the mixed particle state of two particles, in this case, Yield can be further improved. Further, when the particle size distribution of the internally added composite particles is so narrow, the composite particles can be uniformly distributed in the paper, and the weight can be reduced without using a high ash content.

  It is preferable that at least a part of the surface of the composite particle is coated with silica. According to the composite particle, since at least a part of the surface is coated with silica in this way, the two types of particles are more firmly fixed, and this agglomeration state is more reliably ensured even in the papermaking process. Can be maintained, and the yield can be further improved. In addition, the composite particles can obtain a high oil absorption amount due to the excellent oil absorption ability of the porous silica covering at least a part of the surface, and can increase the printing opacity. Therefore, the printing paper can further increase opacity and whiteness.

  The content of silica in the composite particles is preferably 5% by mass or more and 30% by mass or less. According to the composite particles, by setting the silica content in 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. Therefore, the printing paper can further increase opacity and whiteness.

  The average particle diameter of the composite particles is preferably 2 μm or more and 15 μm or less. By setting the average particle diameter of the composite particles in the above range, the printing paper can exhibit more excellent opacity 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, according to the printing paper, the excellent light scattering ability of the titanium dioxide particles can be sufficiently exhibited, and both the opacity and the whiteness can be further increased.

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 printing paper of the present invention can exhibit high opacity and whiteness using a filler made from recycled particles and titanium dioxide particles. Therefore, the printing paper can be suitably used as newsprint paper or the like that is highly demanded of weight reduction.

  Hereinafter, embodiments of the printing paper of the present invention will be described in detail.

  In the printing paper of the present invention, composite particles are internally added as a filler. The printing paper is usually obtained by papermaking a pulp slurry containing pulp and filler.

<Pulp>
As said pulp, a well-known thing can be used and used paper pulp, virgin pulp, or these combined things can be used suitably. In addition, it is preferable from a viewpoint of resource saving to use waste paper pulp as a main component.

  Waste paper pulp includes, for example, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, Kamihiro waste paper, Kent waste paper, imitation waste paper, and old paper waste paper. Examples of such a paper include disaggregation / deinked waste paper pulp (DIP) and disaggregation / deinking / bleached waste paper pulp.

  Among these waste paper pulp, newspaper waste paper pulp derived from newspaper waste paper, magazine waste paper pulp derived from magazine waste paper, and the like are preferable, and it is particularly preferable to use a mixture of newspaper waste paper pulp and magazine waste paper pulp. Such waste paper pulp and magazine waste paper pulp has a high recovery rate of waste paper, and the paper pulp types and fillers that make up news paper and magazine paper are similar in each paper maker, thus suppressing fluctuations in the raw material composition. It is suitable at the point which can do. In particular, wastepaper pulp is generally used in newsprints because it is already 50% or more of wastepaper pulp and the content of virgin mechanical pulp and kraft pulp is low. Since it is once paper-made and used paper pulp by used paper processing, it is particularly preferable in that it has uniform properties and has almost constant properties.

  Examples of virgin pulp include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), Chemical pulp such as softwood semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, softwood sulfite pulp, etc .; Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (TGP), Chemi Grand Pulp (CGP), Ground Pulp (GP), Various well-known pulps such as mechanical pulps such as thermomechanical pulp (TMP); pulps chemically or mechanically produced from non-wood fibers such as kenaf, hemp, and straw can be used.

  Among these virgin pulps, in the production of printing paper, mechanical pulp (MP) having an effect of complementing the decrease in bulk due to the use of used paper pulp is preferable, and thermomechanical pulp suitable for adjustment of used paper pulp obtained from used paper ( TMP) is particularly preferred.

  The content of waste paper pulp in the raw material pulp is preferably 50% by mass or more, particularly preferably 80% by mass or more, and further preferably 90% by mass or more. By setting the content of the used paper pulp in the raw material pulp within the above range, environmental properties such as effective use of resources are improved, and printability such as ink inking properties is also improved. Conversely, the content of virgin pulp in the raw material pulp is preferably 10% by mass or more, and particularly preferably 20% by mass or more. If the content of virgin pulp is less than the above range, it is difficult to adjust strength and bulk, resulting in a low-strength printing paper or a bulky printing paper with no stiffness, and there is a risk that transportability and workability will be reduced.

<Filler>
The filler includes the composite particles, and may include other materials such as titanium dioxide, calcium carbonate, kaolin, talc, hydrated silicon, white carbon, regenerated particles, and silica composite regenerated particles. Hereinafter, the composite particles which are essential components will be described in detail.

<Composite particle>
The composite particles are composite particles obtained by aggregating recycled particles obtained from paper sludge as a main raw material through dehydration, heat treatment and pulverization steps and titanium dioxide particles with a flocculant.

  Since the composite particles are formed by agglomerating regenerated particles having a relatively large particle size and relatively small titanium dioxide particles, the titanium dioxide particles are in an aggregated state so as to cover the surface of the regenerated particles. Therefore, according to such composite particles, although the titanium dioxide particles are used, the particle size is relatively large, and excellent yield and opacity improving ability can be exhibited. In particular, in the composite particles, not only the flocculation effect by the flocculating agent, but also a part of the titanium dioxide particles having a small particle size is firmly adhered to the pore portions 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 excellent yield can be exhibited. Moreover, since the said composite particle is in the state which the titanium dioxide particle with high whiteness covers the reproduction | regeneration particle | grains, it is high in whiteness in spite of using reproduction | regeneration particle | grains.

  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. 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 performance while suppressing a decrease in paper strength, and efficiently increase opacity and the like. be able to.

  When the average particle diameter of the composite particles is less than the 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 above upper limit, when used as a filler, as a result of reducing the strength between pulp fibers, paper strength may be reduced, and because the particle size is large, Uniform dispersibility 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 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 size of the regenerated particles is less than the lower limit, aggregation may not proceed to a sufficient particle size even with the aggregating agent, 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 to 1 μm, and more preferably 0.3 μm to 0.8 μm. 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 the difficulty of entering the pores (recesses) 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 aggregating agent is less than the above lower limit, sufficient aggregating ability cannot be exhibited, and the agglomeration of the particles does not proceed, 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 difficult 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 may be coated with silica. According to such composite particles, since at least a part of the surface is coated with silica, the silica has a function as a binder of the above two types of particles and is more firmly fixed. This agglomerated state can be maintained more reliably and the yield can be further improved. In addition, such composite particles have a high oil absorption amount due to the excellent oil absorption ability of the porous silica covering at least a part of the surface, and can increase the printing opacity.

  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 content (hereinafter sometimes referred to as the coverage) is preferably 5% by mass to 30% by mass, and more preferably 5% by mass to 20% by mass. By making the silica content 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. The silica content is calculated by performing elemental analysis of particles, estimating the content ratio of regenerated particles, titanium dioxide, silica, etc. from the constituents contained, and calculating from the content of the silica component after silica coating. it can. Moreover, the content rate of a silica means the ratio of the mass of the silica with respect to the mass of the whole composite particle.

  When the silica content 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. In addition, there may be a case where a sufficient oil absorption effect by silica is not exhibited. On the contrary, when the silica content 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.

<Quality of composite particles>
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 amount 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 amount are used as an internal filler, the printing opacity of the paper is increased because the composite particles absorb the vehicle of the ink impregnated in the paper layer and the organic solvent in the paper layer. 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, the ink absorbability is high, so that the ink sinks, so-called inferior color development may occur.

<Method for producing composite particles>
The method for producing the composite particles is not particularly limited.
(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. Unlike the means of adding a cationic flocculant to a single particle by this method and adding other particles in the subsequent process, the cationic flocculant is used without consuming the effect of the flocculant in the previous particle. Effect (The cationic flocculant preferentially adheres to the negatively charged regenerated particle surface, and titanium dioxide particles can effectively adhere to the surface, while the cationized relatively large regenerated particles. It is possible to sufficiently exhibit the effect of suppressing aggregation between each other and suppressing an increase in size of the obtained composite particles.

  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 setting the concentration of the particle slurry within the above range, the particles can be efficiently aggregated.

  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 this silica coating method, an alkali silicate aqueous solution and a mineral acid are added to the aggregate slurry in this order, and the silica is coated on the surface of the aggregate, or the aggregate slurry is added to the alkali silicate aqueous solution and mixed. Examples thereof include a method of coating a silica by adding a mineral acid. It is preferable that the mineral acid is added in at least two stages to carry out a silica composite reaction.

  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.

  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. The concentration of the diluted sulfuric acid is preferably about 4 to 10N. If the concentration of dilute sulfuric acid is less than 4N, the reaction is slow, and if it exceeds 10N, a local reaction occurs and the calcium carbonate particles may be altered. Moreover, when mineral acid is added rapidly, silica may precipitate in a short time and may not react uniformly (not uniformly combined), so it is preferable to avoid addition within 5 minutes.

  Regarding the reaction temperature in this step, a range of 50 to 100 ° C, particularly 50 to 98 ° C is preferable. 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. When the reaction temperature is less than 50 ° C, the silica formation / growth rate is slow, the coverage of the formed silica-coated composite particles is inferior, the coating tends to peel off, and the coating breaks due to the shearing force applied during the making of 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 the present invention, it is desirable to add at least two stages of mineral acid and to control the temperature at that time. That is, the slurry temperature at the time of adding the mineral acid in the first stage is 50 to 75 ° C., and the slurry temperature at the time of adding the mineral acid after the second stage is at least 10 ° C. higher than that at the first stage. Is desirable. Specifically, the desirable temperature condition is that the liquid temperature in the first stage is 50 to less than 75 ° C., the second stage is heated to 70 to 100 ° C. in accordance with the number of mineral acid addition stages, and the final stage of the reaction. A temperature state of 90 ° C. or more and 98 ° C. or less is obtained, and more uniform silica composite particles can be obtained under these temperature conditions.

  The pH of the final reaction solution is preferably 8.0 to 11.0, more preferably 8.3 to 10.0, and most preferably 8.5 to 9.0. In the production of silica particles (white carbon) obtained by reacting a conventional alkali silicate and mineral acid, alkali oxalate is used until the pH is 5.5 to 7.0 in order to complete the reaction between the alkali silicate and the mineral acid. A method of adding mineral acid is adopted, but when mineral acid is added until the pH reaches 7.0 or less, the calcium component contained in the regenerated particles easily reacts with calcium hydroxide. The volume average particle diameter of the silica composite particles obtained is excessively decreased or the shape becomes inhomogeneous, so that it is difficult to obtain a decrease in yield on paper, generation of paper dust, and sufficient opacity. When the pH exceeds 11.0, the reaction between the alkali oxalate and the mineral acid becomes dull and it becomes difficult for the silica to form a composite on the surface of the aggregate of the regenerated particles and the titanium dioxide particles. There is a possibility of causing a problem that it is difficult to obtain opacity.

  When adding the mineral acid in one stage, it is preferable to set the addition amount so that the addition time of the mineral acid takes 40 minutes or more. In the present invention, as described above, the mineral acid is preferably added in two or more stages. In this case, it is preferable to uniformly add the mineral acid in each stage in order to obtain a homogeneous silica composite. In addition, after one stage of addition (addition until the mineral acid reaches a neutralization rate of 20 to 50% with respect to the aqueous alkali oxalate solution), a holding time of about 5 minutes to 20 minutes is made, so that the silica complex reaction In addition, the silica is homogeneously combined on the surface of the aggregate of the regenerated particles and the titanium dioxide particles, and by adding the mineral acid in the second stage, it becomes possible to further promote the laminated composite of the silica, Silica can be more uniformly combined on the surface of the aggregate of the regenerated particles and the titanium dioxide particles.

  When adding the mineral acid in two or more stages, the addition amount is set so that the mineral acid addition time for one stage takes 10 minutes to 45 minutes. preferable. When adding the mineral acid in two or more stages, it is preferable for the homogeneous silica composite to set the addition amount so that the addition time of the mineral acid after the second stage takes about 10 minutes to 120 minutes.

  The composite particles obtained have a volume average particle diameter of preferably 2 μm to 15 μm, more preferably 4 μm to 10 μm. If the volume average particle diameter of the composite particles is less than 2 μm, the effect of silica composite cannot be sufficiently exhibited, and the effect of improving the oil absorption and opacity may not be seen, and the volume average particle diameter of the composite particles exceeds 15 μm. When used as a filler internally added to the paper, the bond strength between the pulp fibers may be reduced and the paper strength may be reduced.

When silica coating of aggregates of regenerated particles and titanium dioxide particles is performed, for example, an aggregate slurry and an aqueous alkali silicate solution are added and dispersed to prepare a slurry. The slurry concentration obtained by mixing the aggregate and alkali silicate is 8 -14 mass% is preferable. By adjusting the slurry concentration, the particle diameter of the silica-coated composite particles formed is controlled. In addition, the particle size of the silica-coated composite particles formed by adjusting the solid content ratio of alkali silicate (SiO ₂ equivalent) to the aggregates of regenerated particles and titanium dioxide particles is controlled, and at the same time The composition ratio can be adjusted.

<Other additives>
In addition to the pulp and filler, the pulp slurry (printing paper) includes, for example, starches, polyacrylamide, paper strength enhancers such as epichlorohydrin, rosin, alkyl ketene dimer, ASA (alkenyl succinic anhydride), medium An internal sizing agent such as a reactive rosin, a coagulant such as a sulfuric acid band or polyethyleneimine, and a coagulant such as polyacrylamide or a copolymer thereof can be contained.

<Surface treatment agent>
The printing paper is preferably coated with a surface treatment agent on both sides. The surface treatment agent is not particularly limited, and known materials such as starches, celluloses, water-soluble synthetic adhesives and the like can be used as appropriate, but contain oxidized starch and hydroxyethylated starch (HES). Is preferred.

  In the printing paper, when the surface treatment agent applied to both sides of the base paper includes the oxidized starch and the hydroxyethylated starch as described above, the two kinds of starches are applied when the surface treatment agent is applied. Does not penetrate into the base paper and forms a strong film on the surface. Therefore, the printing paper has high surface strength and can suppress the generation of paper dust, and thus has excellent printing workability. In addition, according to the printing paper, occurrence of nappari trouble during printing is also suppressed.

  By using the above two types of starch, the starch does not penetrate to the inside of the base paper, and the cause of forming a strong film on the surface is not clear, but the carboxyl group etc. of oxidized starch and the hydroxyl group of hydroxyethylated starch It is conceivable that they are polymerized by being bonded (esterification reaction or the like) and cross-linked, making it difficult to penetrate into the inside. In addition, it is considered that the mixing of the two types of starch results in an appropriate viscosity, and the esterification reduces the affinity between the starch and cellulose constituting the pulp fiber, making it difficult to penetrate. It is done. In addition, it is thought that the fall of the said viscosity is a cause of reaction of 2 types of starch. Furthermore, suppression of the occurrence of Nepari trouble on the printing paper is also considered to be caused by a decrease in the hydrophilicity of starch due to the esterification.

  In particular, in the printing paper, since composite particles obtained by aggregating recycled particles and titanium dioxide particles with a flocculant are internally added, a surface treatment agent containing oxidized starch and hydroxyethylated starch is applied. As a result, a firmer film is formed on the surface, and printability and the like can be further improved. More preferably, composite particles obtained by agglomerating regenerated particles and titanium dioxide particles with a flocculant are further added, and composite particles in which at least a part of the surface is coated with silica are further added, and oxidized starch and hydroxyethylated starch are added. By applying the surface treatment agent to be included, a stronger coating film is formed on the surface, the opacity is much higher, the generation of paper dust is less, and the printing paper with good ink setting property can be obtained. The reason why the surface strength is increased by using the composite particles is not clear, but since the composite particles are a mixture formed of various oxides, some component is an ester of the two types of starches. It is conceivable that, when a surface treatment agent is applied by performing a catalytic function such as a conversion reaction, the surface film-forming property is improved by this catalytic action. In addition, since this composite particle has an irregular shape and a porous shape, it is considered that this shape enhances the catalytic function.

  In addition, according to the printing paper, the surface treatment agent does not penetrate into the inside as described above, and a void is left inside the paper by forming a film on the surface. According to the printing paper, because of this gap, the degree of light scattering inside the paper increases, and as a result, the blank paper opacity and the printing opacity can be increased.

  Examples of the oxidized starch include those in which a carboxyl group or the like has been introduced into the molecule by an oxidation reaction with sodium hypochlorite or the like. The mass average molecular weight of the oxidized starch is preferably 500,000 to 1,000,000. The hydroxyethylated starch preferably has a mass average molecular weight of 1.2 million to 2,000,000. By setting the molecular weights of the two types of starch within the above range, the viscosity of the surface treatment agent can be controlled within a suitable range, the coating property can be improved, and the penetration of starch into the paper can be further reduced. The mass average molecular weight is a numerical value measured using a gel permeation chromatography method (GPC method).

  When the weight average molecular weight of the oxidized starch and hydroxyethylated starch is less than the lower limit, the starch easily penetrates into the base paper during coating, and as a result, the surface strength may not be sufficiently improved. On the other hand, when these mass average molecular weights exceed the above upper limit, the viscosity is increased and the applicability may be lowered.

  The content ratio of the oxidized starch and the hydroxyethylated starch is preferably from 1: 9 to 9: 1, more preferably from 5: 5 to 7: 3, on a mass basis. By setting the content ratio of the two types of starch within the above range, it can be prepared to have a suitable viscosity, and it is considered that the above esterification reaction and the like can proceed efficiently. Can be prevented from penetrating into the base paper, and a strong film can be formed on the surface.

  The surface treatment agent may contain other starch, PVA (polyvinyl alcohol), polyacrylamide, antifoaming agent, water-resistant agent, surface sizing agent, preservative, etc., as appropriate, in addition to the two types of starch. it can. Among these, a surface sizing agent is preferably contained in order to improve sizing properties.

  In addition, by using both said 2 types of starch and surface sizing agent as a surface sizing agent, a surface sizing agent becomes easy to stay on the surface, and the addition amount of a surface sizing agent can be reduced. In addition, it is possible to suppress paper stains on the offset printing press that are caused by excessive addition of the surface sizing agent.

  As the surface sizing agent, known ones can be used. For example, styrene-based sizing agent, olefin-based sizing agent, alkyl ketene dimer, alkenyl succinic anhydride, rosin and the like can be used. Styrenic sizing agents are preferred from the viewpoint of compatibility with ink in rotary printing and the effect of preventing the filler from falling off. By using a styrene-based sizing agent as a surface sizing agent for starch having a content ratio of oxidized starch and hydroxyethylated starch of from 1: 9 to 9: 1 on a mass basis, the starch can be applied more uniformly and the surface strength can be increased. The styrenic sizing agent stays on the surface of the paper and the size effect is increased.

  The blending ratio of the styrenic sizing agent to the total starch of the oxidized starch and the hydroxyethylated starch is preferably 5 to 30 parts by mass of the styrenic sizing agent with respect to 100 parts by mass of starch as a solid content. When the styrenic size is less than 5 parts by mass, it is difficult to sufficiently improve the size and surface strength of the paper, and when it exceeds 30 parts by mass, the cost is increased and the opacity and ink drying properties are reduced. There is a fear.

  Examples of the styrene-based sizing agent include styrene acrylic acid copolymer, styrene (meth) acrylic acid copolymer (note that (meth) acrylic acid means “acrylic acid and / or methacrylic acid”), styrene. Examples include (meth) acrylic acid (meth) acrylic acid ester copolymers, styrene maleic acid copolymers, styrene maleic acid half ester copolymers, and styrene maleic acid ester copolymers.

  The B-type viscosity of the surface treatment agent is preferably 5 cps or more and 80 cps or less, and more preferably 10 cps or more and 40 cps or less. According to the printing paper, by setting the viscosity of the surface treatment agent at the time of application to the above range, the applicability can be further improved, and the penetration of starch into the paper can be further reduced. When the viscosity of the surface treatment agent is less than the above lower limit, this surface treatment agent containing starch or the like is likely to penetrate into the inside of the paper at the time of coating, and as a result, it may be difficult to obtain newspaper paper with high surface strength. is there. On the other hand, if this concentration exceeds the above upper limit, workability during application may be reduced, or uniform application may be difficult.

As the coating amount of the surface treatment agent, in order to sufficiently improve the surface strength of the paper, 0.1 to 2.0 g / m ² in dry mass per side on the front and back surfaces of the base paper, and further 0.3 to 1 It is preferably applied in an amount of 0.5 g / m ² . If it is less than 0.1 g / m ² , it may be difficult to obtain a sufficient film with starch or the like, and sufficient paper surface strength may not be obtained. On the other hand, if it exceeds 2.0 g / m ² , a large amount of mist of a surface treatment agent such as starch is generated around the coating equipment, and the peripheral equipment is soiled, and there is a risk of paper breakage and paper defects due to the soiling. .

<Quality etc.>
The printing opacity of the printing paper is required to be high from the viewpoint that it is difficult for the show-through during printing to occur. The lower limit measured in accordance with the printing opacity test method described later is 90%, and 91% preferable. Further, the upper limit of the printing opacity is 96%, preferably 95%. If the printing opacity is less than the above lower limit, show-through tends to occur. Conversely, if the printing opacity exceeds the above upper limit, the necessary filler increases, resulting in a decrease in the adhesion between the pulp fibers, the strength of the printing paper decreases, or printing due to the loss of the filler from the paper surface. Not only the paper dust increases, but also dirt in the machine system in the manufacturing process increases and the operability deteriorates.

  The ash content of the printing paper is preferably 5% to 13%, and more preferably 7% to 12%. The printing paper has high opacity (blank paper opacity and printing opacity) because the ash content is in the above range, and a large amount of filler fills the voids of the fiber, so that the surface treatment agent The penetration can be suppressed, and as a result, the surface strength is increased. Therefore, according to the printing paper, despite the high filler content (high ash content), conversely, the high content of this filler is used to increase the surface strength, resulting in excellent Printing workability can be demonstrated.

The basis weight of the printing paper is measured in accordance with the “basis weight measurement method” described in JIS-P8124 from the viewpoint of weight reduction, for example, ensuring the paper quality strength in high-speed rotary printing, ensuring the printing opacity, It is preferably 38 g / m ² or more, more preferably 40 g / m ² or more, and from the viewpoint of weight reduction, the basis weight is preferably 48 g / m ² or less, more preferably 46 g / m ² or less. If the basis weight is less than the above lower limit, for example, it is difficult to ensure strength in a high-speed offset rotary printing press. If the basis weight exceeds the above upper limit, it will go against the recent weight saving and resource saving.

  The whiteness of the printing paper conforms to “Method for measuring paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)” described in JIS-P8148 so as not to cause eye strain of the subscriber. Measured to be 52% to 57%, more preferably 53% to 56%.

  The printing paper is required to have a high white paper opacity because it is difficult to see through. However, “Paper and paperboard—Opacity test method (backing of paper) —Diffusion illumination method” described in JIS-P8149. 90% is preferable as the lower limit of the white paper opacity measured in accordance with "", and 92% is particularly preferable. The upper limit of the white paper opacity is preferably 96% and particularly preferably 95%. If the blank paper opacity is less than the above lower limit, the back-through tends to occur. On the other hand, when the white paper opacity exceeds the above upper limit, the necessary filler increases, and as a result, the adhesion between the pulp fibers decreases and the strength of the printing paper decreases.

<Printing paper manufacturing method>
The printing paper can be manufactured by a known manufacturing method.

  First, a pulp slurry is prepared as described above to make a paper to obtain a base paper. This papermaking can be performed using a known papermaking machine or the like.

  The surface treatment agent is applied to both sides of the base paper obtained by the paper making. For the application of the surface treatment agent, a coating device generally used in the papermaking field, such as a size press, a blade metalling size press, a rod metalling size press, a blade coater, a bar coater, a gate roll coater, a rod coater, an air knife coater, etc. Can be used.

  The temperature of the base paper during application of the surface treatment agent is preferably 35 ° C. or higher and 85 ° C. or lower, and more preferably 40 ° C. or higher and 75 ° C. or lower. By applying a surface treatment agent on both surfaces of such a relatively high temperature base paper, when the surface treatment agent comes into contact with the base paper, a binding reaction of two types of starch occurs, and so on. Penetration is suppressed, and a thin and high-strength film can be formed on the surface. When the temperature of the base paper is less than the above lower limit, the starch is likely to penetrate into the inside, and the surface strength may not be sufficiently increased. On the other hand, when this temperature exceeds the upper limit, applicability is lowered and a uniform film may not be formed.

  After the surface treatment agent is applied and dried, generally, press finishing is performed by passing the paper 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 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 slurry of the regenerated particles thus obtained is alkaline with a pH of 12 or more. For example, when added to the raw material pulp as a filler, the papermaking pH may be increased, and the effect of the papermaking chemicals in the preparation process may be increased. There is a risk of decline. 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 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.

[Average particle size (unit: μm)]
Using a laser diffraction particle size distribution measuring apparatus [Microtrack / Nikkiso Co., Ltd.] (model number: MT-3300), (volume) average particle diameter (D ₅₀ : μm) was measured. 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 content (% by mass)]
Using an X-ray microanalyzer (model number: E-MAX · S-2150) manufactured by HORIBA, Ltd., elemental analysis is performed at an acceleration voltage (15 KV), and the content ratio of regenerated particles, titanium dioxide, silica, etc. from the contained components The silica content (mass%) was calculated from the content of the silica component after silica coating.

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

[Oil absorption (mL / 100g)]
It measured according to JIS-K5101-13-1 (2004). 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 amount 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 was measured according to “Paper and paperboard—basis weight measurement method” described in JIS-P818124 (1998).

[Ash content (unit:%)]
It was measured in accordance with “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method” described in JIS-P8251 (2003).

[Blank Opacity (Unit:%)]
Measured according to JIS-P8149 (2000) "Paper and paperboard-Opacity test method (backing of paper)-Diffuse illumination method".

[Printing opacity (unit:%)]
JAPAN TAPPI No. No. 45 (2000) “Newspaper—Post-printing opacity test method”, and measured using a measuring instrument ISO whiteness meter (manufactured by Suga Test Instruments Co., Ltd.).

[Whiteness (paper) (unit:%)]
Measured according to JIS-P8148 (2001) “Paper, paperboard and pulp—Measurement method of ISO whiteness (diffuse blue light reflectance)”.

[Tensile strength (longitudinal) (unit: kN / m)]
It was measured according to “Paper and paperboard—Test method for tensile properties—Part 2: Constant speed extension method” described in JIS-P8113 (2006).

[Ink fillability]
Using an offset printer (model number: Komori SYSTEMC-20, manufactured by Komori Corporation), continuous 10,000 copies can be printed with newspaper ink (trade name: Newsjet Naturalis (black), manufactured by Dainippon Ink & Chemicals, Inc.). went. About the obtained printed matter, the clearness and the shading unevenness of an image were observed visually, and it evaluated based on the following evaluation criteria.
(Evaluation criteria)
5: The image is clear and there is no unevenness in density, and the ink deposition property is excellent.
4: The image is clear, there is almost no unevenness in density, and the ink deposition property is good.
3: There are some portions where the image is unclear and some shading unevenness.
2: There are a portion where the image is unclear and uneven density, and ink deposition is not good.
1: Overall, the image is unclear, the density unevenness is remarkable, and the ink deposition property is inferior.

[Blanket paper dust piling]
Using an offset rotary printing press (model number: LITHOPIA BTO-4, manufactured by Mitsubishi Heavy Industries, Ltd.), prints 100,000 copies on both sides of a 50-continuous printing paper, and the paper on the printing paper and blanket non-image area. The presence or absence of powder generation and accumulation was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
5: Generation | occurrence | production of paper surface scraps and paper dust is not recognized at all.
4: Scratch on the paper surface is slightly observed, but no deposition on the blanket is observed.
3: Scratch on the paper surface is slightly recognized and a little accumulation on the blanket is recognized.
2: Generation | occurrence | production of the paper surface scraping was recognized and it has accumulated on the blanket.
1: Accumulation of paper dust on the paper surface and blanket is remarkable.

[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.

<Production 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, a cationic flocculant (“Himoloc FR-740” manufactured by Hymo Co., Ltd.) was added in a solid content of 1,750 ppm with respect to the solid content of the particle to obtain an aggregate slurry.

10,000 kg of the agglomerate slurry (concentration 17.4% by mass) is placed in a tank equipped with a stirrer, and while stirring, an aqueous sodium silicate solution (No. 3 sodium silicate: SiO ₂ concentration 29 wt / wt%, Na ₂ O concentration 9 wt / wt) %) 1,320 kg and dilution water were added, and the solid content ratio of the aggregated particles and silicic acid content (SiO ₂ equivalent) shown in Table 1 and the concentration of the slurry composed of alkali silicate and aggregated particles (11% by mass) were prepared. did. Diluted sulfuric acid (4 N) was added and stirred as a mineral acid to obtain a composite particle slurry. The slurry was stirred using a known mixer, the pH of the slurry was measured with a pH meter manufactured by Horiba, and the reaction temperature was measured with a known thermometer. In the primary reaction step, dilute sulfuric acid was added for the time shown in Table 1 so that the neutralization rate of the aqueous alkali silicate solution and sulfuric acid was 33%. Next, the temperature of the slurry was adjusted to 93 ° C. by heating and stirring. Thereafter, in the secondary reaction step, dilute sulfuric acid was added at the mineral acid addition time shown in Table 1 until the reaction completion pH shown in Table 1 was obtained, thereby obtaining a composite particle slurry containing composite particles 1 coated with silica.

  The obtained composite particles 1 had a silica content of 18% by mass, an average particle size of 6.4 μm, a whiteness of 94.0%, and an oil absorption of 62 mL / 100 g.

<Production Examples 2-14 and Comparative Production Examples 1-3>
Reproduction particles and titanium dioxide particles listed in Table 1, production ratios (mass ratio) thereof, flocculants and production conditions 2 to 14 and comparative production in the same manner as in Production Example 1 except for the reaction conditions in the silica coating. Examples 1 to 3 were performed to obtain composite particles 1 to 14 and i to iii.

  In Production Examples 5, 7, and 14, the silica coating after aggregation was not performed. In Comparative Production Example 1, only the regenerated particles were aggregated and then coated with silica. In Comparative Production Example 2, light calcium carbonate particles having an average particle diameter of 3.0 μm were used instead of the regenerated particles. In Comparative Production 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 average particle diameter, whiteness, and oil absorption of each composite particle obtained.

Example 1
80% by mass of disaggregated / deinked waste paper pulp (DIP) and 20% by mass of thermomechanical pulp (TMP) were added, and the freeness was 120 mLC. S. A pulp slurry adjusted to F (based on JIS-P8121) was obtained. To this pulp slurry, composite particles 1 obtained as a filler are added so that the ash content becomes the value shown in Table 1 (12.0%), and 0.07 parts by mass of a flocculant per 100 parts by mass of absolutely dry pulp. A base paper having a basis weight of 42.3 g / m ² was made with a twin wire paper machine after adding 0.05 part by weight of a coagulant (Himo SC 924 made by Himo Co., Ltd.).

Furthermore, as a surface treatment agent, a starch solution in which 90 parts by mass of oxidized starch (mass average molecular weight of 700,000 manufactured by Nippon Food Processing Co., Ltd.) and 10 parts by mass of hydroxyethylated starch (HES: mass average molecular weight of 150,000 manufactured by Penford) was mixed. A styrene-based sizing agent (“SS2712” manufactured by Seiko PMC Co., Ltd.) was blended in 15 parts by mass with a solid content of 100 parts by mass of starch (solid content concentration 6%, B-type viscosity 22 cps). The surface treatment agent was applied to both surfaces of the base paper having a surface temperature of 50 ° C. in a dry mass of 1.2 g / m ² (each 0.6 g / m ² per side) to obtain a printing paper of Example 1.

(Examples 2 to 17 and Comparative Examples 1 to 3)
The same operations as in Example 1 were performed except that the filler type, surface treatment agent, and ash content were changed as shown in Table 1, and printing papers of Examples 2 to 17 and Comparative Examples 1 to 3 were obtained.

(Evaluation)
Each of the obtained printing papers was evaluated for basis weight, ash content, white paper opacity, printing opacity, whiteness, tensile strength, ink fillability, and blanket paper dusting by the above methods. The evaluation results are shown in Table 2.

  As shown in Table 2 above, the printing paper of the present invention has high opacity (blank paper opacity and printing opacity), and has high ink applicability and evaluation of blanket paper dusting and high printability. I understand. Furthermore, the printing paper of the present invention has high whiteness and tensile strength.

The printing paper of the present invention has excellent opacity and printability, and can be suitably used for newsprint.

Claims (5)

Printing paper with internal fillers,
As the filler, a composite particle in which papermaking sludge is used as a main raw material, and regenerated particles and titanium dioxide particles obtained through dehydration, heat treatment and pulverization steps are aggregated with a flocculant,
A printing paper having a printing opacity of 90% to 96%.   The printing paper according to claim 1, wherein at least a part of the surface of the composite particle is coated with silica.   The printing paper according to claim 2, wherein a content of silica in the composite particles is 5% by mass or more and 30% by mass or less.   The printing paper according to claim 1, wherein the composite particles have an average particle diameter of 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 printing paper 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.