JP5946672B2 - Newspaper - Google Patents

Description

  The present invention relates to newsprint.

In recent years, weight reduction of newsprint has been promoted from the viewpoint of resource saving and transportation cost reduction, and ultralight paper with a basis weight of 43 g / m ² has become the mainstream of newsprint. Because this ultra-lightweight newsprint has a lower basis weight than conventional newsprint, problems such as print back-through due to a decrease in optical suitability such as opacity and concealment, and blurring of print due to a decline in printability occur. It has the property of being easy.

  Conventionally, measures such as adding an inorganic filler such as white carbon have been taken as means for supplementing such opacity (see JP 2011-26714 A). However, the addition of inorganic fillers may cause problems such as increased generation of paper dust due to a decrease in paper surface strength, and waste paper pulp used as a main raw material for newspapers in recent years contains a large amount of inorganic impurities. Therefore, there is a limit to the addition of inorganic fillers. On the other hand, in recent years, there has been a demand for further reduction of newspapers in order to save resources, and demands for optical suitability such as opacity and concealment are further increased.

JP 2011-26714 A

  The present invention has been made based on the above-described circumstances, and an object thereof is to provide a newsprint having high opacity, printability, printing workability and the like even with a low basis weight.

The invention made to solve the above problems is
Newspaper with pulp as the main ingredient and internal filler,
The filler contains inorganic particles,
The volume average particle diameter D50 of the inorganic particles is 2 μm or more and 10 μm or less, and the ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 is 5 or less.

  The newspaper is internally added with inorganic particles having a volume average particle diameter D50 in the above range and a small ratio of the volume 90% particle diameter D90 to the volume 10% particle diameter D10, that is, a sharp particle size distribution. Accordingly, the inorganic particles exhibit high yield with respect to the raw material pulp and high dispersibility in the paper layer, and thus have high opacity and printability.

  The ratio D90 / D50 of the volume 90% particle diameter D90 to the volume average particle diameter D50 of the inorganic particles is preferably 3 or less. Since the particle size of the inorganic particles has such characteristics, the particle size distribution becomes sharper and the content of coarse particles is reduced, so that the inorganic particles exhibit higher dispersibility in the paper layer. However, since moderate voids are formed between the particles, the opacity and printability of the newspaper can be further increased.

  It is preferable that the inorganic particles include silica composite regenerated particles and / or silica composite calcium carbonate particles. By using these particles as the inorganic particles, the opacity, printability, oil absorption, etc. of the newspaper can be improved.

The newspaper preferably has a basis weight of 37 g / m ² or more and 44 g / m ² or less. The newspaper can be suitably used as a lightweight newspaper by setting the basis weight within the above range.

  Here, “volume average particle diameter”, “volume 10% particle diameter”, and “volume 90% particle diameter” mean that the particle size distribution measured by the laser diffraction scattering method is 50 cumulative from the smaller diameter side of the cumulative volume distribution. %, 10% and 90% mean particle diameter. In addition, when a filler contains multiple types of inorganic particles, it measures using the particle size distribution of the whole filler which mixed multiple types of inorganic particles. The “basis weight” is a value measured according to JIS-P8124.

  “Recycled particles” means paper sludge (preferably deinked floss containing filler or pigment separated from pulp fibers in the deinking process of used paper processing equipment) through dehydration, drying, combustion and pulverization processes. Recycled particles.

  As described above, the newsprint of the present invention has high opacity, printability, printing workability, etc. even with a low basis weight. Therefore, the newspaper can be suitably used as a lightweight newspaper.

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

  The newspaper of the present invention contains inorganic particles as a filler. The newsprint is 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 newsprint, mechanical pulp (MP) having an effect of complementing the decrease in bulk due to the use of waste paper pulp is preferable, and thermomechanical pulp suitable for the adjustment of waste paper pulp obtained from waste 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. When the content of virgin pulp is less than the above range, it is difficult to adjust the strength and bulk of the newsprint, and the transportability and workability may be reduced.

<Filler>
In the present invention, inorganic particles are used as a filler. Examples of the inorganic particles include titanium dioxide, calcium carbonate, kaolin, talc, hydrated silicon, white carbon, regenerated particles, silica composite particles, and the like. One or more of these can be used as a filler. Can be used as Among these, silica composite calcium carbonate particles and silica composite regenerated particles having a particle size distribution described below as a simple substance are particularly preferable.

  The inorganic particles used in the present invention have a volume average particle diameter D50 of 2 μm or more and 10 μm or less, more preferably 3 μm or more and 8 μm or less, and further preferably 4 μm or more and 5 μm or less. When the volume average particle diameter of the inorganic particles is less than the above range, the yield of the inorganic particles may be reduced. Conversely, if the volume average particle diameter of the inorganic particles exceeds the above range, the paper strength may be reduced, and the dispersibility of the inorganic particles may not be sufficiently obtained, and the opacity of the newspaper may be reduced. .

  The inorganic particles have a ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 of 2 or more and 5 or less, more preferably 2.5 or more and 4.5 or less. When D90 / D10 exceeds the above range, the dispersion of the particle diameter of the inorganic particles is large, and the dispersibility of the inorganic particles cannot be obtained. As a result, the opacity of the newspaper may be lowered. Further, since the ratio of inorganic particles having a large particle diameter increases, paper powder piling may easily occur. On the other hand, when D90 / D10 is less than the above range, it is necessary to extremely reduce the variation in the particle diameter, which may significantly increase the production cost of the inorganic particles.

  Further, the inorganic particles preferably have a ratio D90 / D50 of the volume 90% particle diameter D90 to the volume average particle diameter D50 of 1 or more and 3 or less, and more preferably 1.5 or more and 2.5 or less. When D90 / D50 exceeds the above range, the ratio of inorganic particles having a large particle diameter increases, so that there is a risk that paper powder piling is likely to occur, and the strength and opacity of the newspaper may be reduced. On the contrary, when D90 / D50 is less than the above range, it is necessary to extremely reduce the variation in particle diameter, and the production cost of the inorganic particles is significantly increased.

  In addition, the particle diameter (D50, D10, D90) of an inorganic particle means what measured the particle diameter of the whole filler which mixed multiple types of inorganic particle, when a filler contains multiple types of inorganic particles.

<Silica composite calcium carbonate particles>
The silica composite calcium carbonate particles include calcium carbonate particles and silica that covers at least a part of the surface of the calcium carbonate particles. The above-mentioned silica composite calcium carbonate particles are usually an aggregate of particles in which calcium carbonate particles coated with silica are aggregated and calcium carbonate particles coated only with silica and not aggregated exist. Is the body.

  The silica composite calcium carbonate particles are coated with silica on the calcium carbonate particles in this manner, so that the ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 is 2 or more and 5 or less. It is smaller than the ratio of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 of calcium carbonate particles or the like. That is, the calcium carbonate particles having a large variation in particle size are in a state in which the variation in particle size is small by the silica coating. According to the above-mentioned silica composite calcium carbonate particles, which are aggregates of such particles, there are few particles having a small particle size, so that they tend to stay between fibers during paper making, yield is improved, and bulkiness is increased due to flexible properties. Also contributes to sex. In particular, it is preferable to adjust the silica content to 2% by mass or more and 30% by mass or less because particles having a small particle diameter are selectively aggregated flexibly with silica. In addition, according to the silica composite calcium carbonate particles, the surface of the particles having originally large particle diameters are coated with silica, so that the wire wear degree can be lowered. Furthermore, the silica composite calcium carbonate particles have a porous shape due to coating by precipitation on the surface of silica, and have a high oil absorption and can increase the opacity after printing.

  In addition, as a reduction range of D90 / D10 in the silica composite calcium carbonate particles after silica composite from the ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 in the primary particles of calcium carbonate particles before silica composite Is preferably 0.2 or more, and more preferably 0.5 or more.

  Thus, the particle diameter is small by setting the decrease range of D90 / D10 in the silica composite calcium carbonate particles after silica composite from D90 / D10 in the primary particles of calcium carbonate particles before silica composite to 0.2 or more. The particles are selectively agglomerated softly with silica, and particles having a large particle diameter are coated with silica without agglomeration, so that an effect of improving opacity and reducing wire wear can be obtained. In particular, when heavy calcium carbonate is used as the calcium carbonate, the reduction range of D90 / D10 in the primary particles of the calcium carbonate particles by silica coating and the silica composite calcium carbonate particles can be effectively made 0.2 or more, and the above effect Can be remarkably exhibited.

<Calcium carbonate particles>
The calcium carbonate particles used in the silica composite calcium carbonate particles preferably have a volume average particle diameter (primary particle diameter) of 0.5 μm to 3 μm, and more preferably 0.8 μm to 2.5 μm. By setting the volume average particle diameter of the calcium carbonate particles in such a range, the yield and opacity of the silica composite calcium carbonate particles can be increased in combination with the aggregation by silica described later.

  Further, as the calcium carbonate particles, those in which the ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 described above is larger than the ratio of the silica composite calcium carbonate particles obtained are suitable. Used. By using calcium carbonate particles having a large ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10, the particles having a small particle diameter are agglomerated together with the silica coating while the particle diameter is increased. In the case of a large particle size, only a silica coating is formed and almost no agglomeration occurs, so that calcium carbonate particles having a wide particle size distribution can be made into silica composite calcium carbonate particles having a narrow particle size distribution width. Yield improvement, oil absorption, opacity, etc. can be increased.

  The ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 of the calcium carbonate particles (primary particles) is preferably 5.1 or more and 8 or less, more preferably 5.3 or more and 7 or less. .

  The calcium carbonate may be either light calcium carbonate or heavy calcium carbonate, but it is preferable to use heavy calcium carbonate. Heavy calcium carbonate particles have a wide primary particle size distribution, that is, an aggregate of calcium carbonate particles with various particle sizes. Those having a large particle size are in a state in which agglomeration is hardly caused only by the silica coating. Therefore, by using heavy calcium carbonate particles as the calcium carbonate particles used for the silica composite calcium carbonate particles, the calcium carbonate particles having the sharp particle size distribution as described above can be obtained easily and reliably.

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

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

<Silica>
The silica that coats the calcium carbonate particles is not particularly limited, and known ones can be used, and the calcium carbonate particles can be efficiently coated by depositing and coating the silica in an aqueous solution as described later. it can.

  The silica content is preferably 2% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 20% by mass or less. By setting the silica content in such a range, for calcium carbonate particles having a small particle size, the amount of silica deposited on the surface is sufficient so that a plurality of particles can be aggregated flexibly. For calcium particles, the silica particles only remain on the surface, particularly the tip portion such as a knife edge that is likely to be precipitated, and the coating is not enough to cause aggregation with other particles. Therefore, according to the above-mentioned silica composite calcium carbonate particles, by covering the calcium carbonate particles having a wide particle size distribution with silica having such a mass ratio, it becomes easy to control to an aggregate state having a narrow particle size distribution. The yield of calcium carbonate particles can be improved, the degree of oil absorption and opacity can be increased, and the degree of wire wear can be reduced.

When the silica content is less than the above lower limit, the calcium carbonate particles cannot be sufficiently aggregated, and the particle size distribution of the obtained silica composite calcium carbonate particles is difficult to narrow, and as a result, the yield may not be improved. On the other hand, when the silica content exceeds the upper limit, the aggregation of calcium carbonate particles having a relatively large particle size can easily proceed. As a result, in the resulting silica composite calcium carbonate particles, the number of particles having a large particle size increases, and similarly, the particle size distribution is not easily narrowed, and the ability to improve opacity is not sufficient. There is a risk that it will decrease or paper dust will be generated easily. By using the silica composite calcium carbonate particles as a filler in the newspaper, particles having a sharp particle diameter are uniformly dispersed in pulp fibers even when the basis weight is a low basis weight of 44 g / m ² or less. Moreover, since the yield is high, news paper with high opacity, good ink fillability, low paper dust, and good tensile strength is preferable.

<Method for producing silica composite calcium carbonate particles>
The method for producing the silica composite calcium carbonate particles is not particularly limited.
(1) a suspension step of suspending calcium carbonate particles in an aqueous alkali silicate solution to obtain a suspension;
(2) A method of adding a mineral acid to the suspension, precipitating silica on the surface of the calcium carbonate particles, covering the suspension, and aggregating the calcium carbonate particles.

  According to the method for producing silica composite calcium carbonate particles, in the agglomeration step, among the calcium carbonate particles, those having a small particle diameter are aggregated with a plurality of particles along with the silica coating, while those having a large particle diameter are silica particles. Only the coating results in almost no aggregation, and the calcium carbonate particles having a wide particle size distribution can be made into silica composite calcium carbonate particles having a narrow particle size distribution. Therefore, according to the said manufacturing method, the silica composite calcium carbonate particle | grains with a high yield, opacity, etc., and a low wire abrasion degree can be obtained.

(1) Suspension process In this process, calcium carbonate particles, preferably wet-pulverized heavy calcium carbonate particles, are mixed in an aqueous alkali silicate solution. The alkali silicate aqueous solution is not particularly limited, but a sodium silicate solution (No. 3 water glass) is preferable in that it is easily available.

  Further, the solid content concentration of the suspension obtained by adding and dispersing the calcium carbonate particles in the alkali silicate aqueous solution is preferably 3 to 35% by mass. By adjusting this concentration within the above range, it becomes easy to control the particle size, particle size distribution, silica content, and the like of the obtained silica composite calcium carbonate particles to a desired range.

Further, as a solid content ratio of the silicate component (SiO ₂ conversion) with calcium carbonate in the alkali silicate aqueous solution is 2: 98 to 30: 70 is preferred, 3: 97-20: 80 is more preferred. By doing in this way, the content rate of the silica of a silica composite calcium carbonate particle becomes like this. Preferably it is 2 to 30 mass%, More preferably, it is 3 to 20 mass%. When the solid content ratio of the silicic acid content (SiO ₂ equivalent) in the alkaline silicate aqueous solution to the calcium carbonate is less than 2:98, the calcium carbonate particles cannot be sufficiently aggregated, and the particle size distribution of the resulting silica composite calcium carbonate particles is It is hard to narrow, and as a result, the ability to improve opacity is not sufficient and the yield may not be improved. On the other hand, if the solid content ratio exceeds 30:70, the aggregation of calcium carbonate particles having a relatively large particle size is likely to proceed. As a result, in the resulting silica composite calcium carbonate particles, the number of particles having a large particle size increases, and similarly, the particle size distribution is not easily narrowed, and the ability to improve opacity is not sufficient. There is a risk that it may decrease or paper dust may be easily generated.

(2) Aggregation step In this step, mineral acid is added to the suspension, and silica is deposited on the surface of the calcium carbonate particles to cover them, thereby aggregating at least a part of the calcium carbonate particles.

  Examples of the mineral acid include diluted solutions of mineral acids such as dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid, but dilute sulfuric acid is preferred in terms of price and handling. Further, the concentration when adding dilute sulfuric acid is preferably 0.2 to 4.0 mol%. Since heavy calcium carbonate suitably used in the production method of the present invention is derived from minerals, it contains impurities such as calcium and aluminum as constituent elements within a predetermined range, and addition of an excessive concentration of mineral acid is obtained. Alteration may occur in the silica composite calcium carbonate particles.

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

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

In this agglomeration step, silica sol is produced by adding a mineral acid as described above, and the suspension is neutral to weakly alkaline, preferably by adjusting the pH to a range of 8 to 11 to obtain silica composite calcium carbonate particles. Can be obtained. Under the present circumstances, while the temperature of the said suspension is 60 degreeC or more and 100 degrees C or less, the silica content rate in the said silica composite calcium carbonate particle is 2 to 30 mass%, More preferably, it is 3 to 20 mass%. It is good to adjust the solid content ratio of the silicic acid content (in terms of SiO ₂ ) and calcium carbonate in the above-described alkali silicate aqueous solution to a range of not more than% and add the mineral acid so that the final reaction solution has a pH of 8-11. . Controlling to the silicic acid content (SiO ₂ conversion) and calcium carbonate solid content ratio, temperature and mineral acid addition amount in such an aqueous alkali silicate solution, more preferably, in the agglomeration step of silica with respect to heavy calcium carbonate By keeping the addition time of the mineral acid from 60 to 120 minutes, more preferably from 70 minutes to 100 minutes, those having a small particle size have agglomeration of a plurality of particles together with the silica coating, while calcium carbonate having a large particle size Silica composites with a narrow particle size distribution as described above, because the particles remain on the surface, especially the tip of the tip, such as a knife edge that is likely to precipitate, and do not have a coating that causes agglomeration with other particles. Calcium carbonate particles can be obtained efficiently. When the addition time of the mineral acid is less than 60 minutes, excessive silica coating may occur, and there is a possibility that silica composite calcium carbonate particles having an excessive particle size may be formed. May become insufficient.

  In this step, it is preferable to add the mineral acid in two or more stages. When the mineral acid is added in two or more stages, the slurry temperature when adding the mineral acid in the first stage is 60 to 75 ° C., and the slurry temperature when adding the mineral acid after the second stage is at least the first stage. It is desirable to raise the temperature by 10 ° C. or more. Specifically, the liquid temperature in the first stage is preferably 60 ° C. or higher and lower than 75 ° C., the second stage is preferably 70 ° C. or higher and lower than 100 ° C., and the final stage of the reaction is preferably 90 ° C. or higher and 98 ° C. or lower. Depending on these temperature conditions, silica composite calcium carbonate particles having a sharper particle diameter can be obtained. In the first stage, by adding a mineral acid with a neutralization rate of 20 to 50% of the aqueous alkali silicate solution, and then performing a second stage mineral acid addition after a holding time of about 5 to 20 minutes, Further, it becomes possible to promote the lamination and compounding of silica, and the silica can be compounded more uniformly on the surface of the calcium carbonate particles.

  Moreover, before the said aggregation process, it is good to further provide the condensation process which obtains the aggregate of a calcium carbonate particle with a coagulant | flocculant. In this way, by condensing the calcium carbonate particles before compounding the silica, it is possible to obtain an aggregate of calcium carbonate particles having a sharp particle size distribution and an appropriate particle size, and combining the aggregate with silica. Thus, the yield of the obtained composite particles can be further improved. As this coagulant, a cationic coagulant is preferable, and for example, diallyldimethylammonium chloride, cationic polyacrylamide and the like can be used.

  The mass average molecular weight of the coagulant is preferably from 100,000 to 1,500,000, more preferably from 200,000 to 800,000. When the mass average molecular weight of the coagulant is less than the above range, sufficient coagulation force may not be obtained. On the other hand, when the mass average molecular weight of the coagulant exceeds the above range, an aggregate of calcium carbonate particles having an excessively large particle size is formed, and the particle size distribution may be broadened to reduce the yield. When a coagulant is added to the slurry, the viscosity becomes too high and workability and yield may be reduced. In particular, if the viscosity of the calcium carbonate particle slurry exceeds 500 cps, the load of the pump for transferring the calcium carbonate particle slurry may increase, and the mixing property of the silica composite calcium carbonate particles with the pulp raw material may decrease. . In addition, there is a possibility that inconveniences in which dirt in the papermaking system becomes obvious. The mass average molecular weight is a numerical value measured using a gel permeation chromatography method (GPC method).

  The cationic charge density of the coagulant is preferably 3 meq / g or more and 25 meq / g or less, and more preferably 5 meq / g or more and 25 meq / g or less. When the cationic charge density of the coagulant is less than the above range, sufficient coagulation force may not be obtained. On the other hand, if the cationic charge density of the coagulant exceeds the above range, the entire surface of the calcium carbonate particles may have a cationic charge, which may make it difficult for condensation to occur due to repulsion due to the charge, and the particle size is excessively large. Aggregates of calcium carbonate particles are formed, the particle size distribution becomes broad, and the yield may decrease. In addition, this cation charge density says the cation charge density as the whole coagulant, when using a some component as a coagulant.

The cationic charge density is a value measured by the following method. First, after adjusting the sample to an aqueous solution of pH 4.0, the amount of anion required 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. Measure. The cation charge density (meq / g) per 1 g of sample is calculated by the following formula (1) using the obtained anion demand.
Cationic charge density = A / B × 1000 (1)
A: Anion requirement of the aqueous coagulant solution adjusted to pH 4.0 (μeq / l)
B: Solid content concentration of coagulant aqueous solution (g / l)

<Silica composite regenerated particles>
The silica composite regenerated particles include regenerated particles and silica that covers at least a part of the surface of the regenerated particles. The silica composite regenerated particles are usually an aggregate of particles in which agglomerated particles of regenerated particles coated with silica and regenerated particles that are coated with silica and not agglomerated are mixed. Recycled particles are obtained from paper sludge as a main raw material and subjected to dehydration, heat treatment and pulverization steps. The regenerated particles obtained through such steps are suppressed from over-combustion and can suppress thickening during slurrying. A preferable method for producing the regenerated particles will be described in detail later.

  The silica composite regenerated particles are coated with silica on the regenerated particles in this way, that is, in the production of the silica composite regenerated particles, based on the regenerated particles having a large variation in particle diameter, The variation is small, and the ratio D90 / D10 of the volume 90% particle diameter D90 to the volume 10% particle diameter D10 is 2 or more and 5 or less. According to the above-mentioned silica composite regenerated particles, which are aggregates of such particles, since there are few particles having a small particle size, it is easy to stay between the fibers during papermaking, the yield is improved, and the bulkiness is increased due to the flexible properties. Also contributes. Furthermore, by adjusting the silica content to 2% by mass or more and 30% by mass or less, particles having a small particle size are selectively aggregated flexibly with silica, which is preferable. According to the silica composite regenerated particles, the surface of the particles having a large particle diameter originally covered with silica can reduce the degree of wire wear.

<Regenerated particles>
The regenerated particles used in the silica composite regenerated particles preferably have a volume average particle size (primary particle size) of 0.5 μm to 3 μm, and more preferably 0.8 μm to 2.5 μm. By setting the volume average particle diameter of the regenerated particles in such a range, the yield and opacity of the silica composite regenerated particles can be increased in combination with the aggregation by silica described later.

<Silica>
The silica for coating the regenerated particles is not particularly limited, and known ones can be used. As described later, the regenerated particles can be efficiently coated by depositing and coating silica in an aqueous solution.

  The silica content is preferably 2% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 20% by mass or less. By setting the silica content in such a range, for the regenerated particles having a small particle size, the amount of silica deposited on the surface is sufficient so that a plurality of particles can be aggregated flexibly, and the regenerated particles having a large particle size. On the other hand, the silica stays on the surface, particularly the tip portion such as a knife edge that is likely to be precipitated, and the coating does not cause agglomeration with other particles. Therefore, according to the silica composite regenerated particles, by covering the regenerated particles having a wide particle size distribution with silica having such a mass ratio, the silica composite regenerated particles can be easily controlled to an aggregate state having a narrow particle size distribution. Yield improvement, oil absorption and opacity can be increased, and wire wear can be reduced.

When the silica content is less than the lower limit, the regenerated particles cannot be sufficiently aggregated, and the particle size distribution of the obtained silica composite regenerated particles is difficult to narrow, and as a result, the yield may not be improved. On the other hand, when the silica content exceeds the above upper limit, it becomes easy to proceed to the aggregation of regenerated particles having a relatively large particle size. As a result, in the resulting composite silica regenerated particles, the number of particles having a large particle size increases, similarly, the particle size distribution is difficult to narrow, the ability to improve opacity is not sufficient, and there are many particles having a large particle size, resulting in a decrease in paper strength. Or paper dust may be generated easily. By using the silica composite recycled particles as a filler in the newspaper, particles having a sharp particle diameter are uniformly dispersed in the pulp fiber even when the basis weight is a low basis weight of 44 g / m ² or less. In addition, since the yield is high, news paper with high opacity, good ink fillability, little paper dust, and good tensile strength is preferable.

<Method for producing silica composite regenerated particles>
Although it does not specifically limit as the manufacturing method of the said silica composite reproduction | regeneration particle | grains,
(1) a suspension step of suspending regenerated particles in an aqueous alkali silicate solution to obtain a suspension;
(2) A method of adding a mineral acid to the suspension, precipitating silica on the surface of the regenerated particles, covering the regenerated particles, and aggregating the regenerated particles can be mentioned.

  According to the method for producing silica composite regenerated particles, in the agglomeration step, among the regenerated particles, those having a small particle diameter proceed with aggregation of a plurality of particles together with the silica coating, while those having a large particle diameter are only the silica coating. Thus, almost no aggregation occurs, and the regenerated particles having a wide particle size distribution can be made into silica composite regenerated particles having a narrow particle size distribution. Therefore, according to the said manufacturing method, the silica composite reproduction | regeneration particle | grains with high yield, opacity, etc., and low wire abrasion degree can be obtained.

(1) Suspension step In this step, the regenerated particles are mixed in an aqueous alkali silicate solution. The alkali silicate aqueous solution is not particularly limited, but a sodium silicate solution (No. 3 water glass) is preferable in that it is easily available.

  Further, the solid content concentration of the suspension obtained by adding and dispersing the regenerated particles in the alkali silicate aqueous solution is preferably 3 to 35% by mass. By adjusting this concentration within the above range, it becomes easy to control the particle size, particle size distribution, silica content and the like of the obtained silica composite regenerated particles to a desired range.

The silicate content in the alkali silicate aqueous solution (SiO ₂ conversion) and a solid content ratio of the reproduced particles 2: 98-30: 70 are preferred, 3: 97-20: 80 is more preferred. By doing in this way, the silica content of the silica composite regenerated particles can be preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less. When the solid content ratio of the silicic acid content (SiO ₂ equivalent) in the alkali silicate aqueous solution to the regenerated particles is less than 2:98, the regenerated particles cannot be sufficiently aggregated, and the particle size distribution of the obtained silica composite regenerated particles is difficult to narrow. As a result, the ability to improve opacity is not sufficient and the yield may not be improved. On the other hand, when the solid content ratio exceeds 30:70, it becomes easy to proceed to aggregation of regenerated particles having a relatively large particle size. As a result, in the resulting composite silica regenerated particles, the number of particles having a large particle size increases, similarly, the particle size distribution is difficult to narrow, the ability to improve opacity is not sufficient, and there are many particles having a large particle size, resulting in a decrease in paper strength. Or paper dust may be generated easily.

(2) Aggregation step In this step, mineral acid is added to the suspension, silica is deposited on the surface of the regenerated particles, and at least a part of the regenerated particles is agglomerated.

  Examples of the mineral acid include diluted solutions of mineral acids such as dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid, but dilute sulfuric acid is preferred in terms of price and handling. Further, the concentration when adding dilute sulfuric acid is preferably 0.2 to 4.0 mol%. Although the regenerated particles suitably used in the production method of the present invention are derived from minerals, they contain impurities such as calcium and aluminum as constituent elements within a predetermined range, and addition of an excessive concentration of mineral acid is obtained. Alteration may occur in the silica composite regenerated particles.

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

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

In this agglomeration step, silica sol is produced by adding a mineral acid as described above, and the suspension is neutral to weakly alkaline, preferably by adjusting the pH to a range of 8 to 11 to obtain silica composite regenerated particles. Can be obtained. At this time, the temperature of the suspension is 60 ° C. or more and 100 ° C. or less, and the silica content in the silica composite regenerated particles is 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass. More preferably, the silicic acid content (in terms of SiO ₂ ) in the above-described aqueous alkali silicate solution and the solid content ratio of the regenerated particles are adjusted to the following range, and the mineral acid is adjusted so that the final reaction solution has a pH of 8-11. It is good to add so that pH may be 8.5-10.5. When pH is less than the said range, the calcium component contained in reproduction | regeneration particle | grains becomes easy to change to calcium hydroxide by excessive addition of a mineral acid, and there exists a possibility that the viscosity of a slurry may increase. In addition, white carbon is generated instead of silica sol, and the whiteness, opacity and oil absorption of the silica composite regenerated particles may be reduced. On the other hand, when the pH exceeds the above range, the reaction between the alkali silicate and the mineral acid becomes dull and it is difficult for silica to precipitate on the surface of the regenerated particles, so that the opacity of the silica composite regenerated particles may be reduced. It is preferable to control the silicic acid content (SiO ₂ equivalent) in the aqueous silicic acid aqueous solution to the solid content ratio of regenerated particles, the temperature, and the amount of mineral acid added. By keeping the addition time of 60 to 120 minutes, more preferably from 70 minutes to 100 minutes, particles having a small particle size are agglomerated together with a silica coating, whereas agglomeration of a plurality of particles proceeds. In this case, the silica composite regenerated particles having a narrow particle size distribution as described above can be obtained by staying in the silica deposition on the surface, in particular, the tip portion such as a knife edge that is likely to precipitate, and not causing the coating to agglomerate with other particles. Can be obtained efficiently. If the addition time of the mineral acid is less than 60 minutes, excessive silica coating may occur, and excessively-sized silica composite regenerated particles may be formed. If the addition time exceeds 120 minutes, aggregation of regenerated particles having a small particle size will not occur. May be sufficient.

  In this step, it is preferable to add the mineral acid in two or more stages. When the mineral acid is added in two or more stages, the slurry temperature when adding the mineral acid in the first stage is 60 to 75 ° C., and the slurry temperature when adding the mineral acid after the second stage is at least the first stage. It is desirable to raise the temperature by 10 ° C. or more. Specifically, the liquid temperature in the first stage is preferably 60 ° C. or higher and lower than 75 ° C., the second stage is preferably 70 ° C. or higher and lower than 100 ° C., and the final stage of the reaction is preferably 90 ° C. or higher and 98 ° C. or lower. Under these temperature conditions, silica composite regenerated particles having a sharper particle diameter can be obtained. In the first stage, by adding a mineral acid with a neutralization rate of 20 to 50% of the aqueous alkali silicate solution, and then performing a second stage mineral acid addition after a holding time of about 5 to 20 minutes, Furthermore, it becomes possible to promote the lamination composite of the silica, and the silica can be more uniformly composited on the surface of the regenerated particles.

<Quality etc. of silica composite particles>
The volume average particle diameter (D50) of the silica composite calcium carbonate particles and the silica composite regenerated composite particles (hereinafter referred to as silica composite particles) is 2 μm or more and 10 μm or less, and more preferably 3 μm or more and 8 μm or less. By setting the volume average particle diameter of the silica composite particles in such a range, the opacity and the like of the newspaper can be efficiently increased. When the volume average particle diameter of the silica composite particles is less than the above lower limit, the yield may not be sufficiently improved, and the opacity improving ability may not be sufficient. On the other hand, if the volume average particle diameter exceeds the upper limit, the strength between the pulp fibers is reduced, and as a result, the paper strength may be reduced or the wire wear degree may be increased. There is a possibility that the uniform dispersibility in the medium is lowered, and the opacity and the printing opacity are lowered.

  The oil absorption amount of the silica composite particles is preferably 30 mL / 100 g or more and 150 mL / 100 g or less, and more preferably 60 mL / 100 g or more and 100 mL / 100 g or less. When the silica composite particles having such an oil absorption amount are used as an internal filler, the silica composite particles absorb the ink of the ink impregnated in the paper layer and the organic solvent in the paper layer. It is possible to suppress a decrease in printing opacity, to improve the drying property of the ink, and to prevent blurring. When the amount of oil absorption of the silica composite particles is less than the above range, the above effect cannot be obtained sufficiently, and the silica composite particles may impair the ink absorption and drying properties. On the other hand, when the oil absorption amount of the silica composite particles exceeds the above range, the ink absorbability becomes too high, and the ink sinks and the color developability of the newspaper may be lowered.

  As a minimum of the addition amount of the said silica composite particle, 1 mass% is preferable with respect to raw material pulp, and 2 mass% is especially preferable. Moreover, as an upper limit of the addition amount of a silica composite particle, 9 mass% is preferable and 6 mass% is preferable. If the addition amount of the silica composite particles is smaller than the above lower limit, the effect of improving the opacity and the effect of improving ink inking by the silica composite particles may not be sufficiently exhibited. On the contrary, if the content of the silica composite particles exceeds the above upper limit, the amount added is too much, so the paper powder piling due to the loss of the filler may occur or the adhesion between the pulp fibers is weakened due to an increase in the filler. There is a risk that the strength of the newspaper will be reduced.

<Other additives>
In addition to the above pulp and filler, the pulp slurry (raw material for the newspaper) includes, for example, starch, polyacrylamide, epichlorohydrin and other paper strength enhancers, rosin, alkyl ketene dimer, ASA (alkenyl succinic anhydride). In addition, an internal sizing agent such as neutral rosin, a coagulant such as sulfuric acid band and polyethyleneimine, and a coagulant such as polyacrylamide or a copolymer thereof can be contained.

<Surface treatment agent>
The newsprint 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 newsprint, 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 newsprint has a high surface strength and can suppress the generation of paper dust, and thus has excellent printing workability. Further, according to the newsprint, occurrence of nappari trouble during printing is also suppressed.

  By using the above two types of starch, the starch does not penetrate into the base paper and the reason for forming a strong coating on the surface is not clear, but the carboxyl group etc. of the oxidized starch and the hydroxyl group of the hydroxyethylated starch It is conceivable that the polymer is polymerized by bonding (esterification reaction, etc.) and cross-linking, making it difficult to penetrate into the interior. 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 in the newspaper is also considered to be caused by the decrease in the hydrophilicity of starch due to the esterification.

  In particular, in the newsprint, when the silica composite particles are internally added, a stronger film is formed on the surface by applying a surface treatment agent containing oxidized starch and hydroxyethylated starch. Suitability and the like can be further enhanced. The reason why the surface strength is increased by using the silica composite particles is not clear, but when the silica composite particles are a mixture formed of various oxides, any component may contain the two types of starch. It is conceivable that, when a surface treatment agent is applied, such as the esterification reaction, the surface film-forming property is improved by this catalytic action. In addition, since this silica composite particle has an indefinite shape and a porous shape, it can be considered that this shape enhances the catalytic function.

  In addition, according to the newsprint, the surface treatment agent does not penetrate into the interior as described above, and a void is left inside the paper by forming a film on the surface. According to the newspaper, the degree of light scattering inside the paper increases due to the gap, 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 oxidized starch and hydroxyethylated starch is less than the above range, 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 range, the viscosity increases, and the applicability may decrease.

  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 the above-described esterification reaction and the like can proceed efficiently. As a result, the penetration of starch into the base paper can be suppressed, and a strong coating 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. It is possible to improve and prevent the filler from falling off, and the styrenic sizing agent remains on the paper surface, and the size effect can be enhanced.

  The blending ratio of the styrenic sizing agent to the whole starch combined with the oxidized starch and the hydroxyethylated starch is preferably 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the starch in solid content. When the blending ratio of the styrenic sizing agent is less than the above range, it is difficult to sufficiently obtain the effect of improving the paper size and surface strength. On the other hand, when the blending ratio of the styrene sizing agent exceeds the above range, the production cost of the newspaper is increased, and the opacity and the ink drying property may be reduced.

  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, more preferably 10 cps or more and 40 cps or less. According to the newsprint, by setting the viscosity of the surface treatment agent at the time of application within 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 range, the 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 news paper with high surface strength. . On the other hand, when the concentration exceeds the above range, workability during application may be reduced, or uniform application may be difficult.

The coating amount of the surface treatment agent is preferably 0.1 g / m ² or more and 2.0 g / m ² or less, and 0.3 g / m ² or more and 1.5 g / m ^{2 in} terms of dry mass per side on the front and back surfaces of the base paper. The following is more preferable. When the coating amount is less than the above range, it may be difficult to obtain a sufficient film with starch or the like, and sufficient paper surface strength may not be obtained. Conversely, if the coating amount exceeds the above range, a large amount of mist of surface treatment agent such as starch is generated around the coating equipment, which may damage peripheral devices and cause paper breaks and paper defects due to contamination. is there.

<Quality etc.>
The basis weight of the newspaper is preferably from 37 g / m ^{2 to} 44 g / m ² . If the basis weight is less than the above range, the strength of the newspaper may be reduced, and printing on a rotary printing press may be difficult, or the printing opacity may be reduced. On the other hand, when the basis weight exceeds the above range, there is a risk that the news paper will be reduced in weight and resources.

  The ash content of the newspaper is preferably 5% to 13%, more preferably 7% to 12%. By making the ash content within the above range, the opacity (blank paper opacity and printing opacity) of the newsprint can be increased, and according to the filler having the particle size distribution of the present invention, fibers can be dispersed by uniformly dispersed filler. Since the voids are filled and the penetration of the surface treatment agent is suppressed, the surface strength can be further increased. As a result, the newspaper can exhibit excellent printing workability.

  The blank paper opacity of the newspaper is preferably 90% or more and 96% or less, and more preferably 92% or more and 95% or less. If the blank paper opacity is less than the above range, the back-through tends to occur. On the other hand, when the blank paper opacity exceeds the above range, it is necessary to increase the amount of filler added, so that the adhesion between pulp fibers may be reduced, and the strength of the newsprint may be reduced.

  The printing opacity of the newspaper is preferably 90% to 96%, more preferably 91% to 95%. If the printing opacity is less than the above range, the show-through may be likely to occur. Conversely, when the printing opacity exceeds the above range, it is necessary to increase the amount of filler added, which may reduce the adhesion between the pulp fibers and reduce the strength of the newsprint paper. There is a possibility that paper dust generated at the time of printing increases due to the removal of the filler from the ink, and the operability may be deteriorated due to an increase in dirt in the machine system in the manufacturing process.

  The whiteness of the newspaper is preferably from 52% to 57%, more preferably from 53% to 56%. By setting the whiteness to the above range, it is possible to prevent the eyestrain of the subscriber.

  The tensile strength of the newsprint is preferably 2.0 kN / m or more, and more preferably 2.2 kN / m or more. If the tensile strength is less than the above range, the handling and productivity of the newsprint may be reduced, and printing on a rotary printing press may be difficult.

<Method of manufacturing newsprint>
The newsprint can be manufactured by a known manufacturing method.

  First, a pulp slurry containing raw material pulp and the above-mentioned filler is prepared to make a paper to obtain a base paper. This papermaking can be performed using a known papermaking machine or the like.

  Next, 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 range, 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 above range, 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 calendars made of a combination of a metal roll and an elastic roll, such as a super calendar, a gloss calendar, and a soft compact calendar, can be appropriately used in on-machine or off-machine specifications.

<Method for producing regenerated particles>
Here, a method for producing regenerated particles that can be suitably used as a raw material for silica composite particles used as a filler in the present invention will be described in detail in the order of the raw material and each step of dehydration, heat treatment and pulverization. In addition, it is preferable to have a mixing | blending and slurry preparation 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 90% to 97% 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 40% or more, preferably 40% or more and less than 90%, more preferably 45% or more and 70% or less, and particularly preferably more than 50% and 60% or less. .

  If the moisture content of the raw material after dehydration exceeds 70%, the processing temperature in the heat treatment process is lowered, energy loss for heating becomes large, and uneven combustion of the raw material is likely to occur and it is 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 40%, it causes excessive combustion of the deinking floss. It also goes against 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 size in the dehydration step and each heat treatment step described below is measured by a metal plate sieve based on JIS-Z-8801-2: 2000, and the ratio of the particle size is determined after sieving. It is a value calculated by measuring the weight for each particle diameter.

(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 furnace temperature of the internal heat kiln furnace) is 300 ° C. or higher and lower than 500 ° C., preferably 400 ° C. or higher and lower than 500 ° C., more preferably 400 ° C. or higher and 450 ° C. or lower. . 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 500 ° C. or higher, drying / combustion proceeds locally faster than the grain 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 However, regenerated particles with high whiteness 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 suitably adjusted to 10 mm or less, preferably 1 mm to 8 mm, more preferably 1 mm to 5 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. Thereafter, the particle size is adjusted to the target particle size in the blending / slurry preparation step and the pulverization step, and then is used as a regenerated particle in a destination such as a filler.

  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 and slurry preparation process)
The blending / slurry preparing step is a step of blending an acid and / or salt into the heat treated product discharged from the second heat treating 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, so that it coexists in the slurry with calcium ions. 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. The reason will be described below.

  Calcium oxide, metakaolin, and the like are generated from calcium carbonate and kaolin, which are constituents of papermaking sludge, by overcombustion in a heat treatment step or the like. When this calcium oxide is mixed with water (in the slurry), it becomes calcium hydroxide, and is attracted to calcium ions resulting from this calcium hydroxide, causing silicate ions and aluminate ions to solidify and solidify the slurry. . The reason for this is not clear, but this calcium ion reacts with silicate ions and aluminate ions that coexist in the slurry, and the hydration hardening reaction of these silicate ions and aluminate ions (formation of hydrates such as ettringite) ). In addition, this silicate ion and aluminate ion originate in the metakaolin etc. which arise by overcombustion.

  Here, when the acid and the salt thereof are added to the slurry, it reacts with calcium ions in the slurry to form a calcium salt. If the solubility of this calcium salt in water is low, it precipitates as a solid, reduces the calcium ions in the slurry, and suppresses the formation of silicate ions and alumina ions due to metakaolin and the like. As a result, it is considered that solidification and solidification of the slurry can be prevented because no hydration curable substance is generated in the slurry.

  As such an acid and / or salt, those having a solubility in 100 g of water at 20 ° C. in a calcium salt state of 1 g or less are preferable. According to such an acid and / or salt having low solubility in water, the calcium salt produced by the reaction reacts with calcium ions in the slurry during the blending / slurry preparation process in the normal production process of regenerated particles. Precipitating on the surface of particles containing calcium oxide or calcium hydroxide can effectively prevent the slurry from solidifying and solidifying.

  Moreover, according to this acid and / or salt, the whiteness of the obtained regenerated particles can be increased. Many calcium salts obtained from acids or salts thereof have high whiteness. Therefore, the whiteness of the regenerated particles obtained by coating these calcium salts with particles containing calcium oxide can be increased.

  As the acid and / or salt, a calcium salt can be precipitated in the presence of calcium ions, and preferably, the solubility in 100 g of water at 20 ° C. in the calcium salt state is 1 g or less. Alternatively, it may be a salt thereof, an inorganic acid or a salt thereof. The precipitation of calcium salt in the presence of calcium ions means that the calcium salt can be precipitated in a slurry in a general process for producing regenerated particles.

Specific examples of the acid include sulfuric acid (solubility of calcium sulfate dihydrate 0.21 g / 100 g), hydrofluoric acid (solubility of calcium fluoride 0.0016 g / 100 g), citric acid (calcium citrate , Phosphoric acid (solubility of tricalcium phosphate 0.0025 g / 100 g), carbonic acid (calcium carbonate solubility 0.0014 g / 100 g), phosphonic acid, and the like. Examples of the salt include calcium salts, potassium salts, aluminum salts, and sodium salts of the above acids. Among the acids or salts thereof, calcium sulfate, potassium carbonate, phosphoric acid, sulfuric acid, and sulfuric acid bands (usually used in paper mills from the viewpoint of workability, economy, and homogeneity of the regenerated particles obtained ( Al ₂ (SO ₄ ) ₃ ) and phosphonic acid are preferred, phosphoric acid or dilute sulfuric acid is particularly preferred, and phosphoric acid is even more particularly preferred.

  In addition, the acid and / or salt is preferably an acid or a salt that exhibits acidity when hydrolyzed from the viewpoint of reducing the pH of the slurry. Since regenerated particles having a high pH may react with other chemicals and cause a reduction in quality, it is effective to reduce the pH by adding an acid.

  It is preferable to mix | blend this acid and / or salt with the heat processing thing (mixing process) before or simultaneously with the slurrying (slurry preparation process) of heat processing thing. When acid and / or salt is added after slurrying the heat-treated product, the calcium oxide in the heat-treated product is already changed to calcium hydroxide, and the hydration hardening reaction due to the generated calcium ions has already started. Therefore, the effect of suppressing solidification and solidification cannot be obtained, or the effect may be reduced.

  As a method of blending the acid and / or salt into the heat-treated product before slurrying the heat-treated product, the solid acid salt (calcium sulfate, tricalcium phosphate, etc.) is added to the heat-treated product in powder form. The method of mixing etc. can be mentioned. As a method of adding acid and / or salt to the heat-treated product at the same time as slurrying of the heat-treated product, (1) a method of dissolving the acid and / or salt in water and suspending the heat-treated product in the aqueous solution ( 2) A method in which an acid and / or salt and a heat-treated product are mixed in water at the same time. According to the method of adding the acid and / or salt to the heat-treated product at the same time as the slurry of the heat-treated product, the acid and / or salt is present only in the aqueous solution (carbonic acid etc.) Even in difficult cases (such as sulfuric acid), it can be blended without any inconvenience.

  The lower limit of the amount of the acid and / or salt is preferably 0.01 parts by weight, more preferably 0.1 parts by weight, and particularly preferably 0.3 parts by weight with respect to 100 parts by weight of the heat-treated product. On the other hand, the upper limit of the amount is preferably 10 parts by mass, and more preferably 7 parts by mass. When the compounding amount of the acid and / or salt is less than 0.01 parts by mass, the contact probability with the particles containing calcium oxide or calcium hydroxide and / or calcium ions generated from the particles is low, and the curing reaction inhibiting effect May not be obtained. On the other hand, even if it exceeds 10 parts by mass, the curing reaction suppressing effect may reach its peak.

(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, a filler for internal addition, and the like by appropriately granulating the slurry to a necessary particle size.

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

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

  The carbonation step may be performed between the blending / slurry preparation step and the pulverization step, simultaneously with the pulverization step, or after the pulverization step. In addition, this carbon dioxide blowing may be replaced with or added to other acids and / or salts, or as a carbonic acid compounding / slurry preparation step.

  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 step, and coarse particles and fine particles are fed back to the previous step. As a result, the 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 the following, unless otherwise specified,% means mass%, and the chemical addition amount means solid mass (kg) per pulp dry mass (t).

  Each measured value in the present example is a value measured by the following method.

[Volume particle size (unit: μm)]
A 10 mg sample of inorganic particles was dispersed with an ultrasonic disperser (output: 80 W) for 3 minutes. Using this solution, a volume average particle diameter (D50), a volume 10% particle diameter (D10), and a volume 90% particle were measured with a laser particle size distribution measuring device (model number: SA-LD-2200, manufactured by Shimadzu Corporation). The diameter (D90) was measured.

[Basis weight (g / m ² )]
It was measured according to “Paper and paperboard—basis weight measurement method” described in JIS-P8124 (1998).

[ash(%)]
Ash content 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:%)]
It was measured according to “Paper and paperboard—Opacity test method (paper backing) —diffuse illumination method” described in JIS-P8149 (2000).

[Printing opacity (unit:%)]
JAPAN TAPPI No. 45 (2000) “Newspaper—Method for testing opacity after printing” was measured using a measuring instrument ISO whiteness meter (manufactured by Suga Test Instruments Co., Ltd.).

[Whiteness (Unit:%)]
It was measured according to “Measuring method of paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)” described in JIS-P8148 (2001).

[Tensile strength (longitudinal) (unit: kN / m)]
The longitudinal direction of newsprint paper was measured in accordance with “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 printing of 10,000 copies was performed with newspaper ink (trade name: Newsz Naturalis (black), manufactured by DIC Corporation). . 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.), printing double-sided 100,000 copies on 50-roll newsprints, and using a non-image area on the printing paper. The occurrence of paper dust and the presence or absence of accumulation were 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.

Example 1
10,000 kg of slurry (concentration 20% by mass) of heavy calcium carbonate particles (volume average particle diameter 1.6 μm) is placed in a tank equipped with a stirrer and stirred with an aqueous sodium silicate solution (No. 3 sodium silicate: SiO ₂ concentration 29 wt / wt). 770 kg of wt%, Na ₂ O concentration 9 wt / wt%), the solid content ratio of silicic acid content (SiO ₂ equivalent) to calcium carbonate is 10:90, diluted water is added, alkali silicate and heavy carbonate The concentration of the slurry composed of calcium particles was adjusted to 10% by mass. A known mixer was used for stirring the slurry. Next, the mixture was heated and stirred to adjust the liquid temperature of the slurry to 89 ° C. Thereafter, dilute sulfuric acid (1 N) was added over 70 minutes until the reaction completion pH was 8.8, and silica composite calcium carbonate particles of Example 1 were obtained. The volume average particle diameter D50, volume 10% particle diameter D10 and volume 90% particle diameter D90, and D90 / D10 and D90 / D50 of the obtained silica composite calcium carbonate particles are as shown in Table 1.

Next, 80% by mass of disaggregated / deinked waste paper pulp (DIP) and 20% by mass of thermomechanical pulp (TMP) were blended, and the freeness was 120 mLC. S. A pulp slurry adjusted to F (based on JIS-P8121) was obtained. To this pulp slurry, 45 kg / pulpton of the above-mentioned silica composite calcium carbonate particles are added in solid content to the absolute dry pulp, and the pH is adjusted to 6 to 7 with a sulfuric acid band. A base paper for newspaper having a basis weight of 40.8 g / m ² was made with a twin-wire paper machine by adding a conductive polymer (manufactured by BASF Japan, polymin PR8150).

Furthermore, a starch solution in which 90 parts by mass of oxidized starch (mass average molecular weight 700,000 manufactured by Nippon Food Processing Co., Ltd.) and 10 parts by mass of hydroxyethylated starch (HES, mass average molecular weight 150,000 manufactured by Penford) was mixed as a surface treatment agent. A styrene-based sizing agent (SS2712 manufactured by Seiko PMC Co., Ltd.) was blended in an amount of 15 parts by mass with respect to 100 parts by mass of starch (solid content concentration 6%, B-type viscosity 22 cps). The surface treatment agent was applied to both sides of the above 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 the newspaper of Example 1.

(Examples 2 and 3)
As shown in Table 1, the same silica composite calcium carbonate particles as in Example 1 were added to the same pulp slurry as in Example 1, and newsprint paper was produced by the same production method as in Example 1.

Example 4
In the production of silica composite calcium carbonate particles used in Example 1, the amount of sodium silicate aqueous solution added was 2,956 kg, and the solid content ratio of silicic acid content (SiO ₂ equivalent) and calcium carbonate was 30:70, Silica composite calcium carbonate particles of Example 4 were produced in the same manner as Example 1. Except for using the silica composite calcium carbonate particles of Example 4, the newsprint of Example 4 was produced in the same manner as in Example 1. The volume average particle diameter D50, the volume 10% particle diameter D10 and the volume 90% particle diameter D90 of the silica composite calcium carbonate particles of Example 4 and the ratio thereof are as shown in Table 1.

(Example 5)
In the production of the silica composite calcium carbonate particles used in Example 1, the amount of the sodium silicate aqueous solution added was 363 kg, and the solid content ratio of silicic acid content (SiO ₂ conversion) and calcium carbonate was 5:95. In the same manner as in Example 1, silica composite calcium carbonate particles of Example 5 were produced. Except for using the silica composite calcium carbonate particles of Example 5, the newsprint paper of Example 5 was produced in the same manner as in Example 1. In addition, the volume average particle diameter D50, the volume 10% particle diameter D10 and the volume 90% particle diameter D90 of the silica composite calcium carbonate particles of Example 5 and the ratio thereof are as shown in Table 1.

(Example 6)
Renewed silica composite particles were added to the same pulp slurry as in Example 1 as shown in Table 1, and newsprint paper was produced by the same production method as in Example 1.

The production conditions for the silica composite regenerated particles are as follows. First, deinking floss was used as a raw material, and the dehydration process was performed so that the moisture content was 45 mass%, the average particle diameter was 10 mm, and the ratio of particles of 50 mm or less was 90 mass%. This dehydrated product was subjected to a first heat treatment step and then a second heat treatment step 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. The pulverized product was classified to obtain regenerated particles having a volume average particle diameter D50 of 2 μm. 10,000 kg of this regenerated particle slurry (concentration 20% by mass) is placed in a tank equipped with a stirrer and stirred with a sodium silicate aqueous solution (No. 3 sodium silicate: SiO ₂ concentration 29 wt / wt%, Na ₂ O concentration 9 wt / wt%). ) 363 kg was added, the solid content ratio of silicic acid content (SiO ₂ equivalent) to regenerated particles was 5:95, dilution water was added, and the concentration of the slurry consisting of alkali silicate and regenerated particles was adjusted to 10% by mass. Then, the liquid temperature of the slurry was adjusted to 60 ° C. by heating and stirring. A known mixer was used for stirring the slurry. Thereafter, dilute sulfuric acid (1 N) was added over 22 minutes with stirring until the alkali silicate neutralization rate became 33%, and a primary reaction was performed. Further, the slurry was heated and stirred until the liquid temperature of the slurry reached 93 ° C. and then held for 10 minutes. Thereafter, dilute sulfuric acid (1 N) was added over 45 minutes until the pH reached 8.5, whereby silica composite regenerated particles of Example 6 were obtained.

  The volume average particle diameter D50, the volume 10% particle diameter D10, the volume 90% particle diameter D90, and the ratio of these silica composite regenerated particles are as shown in Table 1.

(Comparative Examples 1, 2, 3)
The same pulp slurry as in Example 1 was compared with white carbon (manufactured by Elle Paper Chemical Co., Ltd.) in Comparative Example 1, and heavy calcium carbonate (manufactured by Bihoku Flour Chemical Co., Ltd., Hydrocurve 75F) in Comparative Example 2. In Example 3, newsprint paper was produced by the same production method as Example 1 except that light calcium carbonate (TP 121-6S, manufactured by Okutama Kogyo Co., Ltd.) was added as shown in Table 1. The volume average particle diameter D50, the volume 10% particle diameter D10, the volume 90% particle diameter D90, and the ratio of these fillers are as shown in Table 1.

(Evaluation)
For each newsprint obtained, the basis weight, ash content, blank paper opacity, printing opacity, whiteness and tensile strength in the longitudinal direction were measured by the above method, and ink fillability and blanket paper powder piling. evaluated. The evaluation results are shown in Table 1.

  As shown in Table 1 above, the newsprint 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 newsprint of the present invention has a high tensile strength.

  The newsprint of the present invention has high opacity, printability, printing workability, etc., even if it has a low basis weight, and can be suitably used as a lightweight newsprint.

Claims (3)

Newspaper with pulp as the main ingredient and internal filler,
The filler contains silica composite regenerated particles and / or silica composite calcium carbonate particles as inorganic particles,
A newsprint having a volume average particle diameter D50 of the inorganic particles of 2 μm or more and 10 μm or less, and a ratio D90 / D10 of a volume 90% particle diameter D90 to a volume 10% particle diameter D10 of 5 or less.   The newspaper according to claim 1, wherein a ratio D90 / D50 of a volume 90% particle diameter D90 to a volume average particle diameter D50 of the inorganic particles is 3 or less. The newspaper according to claim 1 or 2 , wherein the basis weight is 37 g / m ² or more and 44 g / m ² or less.