JP2006327914A - Manufacturing method of calcium carbonate and coated paper using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of particulate calcium carbonate wherein the pulverization treatment of the calcium carbonate is performed, which can be used for producing calcium carbonate having a sharp particle size distribution and also a low specific surface area. <P>SOLUTION: The calcium carbonate having ≤5.0 μm average particle size and ≤5 m<SP>2</SP>/g BET specific surface area, as measured by the laser diffraction dispersion method is prepared by performing dry classification, then a calcium carbonate slurry having 50-80% solid content concentration is prepared by adding a dispersant, then the coating calcium carbonate having ≤1.0 μm average particle size and ≤13 m<SP>2</SP>/g BET specific surface area as measured by the laser diffraction dispersion method and having an excellent gloss-developing property and opaqueness is manufactured by wet-pulverizing the calcium carbonate by a bead mill in which beads having ϕ0.1-1.0 mm are packed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for pulverizing calcium carbonate, and relates to a method for efficiently producing fine calcium carbonate for coating having a small specific surface area and a sharp particle size distribution.

  In recent years, there is a high demand for high-quality lightweight coated paper having high whiteness, high opacity, and high gloss. In order to meet these requirements, expensive titanium dioxide, plastic pigments, and the like are blended in the coating pigments of high-quality lightweight coated paper, in addition to inorganic pigments such as kaolin, heavy calcium carbonate, and light calcium carbonate.

  Calcium carbonate used for the coating pigment is very inexpensive, and the whiteness and opacity of the coated paper can be improved by increasing the blending ratio in the paint, but the glossiness of the white paper is remarkably lowered. In order to improve the glossiness of this white paper, it is common to make fine particles by wet pulverization, but in order to make fine particles, it is necessary to increase the amount of dispersant added and pulverize for a long time. Cost increases. In addition, since ultrafine particles of 0.2 μm or less are simultaneously generated during pulverization, it is necessary not only to reduce opacity but also to add expensive latex in order to maintain the printing surface strength. There is a problem that decreases.

  Therefore, if it is possible to develop a calcium carbonate atomization and pulverization technology that is inexpensive and hardly generates ultrafine particles of 0.2 μm or less, it is possible to increase the whiteness of white paper without inferior white paper gloss by incorporating the calcium carbonate into the paint. High quality coated paper with excellent opacity can be manufactured. Light calcium carbonate can change its shape with a high degree of freedom by controlling the carbonation conditions, and can be adjusted to a sharp particle size distribution. Such sharp particle size distribution and particle shape adjustment ability produce excellent optical characteristics and may be excellent as a coating pigment, but the concentration is lowered to some extent because of high slurry viscosity and poor fluidity. Otherwise there is a problem that cannot be applied. Heavy calcium carbonate, on the other hand, has higher fluidity than light calcium carbonate, so it can be applied at a high concentration and has the advantage of saving energy for drying. Tend to increase.

Recently, a technology for producing heavy calcium carbonate fine particles that do not contain ultrafine particles that contribute to the transparency of coated paper and that have a sharp particle size distribution has been developed. As a method for producing heavy calcium carbonate having a sharp particle size distribution, a method of removing ultrafine particles increased by wet pulverization by wet classification or a pulverization method in which ultrafine particles are not generated have been proposed. For example, an aqueous slurry having a solid content concentration of 74 to 80% by weight of a heavy calcium carbonate aqueous slurry having a specific particle size range and a B-type viscosity of 300 mPa · s or less obtained by wet grinding such as a bead mill is used as a decanter. Recover the light liquid (aqueous slurry discharged outside the apparatus) using a centrifugal separator of the type, dilute the resulting light liquid to a solid content concentration of 30 to 70% by weight, and make the B-type viscosity 100 mPa · s or less Centrifuging and collecting the heavy liquid (slurry containing coarse particles settled on the inner wall of the device) to recover the coarse and fine particles, sharp particle size distribution, and BET specific surface area of 6-12 m ^A method for producing a heavy calcium carbonate slurry of ² / g has been proposed (see Patent Document 1). Also, centrifugal separation of aqueous slurry obtained by wet milling such as bead mill with heavy calcium carbonate in the specific particle size range with a solid content concentration of 63-72% by weight and B-type viscosity of 160-700 mPa · s or less Supply to the device, separate the 5 to 35% by weight of the supplied heavy calcium carbonate so that it is distributed into the heavy liquid, collect the light liquid, and dilute this light liquid to a solid content concentration of 10 to 29% by weight. The B-type viscosity is adjusted to 30 to 700 mPa · s or less, then supplied to the centrifugal separator, and the heavy liquid is separated so that 50 to 95% by weight of the supplied heavy calcium carbonate is distributed to the heavy liquid. A method for producing a heavy calcium carbonate slurry having a sharp particle size distribution with few coarse particles and fine particles by collecting is proposed (see Patent Document 2). In these methods, a sharp particle size distribution is achieved with a low specific surface area by wet-classifying the calcium carbonate slurry after wet pulverization using a centrifugal separator. However, in this production method, the coarse particles after classification can be used for coating pigments by pulverization and classification. However, since the ultrafine particles are currently unsuitable for the production of coated paper, the yield of calcium carbonate is low. There is a problem that the cost of the coated paper is increased due to the decrease and the deterioration of production efficiency. In addition, in a multi-stage pulverization method using a wet pulverizer, at least one pulverization process uses beads having a diameter larger than the beads used in the previous pulverization process, thereby generating unnecessary ultrafine particles. A method for producing a pigment having a small sharp particle size distribution has been proposed (see Patent Document 3). However, atomization by wet pulverization inevitably generates ultrafine particles, which is insufficient to suppress the formation of ultrafine particles.
JP 2000-34120 A JP 2003-286027 A JP 2004-8959 A

  In view of the situation as described above, the subject of the present invention is a method for producing fine calcium carbonate having a sharp particle size distribution and a low specific surface area, and a method for producing fine calcium carbonate slurry, in a production method for pulverizing calcium carbonate, Furthermore, it is providing the coated paper coated using the granule calcium carbonate.

In the present invention, after the dry classification, the average particle diameter of calcium carbonate by laser diffraction scattering method is 5.0 μm or less and the BET specific surface area is 5 m ² / g or less. Prepare an ~ 80% calcium carbonate slurry, preferably using a bead mill filled with φ0.1-1.0mm beads, the average particle size of calcium carbonate obtained by wet pulverization by laser diffraction scattering method is 1.0μm or less , A method for producing a calcium carbonate for coating having a BET specific surface area of 13 m ² / g or less and excellent glossiness and opacity, and a calcium carbonate slurry, and coated paper coated with the calcium carbonate It is.

  According to the present invention, it is possible to obtain a fine calcium carbonate having a sharp particle size distribution and a low specific surface area, and a method for producing a slurry thereof. In coated paper using the calcium carbonate, excellent white paper glossiness and opacity are obtained. .

  In the present invention, calcium carbonate is atomized by dry classification and then lightly wet pulverized. The calcium carbonate used may be either heavy or light calcium carbonate, but heavy calcium carbonate is preferred from the viewpoint of fluidity. In addition, the calcium carbonate of the present invention may be prepared by pulverizing in advance before dry classification. As the pulverization method, dry pulverization is preferable from the viewpoint of work efficiency. In the case of dry pulverization, a roll mill, a jet mill, a dry ball mill, an impact pulverizer or the like is used.

In the present invention, by dry classification, it is necessary to make the average particle diameter of calcium carbonate by laser diffraction scattering method 5.0 μm or less and the BET specific surface area 5 m ² / g or less, and the average particle diameter is 1.0 The specific surface area is preferably ² to 5 m ² / g. By preparing in this way, since the particle size is reduced to some extent in a state where the particle size distribution is sharp before the wet pulverization, a desired product of calcium carbonate is obtained by the wet pulverization treatment in the next step.

  When the average particle size after dry classification is larger than 5.0 μm, the wet pulverization time becomes long, so that ultrafine particles are generated and the specific surface area is greatly increased, so that the intended pigment slurry cannot be obtained. In addition, the average particle diameter of the pigment in this invention means the average particle diameter measured by the laser diffraction scattering method. In the present invention, specifically, it is an average particle diameter measured using a Mastersizer 2000 type manufactured by Malvern.

In the dry classification of the present invention, the powder raw material is classified into coarse powder and fine powder by a balance of centrifugal force due to rotation of a rotating body provided with a plurality of classification blades, that is, a classification rotor, and centripetal force due to fluid resistance of air flow. Air separators based on the basic principle are widely used. In particular, the classifier built-in media agitation type continuous dry pulverizer, which has been developed recently, is not only capable of dry pulverization of 1 μm or less, but also particles obtained by ordinary dry pulverization and two-stage classification. In comparison, the fine powder obtained by pulverization is immediately categorized without being excessively pulverized, so that there is an advantage that the particle size distribution can be sharpened. Further, the particle diameter of calcium carbonate before dry classification is not particularly limited, but those having an average particle diameter of 10 mm or less, more preferably 10 to 100 μm are preferably used. Next, a calcium carbonate slurry obtained by adding water and a dispersant to calcium carbonate obtained by dry classification is wet-ground using an attritor, ball mill, sand mill or the like filled with balls or beads.

In the present invention, it is necessary that the calcium carbonate obtained by wet pulverization has an average particle size of 1.0 μm or less and a BET specific surface area of 13 m ² / g or less. As a result, the ultrafine particles of calcium carbonate are reduced, so that the particle size distribution becomes very sharp and the porosity in the coating layer increases, and as a result, the micro smoothness of the coating layer surface is improved. Therefore, it is possible to obtain a calcium carbonate for coating having excellent gloss development and opacity. The average particle diameter is preferably 0.5 to 0.8 μm, and the specific surface area is preferably 6 to 10 m ² / g. In addition, the calcium carbonate of the present invention has a ratio (D ₅₀ / D _{10) of} an average particle size of 50% by weight of the particle size distribution measurement curve and a particle size of 10% by weight of the particle size distribution measurement curve.
) Is preferably 1.0 to 5.0.

  In the present invention, the media used for pulverization and classification may be appropriately selected from materials such as glass beads, zirconia beads, zircon beads, and steel balls according to the required particle size for the viscosity, specific gravity and pulverization and classification of the processed material. In order to improve the grinding efficiency, it is preferable that the media bead diameter used is φ0.1 to 1.0 mm. When the bead diameter used during wet grinding is less than 0.1 mm, the grinding hardly progresses, and when it is 1.0 mm or more, the grinding efficiency deteriorates, so the grinding time becomes longer, and therefore the generation of ultrafine particles increases. There is a tendency. As a wet grinding method, a multi-pass grinding method that repeatedly stays at a high flow rate for a short time or several grinding machines in series or in parallel, and a grinding method that changes the model and media diameter, etc., are selected appropriately according to the target particle size and specific surface area it can.

The kind of the dispersant used for wet pulverization is not particularly limited, and an aqueous polymer containing acrylic acid, methacrylic acid, and derivatives or salts thereof as constituent components is used. Moreover, the addition amount of a dispersing agent is suitably adjusted according to the kind of calcium carbonate, a particle diameter, a particle size distribution, slurry concentration, a viscosity, etc. The solid concentration of calcium carbonate slurry in the wet pulverization is preferably 50 to 80% by weight. When the slurry solid content concentration is less than 50%, the pulverization time becomes long, and it is not suitable for high solid differentiation of the coating material or high blending of calcium carbonate obtained in the present invention. Moreover, since the engineered slurry obtained by the treatment of the present invention is easily thickened, when the slurry solid content concentration is higher than 80%, the slurry viscosity is increased and the fluidity tends to be inferior.

  The calcium carbonate slurry thus obtained is blended in the paint. In addition to the pigments obtained in the present invention, the paints include calcium carbonate other than the calcium carbonate obtained in the present invention, kaolin, clay, calcined kaolin, zinc oxide, aluminum hydroxide, titanium dioxide, calcium sulfate, satin white, talc. In addition, an inorganic pigment such as silica can be used as a main component, and if necessary, one or more organic pigments called plastic pigments can be appropriately mixed and used. In order to improve the glossiness of blank paper, kaolin or plastic pigment is preferably used in combination. The calcium carbonate having specific physical properties according to the present invention can improve the glossiness of white paper and the opacity by containing 50 parts by weight or more per 100 parts by weight of the pigment. In addition to the pigment, an adhesive such as starch, polyvinyl alcohol, synthetic polymer latex, or the like can be appropriately blended. As a compounding quantity of an adhesive agent, 5-35 weight part is preferable with respect to 100 weight part of pigments. Further, as required, various commonly used auxiliaries such as a dispersant, a thickener, a water retention agent, an antifoaming agent, and a water-proofing agent can be used as appropriate. The solid content concentration of the paint is about 20 to 70% by weight, preferably 45 to 70% by weight.

  The base paper used in the present invention includes chemical pulp such as LBKP and NBKP, mechanical pulp such as GP, PGW, RMP, TMP, CTMP, CMP and CGP, and pulp such as waste paper pulp such as DIP. It contains various additives such as calcium carbonate, talc, clay and kaolin, sizing agents, fixing agents, retention agents, cationizing agents, paper strength enhancing agents and the like, and is made into an acid, neutral and alkaline paper. As the base paper of the present invention, a no-size press base paper, a base paper size-pressed with starch, polyvinyl alcohol or the like is used.

  The method for coating the base paper with the paint containing the pigment obtained by the present invention to provide a coating layer is not particularly limited, and a gate roll coater, a blade coater or the like that is well known in the past is appropriately used. One or more coating layers can be provided.

  The coated paper obtained by applying the paint blended with the pigment of the present invention is excellent in blank paper glossiness and opacity quality by using a finishing device such as a super calender, gloss calender, or soft calender as required. Coated paper can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto. Moreover, unless otherwise indicated, the part and% in an example show a weight part and weight%, respectively.
<Concentration of solid content>
The absolute dry weight at 105 ± 5 ° C. was determined, and the solid content concentration was calculated.
<Particle size and particle size distribution>
Measured with a Malvern Mastersizer 2000 model. The particle size of 50% by weight of the obtained particle size distribution measurement curve was taken as the average particle size. Further, the ratio of the particle size of 50% by weight of the particle size distribution measurement curve to the particle size of 10% by weight of the particle size distribution measurement curve was determined as D ₅₀ / D ₁₀ . Note that the ratio is closer to 1 as the particle size distribution is sharper.
<BET specific surface area>
Measured by a nitrogen adsorption method (Micromeritics Gemini 2360 manufactured by Shimadzu Corporation)
<Glossiness of blank paper>
According to JIS P-8142, it measured at an angle of 75 degrees.
<Opacity>
According to JIS P-8138, it measured at an angle of 75 degrees.
[Example 1]
Heavy calcium carbonate with an average particle size of 14.5μm obtained by dry milling (Sankyo Seifun PC35) is measured with an air separator dry classifier (Kotobuki Giken UFS75 type) with an average particle size of 1.7μm and a BET specific surface area of 4.0m. ² / g heavy calcium carbonate was obtained. To 100 parts of dry-classified heavy calcium carbonate, add 1.5 parts of dispersant (Kao Poise 535M) to heavy calcium carbonate and add water so that the solid concentration of heavy calcium carbonate becomes 70%. Adjusted. This heavy calcium carbonate slurry was pulverized for 30 minutes at a flow rate of 1.5 L / min in a multipass ball mill filled with 0.3 mm zirconia beads. At this time, the average particle diameter of heavy calcium carbonate was 0.66 μm, and the BET specific surface area was 10.1 m ² / g.

50 parts of the heavy calcium carbonate after wet pulverization thus obtained, 50 parts of kaolin, 8 parts of styrene / butadiene copolymer latex and 3 parts of urea phosphate esterified starch for all pigments as an adhesive. .5 parts and 7 parts of plastic pigment were blended to prepare a paint having a solid content of 63%. The thus-prepared coating material was coated and dried on a high-quality base paper having a basis weight of 45 g / m ² using a blade coater so that the coating amount was 12 g / m ² per side. Subsequently, a super calendar process (temperature 65 ° C., linear pressure 200 kg / cm) was performed to obtain a coated paper for printing.
[Example 2]
In Example 1, heavy calcium carbonate was pulverized by the same method as in Example 1 except that the average particle diameter was adjusted to 4.5 μm and the BET specific surface area was adjusted to 2.1 m ² / g by dry classification. Obtained paper.
[Example 3]
In Example 1, pulverization was carried out in exactly the same manner as in Example 1 except that two-stage pulverization was carried out at a flow rate of 150 ml / min and a rotational speed of 2500 rpm with a horizontal sand grinder filled with 0.3 mm zirconia beads, and the coating for printing was performed. Obtained paper.
[Comparative Example 1]
In Example 1, heavy calcium carbonate was pulverized by the same method as in Example 1 except that the average particle size was adjusted to 6.0 μm and the BET specific surface area was 1.8 m ² / g by dry classification. Obtained paper.
[Comparative Example 2]
A coated paper for printing was obtained by pulverizing in exactly the same manner as in Example 1 except that 1.5 mm zirconia beads were used and pulverized by a multipass ball mill.

The results are shown in Table 1.

  From the results shown in Table 1, Examples 1 to 3 can obtain calcium carbonate having a sharp particle size distribution and a low specific surface area. Excellent opacity. Comparative Examples 1 and 2 are calcium carbonates having a low specific surface area, and printing papers using the same are inferior in white paper glossiness and ISO opacity.

Claims (4)

In the manufacturing method for performing the pulverization treatment of calcium carbonate, by subjecting the calcium carbonate to dry classification, the average particle diameter by the laser diffraction scattering method of calcium carbonate is adjusted to 5.0 μm or less, and the BET specific surface area is adjusted to 5 m ² / g or less. A method for producing calcium carbonate, characterized by further adjusting the average particle size of calcium carbonate by laser diffraction scattering method to 1.0 μm or less and the BET specific surface area to 13 m ² / g or less by wet pulverization.   The method for producing calcium carbonate according to claim 1, wherein a medium is used in the wet pulverization, and a media bead diameter is 0.1 to 1.0 mm. In the manufacturing method for performing the pulverization treatment of calcium carbonate, by subjecting the calcium carbonate to dry classification, the average particle diameter by laser diffraction scattering method of calcium carbonate is adjusted to 5.0 μm or less, and the BET specific surface area is adjusted to 5 m ² / g or less. By adding a dispersant to the calcium carbonate to prepare a calcium carbonate slurry having a solid content concentration of 50 to 80%, and further wet-grinding, the average particle diameter of calcium carbonate by laser diffraction scattering method is 1.0 μm or less, BET A method for producing a calcium carbonate slurry, wherein the specific surface area is adjusted to 13 m ² / g or less. The coated paper which coated the coating liquid containing the calcium carbonate manufactured with the manufacturing method in any one of Claims 1-3.