JP2008230898A - Manufacturing method of slurry containing light calcium carbonate and coated paper using the slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a slurry containing a fine light calcium carbonate with a narrow particle size distribution, in a method wherein the pulverizing treatment of the light calcium carbonate manufactured by a causticizing step is performed, and also to provide a coated paper having an excellent white paper gloss-developing property and excellent opaqueness by coating a sheet of paper with the fine light calcium carbonate. <P>SOLUTION: In the manufacturing method of the slurry containing the light calcium carbonate, the slurry containing the light calcium carbonate manufactured in the causticizing step of a pulp manufacturing process in an amount of ≥50 wt.% and having 60-70 wt.% solid concentration is prepared and the slurry is pulverized in a wet state until the light calcium carbonate has an average particle diameter of 0.4-1.2 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light calcium carbonate-containing slurry which is a fine particle for coating having a narrow particle size distribution in a method for producing a light calcium carbonate-containing slurry by wet-grinding a calcium carbonate-containing slurry produced in a causticizing step of a pulp production process. It is related with the method of manufacturing efficiently.

  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 coating pigments is inexpensive. Above all, in the causticizing process of the pulp manufacturing process by the sulfate method or soda method, the causticizing process is produced by causticizing reaction with green liquor after the quick lime is dehydrated with water or weak liquid (causticizing method). Since the light calcium carbonate produced in 1 is a by-product in producing white liquor, which is the main product, the existing facilities are used in comparison with the light calcium carbonate obtained by the conventional reaction of lime milk and carbon dioxide. This is very cheap because the capital investment is minimal. Calcium carbonate has the advantage of being able to produce a coated paper that is inexpensive and excellent in whiteness and opacity by blending a large amount in the paint, but there is a problem that the glossiness of the white paper is remarkably lowered. This problem can be solved by atomization by pulverization. However, since the fluidity decreases when atomization occurs, it is necessary to increase the amount of the dispersant added, and since it requires pulverization for a long time, the production cost of the pigment is increased. Becomes higher. 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 a technology for atomizing and grinding light calcium carbonate produced in a causticizing process that is inexpensive and hardly produces ultrafine particles of 0.2 μm or less can be developed, the light calcium carbonate produced in the causticizing process can be increased in the paint. By blending, high-quality coated paper having excellent whiteness and opacity can be produced without inferior white paper gloss.

So far, a technique for producing calcium carbonate having a narrow particle size distribution has been developed. As a method for producing calcium carbonate having a narrow 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 After adjustment, the mixture is centrifuged and the heavy liquid (slurry containing coarse particles settled on the inner wall of the apparatus) is collected, so that there are few coarse particles and fine particles, the particle size distribution is narrow, and the BET specific surface area is 6 to 12 m ^2. A method for producing a heavy calcium carbonate slurry that is 1 g / 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 narrow particle size distribution with a small amount of coarse particles and fine particles by collecting is proposed (see Patent Document 2). In these methods, the calcium carbonate slurry after wet pulverization is wet classified using a centrifugal separator to achieve a narrow particle size distribution with a low specific surface area. 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, a method for producing a calcium carbonate slurry having a narrow particle size distribution has been proposed by wet-grinding a calcium carbonate slurry prepared so that the solid content concentration of calcium carbonate is 50% by weight or less (see Patent Document 3). However, since the calcium carbonate slurry produced by this production method has a low solid content concentration as a paper coating pigment, it is necessary to concentrate the slurry after production, which complicates the production process and increases the cost of the coated paper. There is a problem that invites.
JP 2000-34120 A JP 2003-286027 A JP 2005-539124 A

  In view of the situation as described above, the subject of the present invention is a production method for pulverizing a light calcium carbonate-containing slurry produced in a causticizing step, a method for producing a fine light calcium carbonate-containing slurry having a narrow particle size distribution, Furthermore, it is providing the coated paper coated using the fine light calcium carbonate.

  In the present invention, the light calcium carbonate-containing slurry produced in the causticizing step is prepared so that the solid content is 60 to 70% by weight, and using a bead mill filled with beads of φ0.1 to 2.0 mm, Glossy expression of light calcium carbonate containing slurry produced by wet pulverization in the causticizing process, with an average particle size of light calcium carbonate of 0.4 to 1.2 μm or less and D85 / D15 of 6 or less by sedimentation X-ray transmission method It is a manufacturing method of the light calcium carbonate containing slurry manufactured by the causticizing process excellent in property and opacity, and is the coated paper coated using the light calcium carbonate manufactured by the causticizing process.

  By this invention, the manufacturing method of the fine light calcium carbonate containing slurry with a narrow particle size distribution can be obtained, and the coated paper using the same is excellent in white paper glossiness development and opacity.

Hereinafter, the method of the present invention will be specifically described. The light calcium carbonate of this invention uses what was manufactured at the causticizing process of the pulp manufacturing process by a sulfate method or a soda method.
As a light calcium carbonate production method, (1) a reaction between carbon dioxide-containing gas obtained from a lime baking apparatus and others and lime milk, (2) a reaction between ammonium carbonate and calcium chloride in an ammonia soda method, ( 3) Reaction of lime milk and sodium carbonate, which produces sodium hydroxide by causticization of sodium carbonate, is known. Among these methods, in (2) and (3), the production method for obtaining the main product is changed to a new method, or because calcium carbonate is a by-product, the content of impurities is high. The method has not been studied much.

  On the other hand, (1) has a relatively simple reaction system (water, slaked lime, carbon dioxide), and extensive research has been conducted on methods for producing calcium carbonate suitable for various purposes. Some products are also seen. However, the direct purchase from the manufacturer has the disadvantage that the transportation cost is high and the total cost is high. Further, in the on-site carbon dioxide method, if kiln exhaust gas is used, high-quality calcium carbonate can be produced at a low cost, but there is a problem that the capital investment is enormous.

  One possible method is to use calcium carbonate, which is a by-product when producing white liquor in the causticizing process for recovering and regenerating cooking chemicals, in the pulp manufacturing process using the sulfate method or soda method. is there. This method has the advantage that existing facilities can be used and the capital investment is minimized.

  In the pulp manufacturing process by the sulfate method or the soda method, cooking is performed under high temperature and high pressure using a chemical solution in which sodium hydroxide and sodium sulfide are mixed in order to isolate wood fiber. The fiber is separated and purified as a solid layer to become pulp, and the elution components other than the chemical solution and the fiber from the wood are recovered as pulp waste liquid (black liquor) and concentrated to a combustible concentration in the recovery boiler. Further, sodium sulfate is added to replenish the sodium and sulfur lost in the series of processes, and then burned in the recovery boiler. At that time, the organic substance in the black liquor is recovered as a heat source, and the inorganic substance is mainly recovered as sodium carbonate and sodium sulfide. These inorganic substances are called smelt and are taken out from the recovery boiler in a molten state. The smelt taken out from the recovery boiler is dissolved in water or a weak liquid (a liquid containing a small amount of white liquor component obtained after washing calcium carbonate with water) to become a green liquid.

  The causticizing process is a process for changing sodium carbonate in green liquor to sodium hydroxide, a cooking chemical. Mixing the slaked lime and green liquor with a soothing reaction (1) that converts quick lime to slaked lime. It consists of a causticizing reaction (2) that produces sodium and calcium carbonate. The liquid obtained by the causticizing reaction is called white liquor, separated from calcium carbonate, clarified, and sent to the cooking process. In the present invention, calcium carbonate that has been separated and recovered and thoroughly washed is used.

CaO + H ₂ O → Ca (OH) ₂ (1): Saturation reaction
Ca (OH) ₂ + Na ₂ CO ₃ → CaCO ₃ + 2NaOH (2): Causticizing reaction This calcium carbonate is a by-product in producing white liquor, which is the main product. Compared to the light calcium carbonate obtained by the reaction method, there is an advantage that the existing equipment can be used and the capital investment is minimized. Further, by extracting calcium carbonate out of the system from the calcium (quick lime, slaked lime, calcium carbonate) circulation cycle of the causticizing process in the conventional closed system, cleanliness in the system and high purity of the circulating lime are achieved. 1) The reactivity improvement of (2), the improvement of the clarity of white liquor, and the reduction of waste can be expected.

  In the present invention, the light calcium carbonate-containing slurry produced in the causticizing step is prepared so as to have a solid content concentration of 60 to 70% by weight, and then wet pulverized. The light calcium carbonate-containing slurry produced in the causticizing process used here only needs to contain 50% by weight or more of the light calcium carbonate produced in the causticizing process. You may contain inorganic pigments, such as calcium and kaolin.

  In the present invention, it is necessary that the average particle size of light calcium carbonate produced in the causticizing step obtained by wet pulverization is 0.4 to 1.2 μm and D85 / D15 is 6 or less. Thereby, because the ultrafine particles in the slurry containing light calcium carbonate produced in the causticizing process is reduced, the particle size distribution becomes very narrow, and the porosity in the coating layer is increased, as a result, Since the micro smoothness of the coating layer surface is improved, it is possible to obtain a slurry containing light calcium carbonate produced in a causticizing process for coating that is excellent in gloss development and opacity. The average particle diameter is preferably 0.5 to 0.8 μm, and D85 / D15 is preferably 5 or less.

  In the present invention, the media used for pulverization and classification can be appropriately selected from materials such as glass beads, zirconia beads, zircon beads, and steel balls according to the viscosity, specific gravity, and pulverization and classification required for processing. In order to improve the grinding efficiency, the media bead diameter used is φ0.1 to 2.0 mm, preferably 0.1 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 2.0 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 the wet pulverization method, a multi-pass pulverization method in which residence at a high flow rate for a short time or a pulverization method in which several pulverizers are provided in series or in parallel to change the model or the media diameter can be appropriately selected.

  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 content concentration of the calcium carbonate-containing slurry in the wet pulverization is preferably 60 to 70% by weight. When the slurry solid content concentration is less than 60%, the pulverization time becomes long, and it is not suitable for high solid differentiation of coating materials and high blending of calcium carbonate obtained in the present invention. Further, when the slurry solid content concentration is higher than 70%, it becomes difficult to uniformly pulverize, a large amount of ultrafine particles of 0.2 μm or less are generated, and the particle size distribution is not narrowed.

  The slurry containing light calcium carbonate produced in the causticizing process thus obtained is blended in the paint. In addition to the pigment obtained in the present invention, the coating material includes calcium carbonate other than light calcium carbonate produced in the causticizing process obtained in the present invention, kaolin, clay, calcined kaolin, zinc oxide, aluminum hydroxide, titanium dioxide. In addition, inorganic pigments such as calcium sulfate, satin white, talc, and 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 blending amount of calcium carbonate having specific physical properties of the present invention is not particularly limited, but in particular, by containing 50 parts by weight or more per 100 parts by weight of the pigment, white paper glossiness and opacity are further improved. Can do. In addition to the pigment, an adhesive such as starch, polyvinyl alcohol, or synthetic polymer latex 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-resistant 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.

  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. For the base paper of the present invention, no-size press base paper, 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 Sedigraph 5100 manufactured by Micromeritex. 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 85% by weight of the particle size distribution measurement curve to the particle size of 15% by weight of the particle size distribution measurement curve was determined as D ₈₅ / D ₁₅ . This ratio approaches 1 as the particle size distribution becomes narrower.
<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]
Manufactured in a causticizing process prepared by adding 0.9 part of a dispersant (Kao Poise 535M) to 100 parts of light calcium carbonate manufactured in a causticizing process with an average particle size of 15 μm to achieve a solids concentration of 67% by weight. The resulting slurry containing light calcium carbonate was pulverized at 1.8 L / min for 30 minutes in a multipass ball mill filled with 0.5 mm zirconia beads.

In this way, 75 parts of light calcium carbonate produced in the causticizing process was mixed with 25 parts of kaolin, 10 parts of styrene / butadiene copolymer latex as an adhesive, and 3.5 parts of urea phosphated starch. A paint having a solid content of 65% by weight was prepared. This coating material was coated on both sides of a high-quality base paper having a basis weight of 45 g / m ² using a blade coater so that the coating amount was 9 g / m ² per side. After coating, a super calendar process (temperature 65 ° C., linear pressure 100 kg / cm) was performed to obtain a coated paper for printing.
[Example 2]
In Example 1, the light calcium carbonate slurry produced in the causticizing step was pulverized and coated in the same manner as in Example 1 except that the solid content concentration was adjusted to 60% by weight. Obtained.
[Example 3]
In Example 1, grinding and coating were performed in exactly the same manner as in Example 1, except that the horizontal sand grinder filled with 0.3 mm zirconia beads was subjected to two-stage grinding at a flow rate of 70 ml / min and a rotational speed of 2500 rpm, and printing. Coated paper was obtained.
[Example 4]
In Example 1, 1.6 parts of a dispersant was added, and the mixture was pulverized and coated in the same manner as in Example 1 except that it was pulverized for 75 minutes to obtain a coated paper for printing.
[Example 5]
In Example 1, the light calcium carbonate produced in the causticizing process was roughly pulverized to 4.5 μm with an attritor filled with 10 mm alumina beads and pulverized for 20 minutes with a multipass ball mill. Crushing and coating were performed by the method to obtain a coated paper for printing.
[Example 6]
In Example 1, 50 parts of light calcium carbonate produced in the causticizing step was mixed with heavy calcium carbonate having an average particle size of 13 μm before wet grinding, and was ground and coated in exactly the same manner as in Example 1. To obtain a coated paper for printing.
[Comparative Example 1]
In Example 1, except that the solid content concentration of the light calcium carbonate slurry produced in the causticizing step was adjusted to 72% by weight, pulverization and coating were performed in exactly the same manner as in Example 1 to obtain a coated coated paper for printing. Obtained.
[Comparative Example 2]
In Example 2, the light calcium carbonate slurry produced in the causticizing step was pulverized and coated in the same manner as in Example 2 except that the solid content concentration was adjusted to 72% by weight. Obtained.

  The results are shown in Table 1.

  From the results in Table 1, Examples 1 to 6 have D85 / D15 of 6 or less, and light calcium carbonate produced by a causticizing process having a narrow particle size distribution is obtained. Moreover, the coated paper for printing using it is excellent in white paper glossiness and ISO opacity. In Comparative Examples 1 and 2, light calcium carbonate produced by a causticizing process with a narrow particle size distribution is not obtained, and the glossiness of blank paper and ISO opacity are also inferior.

Claims (4)

In the method for producing a light calcium carbonate-containing slurry, a slurry containing 50% by weight or more of light calcium carbonate produced in the causticizing step of the pulp production process and having a solid concentration of 60 to 70% by weight is prepared. The method for producing the light calcium carbonate-containing slurry, wherein the slurry is wet-pulverized until the average particle size of the slurry becomes 0.4 to 1.2 μm. The light calcium carbonate after wet pulverization has a ratio (D85 / D15) of 85% by weight particle size (D85) to 15% by weight particle size (D15) of particle size distribution measurement curve of 6 or less. The method for producing the light calcium carbonate-containing slurry according to claim 1. The method for producing the light calcium carbonate-containing slurry according to claim 1, wherein the wet pulverization is performed using a media, and the media diameter is 0.1 to 2.0 mm. The coated paper which coated the coating liquid containing the said light calcium carbonate containing slurry manufactured with the manufacturing method in any one of Claims 1-3.