JP3861754B2 - Method for producing pigment - Google Patents

Description

【００４９】
（塗被紙の製造）
実施例および比較例にて得られたそれぞれの湿式重質炭酸カルシウム１００部（固形分換算）のスラリーに、澱粉（エースＡ／王子コーンスターチ社）を３部（固形分換算）、スチレンブタジエン共重合体ラテックス（ＪＳＲ−０６１３／ジェイエスアール社）７部（固形分換算）を加えてそれぞれの塗料を得た。塗料の全固形分濃度は６０％であった。
【００５０】
塗被用原紙（坪量４８．０ｇ／ｍ²）に上記の得られた塗料を乾燥固形分が片面１０ｇ／ｍ²になるように卓上ブレードコーターにて両面塗工し乾燥して印刷用紙を得た。得られた両面塗工紙をスーパーカレンダーで平滑化処理した。得られた塗被紙をそれぞれ実施例１−ａ、実施例２−ａ、比較例１−ａ、比較例２−ａとして、表２にまとめた。
【００５１】
【表２】

【００５２】
次に、実施例と比較例で得られた５種類の湿式粉砕処理炭酸カルシウムそれぞれに対して５０部（固形分換算）のスラリーにカオリン（ＨＴ／エンゲルハード社）、澱粉（エースＡ／王子コーンスターチ社）を３部（固形分換算）、スチレンブタジエン共重合体ラテックス（ＪＳＲ−０６１３／ジェイエスアール社）７部（固形分換算）を加えてそれぞれの塗料を得た。塗料の全固形分濃度は６０％であった。
【００５３】
塗被用原紙（坪量４８．０ｇ／ｍ²）に得られた塗料を乾燥固形分が片面１０ｇ／ｍ²になるように卓上ブレードコーターにて両面塗工し乾燥して印刷用紙を得た。得られた両面塗工紙をスーパーカレンダーで平滑化処理した。得られた塗被紙をそれぞれ実施例１−ｂ、実施例２−ｂ、実施例３−ｂ、比較例１−ｂ、比較例２−ｂとして、表３にまとめた。
【００５４】
【表３】

【００５５】
（塗工紙の白色度等の測定）
これらの両面塗工紙の白色度と不透明度は分光白色度測色計（スガ試験機社）を使用してＩＳＯ２４７０、ＩＳＯ２４７１に準拠して測定した。光沢度は光沢度計（ＭＵＲＡＫＡＭＩ ＣＯＬＯＲ ＲＥＳＥＡＲＣＨ ＬＡＢＯＬＡＴＯＲＹ社）を使用してＩＳＯ８２５４−１に準拠して測定した。
【００５６】
また、印刷試験はＲＩテスターを用いて行った。印刷インキ（東洋インキ社製）を０．６ｃｃ使用して印刷し、２３℃、相対湿度５０％の雰囲気で２日間放置してインキを乾燥させ、光沢度計（ＧＭ−２６Ｄ／村上色彩技術研究所製）用いて６０°光沢度を測定した。
【００５７】
インク乾燥性は印刷直後のインクの裏写り濃度から官能評価した。印刷インキ（東洋インキ社製）を０．６ｃｃ使用して印刷し、３分後に白紙と印刷面を重ねて、再度ＲＩ印刷機にてニップし、白紙に転写したインキの濃度を目視評価した。
【００５８】
また、印刷表面強度も官能評価した。印刷インキ（東洋インキ社製）を０．４ｃｃ使用して印刷し、印刷面のピッキングの程度を目視評価した。それぞれの評価結果を表２及び３に示した。
【００５９】
表１において、実施例１と比較例１及び実施例２と比較例２をそれぞれ比較すると、最終製品のＤ_５０は同等であるにも関わらず、実施例で得られた顔料のＤ_７５／Ｄ_２５比が低くシャープな粒度分布を有していることがわかる。実施例は比較例に比べてＤ_２５も大きく、不要な超微粒分も少ないことが分かる。
【００６０】
その結果、表２では、実施例１、２及び比較例１で得られた塗被紙の白色度は、ほぼ同等であるが、比較例２の白色度は超微粒部分が多いために低下している。不透明度は不要な微粒分の少ない実施例の方が明らかに高い。また、実施例のインクセットは並であり、白紙光沢と印刷光沢のバランスが明らかに良い。表面強度も不要な超微粒分の少ない実施例の方が強い結果となった。
【００６１】
表３では、全塗被紙にカオリンを配合しているために、白色度は全体的に低い結果となった。不透明度は明らかに不要な超微粒分の少ない実施例の方が高い。また、実施例のインクセットは並であり、白紙光沢と印刷光沢のバランスが明らかに良い。表面強度も不要な超微粒分の少ない実施例の方が強い結果となった。
【００６２】
以上の結果から、本発明に記載の製造方法によって顔料を製造すると、粒度分布をシャープできることがわかる。また、不要な超微粒分が少ないために、超微粒分を分級処理によって除去する必要がなくなり、製造収率を高めることができる。また、本発明の製造方法によって得られるシャープで超微粒分の少ない粒度分布を有する顔料を塗被紙に用いると、白色度と不透明度が高く、白紙光沢と印刷光沢が高く、通常では相反する品質を高く得られることがわかる。
【００６３】
【発明の効果】
不要な超微粒分の生成が少ないシャープな粒度分布を有する顔料が得られた。
【図面の簡単な説明】
【図１】原料から本発明の湿式粉砕工程にはいるまでの主な三つの工程図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a pigment. More specifically, the present invention relates to a method for producing a fine carbonate-containing pigment by wet grinding.
[Prior art]
Pigments are pesticide spreaders, extenders, paints, modified pigments for printing inks, rubber reinforcements, fillers for plastics (molded articles, films, fibers, etc.), modifiers, and in the paper industry. It is used as an additive filler or coating pigment. Here, a usage form in the paper industry where the amount of pigment used is large will be described as a representative example.
[0002]
In general, in the papermaking industry, in order to improve optical properties such as whiteness and opacity of paper, smoothness, and the like, papermaking is usually performed by adding a filler to a paper stock mainly composed of pulp. In addition, for the purpose of improving printability, a pigment coating layer mainly composed of a pigment and an adhesive is also provided on paper (base paper).
[0003]
As papermaking pigments used for such internal addition or coating, usually kaolin, calcined kaolin, calcium carbonate, zinc oxide, aluminum hydroxide, zinc sulfide, titanium dioxide, calcium sulfate, calcium sulfite, barium sulfate In addition, inorganic pigments such as satin white, talc, and silica are mainly used, and one or more organic pigments called plastic pigments are appropriately mixed and used as necessary.
[0004]
Among them, calcium carbonate and kaolin are representative pigments that are used in large amounts in the paper industry. In particular, calcium carbonate has a higher whiteness than kaolin, and is an essential pigment for producing coated paper with high whiteness.
[0005]
Further, it is known that the gloss of paper depends on the particle size distribution of the pigment contained therein. Therefore, calcium carbonate having a small particle size and a large specific surface area can be more preferably used as a pigment for high gloss paper. In Japanese Patent Laid-Open No. 10-8397, a particle size (D₅₀) Is 0.18 to 0.28 μm, BET / N₂The specific surface area measured by the method is 20m²/ G or more, preferably 20-50 m²Carbonate-containing pigment having a specific surface area of 50 g / g wet milled in a stirred ball mill at a solids concentration of 30-20% without the addition of dispersants or wetting agents, and then concentrated, re-dispersed, and binders, water and additives It is disclosed to manufacture by adding. It is said that gloss and printing gloss can be enhanced in a coated paper containing a carbonate pigment produced by this method. Here, “the particle size of 50% by weight of the particle size distribution measurement curve” means the particle size corresponding to 50% by weight when the particle weight is accumulated from the smaller particle size to the larger particle size of the pigment in which various particle sizes are distributed. Say.
[0006]
Generally, calcium carbonate wet pulverized using a wet pulverizer as described in JP-A-10-8397 is called wet heavy calcium carbonate, compared to dry heavy calcium carbonate, It can be said that the particle size is small and the specific surface area is large. Therefore, wet heavy calcium carbonate is more preferably used than dry heavy calcium carbonate in order to produce coated paper with high gloss.
[0007]
On the other hand, in order to remove unnecessary ultrafine particles that are produced when fine calcium carbonate is pulverized, “Application and characteristics of limestone” (published by the Limestone Mining Association, page 94) includes air after pulverizing calcium carbonate. The classification method is introduced. JP 2000-34120 A proposes wet classification using a centrifugal separator. However, in these methods, it is necessary to install a classifier in addition to the pulverizer, and there is a problem that the production efficiency of calcium carbonate is lowered because the ultrafine particles after classification are lost.
[0008]
[Problems to be solved by the invention]
The pigment is pulverized to an optimum particle size by a wet pulverizer according to the usage form. At this time, there is a problem that the finer the final particle size, the more unnecessary ultrafine particles are increased and the pigment quality is lowered. Unnecessary ultrafine particles can be classified and removed. However, since the ultrafine particles are lost, there is a problem that the yield of the pigment is lowered and the production efficiency is lowered.
An object of the present invention is to provide a method for producing a pigment having a sharp particle size distribution with little generation of unnecessary ultrafine particles in the wet pulverization treatment of the pigment.
[0009]
[Means for Solving the Problems]
  The pigment production method of the present invention is a pigment production method including a multistage pulverization process using a wet pulverizer, and uses a bead mill filled with beads as a wet pulverizer in at least two successive pulverization processes. And the diameter of the beads used in the subsequent grinding process is larger than the diameter of the beads used in the preceding grinding process,In the subsequent pulverization step, the ratio of the particle size of 75% by weight of the particle size distribution measurement curve to the particle size of 25% by weight of the particle size distribution measurement curve (D ₇₅ / D ₂₅ ) Is 5 or less and the particle size (D) is 50% by weight of the particle size distribution measurement curve before and after grinding. ₅₀ ) Ratio is in the range of 0.5-0.9It is characterized by crushing.
  Further, the pigment finally obtained has a particle diameter (D₅₀) Is calcium carbonate of 0.4 to 2 μm, and the diameter of the beads is larger than the diameter of the beads used in the preceding pulverization process and in the range of 0.5 to 2 mm. It is characterized by using a bead mill filled with beads.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As an example of the pigment production method of the present invention, a calcium carbonate pigment production method will be described below.
[0011]
In the calcium carbonate pigment, three main steps from the raw material to the wet pulverization step of the present invention are shown in FIG. In FIG. 1, limestone, which is the raw material, is processed into slurry (1) dry heavy calcium carbonate, (2) precipitated calcium carbonate, which is an intermediate raw material, and finally corresponds to the method for producing the pigment of the present invention. Undergo a wet grinding process. The intermediate raw materials shown in FIG. 1 are as follows: (1) dry heavy calcium carbonate, (2) precipitated calcium carbonate, and (3) regenerated pigment.
[0012]
<▲ 1> Dry heavy calcium carbonate>
The raw material for dry heavy calcium carbonate is limestone mined from the mine. Limestone includes calcite (calcite) and araleite (aragonite), but the latter is unstable under environmental conditions near the surface and is transferred to calcite. Limestone is used as the rock name, and limestone is used as the ore name. The limestone contained in old limestone is mostly composed of calcite. Many limestones are produced in seawater, but there are also freshwater limestones produced in freshwater.
[0013]
The limestone mined from the mine is hand-picked, and then the attached soil is removed by water washing and dry pulverized. Usually, dry pulverized limestone is called dry heavy calcium carbonate. As one of the intermediate raw materials used in the present invention, dry heavy calcium carbonate that has been dry-pulverized in advance to 100 μm or less, more preferably 50 μm or less, can be preferably used as the raw material for the wet pulverization treatment of the present invention.
[0014]
Next, dry pulverization will be described.
Coarse calcium carbonate can be dry pulverized to a size suitable for wet pulverization by a dry pulverizer. By using a dry pulverizer, a material of several mm can be pulverized to several tens of μm. Examples of the pulverizer include a roll crusher, a roll mill, a stamp mill, an edge runner, a cutter mill, and a rod mill. In addition, as a dry fine pulverizer of several μm or less suitable for a papermaking raw material, a roller mill, a jet mill, a dry ball mill, an impact pulverizer, or the like is used. In addition, it is more preferable that these dry pulverizers take into consideration wear such as using wear-resistant steel.
[0015]
The powder after dry pulverization is transferred to a disperser and stirred with water and a small amount of a dispersant to form a slurry. Then, this slurry is sent to a wet pulverizer, and the powder is subjected to a wet pulverization process to become fine wet calcium carbonate. At this time, if the particle size of the dry pulverized powder exceeds 100 μm, the dispersion of the powder in the disperser is deteriorated, the pulverization efficiency in the wet pulverizer is deteriorated, and the disperser and the pulverizer are worn. The whiteness of the slurry containing calcium carbonate decreases. Further, it is not economically preferable to pulverize the powder to less than 2 μm by dry pulverization because the pulverization efficiency is low.
[0016]
Next, slurrying will be described.
Prior to the wet pulverization treatment of the present invention, a dispersant is added to form a slurry to uniformly disperse the dispersion. By adding a dispersant, an increase in viscosity can be prevented even when the concentration of the slurry is increased, and an increase in viscosity due to a wet pulverization treatment can be prevented, and the pulverization efficiency and handling properties can be improved. At this time, if the addition amount exceeds 3%, dispersibility does not improve even if the addition amount is increased, and if it is 0.05% or less, the dispersibility is poor and the subsequent wet pulverization can be efficiently performed. Can not. In addition, the dispersion zone of the disperser can be covered with rubber or wear-resistant plastic. In the present specification, “%” and “part” respectively indicate “% by weight” and “part by weight” unless otherwise specified.
[0017]
<▲ 2> Precipitated calcium carbonate>
As an intermediate material of the present invention, precipitated calcium carbonate (light calcium carbonate) can also be subjected to the wet pulverization treatment of the present invention. Precipitated calcium carbonate is obtained by calcining limestone, adding water to the obtained quick lime to obtain lime milk, and then reacting carbon dioxide gas or sodium carbonate to precipitate calcium carbonate of uniform particle size. Say. In particular, since precipitated calcium carbonate obtained in a causticizing process in a pulp mill is intended to produce caustic soda, coarse calcium carbonate is produced by precipitation. Such precipitated calcium carbonate can also be used as a raw material for the wet pulverization treatment of the present invention. At this time, if necessary, slurrying treatment can be performed according to the method for producing dry heavy calcium carbonate.
[0018]
<(3) Regenerated pigment>
The above description is a case where limestone is used as a raw material, and a regenerated pigment using a waste material such as papermaking sludge as a raw material will be described below.
It has been practiced to recover pigments from waste by heat-treating waste such as paper sludge such as incineration, carbonization, firing and wet oxidation. The regenerated pigment thus obtained can also be subjected to the wet pulverization treatment of the present invention. Also in this case, a dry pulverized product preliminarily pulverized to 100 μm or less, more preferably 50 μm or less, can be preferably used for the wet pulverization treatment of the present invention. Incidentally, the dry pulverization treatment and the slurrying treatment can be carried out according to the dry heavy calcium carbonate production method.
[0019]
Next, the wet pulverization process corresponding to the method for producing a pigment of the present invention will be described in detail.
Usually, the selection of the media diameter in accordance with the particle size of the material to be crushed is considered as an important factor affecting the pulverizability. “Handbook of powder engineering” (issued by the Society of Powder Engineering, page 510) includes D_b(Optimum media diameter) ∝ D_f ^mThe relationship of (particle diameter of the specific pulverized product, m = 0.25 to 0.5) is shown. This indicates a general pulverization principle that, when pulverizing in multiple stages, the optimum media diameter decreases as the material to be pulverized decreases. In view of this, a pulverizer has been developed, such as a conical ball mill, which can be filled with a ball having a large diameter at the inlet of the object to be pulverized in the pulverizing chamber and a ball having a small diameter near the outlet (page 510 of the above-mentioned Powder Engineering Manual).
[0020]
Note that the media refers to grinding media such as steel balls, magnetic balls, cobblestones, steel rods, pebs or various beads filled in the grinding machine. Among the media, a ball mill using a ball having a large particle size is a narrow ball mill, and a ball mill using beads having a diameter of about several mm to 0.3 mm is called a bead mill.
[0021]
In order to produce fine calcium carbonate, the present inventors selected a medium having an optimum particle size according to the particle size of the material to be crushed according to the general pulverization principle described above, and performed wet pulverization treatment. However, it has been found that as the material to be pulverized becomes finer, unnecessary fine particles increase and the pigment quality decreases. In particular, it has been found that coated paper using fine calcium carbonate produced by the above-mentioned general pulverization principle has a low printed gloss after printing. This is because the amount of ultrafine particles contained in the fine calcium carbonate is large, so the solvent absorption in the printing ink of the coating layer is large, and the printing ink dries before a good printing surface is formed. It is thought to be caused by what happens.
[0022]
Accordingly, the present inventors diligently studied a method for producing a pigment having a sharp particle size distribution with little generation of unnecessary ultrafine particles. As a result, it has been found that the problems of the present invention can be solved under conditions opposite to the general pulverization principle.
[0023]
Surprisingly, in the multi-stage pulverization method using a wet pulverizer, at least one pulverization process is performed by using beads having a diameter larger than that of the beads used in the previous pulverization process. It was found that a pigment having a sharp particle size distribution with little generation of minute can be produced. That is, by applying the fine calcium carbonate obtained by the wet pulverization treatment of the present invention, it was possible to produce a coated paper having high white paper gloss and high printing gloss.
Hereinafter, the wet pulverization process of the present invention will be described in more detail.
[0024]
(The most suitable raw material for the wet pulverization process of the present invention)
Examples of the raw material used in the wet pulverization treatment of the present invention include (1) dry heavy calcium carbonate slurry, (2) precipitated calcium carbonate slurry, and (3) regenerated pigment slurry described above. At this time, the ratio of the particle size of 75% by weight of the particle size distribution measurement curve to the particle size of 25% by weight of the particle size distribution measurement curve (D₇₅/ D₂₅) Is preferably used as a raw material for the subsequent wet pulverization. The closer this value is to 1, the more the pigment has a sharp particle size distribution. When the value exceeds 5, the pigment having the sharp particle size distribution, which is the object of the present invention, is produced because of excessively broad particle size distribution. Because it becomes difficult. That is, D₇₅/ D₂₅Can be appropriately selected and treated with a dry pulverizer, a classifier, and a wet pulverizer in the previous stage.
The particle size distribution measurement curve is measured by a Cedigraph X-ray transmission type particle size distribution measurement method. This method is a particle sedimentation method based on Stokes' law, and is a measurement method measured on an aqueous dispersion of a pigment. The sedimentation data of the pigment is collected and analyzed by a sedigraph particle size distribution analyzer (X-ray sedigraph 5100 manufactured by Micromeritics).
[0025]
The slurry concentration can be appropriately selected according to the set concentration of the coating solution. The slurry concentration can be appropriately selected from about 30% to 80%. At this time, if the slurry concentration is lowered, the contact probability between the objects to be crushed decreases, and conversely, the contact probability between the media and the object to be pulverized increases, so that the pulverization time is shortened. Also, the particle size distribution tends to be sharp, and the lower the slurry concentration, the better. However, low-concentration pulverization may be set in consideration of economical pulverization efficiency because the solid content processing amount when the same pulverizer is used may decrease. The slurry is a liquid containing water, a dispersant, a paint stabilizer and the like.
[0026]
(About the number of pulverization stages and media diameter)
In order to wet pulverize the pigment to a particle size that matches the usage pattern, the number of wet pulverization treatment stages can be increased or decreased as appropriate. A number of pulverization steps of approximately 2 to 3 is economically preferable. It is preferable that the media diameter filled in each wet pulverizer is appropriately selected according to the particle diameter of the material to be pulverized. At this time, at least one pulverization process uses a medium having a diameter larger than that of the medium used in the preceding pulverization process to produce a pigment having a sharp particle size distribution with less generation of unnecessary ultrafine particles. Can do.
[0027]
When the media diameter is made larger than the media diameter used in the previous pulverization process, the pulverization time tends to be longer than when a small-diameter media is used. When the media diameter is larger than the media diameter used in the preceding pulverization process, the particle size (D₅₀) Is preferably in the range of 0.5 to 0.9 in order to efficiently achieve the object of the present invention.
[0028]
Although it is possible to make this value less than 0.5, the pulverization time becomes long and it is not economical. Conversely, D₅₀When the ratio is larger than 0.9, there is little change in the particle size and particle size distribution after pulverization, which is not effective. Eventually, it is preferable to use a small particle size medium in the previous stage to shorten the pulverization time, and to use a larger medium in the subsequent stage to make the particle size distribution sharp.
[0029]
In particular, it is more preferable to use beads larger than the media (bead) diameter used in the previous stage in the final stage pulverization treatment because the particle size distribution of the pigment as the final product can be sharpened. Of course, in a wet pulverization process of three or more stages, it is possible to pulverize a material to be pulverized having a sharper particle size distribution by using beads larger than the previous stage in the intermediate pulverization process. As will be described later, the target pigment particle size is 50% by weight of the particle size distribution measurement curve (D₅₀) Is preferably 0.4 to 2 μm. For this reason, the bead diameter used in the final stage is preferably in the range of 0.5 to 2 mm. If the bead diameter used in the final stage is smaller than 0.5 mm, the particle size distribution tends to be broad, and if it is larger than 2 mm, the wet pulverization time becomes long, which is not economical.
[0030]
(About the final pigment particle size as coated paper)
As a result of intensive studies on the particle size distribution of the pigment and the quality of the coated paper by the present inventors, the particle size (D) of 50% by weight of the particle size distribution measurement curve of the pigment obtained in the final pulverization process₅₀) Is 0.4-2 μm, the ratio of the particle size of 75% by weight of the particle size distribution measurement curve to the particle size of 25% by weight of the particle size distribution measurement curve (D₇₅/ D₂₅) Is 3.5 or less, and the particle size (D₂₅) Is 0.2 μm or more, it has been found that the white paper gloss, printing gloss and opacity of the coated paper are high and balanced.
[0031]
D of final crushed material₅₀If the thickness is less than 0.4 μm, the amount of ultrafine particles increases, so that the printing gloss is remarkably reduced. D₅₀Is in the range of 0.4-2 μm,₇₅/ D₂₅When the value exceeds 3.5, the particle size distribution becomes broad, and the quality control of the coated paper tends to be difficult. In addition, D₅₀Is in the range of 0.4-2 μm,₂₅Is less than 0.2 μm, the printing gloss tends to decrease.
[0032]
Highly glossy coated paper (glossy paper) or low glossy coated paper (matte) with a good balance between white paper gloss and printing gloss by using the wet pulverized pigment obtained by the present invention for coated paper and managing calendar conditions Paper). Furthermore, the wet pulverized pigment obtained by the present invention can be preferably used for cast paper or gravure paper.
[0033]
(About wet crusher)
Examples of the wet pulverizer used in the present invention include a wet ball mill, a vibration mill, a stirring tank mill, a flow tube mill, and a coball mill. These pulverizers are filled with media, the flow direction (longitudinal and lateral) of the material to be pulverized, the ratio of the mill diameter to the length (L / d), the method of stirring the media in the pulverizer, the media and the Various different wet pulverizers have been proposed in the method of separating pulverized materials. From these pulverizers, a model that can be filled with the optimum medium can be selected as appropriate. A pulverizer other than a bead mill can also be employed as part of the multistage wet pulverization process.
[0034]
In order to prevent contamination of the pigment due to abrasion of the wet grinder, it is desirable to coat the grinder zone of the grinder with an abrasion resistant material such as rubber or abrasion resistant plastic. The pulverization zone refers to the inner surface of the pulverization chamber, the outer surface of the stirring member, and the like, and is a zone where the powder in the slurry comes into contact during pulverization. When members such as a partition plate are provided in the pulverization chamber, these are also part of the pulverization zone. Examples of wear-resistant plastics include urethane resins and nylon resins, and it is desirable to coat them with a thickness of about 1 mm to 10 mm, but they can be appropriately selected depending on the frequency of use and pulverization conditions. In addition, before and after the wet pulverization treatment, the hardly pulverized object to be pulverized can be removed through a screening apparatus such as an open-type vibrating screen, a multi-tube vibration pressure filter, or a mechanical pressure filter. The media filled in the grinder can also be considered part of the grinding zone.
[0035]
In addition, materials such as glass beads, zircon beads, zirconia beads, and steel balls can be appropriately selected as media according to the viscosity, specific gravity, pulverization, and dispersion required particle size of the processed material. Ceramic media such as alumina and zirconia have higher hardness and higher crushability and durability than glass, and can be preferably used. These media can be appropriately selected in consideration of economy and operability. In addition, it is preferable to pulverize by appropriately combining factors such as the filling amount of the medium, the peripheral speed of the disk, and the liquid feeding amount of the pump.
[0036]
At the time of pulverization, the temperature of the slurry rises due to friction between the object to be crushed and the medium, between the object to be crushed, and the like. It is not preferable that water evaporates and the slurry concentration becomes high or the dispersant is thermally denatured due to the temperature rise. If there is a problem in operation, it is preferable to attach a cooling device to the pulverizer or slurry circulation tank as appropriate.
[0037]
Moreover, although calcium carbonate slurry is alkaline, since calcium carbonate decomposes when it becomes acidic, the pH is preferably about 8 to 10. If the pH is higher than this range, the dispersibility decreases, which is not preferable. When the pH of the slurry shows an alkalinity exceeding 13, it is preferably adjusted to 8 to 12 using an acid. This is because when the pH of the slurry is high, the effect of the dispersant is lowered, and the pulverization property and fluidity are lowered. More preferably, the pH of the slurry is adjusted to 8 to 12 using carbon dioxide. This is because calcium carbonate is generated after pH adjustment. By adjusting the pH before adjusting the slurry and pulverizing, it is possible to perform an efficient process while preventing an increase in viscosity.
[0038]
In the present invention, a pigment production process such as transfer, storage, circulation, agitation, concentration adjustment, viscosity adjustment, pH adjustment, screening, etc. of the object to be crushed can be appropriately provided before and after and in the middle of at least two continuous pulverization treatment steps. Is possible. This is because the essence of the present invention, “a pigment having a sharp particle size distribution can be produced by using beads larger than those used in the previous stage in the subsequent stage” is not affected by these treatments. Because.
[0039]
The wet pulverized pigment thus obtained can be transferred to a coating liquid (paint) adjusting step. An arbitrary amount of wet pulverized pigment can be blended in the coating solution. By blending a larger amount of the pigment obtained by the present invention, a coated paper with higher gloss and higher printing gloss can be produced.
[0040]
The concentration of a normal coating solution is about 20 to 70%. A higher concentration of the coating solution is preferable because less energy is required to dry the coating solution. In particular, when the coating layer is formed by a blade coater, 50 to 70% is a preferable range because a high quality coating layer can be formed with little penetration into the coating base paper.
[0041]
In addition to the wet-pulverized pigment, the coating liquid includes calcium carbonate (meaning calcium carbonate other than calcium carbonate obtained in the present invention, specifically, light calcium carbonate, heavy calcium carbonate having a coarse particle diameter, etc. Kaolin, calcined kaolin, zinc oxide, aluminum hydroxide, zinc sulfide, titanium dioxide, calcium sulfate, calcium sulfite, barium sulfate, satin white, talc, silica and other inorganic pigments, if necessary One kind or two or more kinds of organic pigments called plastic pigments can be appropriately mixed and used. In addition to the pigment, an adhesive such as starch, polyvinyl alcohol (PVA) or latex can be appropriately blended. Also in this case, the wet pulverized pigment obtained according to the present invention does not contain excessive fine particles, and therefore it can be preferably used because it requires less adhesive.
[0042]
【Example】
This will be described in more detail with reference to examples. The particle size distribution of calcium carbonate produced according to the present invention was a sedigraph particle size distribution measuring device (X-ray sedigraph 5100 manufactured by Micromeritics). In addition, weight% of concentration display means the solid content weight ratio in a slurry.
[0043]
(Example 1)
The following is an example of dry heavy calcium carbonate obtained by two-stage wet pulverization of the first and second stages.
First stage grinding: Dry heavy calcium carbonate D₅₀= 3.1 μm, D₇₅/ D₂₅= 4.5 to 0.5% water and dispersant (T-40 manufactured by Toagosei Co., Ltd.) to prepare a slurry with a solid content of 70% by weight, and a pearl mill filled with 80% glass beads with a diameter of 0.5 mm And ground for 14 minutes. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.8 μm, D₇₅/ D₂₅Was 3.6.
Post-stage pulverization: The pulverized slurry obtained by the pre-stage pulverization was pulverized for 9 minutes using a pearl mill filled with 80% glass beads having a diameter of 0.8 mm. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.6 μm, D₇₅/ D₂₅Is 3.0, D₂₅= 0.31 μm.
[0044]
(Example 2)
Pre-stage pulverization: In the same manner as the pre-stage pulverization in Example 1, heavy calcium carbonate obtained by pre-stage wet pulverization was obtained.
Post-stage pulverization: In the same manner as the post-stage pulverization of Example 1, the obtained pre-stage pulverization slurry was pulverized for 20 minutes using a pearl mill filled with 80% glass beads having a diameter of 0.8 mm. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.5 μm, D₇₅/ D₂₅Is 3.0, D₂₅= 0.27 µm.
[0045]
(Example 3)
Pre-stage pulverization: Dry heavy calcium carbonate was pulverized for 11 minutes in the same manner as in the pre-stage pulverization of Example 1 except that the slurry concentration was 40% by weight. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.8 μm, D₇₅/ D₂₅Was 2.6.
Post-stage pulverization: Further, pulverization was performed for 20 minutes using a pearl mill filled with 80% glass beads having a diameter of 0.8 mm. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.4 μm, D₇₅/ D₂₅Is 2.7, D₂₅= 0.24 µm.
[0046]
(Comparative Example 1)
Pre-stage pulverization: In the same manner as the pre-stage pulverization in Example 1, heavy calcium carbonate obtained by pre-stage wet pulverization was obtained.
Subsequent pulverization: The slurry to be pulverized obtained by the initial pulverization was pulverized in the same manner as in the latter pulverization of Example 1, but pulverized for 4 minutes using a pearl mill filled with 80% glass beads having a diameter of 0.3 mm. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.6 μm, D₇₅/ D₂₅Is 4.0, D₂₅= 0.29 µm.
[0047]
(Comparative Example 2)
Pre-stage pulverization: In the same manner as the pre-stage pulverization in Example 1, heavy calcium carbonate obtained by pre-stage wet pulverization was obtained.
Subsequent pulverization: The slurry to be pulverized obtained by the initial pulverization was pulverized in the same manner as in the latter pulverization of Example 1, but pulverization was performed for 8 minutes using a pearl mill filled with 80% glass beads having a diameter of 0.3 mm. At this time, the obtained wet pulverized calcium carbonate was D₅₀= 0.5 μm, D₇₅/ D₂₅= 4.2, D₂₅= 0.19 µm.
The wet pulverized pigments are summarized in Table 1.
[0048]
[Table 1]

[0049]
(Manufacture of coated paper)
In each slurry of 100 parts of wet heavy calcium carbonate obtained in Examples and Comparative Examples (in terms of solid content), 3 parts of starch (Ace A / Oji Cornstarch Co., Ltd.) (in terms of solid content), styrene-butadiene copolymer weight 7 parts (in terms of solid content) of united latex (JSR-0613 / JSR) was added to obtain each paint. The total solid content concentration of the paint was 60%.
[0050]
Base paper for coating (basis weight 48.0 g / m²) The obtained coating material has a dry solid content of 10 g / m on one side.²Then, both sides were coated with a desktop blade coater and dried to obtain a printing paper. The obtained double-sided coated paper was smoothed with a super calendar. The obtained coated papers are summarized in Table 2 as Example 1-a, Example 2-a, Comparative Example 1-a, and Comparative Example 2-a, respectively.
[0051]
[Table 2]

[0052]
Next, kaolin (HT / Engelhard), starch (Ace A / Oji Cornstarch) was added to 50 parts (in terms of solid content) of slurry for each of the five types of wet pulverized calcium carbonate obtained in Examples and Comparative Examples. 3 parts (in terms of solid content) and 7 parts (in terms of solid content) of styrene butadiene copolymer latex (JSR-0613 / JSR) were added to obtain respective paints. The total solid content concentration of the paint was 60%.
[0053]
Base paper for coating (basis weight 48.0 g / m²The dry solid content of the paint obtained in 10) is 10 g / m on one side.²Then, both sides were coated with a desktop blade coater and dried to obtain a printing paper. The obtained double-sided coated paper was smoothed with a super calendar. The obtained coated papers are summarized in Table 3 as Example 1-b, Example 2-b, Example 3-b, Comparative Example 1-b, and Comparative Example 2-b, respectively.
[0054]
[Table 3]

[0055]
(Measurement of whiteness etc. of coated paper)
The whiteness and opacity of these double-coated papers were measured in accordance with ISO2470 and ISO2471 using a spectral whiteness colorimeter (Suga Test Instruments Co., Ltd.). The glossiness was measured according to ISO8254-1 using a gloss meter (MURAKAMI COLOR RESEARCH LABORATORY).
[0056]
The printing test was performed using an RI tester. Printing using 0.6 cc of printing ink (manufactured by Toyo Ink Co., Ltd.), leaving it in an atmosphere of 23 ° C. and 50% relative humidity for 2 days to dry the ink, and measuring the gloss meter (GM-26D / Murakami Color Technology) The glossiness at 60 ° was measured.
[0057]
The ink drying property was sensory evaluated from the show-through density of the ink immediately after printing. Printing was performed using 0.6 cc of printing ink (manufactured by Toyo Ink Co., Ltd.), and after 3 minutes, the white paper and the printing surface were overlapped, niped again with an RI printer, and the density of the ink transferred to the white paper was visually evaluated.
[0058]
The print surface strength was also sensory evaluated. Printing was performed using 0.4 cc of printing ink (manufactured by Toyo Ink Co., Ltd.), and the degree of picking on the printed surface was visually evaluated. The respective evaluation results are shown in Tables 2 and 3.
[0059]
In Table 1, when comparing Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2, respectively, the final product D₅₀D of the pigments obtained in the examples in spite of being equivalent₇₅/ D₂₅It can be seen that the ratio is low and has a sharp particle size distribution. The example is D compared to the comparative example.₂₅It is clear that there are few unnecessary ultrafine particles.
[0060]
As a result, in Table 2, the whiteness of the coated papers obtained in Examples 1 and 2 and Comparative Example 1 is almost the same, but the whiteness of Comparative Example 2 decreases due to the large number of ultrafine particles. ing. The opacity is clearly higher in the example with less unwanted fines. Further, the ink sets of the examples are normal, and the balance between the glossiness of the blank paper and the printing gloss is clearly good. The example with less superfine particles which do not require surface strength was also stronger.
[0061]
In Table 3, since kaolin was blended in all coated papers, the overall whiteness was low. The opacity is clearly higher in the example with less unwanted ultrafine particles. Further, the ink sets of the examples are normal, and the balance between the glossiness of the blank paper and the printing gloss is clearly good. The example with less superfine particles which do not require surface strength was also stronger.
[0062]
From the above results, it can be seen that when the pigment is produced by the production method described in the present invention, the particle size distribution can be sharpened. In addition, since there are few unnecessary ultrafine particles, it is not necessary to remove the ultrafine particles by classification, and the production yield can be increased. Further, when a pigment having a sharp particle size distribution with a small amount of ultrafine particles obtained by the production method of the present invention is used for coated paper, whiteness and opacity are high, white paper gloss and printing gloss are high, and usually contradict each other. It can be seen that high quality can be obtained.
[0063]
【The invention's effect】
A pigment having a sharp particle size distribution with little generation of unnecessary ultrafine particles was obtained.
[Brief description of the drawings]
FIG. 1 is a diagram of three main processes from starting materials to entering the wet grinding process of the present invention.

Claims (2)

A method for producing a pigment including a multistage pulverization process using a wet pulverizer, wherein a bead mill filled with beads is used as a wet pulverizer in at least two successive pulverization processes, and a subsequent pulverization process The diameter of the beads used in the process is larger than the diameter of the beads used in the preceding pulverization process, and in the subsequent pulverization process, the particle diameter is 75% by weight of the particle size distribution measurement curve and 25% by weight of the particle size distribution measurement curve. The particle size ratio (D ₇₅ / D ₂₅ ) of the pre-pulverized material is 5 or less, and the particle size ratio (D ₅₀ ) ratio of 50% by weight of the particle size distribution measurement curve before and after the pulverization is 0.5-0. A method for producing a pigment, characterized by grinding so as to fall within a range of .9 . The pigment finally obtained is calcium carbonate having a particle size (D ₅₀ ) of 50% by weight of the particle size distribution measurement curve and 0.4 to 2 μm. The method for producing a pigment according to claim 1, wherein a bead mill filled with beads having a diameter larger than that of the beads used in the process and in a range of 0.5 to 2 mm is used.

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