JP4069516B2

JP4069516B2 - Light calcium carbonate grinding method and light calcium carbonate

Info

Publication number: JP4069516B2
Application number: JP27836498A
Authority: JP
Inventors: 英治西島; 覚切中; 忠視松井; 勝則世見; 泰徳南里
Original assignee: Nippon Paper Industries Co Ltd
Current assignee: Nippon Paper Industries Co Ltd
Priority date: 1998-09-30
Filing date: 1998-09-30
Publication date: 2008-04-02
Anticipated expiration: 2018-09-30
Also published as: JP2000110096A

Description

【０００１】
【発明の属する技術分野】
本発明は、塗被紙用に顔料として使用される軽質炭酸カルシウムの粉砕方法に関するものである。
【０００２】
【従来の技術】
近年印刷用紙は、通販用カタログ、チラシ、カタログ、パンフレット、ダイレクトメール等広告、宣伝を目的とした商業印刷分野での需要が伸びている。これら商業印刷物は、それ自体の商品価値は低いが、宣伝媒体として目的が達成されることが重要であるので、低コストで印刷仕上がりの良いものが求められており、印刷物と実物の色が違えばクレームや返品等の問題を生じるために、色再現性の良好な高白色度の紙が求められる。そこで製造コストや総合的な品質バランスと操業性を考慮し、塗被紙用顔料として炭酸カルシウムが使用されている。
【０００３】
炭酸カルシウムを大別すると、天然産の重質炭酸カルシウムと化学的に合成される軽質炭酸カルシウムに分けられる。重質炭酸カルシウムは、機械的に乾式粉砕されただけで塗被紙用顔料として使用されるのはごく希であり、さらに顔料分散液として湿式粉砕して使用される。軽質炭酸カルシウムは炭酸ガス法等によって合成され、反応条件を制御することによって粒子の径や形状をコントロールすることが可能である。これらは針状、柱状、紡錘状、立方状および不定形などの各種形状を有し、針状や紡錘状などの軽質炭酸カルシウムは、その独特の形状を生かすために粉砕処理されることなく塗被紙用顔料として使用されるのが一般的である。しかし、これら独特の形状の軽質炭酸カルシウムは重質炭酸カルシウムと比較して非常に高価な顔料であるばかりか、顔料塗被液中に高配合しすぎると塗被液の物性を大きく変化させ、例えば塗被液の粘度を大幅に上昇させる、或いは保水性を大幅に低下させる等によって、しばしば高速操業性などに悪影響を及ぼすことが知られており、これらの使用用途は特殊な場合に限定されているのが現状である。
【０００４】
一方、不定形の軽質炭酸カルシウムは、重質炭酸カルシウムと同様、乾式または湿式粉砕することによって塗被紙用顔料として使用される。粉砕後の形状は重質炭酸カルシウムと同様の形状をしているが、重質炭酸カルシウムと比較して白色度が高く、高白色度で色再現性の優れた塗被紙品質を与える。また、重質炭酸カルシウムよりも疎水性が高く、塗被紙用顔料として塗被液中に配合すると塗被液中の自由水量が多くなり、塗被液の高速流動性が向上し高速操業性を改善するなどの効果を示す。
【０００５】
しかしながら、軽質炭酸カルシウムを湿式粉砕する場合には幾つかの困難な問題がある。一般に、製紙用顔料を湿式粉砕する場合、粉砕効率や生産性の観点から、顔料分散液の濃度はできる限り高いほうが好ましい。しかし、軽質炭酸カルシウムは重質炭酸カルシウムと比較して凝集性、疎水性が高く、高濃度顔料分散液を調製する場合、強力な撹拌装置を使用しても分散しにくく、まま粉状に固まってしまうために分散に時間がかかるばかりか、発熱などの問題を生じてしまうため、高濃度での顔料分散液の調製は非常に困難である。また、一旦分散しても凝集性が非常に強いために分散液中で再凝集して二次粒子を形成して短時間で沈降し始め、沈降が著しい場合は配管ライン内で沈降して配管を閉塞してしまうなどの問題を生じる。また、顔料分散液の粘度も非常に高く粉砕時の粉砕機負荷が大きくなり過ぎるばかりか、場合によっては粉砕機中に充填されているメディアの割れや摩耗が著しくなるなどの問題を生じるため、粉砕機中のメディア充填率や顔料分散液濃度を下げざるを得ず、結果として大幅な粉砕効率の低下を招いてしまう。
【０００６】
これらの問題を解決するためには、顔料分散液の濃度を低くすることが最も有効であるが、粉砕効率や生産効率が低下するのみならず、顔料分散液中の顔料がさらに沈降し易くなる等の問題を新たに生じる。このように軽質炭酸カルシウムの高濃度分散液の調製、粉砕は非常に困難であるのが現状である。
【０００７】
炭酸カルシウムを粉砕する既存技術としては、例えば特開昭６３−２２５５２２号公報、特公平１−５０４５０号公報、特開平６−４１４６３号公報などが提案されている．しかし、特開昭６３−２２５５２２号公報および特公平１−５０４５０号公報は重質炭酸カルシウムの粉砕を目的とした技術であり、また、特開平６−４１４６３号公報では、軽質炭酸カルシウムと重質炭酸カルシウムを重量当たり２：９８〜６０：４０の範囲で混合することによって、軽質炭酸カルシウムを湿式粉砕する技術を提案しているが、重質炭酸カルシウムの割合が高過ぎるため、軽質炭酸カルシウムを高配合した顔料分散液に適応できる技術ではなく、また、これら既存の技術を用いても本発明の抱える課題の解決には至らなかった。
【０００８】
【発明が解決しようとする課題】
以上のような状況に鑑み、本発明の課題は上記のごとき問題を解決し、高濃度分散が容易でかつ粘度が低く沈降の問題の無い軽質炭酸カルシウム顔料分散液が調製でき、該顔料分散液を効率よく湿式粉砕する方法を提供することにある。
【０００９】
【課題を解決するための手段】
本発明者等は上記の課題について鋭意研究を重ねた結果、顔料１００重量部に対して、軽質炭酸カルシウム８０〜９８重量部、カオリンを２〜２０重量部含有した顔料分散液を、湿式粉砕することによって、本発明を成すに至った。
【００１０】
以下発明の詳細を示す。
【００１１】
本発明においては、軽質炭酸カルシウムに対してカオリンを２〜２０重量部配合することによって顔料分散液の調製を容易にし、粘度が低く沈降の問題の無い軽質炭酸カルシウムの高濃度顔料分散液の調製を可能とし、粉砕時の粉砕負荷を軽減できることを認めた。これは、カオリン粒子が比較的親水性に富んでいるのみならず、電気的にマイナスに帯電しているカオリン平面部がアニオン性の炭酸カルシウムと反発する、言い換えればカオリン粒子が一種の分散剤として働くのみならず、アスペクト比や比表面積が大きいカオリン粒子が軽質炭酸カルシウム粒子間に存在することによって、軽質炭酸カルシウム粒子どうしの接触を妨げ、軽質炭酸カルシウム粒子の凝集や二次粒子の形成を阻害し、一次粒子のままで顔料分散液中に浮遊させる等、これらの相乗効果によって軽質炭酸カルシウム顔料分散液の分散性の安定化、低粘度化、沈降抑制効果を発現し、その結果粉砕時の粉砕効果を軽減できるものと考えられる。しかも、軽質炭酸カルシウムの高白色性を損なうこともない。
【００１２】
カオリンの配合部数が２重量部より少ない場合には、軽質炭酸カルシウムが分散し難くなるのみならず、顔料分散液の粘度が高くなるとともに粒子間の凝集が促進されるために、粉砕機での粉砕負荷が大きくなり過ぎる。また、凝集抑制効果が小さいために沈降性も劣る。一方、２０重量部より多い場合には、白色度の低いカオリンによって顔料分散液が黄色味を帯び、軽質炭酸カルシウムの高白色のメリットが失われてしまう。
【００１３】
また、本発明における顔料分散液の固形分濃度は６５％以上の時に、より分散が容易でかつ粘度が低く沈降の問題の無い軽質炭酸カルシウム顔料分散液が調製でき、該顔料分散液を効率よく湿式粉砕することができる。顔料分散液濃度が６５％より低い場合は、本発明の軽質炭酸カルシウム分散効果が発揮されにくいのみならず、粉砕前の顔料分散液が沈降しやすい傾向にある。また、本発明は粉砕される軽質炭酸カルシウムの平均粒子径が５μｍ以上の粗大粒子に対してより一層効果を示す傾向にある。
【００１４】
【発明の実施の形態】
本発明で使用される軽質炭酸カルシウムは炭酸ガス法、或いは苛性化法等によって製造された不定形状の軽質炭酸カルシウムであり、好ましくは平均粒子径が５〜３０μｍの範囲のものが好ましい。５μｍより小さい場合は、沈降性に対する効果が発現されにくく、３０μｍより大きい場合は粉砕後の顔料分散液の粒度分布が広くなる傾向にある。ここでいう苛性化法とは、パルプ製造工程の薬品回収工程において、生石灰を水または白液で消和した後に緑液で苛性化反応することによって軽質炭酸カルシウムを合成する方法のことである。また、不定形状の軽質炭酸カルシウム以外、例えば針状や柱状の軽質炭酸カルシウムに対しても、粉砕処理を必要とする場合には本発明を適用することができる。また、本発明で使用されるカオリンは、塗被紙用としてごく一般に使用される一級カオリン、二級カオリンのほかに、デラミネーテッドカオリン、焼成カオリン、或いはエンジニアードカオリン等が挙げられ、粉末状あるいは分散液状のどちらでも構わない。但し、軽質炭酸カルシウム顔料分散液の粘度を考慮すると、より親水牲や分散性の優れる一級カオリン、二級カオリンが好ましく、粉砕後の顔料の白色度を考慮すると白色度の高いものが好ましい。
【００１５】
また、本発明で使用される顔料としては軽質炭酸カルシウム、カオリン以外特に規定するものではなく、必要に応じて製紙用として一般に使用される、重質炭酸カルシウム、タルク、サチンホワイト、酸化チタン、シリカ、クレー、硫酸バリウム、硫酸カルシウム、水酸化アルミニウム、酸化亜鉛、ペントナイト等を併用してもかまわない。但し、その場合のこれらの顔料の配合量は本発明の効果を損なわないよう適宜選択しなくてはならない。
【００１６】
また顔料分散液中に使用する分散剤としては、一般に製紙用として使用されているポリアクリル酸ソーダ、リグニンスルホン酸ソーダ、リン酸塩およびそれらの変成物等が挙げられ、これ等のうち一種類以上を必要に応じて選択して使用することができ、分散剤の使用量は、顔料１００重量部に対して０．１〜０．６重量部が好ましい。顔料分散液の調製方法は、水に分散剤及びカオリンを先に添加した後に軽質炭酸カルシウムを少量ずつ加えて分散することが必要である。
【００１７】
また、本発明で使用される粉砕機としては製紙用顔料の湿式粉砕にごく一般に使用されるアトライター、振動ミル、ボールミル、竪型サンドミル、横型サンドミル、ジェットミル等が挙げられる。また、メディアとしてはガラス、セラミック、アルミナ、ジルコニア、瑪瑙等の硬質原料で製造された球状のボールが挙げられ、メディア径は０．１〜１０ｍｍであることが好ましい。メディアの充填率はできる限り高いほうが好ましいが、充填率が高すぎる場合は粉砕室内でのメディアの動きが制限され、逆に粉砕効率を低下させることもあり、使用する粉砕機に応じて適宜調節する。
【００１８】
以上のような状況に盤み、本発明の課題は上記のごとき問題を解決し、高濃度分散が容易で粘度が低く沈降の問題の無い軽質炭酸カルシウムの顔料分散液を調製し、その顔料分散液を湿式粉砕することで、効率よく軽質炭酸カルシウムの製紙用顔料分散液を製造することが可能であることを認めた。
【００１９】
【実施例】
以下に実施例を挙げて本発明を具体的に示すが、これらによって本発明は何等制約を受けるものではない。なお、例中の部および％はそれぞれ重量部およぴ重量％を示す。
〈品質評価方法〉
（１）粉砕前軽質炭酸カルシウム平均粒子径
炭酸カルシウム粉末をふるい分けし、重量累積分布の５０％点を平均粒子径として算出した。
（２）顔料分散液の分散性評価
水、分散剤およびカオリンからなる分散液に炭酸カルシウム粉末を少量ずつ投入し、炭酸カルシウム粉末の分散状況を目視で相対評価した。
【００２０】
◎：全く問題なし、○：ほとんど問題なし、△：分散が困難、×：分散が非常に困難
（３）Ｂ型粘度
粉砕前顔料分散液の温度を２５℃に調節し、Ｂ型粘度計（東京計器社製）を用いて回転数６０ｒｐｍの条件下でＮＯ．２ローターを１分間回転させて測定した。この条件で測定不可能な場合、ＮＯ．２ローターの代わりにＮＯ．３ローターを用いて測定した。
（４）沈降性評価
粉砕前の顔料分散液５００ｍｌを、容積５００ｍｌのメスシリンダーに注いで一昼夜静置し、顔料分散液の沈降状況を観察した。
【００２１】
◎：全く沈降しない、○：ほとんど沈降しない、△：沈降する、×：沈降が甚だしい
（５）粉砕後の顔料分散液平均粒子径
セイシン企業製光透過式粒度分布測定装置ＳＨＣ５０００を用いて、重量累積分布の５０％点を平均粒子径として算出した。
（６）白色度
粉砕後の顔料分散液を粉末状にした後にペレット状にし、ハンター白色度計を用いてＪＩＳＰ−８１２３に従って白色度を測定した。
［実施例１］
５０ｋｇのイオン交換水に対して、顔料１００部に対する添加量が０．５部になるようにポリアクリル酸ソーダ系分散剤を添加し、一級カオリン１０部を加えた。さらに、カウレス分散機（アイメックス社製）を用いて分散しながら、平均粒子径が１６μｍの不定形の軽質炭酸カルシウム９０部を少量ずつ加えて、固形分濃度約７５％の顔料分散液を調製した。顔料分散液のＢ型粘度は１２０ｍＰａ・Ｓであった。
【００２２】
次に、３０Ｌの粉砕室を有する定格２２ｋｗｈの竪型サンドミル（アイメックス社製）に、平均粒子径が１．５ｍｍの硬質ガラスビーズ（東芝バロティーニ製）を充填率が９０％になるように投入し、粉砕室の空隙を水で満たした。なお、ここで言う充填率とは粉砕室中の空隙容積に対する、最密充填した時の粉砕メディアの容積（空隙も含む）の割合を意味する。
【００２３】
粉砕機を起動後、定量ポンプ（兵神装備製）を用いて顔料分散液をサンドミルに送液し、粉砕後の平均粒子径が０．４８μｍの顔料分散液１００Ｌを調製した。粉砕時の消費電力は１５ｋｗｈで、粉砕時間は３．５時間であった。なお、粉砕時間および消費電力は粉砕室中の水が顔料分散液に完全に置換されたのを確認した後に測定を開始した。
［実施例２］
カオリンを４部配合した以外は、実施例1と全く同様に顔料分散および粉砕処理を行った。このときの顔料分散液のＢ型粘度は１５０ｍＰａ・Ｓであった。粉砕時の消費電力は１６ｋｗｈで、粉砕時間は３．７時間であった。
［実施例３］
カオリンを１６部配合した以外は、実施例1と全く同様に顔料分散および粉砕処理を行った。このときの顔料分散液のＢ型粘度は１１０ｍＰａ・Ｓであった。粉砕時の消費電力は１５ｋｗｈで、粉砕時間は３．４時間であった。
［実施例４］
カオリンを１０部、重質炭酸カルシウムを５部配合した以外は、実施例1と全く同様に顔料分散および粉砕処理を行った。このときの顔料分散液のＢ型粘度は１４０ｍＰａ・Ｓであった。粉砕時の消費電力は１６ｋｗｈで、粉砕時間は３．５時間であった。
［比較例１］
カオリンを全く配合しなかった以外は、実施例１と全く同様に顔料分散および粉砕処理を行った。顔料分散液の粘度は６２０ｍＰａ・Ｓで、炭酸カルシウムの分散は非常に困難であり沈降性も劣っていた。さらに、粉砕室内が顔料分散液に完全に置換される前に、消費電力が定格を大きく越えてしまったため、ガラスビーズの充填率を７０％まで下げなくてはならなかった。そのときの消費電力は２１ｋｗｈで、粉砕時間は１０時間であった。
［比較例２］
カオリンを２５部配合した以外は、実施例１と全く同様に顔料分散および粉砕処理を行った。このときの顔料分散液のＢ型粘度は１５０ｍＰａ・Ｓであった。粉砕時の消費電力は１６ｋｗｈで、粉砕時間は３．２時間であった。
［比較例３］
カオリンの代わりにタルクを１０部配合した以外は、実施例１と全く同様に顔料分散を行ったが、タルクの疎水牲および増粘効果によって顔料分散液の調製は不可能であった。
［比較例４］
カオリンの代わりに重質炭酸カルシウムを１０部配合した以外は、実施例１と全く同様に顔料分散および粉砕処理を行った。顔料分散液の粘度は５７０ｍＰａ・Ｓで、炭酸カルシウムの分散は非常に困難であり沈降性も劣っていた。さらに、粉砕室内が顔料分散液に完全に置換される前に、消費電力が定格を大きく越えてしまったため、ガラスビーズの充填率を７４％まで下げなくてはならなかった。そのときの消費電力は２２ｋｗｈで、粉砕時間は９．６時間であった。
【００２４】
以上の結果を表１に示した。
【００２５】
【表１】

表１から明らかなように、実施例１〜４は高濃度顔料分散液の調製が非常に容易で、顔料分散液の粘度が低く、沈降性も全く問題なかった。また、ガラスビーズを高充填して粉砕したにも関わらず、粉砕時の粉砕負荷も低く粉砕効率も高かった。
【００２６】
これに対して、比較例１、４は顔料分散液の調製が非常に困難であるうえに、顔料分散液のＢ型粘度が高く沈降性に劣り、粉砕負荷が高すぎ、粉砕効率も非常に低い。比較例２は粉砕後顔料の白色度が低い。比較例３は顔料分散液の調製が不可能であった。従って、本発明の効果は極めて大なるものがある。
【００２７】
【発明の効果】
高濃度分散が容易でかつ粘度が低く沈降の問題の無い軽質炭酸カルシウム顔料分散液の調製方法、および該顔料分散液を効率よく湿式粉砕する方法を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for grinding light calcium carbonate used as a pigment for coated paper.
[0002]
[Prior art]
In recent years, the demand for printing paper in the commercial printing field for the purpose of advertising and promotion such as catalogs for mail order, flyers, catalogs, pamphlets and direct mail has been increasing. Although these commercial printed materials have low commercial value, it is important that the purpose is achieved as an advertising medium, so there is a demand for low-cost and good-printing results. In order to cause problems such as complaints and returns, high whiteness paper with good color reproducibility is required. Therefore, calcium carbonate is used as a pigment for coated paper in consideration of manufacturing cost, comprehensive quality balance and operability.
[0003]
Calcium carbonate can be roughly divided into light calcium carbonate that is chemically synthesized with natural heavy calcium carbonate. Heavy calcium carbonate is rarely used as a pigment for coated paper just by being mechanically dry-pulverized, and further wet-pulverized as a pigment dispersion. Light calcium carbonate is synthesized by the carbon dioxide method or the like, and the diameter and shape of the particles can be controlled by controlling the reaction conditions. These have various shapes such as needle shape, column shape, spindle shape, cubic shape, and irregular shape, and light calcium carbonate such as needle shape and spindle shape is coated without being pulverized to take advantage of its unique shape. Generally used as a pigment for paper. However, light calcium carbonate of these unique shapes is not only a very expensive pigment compared to heavy calcium carbonate, but if it is too high in the pigment coating solution, it will greatly change the physical properties of the coating solution, For example, it is known that the viscosity of the coating solution is greatly increased, or the water retention is significantly decreased. This is the current situation.
[0004]
On the other hand, amorphous light calcium carbonate, like heavy calcium carbonate, is used as a pigment for coated paper by dry or wet grinding. Although the shape after pulverization is the same as that of heavy calcium carbonate, the whiteness is higher than that of heavy calcium carbonate, giving a coated paper quality with high whiteness and excellent color reproducibility. Also, it is more hydrophobic than heavy calcium carbonate, and when blended in the coating solution as a pigment for coated paper, the amount of free water in the coating solution increases, and the high-speed fluidity of the coating solution is improved and high-speed operability is achieved. The effect such as improving.
[0005]
However, there are some difficult problems when lightly grinding calcium carbonate. In general, when wet-grinding a papermaking pigment, the concentration of the pigment dispersion is preferably as high as possible from the viewpoint of grinding efficiency and productivity. However, light calcium carbonate has higher cohesiveness and hydrophobicity than heavy calcium carbonate, and when preparing a highly concentrated pigment dispersion, it is difficult to disperse even if a strong stirring device is used, and it remains in powder form. Therefore, it takes time to disperse and causes problems such as heat generation, so that it is very difficult to prepare a pigment dispersion at a high concentration. Also, once dispersed, the agglomeration is very strong, so it re-aggregates in the dispersion to form secondary particles and starts to settle in a short time. Cause problems such as blocking. In addition, the viscosity of the pigment dispersion is very high, and not only the load on the pulverizer during pulverization becomes too large, but also problems such as significant cracking and wear of the media filled in the pulverizer may occur. The media filling rate and the pigment dispersion concentration in the pulverizer must be lowered, resulting in a significant reduction in pulverization efficiency.
[0006]
In order to solve these problems, it is most effective to reduce the concentration of the pigment dispersion, but not only the pulverization efficiency and production efficiency are lowered, but the pigment in the pigment dispersion is more likely to settle. A new problem arises. Thus, it is very difficult to prepare and pulverize a high concentration dispersion of light calcium carbonate.
[0007]
As existing techniques for pulverizing calcium carbonate, for example, JP-A-63-225522, JP-B-1-50450, JP-A-6-41463, and the like have been proposed. However, Japanese Patent Laid-Open No. 63-225522 and Japanese Patent Publication No. 1-50450 are techniques aimed at pulverizing heavy calcium carbonate, and Japanese Patent Laid-Open No. 6-41463 discloses light calcium carbonate and heavy weight. We have proposed a technology to wet pulverize light calcium carbonate by mixing calcium carbonate in the range of 2:98 to 60:40 per weight. However, since the proportion of heavy calcium carbonate is too high, This technique is not applicable to highly blended pigment dispersions, and the use of these existing techniques has not led to the solution of the problems of the present invention.
[0008]
[Problems to be solved by the invention]
In view of the situation as described above, the problem of the present invention is to solve the above problems, and to prepare a light calcium carbonate pigment dispersion liquid that is easy to disperse at high concentration and has low viscosity and no problem of sedimentation. It is to provide a method for efficiently wet-grinding the powder.
[0009]
[Means for Solving the Problems]
As a result of intensive studies on the above problems, the present inventors wet pulverize a pigment dispersion containing 80 to 98 parts by weight of light calcium carbonate and 2 to 20 parts by weight of kaolin with respect to 100 parts by weight of the pigment. As a result, the present invention has been achieved.
[0010]
Details of the invention will be described below.
[0011]
In the present invention, 2 to 20 parts by weight of kaolin is added to light calcium carbonate to facilitate preparation of a pigment dispersion, and preparation of a high concentration pigment dispersion of light calcium carbonate having low viscosity and no problem of sedimentation. It was recognized that the grinding load during grinding could be reduced. This is because the kaolin particles are not only relatively hydrophilic but also the negatively charged kaolin plane part repels anionic calcium carbonate, in other words kaolin particles as a kind of dispersant. Not only does it work, but the presence of kaolin particles with a large aspect ratio and specific surface area between the light calcium carbonate particles prevents the light calcium carbonate particles from contacting each other and inhibits the aggregation of the light calcium carbonate particles and the formation of secondary particles. The primary particles remain suspended in the pigment dispersion, and the synergistic effect of these effects enables the light calcium carbonate pigment dispersion to have a stable dispersibility, a low viscosity, and a sedimentation-inhibiting effect. It is considered that the grinding effect can be reduced. Moreover, the high whiteness of light calcium carbonate is not impaired.
[0012]
When the amount of kaolin blended is less than 2 parts by weight, not only is the light calcium carbonate difficult to disperse, but also the viscosity of the pigment dispersion increases and aggregation between particles is promoted. The grinding load becomes too large. Moreover, since the aggregation suppressing effect is small, the sedimentation property is also poor. On the other hand, when the amount is more than 20 parts by weight, the pigment dispersion becomes yellowish due to kaolin having a low whiteness, and the high white merit of light calcium carbonate is lost.
[0013]
In addition, when the solid content concentration of the pigment dispersion in the present invention is 65% or more, a light calcium carbonate pigment dispersion that is easier to disperse and has a low viscosity and no sedimentation problem can be prepared. It can be wet pulverized. When the pigment dispersion concentration is lower than 65%, not only the light calcium carbonate dispersion effect of the present invention is hardly exhibited, but also the pigment dispersion before grinding tends to settle. In addition, the present invention tends to be more effective for coarse particles having an average particle size of 5 μm or more of light calcium carbonate to be pulverized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The light calcium carbonate used in the present invention is an irregularly shaped light calcium carbonate produced by a carbon dioxide method or a causticizing method, and preferably has an average particle size in the range of 5 to 30 μm. When the particle size is less than 5 μm, the effect on the sedimentation property is hardly exhibited, and when it is greater than 30 μm, the particle size distribution of the pigment dispersion after pulverization tends to be wide. The causticizing method here is a method of synthesizing light calcium carbonate by causticizing reaction with green liquor after the quick lime is dehydrated with water or white liquor in the chemical recovery step of the pulp manufacturing process. In addition, the present invention can be applied to pulverizing treatment other than light calcium carbonate having an irregular shape, for example, acicular or columnar light calcium carbonate. The kaolin used in the present invention includes, in addition to primary kaolin and secondary kaolin that are generally used for coated paper, delaminated kaolin, calcined kaolin, engineered kaolin, etc. Alternatively, either a dispersed liquid may be used. However, considering the viscosity of the light calcium carbonate pigment dispersion, primary kaolin and secondary kaolin having better hydrophilicity and dispersibility are preferable, and those having high whiteness are preferable when considering the whiteness of the pigment after pulverization.
[0015]
The pigments used in the present invention are not particularly defined except for light calcium carbonate and kaolin, and are generally used for papermaking as required, heavy calcium carbonate, talc, satin white, titanium oxide, silica Clay, barium sulfate, calcium sulfate, aluminum hydroxide, zinc oxide, pentonite, etc. may be used in combination. However, the blending amount of these pigments in that case must be appropriately selected so as not to impair the effects of the present invention.
[0016]
Examples of the dispersant used in the pigment dispersion include polyacrylic acid soda, lignin sulfonic acid soda, phosphates and modified products thereof, which are generally used for papermaking. The above can be selected and used as necessary, and the amount of the dispersant used is preferably 0.1 to 0.6 parts by weight with respect to 100 parts by weight of the pigment. The method for preparing the pigment dispersion requires that light calcium carbonate is added little by little after the dispersant and kaolin are first added to water.
[0017]
Examples of the pulverizer used in the present invention include attritors, vibration mills, ball mills, vertical sand mills, horizontal sand mills, jet mills and the like that are generally used for wet pulverization of papermaking pigments. Examples of the media include spherical balls made of hard raw materials such as glass, ceramic, alumina, zirconia, and cocoons, and the media diameter is preferably 0.1 to 10 mm. The media filling rate is preferably as high as possible. However, if the filling rate is too high, the movement of the media in the grinding chamber is restricted, and conversely, the grinding efficiency may be lowered. To do.
[0018]
In view of the above situation, the object of the present invention is to solve the above problems, prepare a light calcium carbonate pigment dispersion liquid that is easy to disperse at a high concentration and has low viscosity and no sedimentation problem. It was recognized that it was possible to efficiently produce a light calcium carbonate pigment dispersion by wet pulverizing the liquid.
[0019]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited by these. In addition, the part and% in an example show a weight part and weight%, respectively.
<Quality evaluation method>
(1) Light calcium carbonate average particle diameter before pulverization Calcium carbonate powder was sieved, and the 50% point of the weight cumulative distribution was calculated as the average particle diameter.
(2) Evaluation of Dispersibility of Pigment Dispersion Calcium carbonate powder was added little by little to a dispersion composed of water, a dispersant, and kaolin, and the state of dispersion of the calcium carbonate powder was visually evaluated.
[0020]
◎: No problem at all, ○: Almost no problem, △: Difficult to disperse, ×: Very difficult to disperse (3) B-type viscosity The temperature of the pigment dispersion before grinding is adjusted to 25 ° C. NO. Under conditions of 60 rpm. The measurement was performed by rotating 2 rotors for 1 minute. If measurement is impossible under these conditions, NO. No. 2 instead of 2 rotors. Measurements were made using 3 rotors.
(4) Evaluation of sedimentation property 500 ml of the pigment dispersion before pulverization was poured into a graduated cylinder having a volume of 500 ml and allowed to stand overnight, and the sedimentation state of the pigment dispersion was observed.
[0021]
A: No sedimentation, O: Almost no sedimentation, Δ: Sedimentation, X: Severe sedimentation (5) Average particle diameter after pulverization Pigment dispersion average particle diameter The 50% point of the cumulative distribution was calculated as the average particle size.
(6) The pigment dispersion after whiteness pulverization was made into powder and then pelletized, and the whiteness was measured according to JIS P-8123 using a Hunter whiteness meter.
[Example 1]
To 50 kg of ion-exchanged water, a sodium polyacrylate dispersing agent was added so that the amount added to 100 parts of pigment was 0.5 part, and 10 parts of primary kaolin was added. Further, while dispersing using a cowless disperser (manufactured by Imex), 90 parts of amorphous light calcium carbonate having an average particle diameter of 16 μm was added little by little to prepare a pigment dispersion having a solid content concentration of about 75%. . The B-type viscosity of the pigment dispersion was 120 mPa · S.
[0022]
Next, hard glass beads (manufactured by Toshiba Barotini) having an average particle diameter of 1.5 mm are put into a vertical sand mill (manufactured by Imex) having a 30 L grinding chamber and rated at 22 kwh so that the filling rate is 90%. The space in the grinding chamber was filled with water. In addition, the filling rate said here means the ratio of the volume (including a space | gap) of the grinding | pulverization media at the time of closest packing with respect to the space | gap volume in a grinding | pulverization chamber.
[0023]
After starting up the pulverizer, the pigment dispersion was sent to a sand mill using a metering pump (Hyojin Equipment Co., Ltd.) to prepare 100 L of a pigment dispersion having an average particle size of 0.48 μm after pulverization. The power consumption during pulverization was 15 kwh, and the pulverization time was 3.5 hours. The pulverization time and power consumption were measured after confirming that the water in the pulverization chamber was completely replaced with the pigment dispersion.
[Example 2]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that 4 parts of kaolin was added. At this time, the B-type viscosity of the pigment dispersion was 150 mPa · S. The power consumption during pulverization was 16 kwh, and the pulverization time was 3.7 hours.
[Example 3]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that 16 parts of kaolin was added. At this time, the B-type viscosity of the pigment dispersion was 110 mPa · S. The power consumption during pulverization was 15 kwh, and the pulverization time was 3.4 hours.
[Example 4]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that 10 parts of kaolin and 5 parts of heavy calcium carbonate were added. The B type viscosity of the pigment dispersion at this time was 140 mPa · S. The power consumption during pulverization was 16 kwh, and the pulverization time was 3.5 hours.
[Comparative Example 1]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that no kaolin was added. The viscosity of the pigment dispersion was 620 mPa · S, and it was very difficult to disperse calcium carbonate and the sedimentation property was also poor. Furthermore, before the inside of the grinding chamber was completely replaced with the pigment dispersion, the power consumption greatly exceeded the rating, so the glass bead filling rate had to be reduced to 70%. The power consumption at that time was 21 kwh, and the grinding time was 10 hours.
[Comparative Example 2]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that 25 parts of kaolin was added. At this time, the B-type viscosity of the pigment dispersion was 150 mPa · S. The power consumption during pulverization was 16 kwh, and the pulverization time was 3.2 hours.
[Comparative Example 3]
Pigment dispersion was carried out in the same manner as in Example 1 except that 10 parts of talc was added instead of kaolin, but it was impossible to prepare a pigment dispersion due to the hydrophobicity and thickening effect of talc.
[Comparative Example 4]
Pigment dispersion and pulverization were performed in the same manner as in Example 1 except that 10 parts of heavy calcium carbonate was added instead of kaolin. The viscosity of the pigment dispersion was 570 mPa · S, and it was very difficult to disperse the calcium carbonate and the sedimentation property was poor. Furthermore, before the inside of the grinding chamber was completely replaced with the pigment dispersion, the power consumption had greatly exceeded the rating, so the glass bead filling rate had to be reduced to 74%. The power consumption at that time was 22 kwh, and the grinding time was 9.6 hours.
[0024]
The above results are shown in Table 1.
[0025]
[Table 1]

As is clear from Table 1, in Examples 1 to 4, the preparation of the high concentration pigment dispersion was very easy, the viscosity of the pigment dispersion was low, and there was no problem with sedimentation. In addition, although the glass beads were highly filled and pulverized, the pulverization load during pulverization was low and the pulverization efficiency was high.
[0026]
On the other hand, in Comparative Examples 1 and 4, it is very difficult to prepare the pigment dispersion, and the B-type viscosity of the pigment dispersion is high and the sedimentation property is poor, the grinding load is too high, and the grinding efficiency is very high. Low. In Comparative Example 2, the whiteness of the pigment after grinding is low. In Comparative Example 3, it was impossible to prepare a pigment dispersion. Therefore, the effect of the present invention is extremely large.
[0027]
【The invention's effect】
It is possible to provide a method for preparing a light calcium carbonate pigment dispersion which is easy to disperse at a high concentration and has a low viscosity and no sedimentation problem, and a method for efficiently wet pulverizing the pigment dispersion.

Claims

A method for pulverizing light calcium carbonate, comprising wet-pulverizing a pigment dispersion containing 80 to 98 parts by weight of light calcium carbonate and 2 to 20 parts by weight of kaolin with respect to 100 parts by weight of pigment.

2. The method for pulverizing light calcium carbonate according to claim 1, wherein the solid content concentration of the pigment dispersion is 65% or more.

The method for pulverizing light calcium carbonate according to claim 1 or 2, wherein an average particle size of the light calcium carbonate before pulverization is 5 to 30 µm.

A light calcium carbonate pigment produced by the production method according to claim 1.