JP3575844B2

JP3575844B2 - Granular precipitated silicic acid and method for producing the same

Info

Publication number: JP3575844B2
Application number: JP28030194A
Authority: JP
Inventors: 健治内山; 昭藤井
Original assignee: Tosoh Silica Corp
Current assignee: Tosoh Silica Corp
Priority date: 1994-11-15
Filing date: 1994-11-15
Publication date: 2004-10-13
Anticipated expiration: 2019-10-13
Also published as: JPH08133721A

Description

【０００１】
【産業上の利用分野】
本発明は、新規な粒状沈殿ケイ酸に関する。特に、本発明は、ゴム、プラスチック、樹脂等の充填剤に適した大きな粒子径と高い嵩比重を有し、しかも適度な粒子硬度を有しており、充填作業が容易であり、且つ粉じんの発生が著しく改善された新規な粒状沈殿ケイ酸及びその製造方法を提供するものである。
【０００２】
【従来の技術】
沈殿ケイ酸粉末は通称ホワイトカーボンと呼ばれ、表面活性を有す白色度の高い粉末であり、ゴム補強充填剤をはじめ農薬用分散剤、塗料、樹脂、情報用紙、インク、歯磨き等様々な分野で使用されている。一般的に柔らかい凝集粒で、粉体の中でも最も軽い部類に属し、非常に飛散しやすく取扱い時に粉塵による作業環境の悪化が問題となっている。
また、粉体の嵩比重が低く、包装や貯蔵及び輸送費用の不経済、或いは流動性が悪くサイロの底壁等に残るなど問題点もある。このような難点を解消するために粒状品が強く要望されている。
【０００３】
【発明が解決しようとする課題】
ところで、沈殿ケイ酸粉末をエラストマー充填剤として用いる場合、その性能を第一に考えるならば補強効果の上から、エラストマー中へ分散性の良い微粉体である事が望ましい。しかるに補強性能を多少犠牲にしても前述のような難点を解消する為に、種々の造粒方法が提案されている。
しかし、種々の造粒方法より粒状化した場合、オープンロールやバンバリーミキサー等で、ゴム等と混練した場合、沈殿ケイ酸粉末の分散性が損なわれ、ゴムの性質を決める、耐摩耗性、引張り強さ、伸び、反撥弾性等の性能が著しく低下する。例えば、特公昭５６−４１５６６号や特開平２−３０２３１２号に開示される、高濃度沈殿ケイ酸スラリーを噴霧乾燥する方法で得られる粒状品では、粒子径が小さく、又嵩比重も低く、造粒品本来の目的である作業性の改善や貯蔵及び輸送費の改善が不十分であった。
【０００４】
又、特開昭５４−１１０２００号には、沈殿ケイ酸スラリーをフィルタープレスで濾別、洗浄して得られるフィルターケークに、必要により粉末状沈降珪酸を混合して、固体含量が２８〜４０重量％になるように調整し、造粒機で圧縮成形し、乾燥することで顆粒状のケイ酸を得る方法が記載されている。しかし、沈殿ケイ酸のフィルターケークの含水量は一般に約８０％であり、ケーク単独ではペースト状、更にはスラリーとなり顆粒状に成形することが困難である。そのため、実際には、粉末状沈降珪酸を混合して固体含量を所定範囲に調整する必要がある。
【０００５】
本発明者らが、沈殿ケイ酸のフィルターケークに乾燥粉末を混合して含水率を低下させることで顆粒状に成形し易くする方法を試みたところ、粉末状沈降珪酸をフィルターケークと均一に混合することは困難であった。さらに、この方法により得られた顆粒状のケイ酸は、ゴムに添加した場合、所望の物性が安定して得られないという問題があった。
【０００６】
そこで本発明の目的は、ゴムに添加した場合、微粉体を用いた場合と変わらない物性を有する、顆粒状の沈殿ケイ酸を提供することにある。
さらに詳しくは、本発明は、ゴムに添加した場合に微粉体を用いた場合と変わらない物性、即ち、分散性、強度、耐摩耗等が得られる新規な顆粒状の沈殿ケイ酸及びその製造方法を提供することにある。
【０００７】
【課題を解決するための手段】
本発明は、粒子径が５００μｍ〜５ｍｍの範囲に入る粒子の占める割合が８０重量％以上であり、且つ粒子硬度が１０〜３０ｇｆであることを特徴とする粒状沈殿ケイ酸に関する。
【０００８】
さらに本発明は、好ましくは、嵩比重が２５０〜５００ｇ／リットルの範囲であり、ＢＥＴ比表面積が１００〜３００ｍ^２／ｇの範囲である粒状沈殿ケイ酸である。
【０００９】
更に本発明は、湿式法沈殿ケイ酸のフィルターケークを水分が５０〜７５％の範囲になるように乾燥し、次いで得られた沈殿ケイ酸ケークを造粒することを特徴とする、前記本発明の粒状沈殿ケイ酸の製造方法に関する。
以下、本発明を更に詳細に説明する。
【００１０】
本発明の粒状沈殿ケイ酸は、粒子径が５００μｍ〜５ｍｍの範囲に入る粒子の占める割合が８０重量％以上である。粒子径が５００μｍ以下の粒状沈殿ケイ酸はこれまでも、エラストマー充填剤として使用されている。また、更に粒子径の小さい沈殿ケイ酸は、塗料、特殊紙、フィルム等比較的滑らかな表面状態が求められる分野で使用されている。しかし、粒子径が５００μｍ以上の粒子の占める割合が上記範囲以下では、微粉が多いために取扱い時に粉塵の発生による作業環境の悪化が難点とである。それに対して、本発明では粒子径が小さくとも５００μｍである粒子が８０％以上ある粒状沈殿ケイ酸であり、ゴム、樹脂等のエラストマー充填剤としての作業性を改善し、また貯蔵及び輸送費を改善するものである。
【００１１】
一方、粒子径が５ｍｍを超える粒子径が多い沈殿ケイ酸では、エラストマー中への充填が限られた時間で行われる為に分散不良となるという問題が起こる。従って、５００μｍ〜５ｍｍの範囲に入る粒子の占める割合が８０重量％以上であることが必要である。
本発明の粒状沈殿ケイ酸は、好ましくは粒子径が５００μｍ〜５ｍｍの範囲に入る粒子の占める割合が８５重量％以上である。
【００１２】
また、本発明の粒状沈殿ケイ酸は、粒子硬度が１０〜３０ｇｆの範囲である。粒子硬度は３０ｇｆ以下であれば、実質的にゴム等への分散性が未造粒物と同等である。また、粒子硬度が３０ｇｆを超える沈殿ケイ酸は、比較的嵩比重も高く輸送中の粉化も少ないが、分散性が悪くゴム物性の劣化原因となり、本発明の目的とする用途分野では使用できない。一方、粒子硬度が１０ｇｆ未満では、ゴム物性への影響は殆どないが、粉化し易く、取り扱い時に粉塵の発生が多くなり、作業環境の悪化の原因となる。本発明の粒状沈殿ケイ酸は、粒子硬度が好ましくは１５〜２５ｇｆの範囲である。
【００１３】
本発明の粒状沈殿ケイ酸は、嵩比重が２５０〜５００ｇ／リットルの範囲であることが好ましい。嵩比重が２５０ｇ／リットル以上である沈殿ケイ酸造粒物であれば、実質的に粉塵の発生は少なく作業環境は改善され、さらに、貯蔵や輸送費の点でも優れている。また、嵩比重が５００ｇ／リットル以下であれば、エラストマー中への分散性も良好に保てるからである。より好ましい嵩比重は３００〜４００ｇ／リットルの範囲である。
【００１４】
本発明の粒状沈殿ケイ酸は、ＢＥＴ比表面積が、特にゴム補強充填剤として補強効果が充分発揮し得るという観点から、１００〜３００ｍ^２／ｇの範囲であることが好ましい。好ましくは、ＢＥＴ比表面積は１５０〜２５０ｍ^２／ｇの範囲である。
【００１５】
以下、本発明の粒状沈殿ケイ酸の製造方法について説明する。
湿式法沈殿ケイ酸のフィルターケークの水分は一般に約８０％である。本発明者らの検討の結果、このフィルターケークの水分を多くとも７５％になるように乾燥することによって、フィルターケークがペースト状からスラリー状となることなしに造粒が可能であることを見出した。一方、乾燥したフィルターケークの水分が５０％未満になると、造粒して得られる粒状物の粒子硬度が高くなり過ぎ、本発明の所定の範囲の粒子硬度を有する粒状沈殿ケイ酸が得られなくなる。粒子硬度が高くなり過ぎるとゴム等への分散が悪く、ゴム本来の物性である耐摩耗性、引っ張り強度等が劣化する。
フィルターケークの乾燥の程度は、好ましくは７０〜６０％の範囲である。
【００１６】
本発明の方法で用いる湿式法沈殿ケイ酸は、まずケイ酸アルカリと鉱酸を反応させて得られるものである。反応後、得られた沈殿ケイ酸スラリーを濾過及び洗浄することにより、沈殿ケイ酸フィルターケークを得る。沈殿ケイ酸スラリーを得る反応方法は、例えばケイ酸ソーダと硫酸とを反応させて微細な水和ケイ酸スラリーを生成させる反応工程までは、特公昭３８−１７６５１号及び特公昭５４−２５２３５号等に開示されている公知の方法等と同様な操作により行われるが、望ましくは、ケイ酸ナトリウムと硫酸を同時滴下する反応方法である。また、濾過及び洗浄はフィルタープレスやベルトフィルター等を使用して工業的に大量処理することが可能である。
【００１７】
得られた沈殿ケイ酸フィルターケークは、乾燥することにより、所定範囲に含水量を調整する（半乾燥する）。この乾燥に用いる乾燥機には特に制限はないが、例えば、通常の箱型乾燥機等を用いることができる。フィルターケークを所定含水量に乾燥するする本発明の方法は、沈殿ケイ酸ケークに乾燥粉を加えて練り混む方法や乾燥粉に水を加えて調整する方法に比べ、得られる粒状物をゴムに添加した場合、安定したエラストマー物性を得ることができる。
【００１８】
所定の水分量に乾燥した沈殿ケイ酸フィルターケークは、常法により粒状化することができる。例えば、水分を調整した沈殿ケイ酸フィルターケークをニーダー等の混合機を通し、更に押出し造粒機を用いて粒状化し、バンド式乾燥機等の乾燥物に衝撃をあまり与えない方法により乾燥することで、本発明の粒状沈殿ケイ酸を得ることができる。尚、押出し造粒機の場合、成形孔の板厚は成形孔径と同一又は若干厚い方が、成形物の形状が良く微粉発生を押さえる点で望ましい。
【００１９】
造粒機を通して粒状化した後の乾燥機は、乾燥物の移動や衝撃が少なく微粉発生の少ない箱型乾燥機やバンド乾燥又はターボドライヤー等の使用が望ましい。また乾燥時間は、特開昭５４−１１０２００号で示されているように短時間乾燥ではなく、５〜１０時間のゆっくりした乾燥時間をとることで、適度な粒子硬度を示しエラストマー中への分散性の良い粒状品を得ることができる。
【００２０】
【発明の効果】
本発明によれば、従来品と同様なエラストマー補強効果を有しながら、従来の粉状品での難点であった粉塵の発生を抑え、作業環境の改善や、貯蔵タンクや輸送費用の低減、或いは流動性良好な卓越した新規な粒状沈殿ケイ酸が得られる。
【００２１】
【実施例】
以下、本発明を実施例及び比較例を挙げて更に具体的に説明する。
なお、実施例及び比較例における粒子径、嵩比重、ＢＥＴ比表面積及び粒子硬度の測定は次の方法で行った。
（Ｉ）粒子径の測定
ロータップ式標準ふるい振とう機（筒井理化学機器（株）社製）を用いて５ｍｍ、５００μｍ網目の篩をセットし、試料１００ｇを入れ５分間振動した後、篩上の試料重量を測定し、５００μｍ〜５ｍｍ範囲の割合を表した。
（ＩＩ）嵩比重の測定
ＪＩＳＫ−５１０１（顔料試験法）に規定するカサ試験法に準じ測定した。
（ＬｏｏｓｅＷｅｉｇｈｔ法）
（ＩＩＩ）ＢＥＴ比表面積の測定
カンターソーブ（米国Ｑｕａｎｔａｃｈｒｏｍｅ社製）を用いて１点法により測定した。
【００２２】
（ＩＶ）粒子硬度の測定
ＪＩＳＫ−６２２１（造粒粒子の硬さ）試験法に準じ、粒子径１ｍｍの粒子を上皿天秤に乗せ、粒に垂直に力を加え粒が破壊する時の荷重を読み取る、これを２０点行い、その平均値をもって粒子硬度とし、単位はｇｆで表す。
（Ｖ）作業時の粉塵性
試料１００ｇをディスポカップに入れ、約３０ｃｍの高さより試料を受け皿にゆっくり注ぎ、その時の粉塵発生度合いを調べた。
粉塵の発生度合いを◎、○、×で表示した。
（ＶＩ）ゴム物性試験
１）加硫ゴム片の目視判定及び加硫物性より、ゴム中の粒状ケイ酸の分散性（分散均一性）が優れているものは○、普通のものは△、悪いものは×の判定で表示した。
２）引っ張り強度
ＪＩＳＫ６３０１の試験法に準じ測定した。
３）耐摩耗性
アクロン型摩耗試験機を用いて、傾角１５°、分銅６ポンド、試験回数１０００回転での摩耗容積を測定した。
【００２３】
実施例１
９０℃に加熱した温水１７，２００ｍｌに、３号ケイ酸ナトリウム溶液（Ｎａ_２Ｏ約７％、ＳｉＯ_２約２２％）６３７ｍｌを加え攪拌しながら、次いで３号ケイ酸ナトリウム溶液（前記と同濃度）５，９７０ｍｌと４８％硫酸約１，２００ｍｌを、反応液のｐＨが９〜１１を保つように６０分間で同時注加した。更に４８％硫酸を注加して反応液の酸性化を行った。
酸性化終了時のｐＨは約３．０とした。得られた沈殿ケイ酸スラリーをフィルタープレスで濾別し、温水で充分洗浄を行い湿潤フィルターケークを得た。この時のケーク水分は８０％であった。このフィルターケークを不二パウダル社製ディスクペレッター（Ｆ−５型）押し出し造粒機を用いて粒状に成形しようと試みた。しかし、成形時にペースト状、更にはスラリー状になってしまった。そのまま乾燥すると、不均一な径の粒子や一つの塊となってしまい、形状の良い粒子に成形することは困難であった。
【００２４】
そこで、前記方法で得られた水分８０％のフィルターケークを、熱風循環式乾燥機に入れて水分を７０％まで乾燥した。得られたケークを取り出して、不二パウダル社製ディスクペレッター（Ｆ−５型）押出し造粒機を用いて粒状に形成した後、再度、熱風循環式乾燥機で水分約５％まで乾燥を行い本発明の粒状沈殿ケイ酸を得た。
【００２５】
上記本発明の粒状沈殿ケイ酸５０部と固体状有機ゴムとしてスチレン−ブタジエン共重合体ゴム（ＳＢＲ１５０２：日本合成ゴム社製）１００部を配合し、更に加硫剤として硫黄２．０部、加硫促進剤としてジフェニルグアニジン（大内新興化学製ノックセラーＤ）１．２部、ジベンゾチアジルジスルフィド（大内新興化学製ノックセラーＤＭ）０．８部、及び加硫助剤として酸化亜鉛３部とステアリン酸１部を添加した。更に、活性剤としてＰＥＧ（ポリエチレングリコール）＃４０００（第一工業製薬製）２部を添加した。これらを８インチロールを用いて、練り温度３０℃にて混練して、ゴム組成物を得た。
該ゴム組成物を１５０℃で１０分間加硫したものについて、ゴム物性試験を行った。
この時の製品の物性及びゴム配合試験結果を表１に示す。
【００２６】
実施例２
実施例１と同様な方法で得られた水分８０％のフィルターケークを、熱風循環式乾燥機に入れて水分を５２％まで乾燥した。得られたケークを取り出して、実施例１と同様の押出し造粒機を用いて粒状に形成した後、再度熱風循環式乾燥機で水分約５％まで乾燥を行い本発明の粒状沈殿ケイ酸を得た。
得られた粒状沈殿ケイ酸を用いて、実施例１と同様にしてゴム組成物を得た。この時の製品の物性及びゴム配合試験結果を表１に示す。
【００２７】
比較例１
実施例１と同様な方法で得られた水分８０％のフィルターケークを、軽く解砕した後、熱風循環式乾燥機に入れて水分が約５％になるまで乾燥を行い粒状沈殿ケイ酸を得た。
得られた粒状沈殿ケイ酸を用いて、実施例１と同様にしてゴム組成物を得た。この時の製品の物性及びゴム配合試験結果を表１に示す。
【００２８】
比較例２
実施例１と同様な方法で得られた水分８０％のフィルターケークを、熱風循環式乾燥機で水分４０％まで乾燥した後、実施例１と同様の押出し造粒機を用いて粒状に形成した後、再度熱風循環式乾燥機で水分約５％まで乾燥を行い粒状沈殿ケイ酸を得た。
得られた粒状沈殿ケイ酸を用いて、実施例１と同様にしてゴム組成物を得た。この時の製品の物性及びゴム配合試験結果を表１に示す。
【００２９】
【表１】

[0001]
[Industrial applications]
The present invention relates to a novel particulate precipitated silicic acid. In particular, the present invention has a large particle diameter and a high bulk specific gravity suitable for fillers such as rubber, plastics, resins, etc., and also has an appropriate particle hardness, the filling operation is easy, and dust It is an object of the present invention to provide a novel particulate precipitated silicic acid whose generation is significantly improved and a method for producing the same.
[0002]
[Prior art]
Precipitated silicic acid powder, commonly called white carbon, is a highly active white powder with surface activity. It is used in various fields such as rubber reinforcing fillers, dispersants for agricultural chemicals, paints, resins, information papers, inks, and toothpastes. Used in Generally, it is a soft agglomerated particle and belongs to the lightest class among powders, and it is very easily scattered, and there is a problem that the working environment is deteriorated due to dust during handling.
In addition, there are also problems such as low bulk density of the powder, uneconomical packaging, storage and transportation costs, or poor fluidity and remaining on the bottom wall of the silo. Granular products are strongly desired to solve such difficulties.
[0003]
[Problems to be solved by the invention]
By the way, when the precipitated silica powder is used as an elastomer filler, it is desirable that the fine silica powder be a fine powder having good dispersibility in the elastomer from the viewpoint of the reinforcing effect if its performance is considered first. However, various granulation methods have been proposed in order to solve the above-mentioned difficulties even if the reinforcing performance is somewhat sacrificed.
However, when granulated by various granulation methods, when kneaded with rubber, etc. with an open roll or Banbury mixer, the dispersibility of precipitated silica powder is impaired, which determines the properties of rubber, abrasion resistance, tensile Performance such as strength, elongation, and rebound resilience is significantly reduced. For example, granular products obtained by spray-drying a high-concentration precipitated silica slurry disclosed in JP-B-56-41566 and JP-A-2-302312 have a small particle size, a low bulk specific gravity, The improvement of workability and storage and transportation costs, which are the original objectives of the granules, were insufficient.
[0004]
JP-A-54-110200 discloses that a precipitated silica slurry is separated by filtration with a filter press and washed to obtain a filter cake, and if necessary, a powdered precipitated silica is mixed to obtain a solid content of 28 to 40% by weight. %, Obtained by compression molding with a granulator and drying to obtain granular silicic acid. However, the water content of the precipitated silica filter cake is generally about 80%, and it is difficult for the cake alone to form a paste, or even a slurry, to form a granule. Therefore, in practice, it is necessary to adjust the solids content to a predetermined range by mixing powdered precipitated silica.
[0005]
The present inventors have tried a method of mixing the dry powder with the filter cake of precipitated silica to reduce the water content to facilitate the formation into granules, and the powder precipitated silica was uniformly mixed with the filter cake. It was difficult to do. Furthermore, when the granular silicic acid obtained by this method is added to rubber, there is a problem that desired physical properties cannot be stably obtained.
[0006]
Therefore, an object of the present invention is to provide granular precipitated silica having the same physical properties as when a fine powder is used when added to rubber.
More specifically, the present invention relates to a novel granular precipitated silicic acid having the same physical properties as when a fine powder is used when added to rubber, that is, dispersibility, strength, abrasion resistance and the like, and a method for producing the same. Is to provide.
[0007]
[Means for Solving the Problems]
The present invention relates to granular precipitated silicic acid, wherein the proportion of particles having a particle size in the range of 500 μm to 5 mm is 80% by weight or more and the particle hardness is 10 to 30 gf.
[0008]
Furthermore, the present invention is preferably a particulate precipitated silicic acid having a bulk specific gravity in the range of 250 to 500 g / liter and a BET specific surface area in the range of 100 to 300 m ² / g.
[0009]
Furthermore, the present invention is characterized in that the wet-precipitated silicic acid filter cake is dried so that the water content is in the range of 50 to 75%, and then the obtained precipitated silicic acid cake is granulated. And a method for producing granular precipitated silica.
Hereinafter, the present invention will be described in more detail.
[0010]
In the granular precipitated silica of the present invention, the proportion of particles having a particle diameter in the range of 500 μm to 5 mm is 80% by weight or more. Granular precipitated silica having a particle size of 500 μm or less has been used as an elastomer filler. Further, precipitated silica having a smaller particle size is used in fields requiring relatively smooth surface conditions such as paints, special papers and films. However, when the proportion of particles having a particle diameter of 500 μm or more occupies the above range or less, there is a difficulty in deteriorating the working environment due to generation of dust during handling due to the large amount of fine powder. On the other hand, in the present invention, it is a granular precipitated silica in which 80% or more of the particles having a particle diameter of at least 500 μm are improved to improve workability as an elastomer filler such as rubber and resin, and to reduce storage and transportation costs. It will improve.
[0011]
On the other hand, in the case of precipitated silicic acid having a large particle diameter exceeding 5 mm, the filling into the elastomer is performed in a limited time, which causes a problem of poor dispersion. Therefore, it is necessary that the proportion of particles falling within the range of 500 μm to 5 mm is 80% by weight or more.
In the granular precipitated silica of the present invention, the proportion of particles having a particle diameter in the range of 500 μm to 5 mm is preferably 85% by weight or more.
[0012]
The granular precipitated silica of the present invention has a particle hardness in the range of 10 to 30 gf. If the particle hardness is 30 gf or less, the dispersibility in rubber or the like is substantially equal to that of an ungranulated material. Precipitated silicic acid having a particle hardness of more than 30 gf has a relatively high bulk specific gravity and little powdering during transportation, but has poor dispersibility and causes deterioration of rubber physical properties, and cannot be used in the intended application field of the present invention. . On the other hand, if the particle hardness is less than 10 gf, there is almost no effect on the rubber properties, but it is easy to be powdered, and the amount of dust generated during handling is increased, which causes deterioration of the working environment. The granular precipitated silica of the present invention preferably has a particle hardness in the range of 15 to 25 gf.
[0013]
The granular precipitated silica of the present invention preferably has a bulk specific gravity in the range of 250 to 500 g / liter. If the precipitated silica has a bulk specific gravity of 250 g / liter or more, the generation of dust is substantially reduced, the working environment is improved, and the storage and transportation costs are excellent. Further, when the bulk specific gravity is 500 g / liter or less, good dispersibility in the elastomer can be maintained. More preferable bulk specific gravity is in the range of 300 to 400 g / liter.
[0014]
The granular precipitated silica of the present invention preferably has a BET specific surface area in the range of 100 to 300 m ² / g, particularly from the viewpoint that the reinforcing effect can be sufficiently exhibited as a rubber reinforcing filler. Preferably, BET specific surface area is in the range of 150 to 250 ² / g.
[0015]
Hereinafter, the method for producing the granular precipitated silica of the present invention will be described.
The wet cake of the precipitated silica is generally about 80% moisture. As a result of the study by the present inventors, it has been found that by drying the filter cake so that the water content of the filter cake becomes at most 75%, the filter cake can be granulated without changing from a paste state to a slurry state. Was. On the other hand, when the moisture content of the dried filter cake is less than 50%, the particle hardness of the granules obtained by granulation becomes too high, and it is not possible to obtain the granular precipitated silicic acid having the particle hardness in the predetermined range of the present invention. . If the particle hardness is too high, dispersion in rubber or the like is poor, and the physical properties of rubber, such as abrasion resistance and tensile strength, deteriorate.
The degree of drying of the filter cake is preferably in the range of 70-60%.
[0016]
The wet method precipitated silicic acid used in the method of the present invention is obtained by first reacting an alkali silicate with a mineral acid. After the reaction, the obtained precipitated silica slurry is filtered and washed to obtain a precipitated silica filter cake. A reaction method for obtaining a precipitated silica slurry is, for example, JP-B-38-17651 and JP-B-54-25235 until the reaction step of reacting sodium silicate and sulfuric acid to produce a fine hydrated silica slurry. And the like, but is preferably a reaction method of simultaneously dropping sodium silicate and sulfuric acid. In addition, filtration and washing can be carried out on a large scale industrially using a filter press, a belt filter or the like.
[0017]
The obtained precipitated silica filter cake is dried to adjust the water content to a predetermined range (semi-dried). The dryer used for this drying is not particularly limited, and for example, an ordinary box-type dryer can be used. The method of the present invention for drying a filter cake to a predetermined moisture content is based on a method of adding a dry powder to a precipitated silicate cake and kneading the mixture, or a method of adding water to a dry powder and adjusting the obtained granular material to rubber. When added, stable elastomer properties can be obtained.
[0018]
The precipitated silica filter cake dried to a predetermined water content can be granulated by a conventional method. For example, the precipitated silica filter cake whose water content has been adjusted is passed through a mixer such as a kneader, granulated using an extrusion granulator, and dried by a method that does not significantly affect the dried product such as a band dryer. Thus, the granular precipitated silica of the present invention can be obtained. In the case of an extrusion granulator, it is desirable that the plate thickness of the forming hole is equal to or slightly larger than the forming hole diameter, since the shape of the formed product is good and the generation of fine powder is suppressed.
[0019]
As for the dryer after granulation through a granulator, it is desirable to use a box-type dryer, a band dryer, a turbo dryer, or the like, which causes less movement of the dried material and less impact and generates less fine powder. The drying time is not short-time drying as shown in JP-A-54-110200, but rather takes a slow drying time of 5 to 10 hours to show an appropriate particle hardness and disperse in the elastomer. Good granularity can be obtained.
[0020]
【The invention's effect】
According to the present invention, while having the same elastomer reinforcing effect as conventional products, suppresses the generation of dust, which is a problem with conventional powder products, improves the working environment, reduces storage tanks and transportation costs, Alternatively, a novel granular precipitated silica having excellent fluidity is obtained.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
The particle diameter, bulk specific gravity, BET specific surface area and particle hardness in Examples and Comparative Examples were measured by the following methods.
(I) Measurement of Particle Size A 5-mm, 500-μm mesh sieve was set using a low-tap standard sieve shaker (manufactured by Tsutsui Physical and Chemical Instruments Co., Ltd.). The sample weight was measured and represented the ratio in the range of 500 μm to 5 mm.
(II) Measurement of Bulk Specific Gravity It was measured according to the bulk test method specified in JIS K-5101 (pigment test method).
(Loose Weight method)
(III) Measurement of BET specific surface area The BET specific surface area was measured by a one-point method using Cantersorb (manufactured by Quantachrome, USA).
[0022]
(IV) Measurement of Particle Hardness In accordance with JIS K-6221 (hardness of granulated particles) test method, a particle having a particle diameter of 1 mm is placed on an upper balance and a load is applied when a force is applied vertically to the particles to break the particles. This is performed at 20 points, and the average value is defined as the particle hardness, and the unit is represented by gf.
(V) 100 g of the dusty sample during the operation was put into a disposable cup, and the sample was slowly poured into a receiving tray from a height of about 30 cm, and the degree of dust generation at that time was examined.
The degree of dust generation was indicated by ◎, 、, and ×.
(VI) Rubber physical property test 1) According to the visual judgment and vulcanized physical properties of vulcanized rubber pieces, those having excellent dispersibility (dispersion uniformity) of granular silicic acid in rubber were evaluated as good, and those as ordinary were evaluated as poor and poor. Those were indicated by judgment of x.
2) Tensile strength Measured according to the test method of JIS K6301.
3) Abrasion resistance The abrasion volume at an inclination of 15 °, a weight of 6 lbs, and the number of test cycles of 1,000 was measured using an Akron abrasion tester.
[0023]
Example 1
To 17,200 ml of warm water heated to 90 ° C., 637 ml of a No. 3 sodium silicate solution (about 7% of Na ₂ O, about 22% of SiO ₂ ) was added, and the mixture was stirred while stirring. 5) 5,970 ml and about 1,200 ml of 48% sulfuric acid were simultaneously added over 60 minutes so that the pH of the reaction solution was kept at 9 to 11. Further, 48% sulfuric acid was added to acidify the reaction solution.
The pH at the end of the acidification was about 3.0. The obtained precipitated silica slurry was separated by filtration with a filter press, and sufficiently washed with warm water to obtain a wet filter cake. The cake moisture at this time was 80%. An attempt was made to form the filter cake into granules using a disk pelletizer (F-5 type) extruder manufactured by Fuji Paudal Co., Ltd. However, it became a paste or a slurry during molding. If dried as it is, particles of non-uniform diameter or one lump would be formed, and it was difficult to form particles with good shape.
[0024]
Therefore, the filter cake having a water content of 80% obtained by the above method was placed in a hot air circulation type drier to dry the water content to 70%. The cake obtained was taken out, formed into granules using a disk pelletizer (F-5 type) extruder manufactured by Fuji Paudal Co., Ltd., and then dried again to a water content of about 5% with a hot air circulation type drier. Then, the granular precipitated silica of the present invention was obtained.
[0025]
50 parts of the granular precipitated silicic acid of the present invention and 100 parts of a styrene-butadiene copolymer rubber (SBR1502: manufactured by Nippon Synthetic Rubber Co., Ltd.) were blended as a solid organic rubber, and 2.0 parts of sulfur was added as a vulcanizing agent. 1.2 parts of diphenylguanidine (knock cellar D manufactured by Ouchi Shinko Chemical) as a sulfur accelerator, 0.8 parts of dibenzothiazyl disulfide (knock cellar DM manufactured by Ouchi Shinko Chemical), and 3 parts of zinc oxide as a vulcanization aid And 1 part of stearic acid. Further, 2 parts of PEG (polyethylene glycol) # 4000 (Daiichi Kogyo Seiyaku) was added as an activator. These were kneaded using an 8-inch roll at a kneading temperature of 30 ° C. to obtain a rubber composition.
A rubber physical property test was performed on the rubber composition vulcanized at 150 ° C. for 10 minutes.
Table 1 shows the physical properties of the product and the results of the rubber compounding test at this time.
[0026]
Example 2
The filter cake having a water content of 80% obtained in the same manner as in Example 1 was placed in a hot-air circulating drier to dry the water content to 52%. The cake obtained was taken out, formed into granules using the same extrusion granulator as in Example 1, and then dried again with a hot air circulating drier to a water content of about 5% to obtain the precipitated silica of the present invention. Obtained.
A rubber composition was obtained in the same manner as in Example 1 using the obtained granular precipitated silica. Table 1 shows the physical properties of the product and the results of the rubber compounding test at this time.
[0027]
Comparative Example 1
A filter cake having a water content of 80% obtained in the same manner as in Example 1 was lightly crushed, and then placed in a hot-air circulating drier and dried until the water content became about 5% to obtain granular precipitated silica. Was.
A rubber composition was obtained in the same manner as in Example 1 using the obtained granular precipitated silica. Table 1 shows the physical properties of the product and the results of the rubber compounding test at this time.
[0028]
Comparative Example 2
The filter cake having a water content of 80% obtained in the same manner as in Example 1 was dried to a water content of 40% with a hot-air circulating drier, and then formed into granules using the same extrusion granulator as in Example 1. Thereafter, drying was performed again to a water content of about 5% by a hot air circulation type drier to obtain granular precipitated silicic acid.
A rubber composition was obtained in the same manner as in Example 1 using the obtained granular precipitated silica. Table 1 shows the physical properties of the product and the results of the rubber compounding test at this time.
[0029]
[Table 1]

Claims

A particulate precipitated silicic acid characterized in that the proportion of particles having a particle diameter in the range of 500 μm to 5 mm is 80% by weight or more and the particle hardness is 10 to 30 gf.

2. The granular precipitated silicic acid according to claim 1, wherein the bulk specific gravity is in the range of 250 to 500 g / l.

The granular precipitated silicic acid according to claim 1 or ^{2, wherein the} BET specific surface area is in the range of 100 to 300 m2 / g.

The granular precipitated silica according to claim 1, characterized in that the wet-precipitated silica cake is dried so that the water content is in the range of 50 to 75%, and then the obtained precipitated silica cake is granulated. Method for producing acid.