JP2004075479A

JP2004075479A - Coated granular fertilizer

Info

Publication number: JP2004075479A
Application number: JP2002240379A
Authority: JP
Inventors: Daruma Fukumoto; 福本　達磨; Hisato Saito; 斉藤　久登; Takahiro Watanuki; 渡貫　孝浩; Masaaki Nishitani; 西谷　正明
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2002-08-21
Filing date: 2002-08-21
Publication date: 2004-03-11

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated granular fertilizer which stably elutes fertilizer components into soil under the environment subjected to fertilizer application and reduces the burden on the peripheral environment by rapid degradation and decomposition of the films after the elution. <P>SOLUTION: The coated granular fertilizer is formed by coating the surface of the granular fertilizer with the films containing a copolymer containing ≥3C olefin and ethylene and/or water repelling starch and a metal oxide. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は施肥された環境下において、土壌中への肥料成分の溶出制御が可能な被覆粒状肥料に関する。詳しくは、土壌中への肥料成分の溶出が安定して行われ、且つ溶出後の皮膜が速やかに崩壊および分解することにより、周辺環境への負荷を軽減した、被覆粒状肥料に存する。
【０００２】
【従来の技術】
農作物の栽培には、その生長段階に応じた肥料が必要であり、その必要時期に合わせるために従来から元肥、追肥等、作物の収穫までに数回の施肥を行ってきた。近年、農業が近代化され、また農業人口の減少に伴い、より手間の掛からない、施肥回数が少なくて済む肥料の開発が求められ、肥料成分の溶出を作物の養分要求特性に適合させるように制御すべく様々な肥料が開発された。
【０００３】
例えば、土壌中に施肥された肥料成分の溶出を物理的に制御するために、粒状肥料の表面を高分子樹脂皮膜で被覆する検討が広く実施され、そのうち幾つかは実用化されている。具体的には、皮膜材料として低透湿性のポリオレフィン樹脂を使用し、肥料成分の溶出曲線が直線となるリニヤー型溶出タイプや、Ｓ字曲線となるシグモイド型溶出タイプ等の様々なタイプがあり、作物の生育に合わせた施肥管理が可能となる。これらは、特公昭５４−３１０４号、特公昭６０−３０４０号、及び特公昭６０−３７０７４号の各号公報等に開示されている。
【０００４】
しかしながら近年、かかるポリオレフィン樹脂が非分解性であるため、被覆粒状肥料が投入された圃場で皮膜殻が蓄積し、さらにはこの殻が圃場域外へ流出し、その結果、生態系に蓄積するなどの環境負荷が懸念されている。そこで、ポリオレフィン樹脂に生分解性資材を添加し、皮膜を崩壊に至らしめる技術が提案されている。例えば、特開平６−８７６８４号公報や特開平１１−３２２４７９号公報等にあるように、生分解性資材として糖重合体及びその誘導体を添加する方法、特開平９−２６３４７６号公報にあるような脂肪族ポリエステルを添加する方法がある。但し、これらは被覆材の多くを占めるポリオレフィン樹脂の分解を促進するものではなく、生分解性資材の増加に伴い土壌中の溶出制御性が不安定となる欠点がある。
【０００５】
これを受けて、生分解樹脂を皮膜の主成分とする技術も提案され、その生分解性樹脂として、変性天然ゴム（特開昭５９−９２９８９号公報等）や、種々の脂肪族ポリエステル類（特公平２−２３５１７号、特公平７−５０５号、特開平４−８９３８４号、特開平５−８５８７３号、特開平７−３３５７７号、特開平７−６１８８４号、特開平７−３１５９７６号、特開平８−１５７２９０号、特開平９−２４９７７号、特開平１０−７４８４号の各号公報等）を利用した技術が開発されている。
しかしこれらは樹脂の透湿性が高いため、溶出停滞期を有するシグモイド型の溶出タイプ肥料を形成し難く、また土壌中での生分解速度が大きく、溶出制御性が不安定になる欠点がある。
【０００６】
また更に、皮膜材料に生分解性を付与させ、かつ長期間にわたる溶出制御性を維持する目的で、低分子量のポリエチレン、石油ワックス類およびパラフィンワックスなどを皮膜の主成分とする技術も提案されている（特公昭４９−３３３９号、特開平９−２６３４７６号、特開平１０−２３１１９０号、特開平１０−２３１１９１号、特開平１０−２９１８８０号、特開平１１−７１１９２号、及び特開平１１−２６３６８９号公報等）。
しかし、これらは皮膜材料の融点が低く、成膜中に肥料粒子同士が融着して成膜が困難となり、皮膜の力学的強度、つまり耐衝撃性、耐磨耗性に乏しいために、物理的な衝撃により皮膜が損傷しやすくなる結果、溶出制御性が不安定となり、本来期待した溶出制御ができないなどの欠点がある。
【０００７】
一方、皮膜材自体を何らかの作用によって崩壊または分解する技術も検討されているが、各々に問題があり、これを解決するに至っていない。
例えば、光分解性樹脂を皮膜の主成分とする技術が提案され、光分解性樹脂としてエチレン・一酸化炭素共重合体を用いるもの（特公平２−２３５１６号公報）、ビニルケトン共重合体を用いるもの（特公平７−５０６号公報）、オレフィン類・一酸化炭素・オレフィン性不飽和化合物共重合体を用いるもの（特開平６−５６５６８号公報）、さらに、金属錯体などの光分解剤を皮膜に分散させるもの（特公平７−９１１４３号、特開平１０−２３１１９０号、特開平１０−２３１１９１号、特開平１１−４３３９１号等の各号公報）などが挙げられる。
【０００８】
これらは被覆粒状肥料が日光等に露光している条件下でのみ分解するため、皮膜殻の圃場での蓄積及び圃場域外への流出を回避できるものではない。また製法上皮膜中の光分解剤の分散性が悪いため、崩壊または分解速度にばらつきが生じ易く、溶出制御性が変化してしまうという問題があるだけでなく、製品保存時の安定性および環境中での分解性を両立できるものではない。
【０００９】
また、ポリオレフィン系樹脂に酸化分解反応を促進する物質を含有した皮膜に、昇華性物質（特開平７−４８１９４号公報、特開平１０−１３８６号公報等）や、水溶性且つ非昇華性微粉体（特開平９−３０９７８３号公報）、生分解性ポリエステル微粒子（特開平９−３０９７８４号公報）、を分散させる技術も提案されている。
しかしながら、これらは土壌系内において、被覆粒状肥料が期中の過酷な温度と湿度の変化に感応しやすいため酸化分解を受けやすく、安定した溶出制御を維持することは困難である。
【００１０】
このように、従来から溶出後の皮膜をできる限り早期に分解させるべく、生分解性資材を皮膜の有効成分としたり、皮膜中の劣化促進剤の絶対量を多くする等の技術が提案されてきたが、前者では、皮膜の透湿性が高いため土壌中での溶出制御性が困難であること、また後者では、形成される皮膜中の樹脂成分の連続性が阻害され、皮膜の力学的強度が弱くなる結果、溶出制御ができなくなる等の問題があった。
【００１１】
【発明が解決しようとする課題】
本発明の目的は、特定の樹脂皮膜中に樹脂の劣化促進剤を相当量添加しても溶出制御性が良好で、かつ溶出後の皮膜が自然環境下で速やかに崩壊または分解することにより、環境への負荷を軽減した被覆粒状肥料を提供することである。
【００１２】
【発明を解決するための手段】
本発明者らは、上述の課題を解決するために鋭意検討した結果、被覆粒状肥料における皮膜材料として、皮膜中に『エチレンと炭素数が３以上のオレフィンのコポリマーおよび／または撥水化澱粉』と『金属酸化物』を含む皮膜で肥料を被覆することにより、製品保存中の安定性および皮膜の力学的強度に優れるとともに、土壌中における溶出制御性が良好でかつ溶出後の皮膜の崩壊性および分解性も付与できるという、上述したような課題を解決する被覆粒状肥料となることを見い出し本発明を完成させた。
【００１３】
即ち本発明は、粒状肥料の表面を、炭素数が３以上のオレフィンとエチレンとを含むコポリマー、および／または撥水化澱粉と、金属酸化物を含む皮膜で被覆された被覆粒状肥料に存する。
【００１４】
本発明において被覆粒状肥料の皮膜が「崩壊する」または「分解する」とは、光、特に紫外線を含む日光等に曝されることによって劣化するメカニズムの他に、適当な温度と湿度の条件下で空気中の酸素により酸化される化学的メカニズム、土壌中の微生物により皮膜中の高分子材料が低分子化されて最終的に水と二酸化炭素に分解される生物学的メカニズム、農耕地土壌における土壌耕運・解砕時の皮膜への物理的衝撃、温度と湿度の変化による土壌の圧縮膨張メカニズム、および植物根の皮膜への侵入等による皮膜崩壊等の物理的メカニズムをも意味するものである。
【００１５】
例えばこの様な化学的、物理的メカニズムにより皮膜強度が粒子形状を維持できない程度まで減少し、さらには皮膜が極小片化に至る程度まで崩壊した状態であれば、粒子状態のままで土壌中に残留することがなく、浮上等により系外へ流出することが抑制されるので、実質的に環境負荷が抑制される。ここで極小片化した皮膜は、これらに微生物がより繁殖しやすくなるため、生物的メカニズムによる分解が促進され、最終的に消失する。
【００１６】
【発明の実施の形態】
以下、本発明につき詳細に説明する。
本発明の被覆粒状肥料における皮膜材料には、炭素数が３以上のオレフィンとエチレンとを共重合させたコポリマーを用いる。このコポリマーは、その構造上、非結晶もしくは低結晶性の共重合体の様に低密度で柔軟性に富んでいるものが好ましく、製品保存中や施肥機などの物理的、機械的な摩擦や衝撃などによって皮膜が損傷することが殆どなく、溶出期間中において良好な溶出制御性を奏する。
【００１７】
本発明に用いるコポリマーを構成する、炭素数が３以上のオレフィンには、任意のものを用いることが出来る。具体的には例えばプロピレン、１−ブテン、イソブテン、１−ペンテン、２−メチル−１−ブテン、１−ヘキセン、２−メチル−１−ペンテン、４−メチル−１−ペンテン、１−ヘプテン、４−メチル−１−ヘキセン、５−メチル−１−ヘキセン、１−オクテン、５−メチル−１−ヘプテン、１−ドデセン、１−オクタドデセンなどが挙げられる。中でも、オレフィンのホモポリマーに代表されるポリエチレンやポリプロピレンとの相溶性が高いプロピレン、１−ブテン、イソブテン等が好ましい。これらのオレフィンは、単独でも、２種類以上を任意の割合で用いてもよい。
【００１８】
該コポリマーにおいて炭素数が３以上のオレフィンの含有量が少ないと、皮膜全体の耐衝撃強度が低下する場合がある。また、逆に含有量が多いと皮膜全体が柔らかくなり、ピンホールなどの皮膜欠陥が生じたり皮膜全体の透湿性が増加し溶出制御が困難となる場合がある。これらのことから、該コポリマー中における炭素数が３以上のオレフィンの含有量は、０．１〜５０モル％、中でも１〜１０モル％であることが好ましい。また皮膜を構成する成分中のコポリマーの含有量は、皮膜重量に対して、１０〜８０重量％、好ましくは３０〜６５重量％である。尚、エチレンと炭素数が３以上のオレフィンのコポリマーを本発明の目的を損なわない範囲で、一種または二種以上を任意の割合で併用してもよい。
【００１９】
また本発明においては、粒状被覆肥料の皮膜材料として、先述の上述のコポリマーと併用、またはこのコポリマーに代えて、撥水化処理した澱粉（以下「撥水化澱粉」ということがある。）を用いてもよい。この撥水化澱粉を用いることによって、本発明の粒状被覆肥料を施肥後、皮膜中の撥水化澱粉が徐々に生分解を受け、皮膜の崩壊性および分解性が向上するので好ましい。
【００２０】
天然物から採れた、いわゆる未処理の澱粉は、自然環境下において数日で生分解してしまうので、このような未処理澱粉を皮膜中に含有した被覆肥料は、施肥後間もなく皮膜中の澱粉が生分解し、溶出制御性が不安定になる。本発明においては撥水化澱粉を用いることによって、施肥後長期間に亘って溶出制御性を安定化させ、且つ溶出後の皮膜の崩壊性および分解性に優れた被覆肥料とすることができる。
さらに撥水化澱粉を用いることによって皮膜表面が低透湿性となり、この低透湿性によって、施肥後、被覆粒状肥料中の肥料成分の溶出が一定期間抑制され、その後急激に溶出させることが可能となる。よって本発明の被覆粒状肥料をシグモイド型溶出タイプの被覆粒状肥料とする際には、この撥水化澱粉を用いることが好ましい。
【００２１】
撥水化澱粉の原料、いわゆる未処理澱粉は任意の穀物類から作られるものを用いることが出来る。具体的な穀物類としては例えばトウモロコシ、タピオカ、馬鈴薯、甘藷、小麦、米、サゴ等が挙げられる。本発明に用いる撥水化澱粉原料としては、特に、生産性、加工性、生分解性に優れたトウモロコシ由来の澱粉が好ましい。本発明における撥水化澱粉は、これらの作物から採取し精製した澱粉を、化学的な処理によって撥水化し、且つ室温下での水に対する溶解度を低減した澱粉およびその誘導体をいう。
【００２２】
撥水化処理の方法及び撥水性の程度は、適宜選択すればよいが、例えば澱粉の無水グルコース残基の水酸基に、反応性に富む種々の官能基を結合させる方法が挙げられる。本発明に於ける撥水化澱粉は、その他の方法によって処理された澱粉、例えば硫酸、硝酸、リン酸、コハク酸などの無機酸および有機酸またはその塩類を反応させて得られるエステル化澱粉や、メチル化、カルボキシルメチル化、ヒドロキシメチル化などのアルキル化処理または一級、二級、三級アルキルアミンや四級アルキルアンモニウム塩を導入して得られるエーテル化澱粉、また澱粉にホルマリン、アルデヒド、リン酸を作用させることにより澱粉の水酸基間に多官能基を結合させて得られる架橋澱粉、および澱粉にポリアクリルアマイド、ポリアクリル酸、ポリ酢酸ビニル、ポリアクリロニトリルなどの有機高分子物質を化学的に結合させて得られるグラフト化澱粉等をも含む。
【００２３】
中でも、エステル化澱粉およびエーテル化澱粉については、撥水化処理が比較的容易であるので、好ましい。この場合、撥水性の程度は導入する官能基の疎水性に依存するので、目的に応じて適宜、官能基を修飾すればよい。本発明に於ける撥水性とは、１００ｍｌメスシリンダーに水７５ｍｌ、撥水化澱粉５ｇを入れ、２０回激しく振蕩した後、１時間静置したときの撥水化澱粉の沈降体積をいい、得られた測定値については、数値が低いほど撥水性が大きいことを示す。撥水性の程度は大きいほど好ましいが、大きすぎると、皮膜の崩壊性または分解性の効果が充分に発現しない場合がある。このことから、澱粉の撥水性は１０ｍｌ未満で、中でも０．１〜０．５ｍｌであることが好ましい。
【００２４】
本発明の被覆粒状肥料における皮膜中の撥水化澱粉の含有量は適宜選択すればよいが、含有量が少な過ぎると初期の溶出防止期間が確保できず、逆に多すぎると皮膜全体が撥水性となり、施肥時に肥料粒が浮上し系外へ流出する場合がある。よって撥水化澱粉の含有量は、皮膜重量に対して１〜５０％、中でも５〜３０％であることが好ましい。
【００２５】
また撥水化澱粉の平均粒子径は任意であるが、本発明の被覆粒状肥料における皮膜の連続性を阻害せず、且つ澱粉粒子同士が凝集を起こさない程度の均一粒子径であることが好ましく、例えば平均粒子径は皮膜膜厚の１／２以下であることが好ましい。また、これらの撥水化澱粉は、本発明の目的を損なわない範囲で一種または二種以上を任意の割合で併用してもよい。
以上のように、撥水化澱粉の処理の程度、皮膜中における含有量、平均粒子径および添加方法を適宜設定することにより、本発明の被覆粒状肥料は、種々の溶出タイプの被覆粒状肥料とすることができる。
【００２６】
本発明に用いる金属酸化物は、任意の金属酸化物を使用することが出来、本発明の目的を損なわない範囲で、一種または二種以上を任意の割合で併用してもよい。
中でも、ポリオレフィン樹脂の光、特に太陽光による劣化を促進し、自然環境下で樹脂を崩壊または分解する性質を与えるものであることが好ましく、具体的には例えば二酸化チタン、弁柄、黄鉛、アルミナ、コバルト緑、コバルト青、群青、酸化亜鉛（亜鉛華）、酸化クロムなどが挙げられる。
これらの中でも、周辺環境への影響が低く、使用環境下で安定、且つハンドリング性が良好であり、さらに光化学的に有機物を分解する活性が高いことから、二酸化チタンが好ましい。二酸化チタンの結晶構造はアナタース形、ルチル形およびブルッカイト形があるが、中でもアナタース形は光化学的に活性が高く、有機物を分解しやすいので好ましい。
【００２７】
本発明に用いる二酸化チタンは任意の方法により得られたものを使用できるが、一般的な製法としては例えば、原料のイルメナイト鉱を濃硫酸と反応させた溶液を加水分解することにより得られたチタンの水酸化物を高温で焼成する硫酸法や、原料のルチル鉱を１０００℃程度の高温炉で塩素ガスと反応させて得られた四塩化チタンを燃焼する塩素法が挙げられる。
【００２８】
本発明に用いる金属酸化物は、表面処理を施したものを用いてもよい。例えば、金属酸化物として二酸化チタン粒子を用いる際には、その表面をシリカやアルミニウム等で表面を処理することで、有機物に対する活性を制御できるので好ましい。またＡｌやＳｉなどの含水酸化物で表面を処理することで、媒体との親和性および分散性を向上させることもできる。このように金属酸化物の表面処理、およびそれらの皮膜中の含有量を最適化すれば、皮膜の崩壊／分解速度および溶出速度をコントロールすることが可能となるので好ましい。
【００２９】
皮膜中における金属酸化物の含有量は適宜選択すればよいが、少ないと皮膜の崩壊性または分解性を得ることができず、多いと必要以上に分解が促進されるため、製品保存中に皮膜が劣化し溶出制御が困難となる場合がある。これらのことから、皮膜中における金属酸化物の含有量は５０重量％以下であり、好ましくは３０重量％以下、さらに好ましくは０．１〜２０重量％である。また、これらの金属酸化物は本発明の目的を損なわない範囲で、一種または二種以上を任意の割合で併用してもよい。さらに、効果を充分発揮できるように金属酸化物を皮膜中に均一に分散させることが好ましい。例えば、本発明におけるポリマー成分と金属酸化物を適当な有機溶媒に完全に溶解または分散させ、肥料粒にスプレー展着させた場合には、形成される皮膜中にこれらの金属酸化物が均一に分散されるので好ましい。
【００３０】
さらに、本発明の被覆粒状肥料においては、その皮膜中にオレフィンのホモポリマーを含有してもよい。オレフィンのホモポリマーとしては、その種類に特に限定はなく、例えばポリエチレン、ポリプロピレン、ポリ塩化ビニリデン、ポリ塩化ビニル、ポリスチレン等が挙げられる。中でも、成形加工性および工業的にポリエチレンやポリプロピレン等のポリオレフィン系樹脂能であることが好ましい。またこれらのホモポリマーを先述したコポリマーと混合し皮膜を形成した場合、皮膜強度が著しく向上するため、製品保存中や施肥機などの物理的、機械的な摩擦や衝撃などによって、皮膜が損傷する危険性も低下するので好ましい。
【００３１】
本発明の被覆粒状肥料における皮膜の膜厚は、所望の溶出制御性、保存安定性、皮膜強度および分解性等によって適宜選択すればよい。膜厚が薄過ぎると経済的に有利であるが、皮膜の強度が弱く、剥離や欠損が生じやすい。逆に膜厚が厚過ぎると皮膜の強度、初期の溶出防止性および長期間に亘る溶出制御性に優れるが、経済的に不利である。一般的には３０〜３００μｍ、中でも４０〜２００μｍ、特に４５〜１７５μｍとするのが好ましい。中でも水稲用の緩効性肥料とする際には５０〜２００μｍ、特に５０〜１４０μｍとするのが好ましい。
【００３２】
本発明における被覆粒状肥料の皮膜の被覆率（被覆される肥料粒の重量に対する皮膜の重量％）は通常、６〜２５重量％、好ましくは７〜２０重量％の範囲である。被覆率は、被覆粒状肥料の皮膜膜厚、肥料粒子径およびその比重を測定することにより、計算によって求めることができる。
【００３３】
本発明における被覆粒状肥料の皮膜中には、無機充填剤を含有させてもよい。無機充填材を本発明の被覆粒状肥料の被覆中に含有させることで、被覆粒状肥料の溶出制御調整や、温度依存性低減および皮膜の崩壊速度を制御することができるので好ましい。無機充填剤としては任意のものを使用できるが、例えばタルク、クレー、マイカ、モンモリロナイト、ベントナイト、活性白土、セピオライト、イモゴライト、セリサイト、ガラス繊維、ガラスビーズ、ガラスフレーク、シリカ系バルン、シリカ、珪藻土、フェライト類、水酸化カルシウム、水酸化マグネシウム、水酸化アルミニウム、炭酸カルシウム、炭酸マグネシウム、炭酸亜鉛、炭酸バリウム、ドーソナイト、ハイドロタルサイト、硫酸カルシウム、硫酸バリウム、石膏繊維、ケイ酸カルシウム、窒化アルミニウム、窒化ホウ素、窒化ケイ素、カーボンブラック、グラファイト、炭素繊維、炭素バルン、木炭粉末、各種金属粉、金属箔、アルミニウムボレート、炭化ケイ素、ホウ酸亜鉛、ホウ酸アルミニウム、黒鉛、リサージ、イオウなどが挙げられる。
【００３４】
中でも、皮膜強度を向上させる目的等で添加量を増加させても被覆粒状肥料の溶出制御性への影響が小さいもの、例えばタルク、クレー、マイカ、シリカ、炭酸カルシウムなどが好ましい。皮膜中の無機充填材の添加量は任意であるが、皮膜重量に対して１０〜８０重量％の範囲が好ましく、更には２０〜７５重量％、特に３０〜７０重量％とするのが好ましい。無機充填材の添加量が多過ぎると皮膜強度が極端に低下し、溶出制御性が低下する場合があり、逆に添加量が少な過ぎると充分な効果を得ることができない場合がある。また無機充填材は皮膜の連続性を阻害せず、且つ無機充填剤同士が凝集を起こさない程度の平均粒子径であることが好ましく、例えば膜厚の１／２以下の平均粒子径が好ましい。また、これらの無機充填材は、本発明の目的を損なわない範囲で一種または二種以上を任意の割合で併用してもよい。
【００３５】
また先述の無機充填剤と同様に、本発明の被覆粒状肥料においては、肥料成分の溶出速度を制御する目的で、その皮膜中に界面活性剤を含有させてもよい。界面活性剤としてはカチオン系、アニオン系、ノニオン系、及び両性界面活性剤の何れか任意のもの、およびこれらの混合物等を使用できる。中でも溶出制御の調整が容易で且つ被覆粒状肥料の保存安定性に優れたノニオン系界面活性剤が好ましい。ノニオン系界面活性剤としては、例えばポリオキシエチレンアルキルフェニルエーテル、ポリオキシエチレンアルキルエーテル、ポリオキシエチレンポリスチリルフェニルエーテル、ポリオキシエチレンポリオキシプロピレンアルキルエーテル、ポリオキシエチレンポリオキシプロピレングリコール、ポリエチレングリコール、グリコールエーテル、ポリエチレングリコール脂肪酸エステル、アルキロールアマイド、ソルビタン脂肪酸エステル、蔗糖脂肪酸エステル等が挙げられる。中でも、ポリオキシエチレンアルキルフェニルエーテル、ポリオキシエチレンアルキルエーテルが、少量の添加で溶出制御が行えるので特に好ましい。
【００３６】
界面活性剤のＨＬＢは任意であるが、通常３〜２０であればよい。皮膜中の界面活性剤の添加量は任意であるが、皮膜重量に対して０．０１〜２０重量％の範囲が好ましく、更には０．０５〜１５重量％、特に０．１〜１０重量％であることが好ましい。界面活性剤の添加量が多すぎると皮膜の親水性が高くなるため、溶出制御性が低下する場合があり、逆に添加量が少な過ぎると、溶出速度の制御に充分な効果を得ることができない場合がある。
【００３７】
更に、本発明の被覆粒状肥料皮膜の分解性を促進する目的で、皮膜中に生分解性資材を含有させてもよい。生分解性資材としては、自然界において微生物が関与して低分子化合物に分解されるものであればよい。例えば、３−ヒドロキシブチレートと３−ヒドロキシバリレートからなる共重合ポリエステル、バクテリアセルロース等に代表される微生物生産型樹脂、ポリアミノ酸、ポリグルタミン酸、ポリリジン、セルロース、澱粉、キチン・キトサン、アルギン酸、グルテン、コラーゲン、カードラン、プルラン、デキストラン、ゼラチン、リグニン、キサンタンガム、天然ゴム等に代表される天然化合物型樹脂、及びエチレングリコール、プロピレングリコール、ブタンジオール、ヘキサンジオール、ジプロピレングリコール等のジオール類から選ばれる１種とコハク酸、テレフタル酸、イソフタル酸、アジピン酸、セバシン酸等のジカルボン酸から選ばれる１種との脱水縮合により得られる脂肪族ポリエステル類、ポリε−カプロラクトン、ポリ乳酸、ポリグリコール酸等に代表される化学合成型樹脂が挙げられる。これらは一種又は二種以上を任意の割合で併用してもよい。添加量としては、溶出制御性、分解性、保存安定性を考慮して適宜決定されるが、概ね皮膜中の樹脂全体に対して０．０５〜５０重量％、好ましくは０．１〜２０重量％、特に好ましくは０．５〜１０重量％である。
【００３８】
また本発明の効果を損ねない範囲に於いて、被覆粒状肥料の保存安定性を考慮し、光安定剤や酸化防止剤を皮膜中に添加してもよい。例えば、芳香族アミン系、フェノール系、サリシレート系、ベンゾフェノン系、ベンゾトリアゾール系、ニッケル系、シアノアクリレート系、オキザリックアシッドアニリド系、ヒンダートアミン系などが挙げられる。その添加量は、溶出制御性、保存安定性を考慮して適宜決定され、通常皮膜重量に対して０．００１〜１０重量％、好ましくは０．０１〜１重量％程度である。
【００３９】
上述の様な添加物以外にも、皮膜中に他の肥料成分、農薬、植物生理活性物などの農業資材、または植物の生長促進物質などを添加してもよく、それらの資材の皮膜中の分散状態も適宜選択すればよい。さらに皮膜の撥水性により該被覆肥料が浮上する場合は、浮上防止のために皮膜表面に上述したような界面活性剤を展着等によって添加することが好ましい。添加量は溶出制御性、分解性、保存安定性、および皮膜の力学的強度を考慮して適宜選択すればよいが、通常、皮膜重量に対して０．１〜５．０重量％、好ましくは０．０１〜３．０重量％程度である。
【００４０】
本発明の被覆粒状肥料に用いる肥料成分粒子としては、従来公知の任意ものを使用でき、例えば尿素、硫安、塩安、硝安、石灰窒素、燐安、過燐酸石灰、重過石、重焼燐、塩加、硫加等の単肥の他に、Ｎ、Ｐ_２Ｏ_５、Ｋ_２Ｏ等の２成分以上からなる化成肥料、およびこれらを２種以上複合したバルクブレンド肥料が挙げられる。中でも溶出制御の観点から、肥料成分が高く肥効が最も顕著に現れる尿素が特に好ましい。また、肥料自体に溶出制御性のあるイソブチリデンジウレアなどの化合物型緩効性肥料を用いるとさらに多様な溶出制御性が得られるので好ましい。
【００４１】
肥料成分粒子の粒子径は任意であるが、通常０．５〜１５ｍｍ、好ましくは１〜５ｍｍである。肥料成分粒子の形状も任意であるが、真球性が高い程、被覆均一性が高くなるので好ましい。
【００４２】
本発明の被覆粒状肥料においては、上述した各項の好ましい範囲を組み合わせることで、保存中に皮膜の変質により溶出制御性を変化させることなく、長期間にわたり土壌中での溶出制御性が良好で、且つ溶出後の皮膜が土壌内外の自然環境下で崩壊または分解し、環境への負荷を低減できるので好ましい。具体的には、エチレンと炭素数が３以上のオレフィンのコポリマーおよび／または撥水化処理した澱粉、および金属酸化物を含む皮膜で被覆されてなる被覆粒状肥料である。特に、金属酸化物の含有量が、皮膜重量に対して５０％以下、好ましくは３０％以下、さらに好ましくは０．１〜２０％のとき、製品保存中での安定性と溶出後の皮膜の崩壊性または分解性を両立することができる。
【００４３】
本発明の被覆粒状肥料の製造方法及び装置は、従来公知の被覆肥料製造技術のうち、任意のものを適宜選択して採用すればよい。例えば装置自体の運動に付随して粒状物質を攪拌する回転ドラム式、回転パン式、回転落下式、気流で粒状物質を攪拌する流動式等の各型の被覆装置を用いた方法が挙げられる。中でも被覆中の粒状肥料を主として気流により攪拌し、肥料粒子に対する衝撃が小さい噴流層、流動層を用いる方法が好ましい。粒状肥料表面への被覆材の適用は、一般的に被覆材またはその皮膜溶液を噴霧することによって行い、噴霧には一流体もしくは二流体スプレーノズルを用いる。中でも噴霧粒子径が細かく、より均一に成膜できる二流体スプレーノズルが好ましい。また被覆均一性をより高くするために、スプレー位置を適宜変更できる装置が好ましい。
【００４４】
皮膜の被覆方法としては一般的に、溶剤を使用する方法（以下「溶剤法」と言うことがある。）と、溶剤を使用しない方法（以下「無溶剤法」と言うことがある。）とに分けられる。
溶剤法では用いる被覆材を溶剤に溶解及び／または分散した溶解液または分散液を肥料表面に噴霧後、瞬時に溶剤を乾燥させる方法で、被覆均一性が高くなるので好ましい。溶剤法で用いる溶剤種は任意であり、被覆材を溶解及び／または分散させるものであればよい。具体的には、クロロホルム、ジクロロメタン、トリクロロエチレン、テトラクロロエチレン等に代表される塩素化炭化水素系溶剤、ヘキサン、オクタン、トルエン、キシレン、ベンゼン、エチルシクロヘキサン等に代表される炭化水素系溶剤が好ましい。また先述の生分解資材を使用する場合は、水、エチルアルコール、イソプロピルアルコール、エチレングリコール、アセトン、メチルイソブチルケトン、アセトニトリル、ジオキサン、ジメチルホルムアミド、酢酸エチル、テトラヒドロフラン、ジメチルスルホキサイド等に代表される極性溶剤を用いればよい。
これら溶剤の除去および被覆材の乾燥は熱乾燥風下で実施されるが、そのガス種としては、空気のほかに窒素ガス、炭酸ガスなどの不活性ガスや、これらの混合ガス等が挙げられる。
【００４５】
一方無溶剤法は、具体的には被覆材の溶融物または溶融分散物を肥料表面に噴霧して被覆する方法や、さらには被覆後、表面を加熱溶融させて被覆均一性を高める方法が挙げられる。これらは溶剤を使用しないので安全性、経済性、環境負荷低減の面で好ましい。
【００４６】
本発明の皮膜の被覆においては、各製造条件の好適な範囲を選択することで、均一な皮膜を形成し、かつ溶出制御性に優れた被覆肥料を提供することができる。以下、溶剤法における製造条件について説明する。
【００４７】
本発明の被覆粒状肥料を溶媒法にて製造する際、用いる溶解液または分散液の全重量に対する被覆材の重量（以下「液濃度」と言うことがある。）は任意であるが、液濃度を高くすることで溶剤の使用量が低減し、被覆時間が短くなるので生産性の面からも好ましい。尚、用いる溶解液または分散液の粘度が高く、成膜中にスプレーノズル部で被覆材が閉塞し成膜が困難となる場合は、使用するスプレーノズルおよび噴霧圧力に応じて、適当な噴霧状態が得られる粘度になるように適宜調整すればよい。これらの観点から液濃度は好ましくは０．１〜３０重量％、さらに好ましくは０．５〜２５重量％、最も好ましくは１〜２０重量％である。
【００４８】
この溶解液または分散液の肥料粒子への時間当たりの噴霧量（スプレー速度）は、被覆均一性、生産性、および溶剤種により適宜選択すればよい。一般に噴霧量を多くし過ぎる（スプレー速度を速くし過ぎる）と溶剤の乾燥が不充分となり肥料粒同士が融着し易くなるので所望の成膜が困難となる場合がある。更には噴霧時間が短くなる結果、皮膜の均一性が低下する。逆に噴霧量が少な過ぎる（スプレー速度が遅すぎる）と噴霧液のミスト径が小さくなるため、肥料粒子に展着する前に被覆材が乾燥し、肥料表面での展着性が悪化する結果、皮膜の均一性が低下する場合がある。さらに被覆効率が低下し生産性の面からも好ましくない。これらの観点から、粒状肥料１ｋｇに対し、１分間あたりのスプレー速度は、例えば溶解または分散液における液濃度が５重量％の場合には２５〜３００ｇ／分・ｋｇ、好ましくは８０〜２５０ｇ／分・ｋｇの範囲である。
【００４９】
被覆を行う際の肥料粒子の表面温度（以下、「品温」ということがある。）および熱乾燥風量は特に限定されず、肥料粒子が融着することなく均一に混合され、安定した転動または噴流状態を維持し、かつ溶剤の除去および被覆材の乾燥が良好である範囲であればよい。しかし品温については影響を受け易く、一般に、高すぎると成膜中に皮膜材が軟化または溶融する結果、肥料粒同士が融着し成膜性が悪化する場合がある。逆に低すぎると乾燥が不充分となり成膜不良となる場合がある。これらの観点から、例えば噴霧する液の溶媒としてテトラクロロエチレンを使用する場合の品温は、好ましくは４０〜１３０℃の範囲であり、更に好ましくは５０〜１１０℃、最も好ましくは６０〜９０℃である。
【００５０】
先述の無機充填剤や界面活性剤は、本発明の被覆粒状肥料の被覆方法において、エチレンと炭素数が３以上のオレフィンのコポリマーおよび／または撥水性の澱粉、および金属酸化物を含む皮膜溶液中に、無機充填剤および／または界面活性剤を溶解または分散させて使用する方法が一般的である。但し、乾燥風とともにそのまま肥料粒に展着または付着させてもよい。また皮膜中での分散状態は目的に応じて適宜選択されるが、通常は皮膜の均一性を重視して均一に分散させることが好ましい。例えば無機充填剤は皮膜強度を制御するため、界面活性剤においては被覆肥料粒の浮上防止を抑制するために、皮膜の外殻に分散させるなどの濃度勾配があってもよい。
【００５１】
本発明の被覆粒状肥料の用途は特に限定されるものではなく、作物の養分要求特性に合わせて適宜選択される。例えば、シグモイド型の溶出パターンを示す被覆窒素肥料は、生育中期に窒素の追肥が必要な水稲の栽培で好適に使用される。また、リニアー型の溶出パターンを示す被覆窒素肥料は、水稲その他の作物の生育初期の元肥で好適に使用される。さらに、溶出制御期間が１年以上の被覆肥料は、樹木などの生育期間が長期にわたる永年植物に好適に使用される。
【００５２】
【実施例】
以下に実施例を示し、本発明をさらに具体的に説明するが、本発明はその要旨を超えない限り以下の実施例に限定されるものではない。
本発明においては、実施例で得られた被覆粒状肥料について、被覆率、欠陥粒子数、水中溶出特性および皮膜の引張強度の測定を実施した。さらに、これらの被覆粒状肥料について、皮膜の崩壊性を評価した。
【００５３】
なお、使用した各皮膜素材は以下の通りである。
・ホモポリマー；
低密度ポリエチレン（日本ポリケム社製、ＬＡ３２０、密度０．９２ｇ／ｃｍ^２、メルトフローレート１．１ｇ／１０ｍｉｎ、融点１１２℃、数平均分子量（Ｍｎ）１７９００、重量平均分子量（Ｍｗ）８８８００）
・コポリマー；
エチレン−１−ブテン共重合体（三井化学社製、タフマーＡ４０８５、密度０．８８ｇ／ｃｍ^２、メルトフローレート３．６ｇ／１０ｍｉｎ、数平均分子量（Ｍｎ）２９９００、重量平均分子量（Ｍｗ）７００００）
・金属酸化物；
二酸化チタンＡ−１００（石原産業社製、平均粒子径０．１５μｍ、アナタース形）
二酸化チタンＳＴ−０１（石原産業社製、平均粒子径７ｎｍ、アナタース形）
・有機金属化合物；
ステアリン酸鉄（ＩＩＩ）（キシダ化学社製、試薬グレード、純度９９％以上）
・撥水化澱粉；
（王子コーンスターチ社製、ビオレッツ、撥水性０．１ｍｌ、平均粒子径１５±５μｍ）
・無機充填材；
タルク（松村産業社製、ハイフィラー＃５０００ＰＪ、平均粒子径１．８μｍ）
・界面活性剤；
ノニオン系ポリオキシエチレンアルキルエーテル（東邦化学工業社製、ペグノールＳＴ−１２、ＨＬＢ１４．５）
【００５４】
（１）被覆肥料の製造
（実施例１）
低密度ポリエチレン８．８ｇ、エチレン−１−ブテン共重合体８．８ｇ、二酸化チタン（Ａ−１００）０．０４４ｇ、タルク２６．４ｇ、およびノニオン系ポリオキシエチレンアルキルエーテル１．３２ｇをテトラクロロエチレン８６３．２ｇに溶解させ、この溶液（液濃度５重量％、液温度９０℃）９０７．３ｇを、粒径２．８〜３．４ｍｍの尿素粒４００ｇに流動層式コーティング装置を使用し、スプレー速度１４３．８ｇ／分・ｋｇ、品温６０℃で噴霧被覆し、皮膜の平均膜厚９２．７μｍ、被覆率１１．２％（対尿素粒重量）の被覆粒状肥料４４４．８ｇを得た。上記の流動層式コーティング装置においては、槽内に充填した粒状肥料を、装置下部より導入される熱乾燥風および装置底部に設置される攪拌浴で流動させながら、これに被覆肥料を溶解または分散した噴霧液を噴霧後、さらに熱乾燥風にて溶剤を除去し、被覆材を乾燥することにより実施した。
【００５５】
（実施例２）
二酸化チタン（Ａ−１００）０．４４ｇを使用した以外は、実施例１と同様の方法により、皮膜の平均膜厚９１．９μｍ、被覆率１１．１％（対尿素粒重量）の被覆粒状肥料４４４．４ｇを得た。
【００５６】
（実施例３）
低密度ポリエチレン２３．８ｇ、二酸化チタン（ＳＴ−０１）３．５ｇ、タルク１７．６ｇ、撥水性澱粉２．６ｇおよびノニオン系ポリオキシエチレンアルキルエーテル０．６６ｇを使用した以外は、実施例１と同様の方法により、皮膜の平均膜厚１０２．７μｍ、被覆率１２．４％（対尿素粒重量）の被覆粒状肥料４４９．６ｇを得た。
【００５７】
（実施例４）
二酸化チタン（Ａ−１００）４．４ｇを使用した以外は、実施例１と同様の方法により、皮膜の平均膜厚８９．４μｍ、被覆率１０．８％（対尿素粒重量）の被覆粒状肥料４４３．２ｇを得た。
【００５８】
（実施例５）
二酸化チタン（Ａ−１００）２２ｇを使用した以外は、実施例１と同様の方法により、皮膜の平均膜厚８６．９μｍ、被覆率１０．５％（対尿素粒重量）の被覆粒状肥料４４２．０ｇを得た。
【００５９】
（比較例１）
低密度ポリエチレン８．８ｇ、エチレン−１−ブテン共重合体８．８ｇ、タルク２６．４ｇ、およびノニオン系ポリオキシエチレンアルキルエーテル１．３２ｇを使用した以外は、実施例１と同様の方法により、皮膜の平均膜厚９２．７μｍ、被覆率１１．２％（対尿素粒重量）の被覆粒状肥料４４４．８ｇを得た。
【００６０】
（比較例２）
低密度ポリエチレン３３０ｇ、エチレン−１−ブテン共重合体３３０ｇ、ステアリン酸鉄（ＩＩＩ）０．１６５ｇ、タルク９９０ｇ、およびノニオン系ポリオキシエチレンアルキル
エーテル６１．０５ｇをテトラクロロエチレン２５８５０ｇに溶解させ、この溶液（液濃度６重量％、液温度９０℃）２７５６０ｇを、粒径２．８〜３．４ｍｍの尿素粒１５０００ｇに流動層式コーティング装置を使用し、スプレー速度８８．９ｇ／分・ｋｇ、品温６０℃で噴霧被覆し、皮膜の平均膜厚７９．５μｍ、被覆率１０．８％（対尿素粒重量）の被覆粒状肥料１６６２０ｇを得た。
【００６１】
（比較例３）
ステアリン酸鉄（ＩＩＩ）０．８２５ｇを使用した以外は、比較例２と同様の方法により、
皮膜の平均膜厚７９．５μｍ、被覆率１０．８％（対尿素粒重量）の被覆粒状肥料１６６２０ｇを得た。
【００６２】
（比較例４）
ステアリン酸鉄（ＩＩＩ）１．６５ｇを使用した以外は、比較例２と同様の方法により、皮
膜の平均膜厚７８．７μｍ、被覆率１０．７％（対尿素粒重量）の被覆粒状肥料１６６０５ｇを得た。
【００６３】
（２）被覆肥料の被覆率の測定
被覆粒状肥料１０ｇを秤取り、小型粉砕器で粉砕した後、水を加えて尿素を溶解させ、皮膜のみを濾過回収した。さらにこの皮膜を乾燥した後秤量し、次式から被覆率を算出した。
被覆率（％）＝（皮膜重量［ｇ］／（１０−皮膜重量）［ｇ］）×１００
【００６４】
（３）被覆肥料の欠陥粒子数の測定
被覆肥料１０ｇ（総粒子数約４７０個）を試験管に秤取り、インク１０ｃｃを加え、４０
℃の恒温水中で１時間放置した後、被覆肥料を濾過回収する。被覆肥料に付着したインクを水洗すると皮膜の欠陥部分にインクの色が残るので、これにより欠陥皮膜を有する粒子を区別できる。欠陥粒子の数が多いほど、皮膜の強度が弱いかまたは被覆均一性が悪いため、皮膜の一部が損傷しやすく、施肥後の溶出制御が困難となる。従って、欠陥粒子数は少ないほど好ましい。
【００６５】
（４）被覆肥料の皮膜強度測定
被覆粒状肥料の皮膜の一部に微小孔を開け、水洗にて内部の肥料成分を完全に除去した後、常温、真空条件下にて該皮膜を完全に乾燥させた。さらに得られた皮膜粒子の中心部に糸を通し、図１のように両端を結びあわせ測定用サンプルとした。続いて、強度測定装置（島津ＥＺｔｅｓｔ−２０Ｎ）の両フックに、測定用サンプルの糸を固定し、２０ｍｍ／ｍｉｎの速度で一方に荷重を掛け、肥料粒子の破断点での重量を測定した。各サンプルにつき１０粒測定し、それらの最大値と最小値を除いた平均値を皮膜強度（ｇ／粒）とした。また、皮膜の強度を測定することで、保存時、流通時、機械施肥時の被覆肥料粒同士の摩擦や衝撃による皮膜の剥離や損傷、および溶出後の皮膜の崩壊または分解の程度の指標となる。なお、ここでいう皮膜強度とは、本測定法により測定した皮膜の引張り破断強度をいう。
【００６６】
本発明者等は、先に被覆肥料の皮膜強度と、皮膜の崩壊性に高い相関性があることを見出している（特開平１１−３２２４７９）。これによれば、皮膜強度が大きくなると崩壊の程度が小さくなり、逆に皮膜強度が小さくなると崩壊の程度が顕著となる傾向を示し、具体的には、皮膜強度が５０ｇ／粒未満であると皮膜に亀裂が生じやすくなる。従って、製造直後の被覆肥料における皮膜強度が５０ｇ／粒未満であると、保存時や流通時さらに施肥時における被覆肥料粒同士の摩擦や衝撃等により、皮膜の一部が亀裂または剥離し、溶出制御の機能を維持できない場合がある。一方皮膜強度が３００ｇ／粒より大きいと、溶出後の皮膜の崩壊または分解は期待できない。以上のことから、製造直後における皮膜強度は５０ｇ／粒〜３００ｇ／粒がよい。
【００６７】
（５）被覆肥料の溶出特性の評価
（１）で製造した被覆肥料を、２５℃恒温水中に７ｇ／２００ｃｃの割合で投じ、経時的
に水中の尿素態窒素を定量した。
【００６８】
実施例１〜５、および比較例１〜４で得られた各被覆肥料につき、製造処方、被覆率、欠陥粒子数および皮膜強度の結果を表１に、また溶出特性の結果を表２，３及び図２にまとめた。
【００６９】
【表１】

【００７０】
【表２】

【００７１】
【表３】

【００７２】
表１、図２及び表２、３の結果から、実施例および比較例に挙げるすべてにつき、被覆肥料の製造性は良好であり、被覆率、欠陥粒子数ともに目標レベルであった。また、皮膜強度についても、金属酸化物および有機金属化合物の添加量に殆ど影響なく、使用上強度的に問題ない範囲であることは明らかである。
【００７３】
（６）皮膜崩壊性の評価
（１）で製造した各被覆肥料について皮膜の崩壊性を以下のように実施した。＜前処理＞
被覆肥料をカッターミルで粉砕後水洗して尿素を除去し、真空乾燥機（常温）で乾燥させた。得られた皮膜片２ｇを精秤し、内径１４ｃｍの透明ガラス製シャーレの底面に均一に広げた。このとき、蓋をしても密閉されないようにシャーレ口にテープで段差をつけた。
＜露光処理＞
シャーレに蓋をし、日光を遮ることがない平面露地に静置し、約７ヶ月間露光処理した。
露光時期：９月５日〜４月１日
＜重量測定＞
一定期間露光後、シャーレに軽く蓋をした状態で、乾燥機（４５℃通風下）内で４時間乾燥後、室温まで冷却し重量を測定した。一定期間露光後の重量変化率を皮膜残存率（初期値を１００％）として算出した。
以上の結果を表１、４および図３に示した。
【００７４】
図３の結果から、実施例１〜５については、皮膜中の二酸化チタンの含有量が増加するとともに皮膜が崩壊または分解している。特に実施例５のように、二酸化チタンを皮膜中に５０重量％添加した場合においても、充分な皮膜強度を維持し且つ皮膜の崩壊性に優れていることがわかる。一方、比較例１については、二酸化チタンを含有していない皮膜は殆ど分解していない。また、比較例２〜４の結果から、ステアリン酸鉄（ＩＩＩ）を含有した
皮膜の場合、二酸化チタンと比較して皮膜の崩壊・分解速度が遅いことがわかる。特に、比較例４で示したように、ステアリン酸鉄（ＩＩＩ）と同量の二酸化チタンを添加した実施例
１と比較すれば明らかである。
【００７５】
【表４】

【００７６】
【発明の効果】
以上のことから、本発明の被覆粒状肥料は、特定のポリマー成分中に金属酸化物を相当量添加しても溶出制御性が良好で、かつ溶出後皮膜が自然環境下で速やかに崩壊または分解することにより、環境への負荷を軽減する。さらに、皮膜の力学的強度が優れ、他の肥料との配合時や輸送中および機械施肥時などにおいて、皮膜の一部が剥離または欠損等の損傷を受けず、且つ溶出制御性に影響を与えない。即ち、作物の生育期間中は安定した肥効成分の供給機能を有し、且つ製品保存中の安定性と環境中での皮膜の崩壊性を両立できる被覆粒状肥料である。
【図面の簡単な説明】
【図１】皮膜強度測定用サンプルを示す図。
【図２】被覆肥料の溶出特性を示す図。
【図３】被覆肥料の皮膜の崩壊性を示す図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coated granular fertilizer capable of controlling elution of a fertilizer component into soil in a fertilized environment. More specifically, the present invention resides in a coated granular fertilizer in which the elution of a fertilizer component into soil is stably performed, and the coating after the elution is rapidly disintegrated and decomposed, thereby reducing the load on the surrounding environment.
[0002]
[Prior art]
Cultivation of agricultural crops requires fertilizers according to the stage of growth, and several fertilizers have been conventionally applied, such as main fertilizer and top fertilizer, until the crop is harvested in order to meet the required time. In recent years, with the modernization of agriculture and the decrease in the agricultural population, there has been a need for the development of fertilizers that require less fertilization and require less fertilization, so that the elution of fertilizer components can be adapted to the nutrient requirements of crops. Various fertilizers have been developed to control.
[0003]
For example, in order to physically control the dissolution of fertilizer components applied to soil, coating of the surface of granular fertilizer with a polymer resin film has been widely studied, and some of them have been put to practical use. Specifically, there are various types such as a linear type elution type in which the elution curve of the fertilizer component is a straight line, and a sigmoid type elution type in which the elution curve of the fertilizer component is a straight line, using a polyolefin resin having low moisture permeability as a film material. Fertilization management according to the growth of crops becomes possible. These are disclosed in JP-B-54-3104, JP-B-60-3040, and JP-B-60-37074.
[0004]
However, in recent years, since such polyolefin resin is non-degradable, the shell of the shell has accumulated in the field where the coated granular fertilizer has been introduced, and furthermore, the shell has flowed out of the field, and as a result, has accumulated in the ecosystem. Environmental impact is a concern. Therefore, a technique has been proposed in which a biodegradable material is added to a polyolefin resin to cause the film to collapse. For example, as disclosed in JP-A-6-87684 and JP-A-11-322479, a method of adding a saccharide polymer and a derivative thereof as a biodegradable material, as disclosed in JP-A-9-263476. There is a method of adding an aliphatic polyester. However, these do not promote the decomposition of the polyolefin resin that occupies most of the coating material, and have a drawback that the control of dissolution in soil becomes unstable with the increase of biodegradable materials.
[0005]
In response to this, a technique using a biodegradable resin as a main component of the film has also been proposed. As the biodegradable resin, modified natural rubber (JP-A-59-92989, etc.) and various aliphatic polyesters ( JP-B-2-23517, JP-B-7-505, JP-A-4-89384, JP-A-5-85873, JP-A-7-33577, JP-A-7-61884, JP-A-7-315976, Japanese Patent Application Laid-Open Nos. 8-157290, 9-24977, and 10-7484) have been developed.
However, since these resins have high moisture permeability, it is difficult to form a sigmoid-type elution-type fertilizer having an elution stagnation period, and the biodegradation rate in soil is high, and the elution controllability is unstable.
[0006]
Further, a technique using a low molecular weight polyethylene, petroleum wax, paraffin wax, or the like as a main component of the coating for the purpose of imparting biodegradability to the coating material and maintaining long-term dissolution controllability has also been proposed. (JP-B-49-3339, JP-A-9-263476, JP-A-10-231190, JP-A-10-231191, JP-A-10-291880, JP-A-11-71192, and JP-A-11-263689. No.).
However, these materials have a low melting point of the film material, fertilizer particles fuse together during film formation, making film formation difficult, and the film has poor mechanical strength, that is, poor impact resistance and abrasion resistance. As a result, the film tends to be damaged due to a mechanical impact, so that the dissolution controllability becomes unstable, and the dissolution control originally expected cannot be performed.
[0007]
On the other hand, techniques for collapsing or decomposing the coating material itself by some action have been studied, but each has a problem and has not been solved yet.
For example, a technique in which a photodegradable resin is used as a main component of a film has been proposed, one using an ethylene / carbon monoxide copolymer as the photodegradable resin (Japanese Patent Publication No. 23516/1990), and one using a vinyl ketone copolymer. (Japanese Patent Publication No. 7-506), olefins / carbon monoxide / olefinically unsaturated compound copolymers (JP-A-6-56568), and a photodecomposition agent such as a metal complex. (JP-B-7-91143, JP-A-10-231190, JP-A-10-231191, JP-A-11-43391, and the like).
[0008]
Since these are decomposed only under conditions in which the coated granular fertilizer is exposed to sunlight or the like, it is not possible to avoid accumulation of the shell in the field and outflow outside the field. In addition, due to the poor dispersibility of the photodegrading agent in the film due to the manufacturing method, the disintegration or decomposition rate is liable to vary, and the dissolution controllability is changed. It is not compatible with the decomposability in the atmosphere.
[0009]
In addition, a film containing a substance that promotes an oxidative decomposition reaction in a polyolefin-based resin may be coated with a sublimable substance (JP-A-7-48194, JP-A-10-1386, etc.) or a water-soluble and non-sublimable fine powder. (JP-A-9-309784) and a technique for dispersing biodegradable polyester fine particles (JP-A-9-309784) have also been proposed.
However, these are susceptible to oxidative decomposition in soil systems because the coated granular fertilizer is susceptible to severe temperature and humidity changes during the period, and it is difficult to maintain stable elution control.
[0010]
As described above, conventionally, in order to decompose a film after elution as early as possible, techniques such as using a biodegradable material as an active ingredient of the film and increasing the absolute amount of a deterioration accelerator in the film have been proposed. In the former, however, it is difficult to control the dissolution in soil due to the high moisture permeability of the film, and in the latter, the continuity of the resin components in the formed film is impaired, and the mechanical strength of the film is high. As a result, there was a problem that the elution could not be controlled.
[0011]
[Problems to be solved by the invention]
The object of the present invention is to provide good dissolution controllability even when a considerable amount of a resin degradation accelerator is added to a specific resin film, and that the film after dissolution is rapidly disintegrated or decomposed in a natural environment, An object of the present invention is to provide a coated granular fertilizer with reduced environmental load.
[0012]
[Means for Solving the Invention]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, as a coating material in the coated granular fertilizer, a “copolymer of ethylene and an olefin having 3 or more carbon atoms and / or a water-repellent starch” is contained in the coating. By coating the fertilizer with a film that contains and metal oxide, the product has excellent stability during storage and excellent mechanical strength, good control over dissolution in soil, and disintegration of the film after dissolution. The present invention has been found to be a coated granular fertilizer that solves the above-mentioned problem that it can also impart decomposability, and has completed the present invention.
[0013]
That is, the present invention resides in a coated granular fertilizer in which the surface of the granular fertilizer is coated with a copolymer containing an olefin having 3 or more carbon atoms and ethylene and / or a water-repellent starch and a metal oxide.
[0014]
In the present invention, "disintegration" or "decomposition" of the film of the coated granular fertilizer means that, in addition to the mechanism of deterioration by exposure to light, particularly sunlight including ultraviolet rays, etc., under appropriate temperature and humidity conditions Mechanism of oxidation in the air by oxygen in the air, microorganisms in the soil reduce the molecular weight of the polymer material in the film and eventually break it down into water and carbon dioxide, in agricultural soil It also means the physical impact on the film during soil cultivation and crushing, the mechanism of compression and expansion of the soil due to changes in temperature and humidity, and the physical mechanism such as film collapse due to penetration of plant roots into the film. is there.
[0015]
For example, if the film strength is reduced to such an extent that the particle shape cannot be maintained due to such a chemical or physical mechanism, and furthermore, the film has collapsed to such an extent that it becomes extremely small, the particle state remains in the soil. Since it does not remain and is prevented from flowing out of the system by floating or the like, the environmental load is substantially suppressed. In this case, the coating film that has been miniaturized becomes more easily propagated by microorganisms, so that decomposition by a biological mechanism is promoted and eventually disappears.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
As a film material in the coated granular fertilizer of the present invention, a copolymer obtained by copolymerizing an olefin having 3 or more carbon atoms with ethylene is used. Due to its structure, the copolymer is preferably a low-density one having high flexibility, such as an amorphous or low-crystalline copolymer, and has physical and mechanical frictions during product storage and fertilizer application. The film is hardly damaged by impact or the like, and exhibits good elution controllability during the elution period.
[0017]
Any olefin having 3 or more carbon atoms constituting the copolymer used in the present invention can be used. Specifically, for example, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, -Methyl-1-hexene, 5-methyl-1-hexene, 1-octene, 5-methyl-1-heptene, 1-dodecene, 1-octadodecene and the like. Among them, propylene, 1-butene, isobutene, and the like having high compatibility with polyethylene and polypropylene represented by olefin homopolymers are preferable. These olefins may be used alone or in any combination of two or more.
[0018]
If the content of the olefin having 3 or more carbon atoms in the copolymer is small, the impact strength of the entire coating film may decrease. Conversely, if the content is large, the whole film becomes soft, which may result in film defects such as pinholes or increase in moisture permeability of the whole film, making it difficult to control elution. From these facts, the content of the olefin having 3 or more carbon atoms in the copolymer is preferably from 0.1 to 50 mol%, particularly preferably from 1 to 10 mol%. The content of the copolymer in the components constituting the film is from 10 to 80% by weight, preferably from 30 to 65% by weight, based on the weight of the film. One or more copolymers of ethylene and an olefin having 3 or more carbon atoms may be used in any proportion as long as the object of the present invention is not impaired.
[0019]
In the present invention, starch coated with water repellency (hereinafter sometimes referred to as “water repellent starch”) is used as a coating material of the granular coated fertilizer in combination with the above-mentioned copolymer or in place of the copolymer. May be used. The use of this water-repellent starch is preferable since the water-repellent starch in the film gradually undergoes biodegradation after fertilization of the granular coated fertilizer of the present invention, thereby improving the disintegration and degradability of the film.
[0020]
Since so-called untreated starch obtained from natural products is biodegraded in a few days in the natural environment, the coated fertilizer containing such untreated starch in the film, the starch in the film shortly after fertilization is applied. Is biodegraded, and the dissolution controllability becomes unstable. In the present invention, by using the water-repellent starch, the dissolution controllability can be stabilized over a long period of time after fertilization, and a coated fertilizer excellent in disintegration and degradability of the film after dissolution can be obtained.
Furthermore, the use of water-repellent starch makes the surface of the film low moisture permeable, and this low moisture permeability makes it possible to suppress the elution of fertilizer components in the coated granular fertilizer for a certain period after fertilization, and to allow rapid elution thereafter. Become. Therefore, when the coated granular fertilizer of the present invention is used as a sigmoid-type elution-type coated granular fertilizer, it is preferable to use this water-repellent starch.
[0021]
As a raw material of the water-repellent starch, so-called untreated starch, one made from any grain can be used. Specific cereals include, for example, corn, tapioca, potato, sweet potato, wheat, rice, sago and the like. As the water-repellent starch raw material used in the present invention, corn-derived starch excellent in productivity, processability, and biodegradability is particularly preferable. The water-repellent starch in the present invention refers to starch and derivatives thereof in which starch collected and purified from these crops is made water-repellent by a chemical treatment and the solubility in water at room temperature is reduced.
[0022]
The method of the water repellent treatment and the degree of the water repellency may be appropriately selected, and examples thereof include a method in which various reactive functional groups are bonded to the hydroxyl groups of an anhydrous glucose residue of starch. The water-repellent starch in the present invention may be a starch treated by another method, for example, an esterified starch obtained by reacting an inorganic acid such as sulfuric acid, nitric acid, phosphoric acid or succinic acid and an organic acid or a salt thereof. , Methylation, carboxymethylation, alkylation treatment such as hydroxymethylation or etherified starch obtained by introducing a primary, secondary, tertiary alkylamine or quaternary alkylammonium salt, or formalin, aldehyde, phosphorus Cross-linked starch obtained by binding a polyfunctional group between the hydroxyl groups of starch by the action of an acid, and organic polymer substances such as polyacrylamide, polyacrylic acid, polyvinyl acetate and polyacrylonitrile are chemically added to the starch. It also includes a grafted starch obtained by binding.
[0023]
Among them, esterified starch and etherified starch are preferable because the water-repellent treatment is relatively easy. In this case, since the degree of water repellency depends on the hydrophobicity of the functional group to be introduced, the functional group may be appropriately modified according to the purpose. The water repellency in the present invention refers to the sedimentation volume of water repellent starch when 75 ml of water and 5 g of water repellent starch are placed in a 100 ml measuring cylinder, shaken vigorously 20 times, and allowed to stand for 1 hour. As for the measured values obtained, lower values indicate higher water repellency. The higher the degree of water repellency, the better. However, if the degree of water repellency is too large, the disintegration or decomposability of the film may not be sufficiently exhibited. For this reason, the water repellency of the starch is less than 10 ml, preferably 0.1 to 0.5 ml.
[0024]
The content of the water-repellent starch in the coating in the coated granular fertilizer of the present invention may be appropriately selected. However, if the content is too small, the initial elution prevention period cannot be secured, and if it is too large, the entire coating is repelled. It becomes water-based, and fertilizer particles may float up during fertilization and flow out of the system. Therefore, the content of the water-repellent starch is preferably 1 to 50%, more preferably 5 to 30%, based on the weight of the film.
[0025]
Further, the average particle size of the water-repellent starch is optional, but is preferably a uniform particle size that does not inhibit the continuity of the film in the coated granular fertilizer of the present invention and does not cause aggregation of the starch particles. For example, the average particle diameter is preferably not more than 1/2 of the film thickness. These water-repellent starches may be used alone or in combination of two or more at an arbitrary ratio as long as the object of the present invention is not impaired.
As described above, by appropriately setting the degree of treatment of the water-repellent starch, the content in the film, the average particle size and the method of addition, the coated granular fertilizer of the present invention can be coated with various elution types. can do.
[0026]
As the metal oxide used in the present invention, any metal oxide can be used, and one or two or more kinds may be used in an arbitrary ratio as long as the object of the present invention is not impaired.
Above all, it is preferable that the polyolefin resin promotes the deterioration by light, particularly sunlight, and imparts the property of decomposing or decomposing the resin under a natural environment.Specifically, for example, titanium dioxide, red iron oxide, graphite, Examples include alumina, cobalt green, cobalt blue, ultramarine, zinc oxide (zinc white), and chromium oxide.
Among them, titanium dioxide is preferred because it has a low effect on the surrounding environment, is stable under the use environment, has good handling properties, and has a high photochemically decomposing activity. Titanium dioxide has an anatase type, a rutile type and a brookite type in crystal structure. Among them, the anatase type is preferable because it has high photochemical activity and easily decomposes organic substances.
[0027]
As the titanium dioxide used in the present invention, any one obtained by any method can be used. As a general production method, for example, a titanium dioxide obtained by hydrolyzing a solution obtained by reacting a raw material ilmenite ore with concentrated sulfuric acid is used. Sulfuric acid method in which the hydroxide of the above is calcined at a high temperature, and a chlorine method in which the raw material rutile ore is reacted with chlorine gas in a high-temperature furnace at about 1000 ° C. to burn titanium tetrachloride.
[0028]
The metal oxide used in the present invention may be subjected to a surface treatment. For example, when using titanium dioxide particles as a metal oxide, it is preferable to treat the surface with silica, aluminum, or the like, since the activity with respect to organic substances can be controlled. Further, by treating the surface with a hydrated oxide such as Al or Si, the affinity with the medium and the dispersibility can be improved. It is preferable to optimize the surface treatment of the metal oxide and the content of the metal oxide in the film as it is possible to control the disintegration / decomposition rate and the elution rate of the film.
[0029]
The content of the metal oxide in the coating may be appropriately selected.However, if the content is small, the disintegration or decomposability of the coating cannot be obtained, and if the content is large, the decomposition is promoted more than necessary. May be deteriorated and elution control may be difficult. From these facts, the content of the metal oxide in the coating is 50% by weight or less, preferably 30% by weight or less, and more preferably 0.1 to 20% by weight. In addition, these metal oxides may be used alone or in combination of two or more at an arbitrary ratio as long as the object of the present invention is not impaired. Further, it is preferable to uniformly disperse the metal oxide in the film so that the effect can be sufficiently exhibited. For example, when the polymer component and the metal oxide in the present invention are completely dissolved or dispersed in a suitable organic solvent and spray-spread on fertilizer granules, these metal oxides are uniformly formed in the formed film. It is preferable because it is dispersed.
[0030]
Furthermore, the coated granular fertilizer of the present invention may contain an olefin homopolymer in the film. The type of the olefin homopolymer is not particularly limited, and examples thereof include polyethylene, polypropylene, polyvinylidene chloride, polyvinyl chloride, and polystyrene. Among them, it is preferable that the resin has a polyolefin resin such as polyethylene and polypropylene in terms of moldability and industrial properties. When these homopolymers are mixed with the above-mentioned copolymer to form a film, the film strength is significantly improved, and the film is damaged by physical and mechanical friction and impact during storage of products and fertilizers. This is preferable because the risk is reduced.
[0031]
The film thickness of the film in the coated granular fertilizer of the present invention may be appropriately selected depending on desired elution controllability, storage stability, film strength, decomposability and the like. If the film thickness is too thin, it is economically advantageous, but the strength of the film is weak, and peeling or breakage tends to occur. Conversely, if the film thickness is too large, the strength of the film, the initial dissolution preventing property and the control of dissolution over a long period of time are excellent, but it is economically disadvantageous. Generally, it is preferably 30 to 300 μm, particularly preferably 40 to 200 μm, particularly preferably 45 to 175 μm. In particular, when it is used as a slow-release fertilizer for paddy rice, the thickness is preferably 50 to 200 μm, particularly preferably 50 to 140 μm.
[0032]
In the present invention, the coverage of the coating of the coated granular fertilizer (weight% of the coating with respect to the weight of the fertilizer particles to be coated) is usually in the range of 6 to 25% by weight, preferably 7 to 20% by weight. The coverage can be determined by calculation by measuring the film thickness of the coated granular fertilizer, the particle diameter of the fertilizer, and the specific gravity thereof.
[0033]
In the film of the coated granular fertilizer in the present invention, an inorganic filler may be contained. It is preferable to include an inorganic filler in the coating of the coated granular fertilizer of the present invention because it is possible to control the dissolution control of the coated granular fertilizer, reduce the temperature dependency, and control the disintegration rate of the coating. As the inorganic filler, any one can be used. , Ferrites, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dawsonite, hydrotalcite, calcium sulfate, barium sulfate, gypsum fiber, calcium silicate, aluminum nitride, Boron nitride, silicon nitride, carbon black, graphite, carbon fiber, carbon balun, charcoal powder, various metal powders, metal foil, aluminum borate, silicon carbide, zinc borate, aluminum borate, graphite, litharge, sulfur Etc., and the like.
[0034]
Among them, those having little influence on the dissolution controllability of the coated granular fertilizer even when the added amount is increased for the purpose of improving the film strength, for example, talc, clay, mica, silica, calcium carbonate and the like are preferable. The addition amount of the inorganic filler in the coating is optional, but is preferably in the range of 10 to 80% by weight, more preferably 20 to 75% by weight, particularly preferably 30 to 70% by weight, based on the weight of the coating. If the added amount of the inorganic filler is too large, the film strength may be extremely reduced, and the dissolution controllability may be reduced. Conversely, if the added amount is too small, a sufficient effect may not be obtained. The inorganic filler preferably has an average particle diameter that does not hinder the continuity of the film and does not cause aggregation between the inorganic fillers, and for example, an average particle diameter of １／ or less of the film thickness is preferable. These inorganic fillers may be used alone or in combination of two or more at an arbitrary ratio as long as the object of the present invention is not impaired.
[0035]
Further, like the above-mentioned inorganic filler, in the coated granular fertilizer of the present invention, a surfactant may be contained in the film for the purpose of controlling the elution rate of the fertilizer component. As the surfactant, any one of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant, a mixture thereof and the like can be used. Among them, a nonionic surfactant which is easy to adjust the dissolution control and has excellent storage stability of the coated granular fertilizer is preferable. Examples of the nonionic surfactant include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene polystyryl phenyl ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyethylene glycol, Glycol ether, polyethylene glycol fatty acid ester, alkylol amide, sorbitan fatty acid ester, sucrose fatty acid ester and the like. Among them, polyoxyethylene alkyl phenyl ether and polyoxyethylene alkyl ether are particularly preferable because elution can be controlled by adding a small amount.
[0036]
The HLB of the surfactant is optional, but may be generally 3 to 20. The addition amount of the surfactant in the coating is optional, but is preferably in the range of 0.01 to 20% by weight, more preferably 0.05 to 15% by weight, particularly 0.1 to 10% by weight based on the weight of the coating. It is preferable that If the amount of the surfactant added is too large, the hydrophilicity of the film becomes high, so that the elution controllability may decrease.On the other hand, if the amount is too small, a sufficient effect for controlling the elution rate may be obtained. It may not be possible.
[0037]
Furthermore, a biodegradable material may be contained in the coated granular fertilizer film for the purpose of promoting the degradability of the film. The biodegradable material may be any material as long as it is decomposed into low molecular compounds by a microorganism in nature. For example, a copolymerized polyester composed of 3-hydroxybutyrate and 3-hydroxyvalerate, a microorganism-producing resin represented by bacterial cellulose, polyamino acid, polyglutamic acid, polylysine, cellulose, starch, chitin / chitosan, alginic acid, gluten , Collagen, curdlan, pullulan, dextran, gelatin, lignin, xanthan gum, natural compounds represented by natural rubber and the like, and diols such as ethylene glycol, propylene glycol, butanediol, hexanediol and dipropylene glycol. Aliphatic polyesters, polyε-caprolactone, poly (polyester) obtained by dehydration condensation of one of the above-mentioned ones with one of dicarboxylic acids such as succinic acid, terephthalic acid, isophthalic acid, adipic acid and sebacic acid. Acid, chemically synthetic resin typified by polyglycolic acid, and the like. These may be used alone or in combination of two or more at an arbitrary ratio. The addition amount is appropriately determined in consideration of dissolution controllability, decomposability and storage stability, but is generally 0.05 to 50% by weight, preferably 0.1 to 20% by weight based on the whole resin in the film. %, Particularly preferably 0.5 to 10% by weight.
[0038]
In addition, as long as the effect of the present invention is not impaired, a light stabilizer or an antioxidant may be added to the film in consideration of the storage stability of the coated granular fertilizer. Examples thereof include aromatic amines, phenols, salicylates, benzophenones, benzotriazoles, nickels, cyanoacrylates, oxalic acid anilides, and hindered amines. The addition amount is appropriately determined in consideration of the dissolution controllability and storage stability, and is usually about 0.001 to 10% by weight, preferably about 0.01 to 1% by weight, based on the weight of the film.
[0039]
In addition to the additives as described above, other fertilizer components, agricultural chemicals, agricultural materials such as plant physiologically active substances, or plant growth promoting substances may be added to the film. The dispersion state may be appropriately selected. Further, when the coated fertilizer floats due to the water repellency of the film, it is preferable to add the above-described surfactant to the surface of the film by spreading or the like in order to prevent floating. The amount to be added may be appropriately selected in consideration of dissolution controllability, decomposability, storage stability, and mechanical strength of the film, but is usually 0.1 to 5.0% by weight, preferably 0.1 to 5.0% by weight, based on the weight of the film. It is about 0.01 to 3.0% by weight.
[0040]
As the fertilizer component particles used for the coated granular fertilizer of the present invention, any conventionally known fertilizer component particles can be used, for example, urea, ammonium sulfate, salt ammonium, ammonium nitrate, lime nitrogen, phosphorus ammonium, superphosphate, heavy persulfate, heavy burnt phosphorus. , Salting, vulcanization, etc., N, P ₂ O ₅ , K ₂ Chemical fertilizers composed of two or more components such as O, and bulk blend fertilizers in which two or more of these are combined are exemplified. Among them, urea is particularly preferable from the viewpoint of elution control, in which the fertilizer component is high and the fertilizer effect is most conspicuous. In addition, it is preferable to use a compound-type slow-release fertilizer such as isobutylidene diurea, which has elution controllability in the fertilizer itself, because more various elution controllability can be obtained.
[0041]
The particle diameter of the fertilizer component particles is arbitrary, but is usually 0.5 to 15 mm, preferably 1 to 5 mm. The shape of the fertilizer component particles is also optional, but the higher the sphericity, the better the uniformity of coating.
[0042]
In the coated granular fertilizer of the present invention, by combining the preferred ranges of the above-mentioned items, without changing the dissolution controllability due to deterioration of the film during storage, the dissolution controllability in soil over a long period of time is good. In addition, it is preferable because the film after dissolution is disintegrated or decomposed in the natural environment inside and outside the soil, and the load on the environment can be reduced. Specifically, it is a coated granular fertilizer coated with a film containing a copolymer of ethylene and an olefin having 3 or more carbon atoms and / or a starch treated with water repellency, and a metal oxide. In particular, when the content of the metal oxide is 50% or less, preferably 30% or less, more preferably 0.1 to 20%, based on the weight of the film, the stability during storage of the product and the film after elution Both disintegration and degradability can be achieved.
[0043]
The method and apparatus for producing a coated granular fertilizer of the present invention may be appropriately selected and adopted from among conventionally known techniques for producing coated fertilizer. For example, a method using a coating device of each type such as a rotary drum type, a rotary pan type, a rotary drop type, and a flow type in which the granular material is agitated by an air flow, which agitates the granular material in association with the movement of the device itself, may be used. Among them, a method in which the granular fertilizer being coated is mainly stirred by an air stream and a spouted bed or a fluidized bed which has a small impact on the fertilizer particles is preferable. Application of the dressing to the surface of the granular fertilizer is generally carried out by spraying the dressing or its coating solution, using a one-fluid or two-fluid spray nozzle. Among them, a two-fluid spray nozzle having a fine spray particle diameter and capable of forming a film more uniformly is preferable. In order to further increase the coating uniformity, a device that can appropriately change the spray position is preferable.
[0044]
In general, a coating method of a film includes a method using a solvent (hereinafter sometimes referred to as a “solvent method”) and a method not using a solvent (hereinafter sometimes referred to as a “solventless method”). Divided into
The solvent method is preferable because a coating solution to be used is dissolved and / or dispersed in a solvent and a solution or dispersion liquid is sprayed onto the surface of the fertilizer, and then the solvent is dried instantaneously. The type of solvent used in the solvent method is arbitrary, and may be any as long as it can dissolve and / or disperse the coating material. Specifically, chlorinated hydrocarbon solvents such as chloroform, dichloromethane, trichloroethylene and tetrachloroethylene, and hydrocarbon solvents such as hexane, octane, toluene, xylene, benzene, and ethylcyclohexane are preferred. When using the biodegradable material described above, water, ethyl alcohol, isopropyl alcohol, ethylene glycol, acetone, methyl isobutyl ketone, acetonitrile, dioxane, dimethylformamide, ethyl acetate, tetrahydrofuran, dimethyl sulfoxide and the like are represented. A polar solvent may be used.
The removal of the solvent and the drying of the coating material are performed under a hot drying wind. Examples of the gas species include air, an inert gas such as a nitrogen gas and a carbon dioxide gas, and a mixed gas thereof.
[0045]
On the other hand, the solventless method specifically includes a method of spraying a melt or a melt dispersion of a coating material onto a fertilizer surface to coat the fertilizer, and a method of heating and melting the surface after coating to improve coating uniformity. Can be Since these do not use a solvent, they are preferable in terms of safety, economy and reduction of environmental load.
[0046]
In the coating of the film of the present invention, by selecting a suitable range of each production condition, it is possible to form a uniform film and provide a coated fertilizer excellent in elution controllability. Hereinafter, the manufacturing conditions in the solvent method will be described.
[0047]
When the coated granular fertilizer of the present invention is produced by a solvent method, the weight of the coating material (hereinafter sometimes referred to as “liquid concentration”) with respect to the total weight of the dissolving solution or dispersion used is arbitrary, but the liquid concentration is not limited. By increasing the value, the amount of solvent used is reduced, and the coating time is shortened, which is also preferable from the viewpoint of productivity. If the solution or dispersion used has a high viscosity and the coating material is blocked at the spray nozzle during film formation, making it difficult to form a film, an appropriate spray state may be selected according to the spray nozzle and spray pressure used. May be appropriately adjusted so that the viscosity is obtained. From these viewpoints, the liquid concentration is preferably 0.1 to 30% by weight, more preferably 0.5 to 25% by weight, and most preferably 1 to 20% by weight.
[0048]
The spray amount (spray speed) of this solution or dispersion onto fertilizer particles per hour may be appropriately selected depending on coating uniformity, productivity, and solvent type. In general, if the spray amount is too large (the spray speed is too high), drying of the solvent is insufficient and fertilizer particles are easily fused to each other, so that a desired film formation may be difficult. Furthermore, as a result of the shorter spraying time, the uniformity of the coating decreases. Conversely, if the spray amount is too small (spray speed is too slow), the mist diameter of the spray liquid becomes small, so the coating material dries before spreading on the fertilizer particles, resulting in poor spreadability on the fertilizer surface. In addition, the uniformity of the film may be reduced. Further, the coating efficiency is reduced, which is not preferable in terms of productivity. From these viewpoints, for 1 kg of granular fertilizer, the spray rate per minute is, for example, 25 to 300 g / min · kg, preferably 80 to 250 g / min when the concentration of the solution in the dissolution or dispersion is 5% by weight.・ It is in the range of kg.
[0049]
The surface temperature of the fertilizer particles (hereinafter, sometimes referred to as “product temperature”) and the amount of hot drying air at the time of coating are not particularly limited, and the fertilizer particles are uniformly mixed without fusing, and are stably rolled. Alternatively, the temperature may be within a range in which the jet state is maintained and the removal of the solvent and the drying of the coating material are good. However, the product temperature is easily affected. In general, if the temperature is too high, the film material softens or melts during film formation, so that fertilizer particles may fuse with each other to deteriorate the film formability. Conversely, if it is too low, drying may be insufficient and film formation may be poor. From these viewpoints, for example, when using tetrachloroethylene as the solvent of the liquid to be sprayed, the product temperature is preferably in the range of 40 to 130 ° C, more preferably 50 to 110 ° C, and most preferably 60 to 90 ° C. .
[0050]
In the coating method of the coated granular fertilizer of the present invention, the inorganic filler and the surfactant described above are used in a coating solution containing a copolymer of ethylene and an olefin having 3 or more carbon atoms and / or a water-repellent starch, and a metal oxide. In general, a method of dissolving or dispersing an inorganic filler and / or a surfactant is used. However, it may be spread or adhered to the fertilizer grains as they are together with the drying air. The state of dispersion in the film is appropriately selected depending on the purpose, but it is usually preferable to uniformly disperse the film in consideration of the uniformity of the film. For example, the inorganic filler may have a concentration gradient such as dispersing it in the outer shell of the film in order to control the film strength, and in the case of the surfactant, in order to suppress the floating of the coated fertilizer particles from occurring.
[0051]
The use of the coated granular fertilizer of the present invention is not particularly limited, and is appropriately selected according to the nutrient requirement characteristics of the crop. For example, a coated nitrogen fertilizer exhibiting a sigmoid-type elution pattern is suitably used for cultivation of paddy rice that requires nitrogen topdressing during the middle stage of growth. A coated nitrogen fertilizer having a linear elution pattern is suitably used as a primary fertilizer in the early growth stage of paddy rice and other crops. Further, the coated fertilizer having an elution control period of one year or more is suitably used for a perennial plant having a long growth period such as a tree.
[0052]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.
In the present invention, the coverage, the number of defective particles, the dissolution characteristics in water and the tensile strength of the film were measured for the coated granular fertilizer obtained in the examples. Furthermore, the disintegration of the film was evaluated for these coated granular fertilizers.
[0053]
The coating materials used are as follows.
・ Homopolymer;
Low density polyethylene (LA320, density 0.92 g / cm, manufactured by Nippon Polychem Co., Ltd.) ² , Melt flow rate 1.1 g / 10 min, melting point 112 ° C., number average molecular weight (Mn) 17900, weight average molecular weight (Mw) 88800)
A copolymer;
Ethylene-1-butene copolymer (manufactured by Mitsui Chemicals, Tuffmer A4085, density 0.88 g / cm) ² , Melt flow rate 3.6 g / 10 min, number average molecular weight (Mn) 29900, weight average molecular weight (Mw) 70000)
.Metal oxides;
Titanium dioxide A-100 (Ishihara Sangyo Co., Ltd., average particle diameter 0.15 μm, anatase type)
Titanium dioxide ST-01 (Ishihara Sangyo Co., Ltd., average particle diameter 7 nm, anatase type)
· Organometallic compounds;
Iron (III) stearate (manufactured by Kishida Chemical Co., reagent grade, purity 99% or more)
Water-repellent starch;
(Oji Corn Starch Co., Ltd., Bioretz, 0.1 ml water repellency, average particle size 15 ± 5 μm)
・ Inorganic filler;
Talc (Matsumura Sangyo Co., Ltd., High Filler # 5000PJ, average particle size 1.8 μm)
A surfactant;
Nonionic polyoxyethylene alkyl ether (Pegnol ST-12, HLB 14.5, manufactured by Toho Chemical Industry Co., Ltd.)
[0054]
(1) Manufacture of coated fertilizer
(Example 1)
8.8 g of low-density polyethylene, 8.8 g of an ethylene-1-butene copolymer, 0.044 g of titanium dioxide (A-100), 26.4 g of talc, and 1.32 g of nonionic polyoxyethylene alkyl ether were converted to 863. 90 g of this solution (liquid concentration 5% by weight, liquid temperature 90 ° C.) was applied to 400 g of urea particles having a particle size of 2.8 to 3.4 mm using a fluidized bed type coating apparatus at a spray rate of 143 g. Spray coating was performed at 2.8 g / min.kg at a product temperature of 60 ° C. to obtain 444.8 g of a coated granular fertilizer having an average film thickness of 92.7 μm and a coverage of 11.2% (based on urea particles). In the above-mentioned fluidized bed type coating apparatus, the granular fertilizer filled in the tank is melted or dispersed in the hot fertilizer introduced from the lower part of the apparatus and the stirring bath installed at the bottom of the apparatus while the granular fertilizer is fluidized. After spraying the spray liquid thus obtained, the solvent was further removed by hot drying air, and the coating material was dried.
[0055]
(Example 2)
Except that 0.44 g of titanium dioxide (A-100) was used, a coated granular fertilizer having an average film thickness of 91.9 μm and a coverage of 11.1% (based on the weight of urea particles) was obtained in the same manner as in Example 1. 444.4 g were obtained.
[0056]
(Example 3)
Example 1 was repeated except that 23.8 g of low density polyethylene, 3.5 g of titanium dioxide (ST-01), 17.6 g of talc, 2.6 g of water-repellent starch, and 0.66 g of nonionic polyoxyethylene alkyl ether were used. In a similar manner, 449.6 g of a coated granular fertilizer having an average film thickness of 102.7 μm and a coverage of 12.4% (based on the weight of urea particles) was obtained.
[0057]
(Example 4)
Except that 4.4 g of titanium dioxide (A-100) was used, a coated granular fertilizer having an average film thickness of 89.4 μm and a coverage of 10.8% (based on the weight of urea particles) was prepared in the same manner as in Example 1. 443.2 g were obtained.
[0058]
(Example 5)
Except that 22 g of titanium dioxide (A-100) was used, a coated granular fertilizer 442. having an average film thickness of 86.9 μm and a coverage of 10.5% (based on urea particles) was obtained in the same manner as in Example 1. 0 g was obtained.
[0059]
(Comparative Example 1)
Except for using 8.8 g of low-density polyethylene, 8.8 g of ethylene-1-butene copolymer, 26.4 g of talc, and 1.32 g of nonionic polyoxyethylene alkyl ether, a method similar to that of Example 1 was used. 444.8 g of a coated granular fertilizer having an average film thickness of 92.7 μm and a coverage of 11.2% (based on the weight of urea particles) was obtained.
[0060]
(Comparative Example 2)
330 g of low density polyethylene, 330 g of ethylene-1-butene copolymer, 0.165 g of iron (III) stearate, 990 g of talc, and nonionic polyoxyethylene alkyl
61.05 g of ether was dissolved in 25850 g of tetrachloroethylene, and 27560 g of this solution (liquid concentration: 6% by weight, liquid temperature: 90 ° C.) was applied to 15000 g of urea particles having a particle size of 2.8 to 3.4 mm using a fluidized bed type coating apparatus. The spray coating was performed at a spray rate of 88.9 g / min.kg at a product temperature of 60 ° C. to obtain 16620 g of a coated granular fertilizer having an average film thickness of 79.5 μm and a coverage of 10.8% (based on the weight of urea particles).
[0061]
(Comparative Example 3)
Except that 0.825 g of iron (III) stearate was used, a method similar to that of Comparative Example 2 was used.
16620 g of a coated granular fertilizer having an average film thickness of 79.5 μm and a coverage of 10.8% (based on the weight of urea particles) was obtained.
[0062]
(Comparative Example 4)
Skin was prepared in the same manner as in Comparative Example 2 except that 1.65 g of iron (III) stearate was used.
16605 g of a coated granular fertilizer having an average film thickness of 78.7 μm and a coverage of 10.7% (based on the weight of urea particles) was obtained.
[0063]
(2) Measurement of coverage rate of coated fertilizer
After 10 g of the coated granular fertilizer was weighed and pulverized by a small pulverizer, water was added to dissolve urea, and only the film was collected by filtration. The coating was dried and weighed, and the coverage was calculated from the following equation.
Coverage (%) = (coating weight [g] / (10-coating weight) [g]) × 100
[0064]
(3) Measurement of the number of defective particles in coated fertilizer
10 g of the coated fertilizer (total number of particles: about 470) was weighed into a test tube, and 10 cc of the ink was added.
After standing for 1 hour in constant temperature water at ℃, the coated fertilizer is collected by filtration. When the ink attached to the coated fertilizer is washed with water, the color of the ink remains at the defective portion of the film, so that the particles having the defective film can be distinguished. The greater the number of defective particles, the lower the strength of the film or the poorer the uniformity of the coating, so that a portion of the film is easily damaged, and it is difficult to control the dissolution after fertilization. Therefore, the smaller the number of defective particles, the better.
[0065]
(4) Film strength measurement of coated fertilizer
Micropores were formed in a part of the film of the coated granular fertilizer, and the inside fertilizer components were completely removed by washing with water, and then the film was completely dried under normal temperature and vacuum conditions. Further, a thread was passed through the central part of the obtained coating particles, and both ends were connected as shown in FIG. 1 to obtain a measurement sample. Subsequently, the yarn of the measurement sample was fixed to both hooks of a strength measuring device (Shimadzu EZtest-20N), a load was applied to one of the hooks at a speed of 20 mm / min, and the weight of the fertilizer particles at the breaking point was measured. Ten grains were measured for each sample, and the average value excluding the maximum value and the minimum value was defined as the film strength (g / particle). In addition, by measuring the strength of the film, during storage, distribution, peeling and damage of the film due to friction and impact between the coated fertilizer particles during machine fertilization, and an index of the degree of collapse or decomposition of the film after elution and Become. In addition, the film strength mentioned here means the tensile breaking strength of the film measured by this measuring method.
[0066]
The present inventors have previously found that there is a high correlation between the film strength of the coated fertilizer and the disintegration of the film (JP-A-11-322479). According to this, when the film strength increases, the degree of collapse decreases, and conversely, when the film strength decreases, the degree of collapse tends to be remarkable. Specifically, when the film strength is less than 50 g / particle, Cracks easily form in the coating. Therefore, if the coating strength of the coated fertilizer immediately after production is less than 50 g / particle, part of the coating is cracked or peeled off due to friction or impact between the coated fertilizer particles during storage, distribution, and fertilization, and elution occurs. Control function may not be maintained. On the other hand, if the film strength is more than 300 g / particle, the disintegration or decomposition of the film after elution cannot be expected. From the above, the film strength immediately after production is preferably 50 g / grain to 300 g / grain.
[0067]
(5) Evaluation of elution characteristics of coated fertilizer
The coated fertilizer produced in (1) is thrown at a rate of 7 g / 200 cc in constant temperature water at 25 ° C.
The amount of urea nitrogen in water was determined.
[0068]
For each of the coated fertilizers obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the results of the production formula, the coverage, the number of defective particles and the film strength are shown in Table 1, and the results of the elution characteristics are shown in Tables 2 and 3. And FIG.
[0069]
[Table 1]

[0070]
[Table 2]

[0071]
[Table 3]

[0072]
From the results in Table 1, FIG. 2 and Tables 2 and 3, all of the examples and comparative examples showed that the productivity of the coated fertilizer was good, and that both the coverage and the number of defective particles were at target levels. Also, it is clear that the coating strength has almost no effect on the addition amounts of the metal oxide and the organometallic compound, and is within a range in which there is no problem in use strength.
[0073]
(6) Evaluation of film disintegration
For each coated fertilizer produced in (1), the disintegration of the film was carried out as follows. <Pre-processing>
The coated fertilizer was pulverized by a cutter mill and then washed with water to remove urea, and dried by a vacuum drier (normal temperature). 2 g of the obtained film piece was precisely weighed and uniformly spread on the bottom surface of a transparent glass petri dish having an inner diameter of 14 cm. At this time, a step was provided with tape on the petri dish so that the lid was not hermetically sealed.
<Exposure processing>
The petri dish was covered with the lid, allowed to stand still in a flat open-air area without obstructing sunlight, and exposed for about 7 months.
Exposure time: September 5-April 1
<Weight measurement>
After exposure for a certain period, the dish was lightly covered with a lid and dried in a dryer (under ventilation at 45 ° C.) for 4 hours, cooled to room temperature, and weighed. The rate of change in weight after exposure for a certain period was calculated as the film remaining rate (initial value: 100%).
The above results are shown in Tables 1 and 4 and FIG.
[0074]
From the results of FIG. 3, in Examples 1 to 5, the content of titanium dioxide in the coating increased and the coating collapsed or decomposed. In particular, it can be seen that even when titanium dioxide is added at 50% by weight in the film as in Example 5, sufficient film strength is maintained and the film is excellent in collapsibility. On the other hand, in Comparative Example 1, the film containing no titanium dioxide was hardly decomposed. Further, from the results of Comparative Examples 2 to 4, iron (III) stearate was contained.
It can be seen that the film has a slower disintegration / decomposition rate than the titanium dioxide. In particular, as shown in Comparative Example 4, an example in which the same amount of titanium dioxide as iron (III) stearate was added.
It is clear when compared with 1.
[0075]
[Table 4]

[0076]
【The invention's effect】
From the above, the coated granular fertilizer of the present invention has good dissolution controllability even when a considerable amount of metal oxide is added to a specific polymer component, and the film after dissolution rapidly disintegrates or decomposes in a natural environment. By doing so, the burden on the environment is reduced. Furthermore, the mechanical strength of the film is excellent, and during compounding with other fertilizers, during transportation and during mechanical fertilization, part of the film is not damaged such as peeling or chipping, and affects the dissolution controllability. Absent. That is, it is a coated granular fertilizer which has a function of supplying a stable fertilizing component during the growing period of the crop and can achieve both stability during storage of the product and disintegration of the film in the environment.
[Brief description of the drawings]
FIG. 1 is a view showing a sample for film strength measurement.
FIG. 2 is a view showing dissolution characteristics of a coated fertilizer.
FIG. 3 is a view showing the disintegration property of a film of a coated fertilizer.

Claims

A coated granular fertilizer in which the surface of the granular fertilizer is coated with a film containing a copolymer containing an olefin having 3 or more carbon atoms and ethylene and / or a water-repellent starch and a metal oxide.

The coated granular fertilizer according to claim 1, wherein the olefin having 3 or more carbon atoms is propylene or 1-butene.

The coated granular fertilizer according to claim 1 or 2, wherein the metal oxide is titanium dioxide.

The coated granular fertilizer according to any one of claims 1 to 3, wherein the titanium dioxide has an anatase crystal structure.

The coated granular fertilizer according to any one of claims 1 to 4, wherein the content of the metal oxide is 50% or less based on the weight of the coating.

The coated granular fertilizer according to any one of claims 1 to 5, wherein the coating further contains an olefin homopolymer.

The coated granular fertilizer according to any one of claims 1 to 6, wherein the olefin homopolymer is polyethylene or polypropylene.