JP6083165B2 - Method for producing metal / cellulose composite fine fiber, dispersion containing metal / cellulose composite fine fiber, and method for producing transparent conductive film - Google Patents
Method for producing metal / cellulose composite fine fiber, dispersion containing metal / cellulose composite fine fiber, and method for producing transparent conductive film Download PDFInfo
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- JP6083165B2 JP6083165B2 JP2012200381A JP2012200381A JP6083165B2 JP 6083165 B2 JP6083165 B2 JP 6083165B2 JP 2012200381 A JP2012200381 A JP 2012200381A JP 2012200381 A JP2012200381 A JP 2012200381A JP 6083165 B2 JP6083165 B2 JP 6083165B2
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- cellulose
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- HFHDHCJBZVLPGP-UHFFFAOYSA-N schardinger α-dextrin Chemical compound O1C(C(C2O)O)C(CO)OC2OC(C(C2O)O)C(CO)OC2OC(C(C2O)O)C(CO)OC2OC(C(O)C2O)C(CO)OC2OC(C(C2O)O)C(CO)OC2OC2C(O)C(O)C1OC2CO HFHDHCJBZVLPGP-UHFFFAOYSA-N 0.000 description 1
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Description
本発明は、微細化されたセルロース繊維が少なくとも１種類以上の金属により被覆された金属／セルロース複合化微細繊維、前記金属／セルロース複合化微細繊維の製造方法および前記金属／セルロース複合化微細繊維を含む透明導電膜に関する。 The present invention relates to a metal / cellulose composite fine fiber in which a refined cellulose fiber is coated with at least one metal, a method for producing the metal / cellulose composite fine fiber, and the metal / cellulose composite fine fiber. It is related with the transparent conductive film containing.
一般的に透明導電膜とは可視光領域での光透過性が８０％以上、表面抵抗値が１０５Ω／□以下となる薄膜がこれに相当する。透明導電膜の用途は、タッチパネル、電磁波シールド、電子ペーパー、太陽電池用電極、有機EL用電極など多岐に渡り、現在及び未来の我々の生活に欠かせない素材であることから、その需要は増加の一途をたどっている。 In general, the transparent conductive film corresponds to a thin film having a light transmittance in the visible light region of 80% or more and a surface resistance value of 10 5 Ω / □ or less. The use of transparent conductive films is diverse, such as touch panels, electromagnetic wave shields, electronic paper, solar cell electrodes, and organic EL electrodes, and the demand for them is increasing because they are indispensable materials for our current and future lives. I'm following a course.
汎用的に用いられている透明導電膜として、ガラス板または各種プラスチックを基材としたものに酸化インジウム錫（ＩＴＯ）を真空蒸着したものが挙げられる。このＩＴＯフィルムは、導電性や可視光透過性の点で優れた物性を有することから、現在の業界標準となっている。 As a transparent conductive film that is used for general purposes, a glass plate or various plastics as a base material and indium tin oxide (ITO) vacuum-deposited can be used. This ITO film has become a current industry standard because it has excellent physical properties in terms of conductivity and visible light transmission.
しかし、インジウムは高価であり、将来的には資源枯渇の恐れもあることから安定供給の面で課題が残る。また、曲げ耐性がないため変形に弱いことからフレキシブル基盤への適用が難しい、薄膜の作製には真空過程を必要とするため生産コストがかさむ、といった問題もある。 However, since indium is expensive and there is a risk of resource depletion in the future, problems remain in terms of stable supply. In addition, there is a problem that it is difficult to apply to a flexible substrate because it does not have bending resistance, and it is difficult to apply to a flexible substrate.
このような状況を鑑み、ＩＴＯに代わる透明導電材料の研究が盛んに行われている。例えば柔軟性・化学的安定性に優れるカーボンナノチューブ（ＣＮＴ）を用いた薄膜成形が試みられている。また、ポリアニリン、ポリアセチレン等に代表される導電性高分子も、製膜性に優れ、曲げにも強いことから代替物質として注目されている。 In view of such a situation, research on transparent conductive materials replacing ITO has been actively conducted. For example, thin film molding using carbon nanotubes (CNT) excellent in flexibility and chemical stability has been attempted. In addition, conductive polymers typified by polyaniline, polyacetylene, and the like are also attracting attention as alternative substances because of their excellent film forming properties and resistance to bending.
ＣＮＴは層構造の違いによって導電性が大きく異なり、単層のものが比較的良好な導電性を示すことが報告されている。しかしながら、単層ＣＮＴだけを合成する方法は現在のところ報告されておらず、また単層ＣＮＴだけを精製分離した場合、その収率は著しく低下してしまう。そのため現在のところ、ＣＮＴを用いた透明導電膜ではＩＴＯに比べ十分な導電性を発揮できていないのが現状である。導電性高分子については、その安定性、透明性において課題があり、導電性も半導体レベルにとどまっているうえ、化石燃料由来の有機物質を原料に合成されることから環境への負荷は免れない。 It has been reported that the conductivity of CNTs varies greatly depending on the layer structure, and that a single layer has a relatively good conductivity. However, a method for synthesizing only single-walled CNTs has not been reported at present, and when only single-walled CNTs are purified and separated, the yield is significantly reduced. Therefore, at present, a transparent conductive film using CNTs does not exhibit sufficient conductivity as compared with ITO. For conductive polymers, there are problems in stability and transparency, conductivity remains at the semiconductor level, and organic substances derived from fossil fuels are synthesized from raw materials, so the burden on the environment is unavoidable. .
また、各種金属を用いて作製された金属ナノワイヤーも、透明導電材料として注目を集めている。その中でも特に高い導電性を有する銀ナノワイヤーおよびその製造法に関しては特許文献１から４に示されるように多くの報告がある。 In addition, metal nanowires produced using various metals are attracting attention as transparent conductive materials. Among them, there are many reports on silver nanowires having particularly high conductivity and methods for producing the same as shown in Patent Documents 1 to 4.
銀ナノワイヤーの製造方法はポリオール法、テンプレート法、電気化学法など様々であるが、どの方法を用いても比較的容易に作製することが可能である。また、銀ナノワイヤーは各種溶媒に分散したものを基材上に塗布することで簡単に透明導電膜を形成できることから成膜性に優れているうえ、曲げなどの変形にも強いことからフレキシブル基材への適用も可能である。 There are various methods for producing silver nanowires, such as a polyol method, a template method, and an electrochemical method, but any method can be used to produce the silver nanowire relatively easily. In addition, silver nanowires can be easily formed on a substrate by applying a dispersion in various solvents onto a base material, so it has excellent film-forming properties and is resistant to deformation such as bending. Application to materials is also possible.
この銀ナノワイヤーを用いた透明導電膜においては、ワイヤー自体のアスペクト比が透明性および導電性に影響を及ぼすことが知られている。すなわち、ワイヤーの短軸径が小さいほど可視光の散乱が減少して透明性が向上し、長軸径が大きいほどパーコレーション効果に基づいて導電性が向上する。特に銀ナノワイヤーの製造においては透明性の向上という観点から、短軸径の縮小が課題となっており、現在工業生産可能レベルで提供されているものは短軸径が４０〜５０ｎｍである。各種用途、特に電子ペーパー、太陽電池用電極、有機EL用電極として用いるにはさらなる透明性の向上が必要であり、より極細の、具体的には幅２０ｎｍ以下の極細の銀ナノワイヤーの開発が待たれているのが現状である。 In transparent conductive films using silver nanowires, it is known that the aspect ratio of the wires themselves affects transparency and conductivity. That is, the smaller the short axis diameter of the wire is, the less visible light is scattered and the transparency is improved. The larger the long axis diameter is, the more the conductivity is improved based on the percolation effect. In particular, in the production of silver nanowires, from the viewpoint of improving transparency, reduction of the short axis diameter is an issue, and what is currently provided at a level that can be industrially produced has a short axis diameter of 40 to 50 nm. For use in various applications, especially for electronic paper, solar cell electrodes, and organic EL electrodes, further improvement in transparency is required, and the development of ultrafine silver nanowires with a width of 20 nm or less has been developed. The current situation is waiting.
極細の銀ナノワイヤーの製造例としては例えば特許文献５に示されるようにＤＮＡやタンパク質フィラメント上に銀ナノ粒子を担持させた方法が報告されている。しかしながらこれらの方法はテンプレートとなるＤＮＡやタンパク質フィラメントが高価であり取り扱いも複雑であることから実用化には至っていない。 As an example of producing ultrafine silver nanowires, for example, as disclosed in Patent Document 5, a method of supporting silver nanoparticles on DNA or protein filaments has been reported. However, these methods have not yet been put into practical use because DNA and protein filaments serving as templates are expensive and complicated to handle.
一方近年、化石資源の枯渇問題の解決を目指して、持続的に利用可能な環境調和型材料であるバイオマスを用いた機能性材料の開発が盛んに行われている。その中でも木材の主成分であるセルロースは地球上に最も大量に蓄積された天然高分子材料であることから、資源循環型社会の中核を担う物質として期待が寄せられている。 On the other hand, in recent years, with the aim of solving the problem of depletion of fossil resources, development of functional materials using biomass, which is an environmentally friendly material that can be used continuously, has been actively conducted. Among them, cellulose, which is the main component of wood, is a natural polymer material accumulated in large quantities on the earth, and is expected as a material that plays a central role in a resource recycling society.
しかしながら、木材中のセルロースは、その分子鎖が数十本束になることで高結晶性のナノサイズの繊維径をもつ微細繊維を構成しており、それらが互いに水素結合して植物の支持体となっている。この極めて安定な構造のため特殊な溶媒以外には不溶であり、成形性にも乏しく、高機能部材としては扱いにくい面があった。 However, cellulose in wood is composed of dozens of molecular chains to form fine fibers with highly crystalline nano-sized fiber diameters, which are hydrogen bonded to each other to support the plant. It has become. Because of this extremely stable structure, it is insoluble except for special solvents, has poor moldability, and is difficult to handle as a highly functional member.
そこで、このような特徴を持つ木材中のセルロースをダウンサイジングし、微細繊維単位で利用しようとする試みが活発に行われている。例えば特許文献６に示されるように、木材セルロースに対しブレンダーやグラインダーによる機械処理を繰り返すことで微細化セルロース繊維が得られることが開示されている。この方法で得られる微細化セルロース繊維の短軸径は１０〜５０ｎｍ、長軸径は１μｍから１０ｍｍに及ぶことが報告されている。 Therefore, attempts have been actively made to downsize cellulose in wood having such characteristics and use it in units of fine fibers. For example, as disclosed in Patent Document 6, it is disclosed that fine cellulose fibers can be obtained by repeating mechanical processing using wood blender or grinder on wood cellulose. It has been reported that the short axis diameter of the refined cellulose fiber obtained by this method ranges from 10 to 50 nm and the long axis diameter ranges from 1 μm to 10 mm.
また、化学的処理による微細化として、特許文献７に示されるように比較的安定なＮ−オキシル化合物である２,２,６,６−テトラメチルピペリジニル−１−オキシラジカル（ＴＥＭＰＯ）を触媒として用い、セルロースの微細繊維表面を選択的に酸化する手法が報告されている。ＴＥＭＰＯ酸化反応は水系、常温、常圧で進行する環境調和型の化学改質が可能で、木材中のセルロースに適用した場合、結晶内部には反応が進行せず、結晶表面のセルロース分子鎖が持つアルコール性1級炭素のみを選択的にカルボキシル基へと変換することができる。 Further, as shown in Patent Document 7, 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO) is a relatively stable N-oxyl compound as refined by chemical treatment. A technique for selectively oxidizing the surface of cellulose fine fibers has been reported as a catalyst. The TEMPO oxidation reaction can be chemically modified in an environmentally friendly manner that proceeds in water, normal temperature, and normal pressure. When applied to cellulose in wood, the reaction does not proceed inside the crystal, and the cellulose molecular chains on the crystal surface Only the alcoholic primary carbon possessed can be selectively converted into a carboxyl group.
このように結晶表面に導入されたカルボキシル基同士の静電的な反発を利用して、水溶媒中で一本一本の微細繊維単位に分散させた、セルロースシングルナノファイバー（以下ＣＳＮＦと称する）を得ることが可能となった。木材からＴＥＭＰＯ酸化によって得られる木材ＣＳＮＦは短軸径４ｎｍ前後、長軸径５００ｎｍ〜数μｍに及ぶ高アスペクト比を有する構造体であり、その水分散液および積層体は透明性が高いことが報告されている。 Cellulose single nanofibers (hereinafter referred to as CSNF) dispersed in individual fine fiber units in an aqueous solvent using electrostatic repulsion between carboxyl groups introduced on the crystal surface in this way. It became possible to get. It is reported that wood CSNF obtained by TEMPO oxidation from wood is a structure having a high aspect ratio ranging from about 4 nm short axis diameter to 500 nm to several μm long axis diameter, and its aqueous dispersion and laminate are highly transparent. Has been.
一方、セルロース合成菌の産出するバクテリアセルロース（ＢＣ）は微細繊維の形で合成されることが知られており、ＢＣは微細化セルロース繊維として扱うことが出来る。このＢＣに関しては繊維幅が木材ＣＳＮＦよりも太い（〜１００ｎｍ）あるいは培養が必要なため生産性の改善が必要、という課題が残るものの、木材ＣＳＮＦより長い繊維長（１〜十数ｍｍ）を有するという特徴がある。 On the other hand, bacterial cellulose (BC) produced by cellulose-synthesizing bacteria is known to be synthesized in the form of fine fibers, and BC can be handled as fine cellulose fibers. This BC has a longer fiber length (1 to several tens of millimeters) than wood CSNF, although the fiber width is thicker (˜100 nm) than wood CSNF or there is a problem that productivity needs to be improved because culture is required. There is a feature.
ＩＴＯ代替材料として銀ナノワイヤーを用いた透明導電膜が提案されているが、良好な透明性を発現するにはさらにワイヤー幅を狭める必要がある。
したがって本発明の目的は、透明性がさらに向上し得る透明導電膜の製造に適した材料および該材料を用いてなる透明導電膜を提供することにある。
A transparent conductive film using silver nanowires has been proposed as an ITO alternative material, but it is necessary to further narrow the wire width in order to achieve good transparency.
Therefore, the objective of this invention is providing the material suitable for manufacture of the transparent conductive film which can further improve transparency, and the transparent conductive film which uses this material.
上記課題の解決のため鋭意検討を重ねたところ、微細化されたセルロース繊維と各種金属を複合化することで極細の導電性材料の開発に成功し、本発明に至った。すなわち、前述の微細化されたセルロース繊維をテンプレートとし、微細化されたセルロース繊維の表面上に選択的に還元性を有する官能基を導入することで、微細化セルロース繊維上に各種金属より成る被覆層を均一に還元析出させる手法を確立した。この手法により導電性を有する金属／セルロース複合化微細繊維とその製造方法、ならびに該金属／セルロース複合化微細繊維を含む高透明導電膜を提供することが可能となった。 As a result of extensive studies to solve the above problems, the inventors succeeded in developing an ultrafine conductive material by compositing finely divided cellulose fibers and various metals, leading to the present invention. That is, by using the above-mentioned refined cellulose fiber as a template, a functional group having a reducing property is selectively introduced onto the surface of the refined cellulose fiber, thereby coating the refined cellulose fiber with various metals. A method for uniformly reducing and depositing the layer was established. This technique makes it possible to provide conductive metal / cellulose composite fine fibers, a method for producing the same, and a highly transparent conductive film containing the metal / cellulose composite fine fibers.
すなわち、本発明は以下の項目によって規定されるものである。
請求項１に記載の発明は、数平均短軸径が１ｎｍ以上１００ｎｍ以下、数平均長軸径が１００ｎｍ以上であり、かつ数平均長軸径が数平均短軸径の５０倍以上であるカルボキシル基が導入された微細化されたセルロース繊維に、前記微細化されたセルロース繊維のカルボキシル基量に相当する還元性の官能基を導入する過よう素酸処理を行い、前記微細化されたセルロース繊維表面上に還元性を有する官能基であるアルデヒド基を導入する工程と、該還元性の官能基を利用し、溶液中で微細化されたセルロース繊維の表面上にのみ選択的に１種類以上の金属を還元析出し、前記金属から成る被覆層を形成する工程とを具備することを特徴とする、金属／セルロース複合化微細繊維の製造方法である。
請求項２に記載の発明は、前記アルデヒド基が導入された微細化されたセルロース繊維を溶媒中に分散させる工程と、銀アンモニア錯体および保護コロイド剤を該溶媒中に添加し沸点以下の温度で加熱あるいは冷却する工程とを具備することを特徴とする、請求項１に記載の製造方法である。
請求項３に記載の発明は、請求項１または２に記載の金属／セルロース複合化微細繊維の製造方法により製造された金属／セルロース複合化微細繊維および保護コロイド剤を溶媒中に含ませる分散体の製造方法である。
請求項４に記載の発明は、請求項３に記載の分散体の製造方法により製造された分散体からなる塗液を基材上に塗布し、乾燥させる工程を有する、透明導電層を有する透明導電膜の製造方法である。
That is, the present invention is defined by the following items.
The invention according to claim 1 is a carboxyl having a number average minor axis diameter of 1 nm to 100 nm, a number average major axis diameter of 100 nm or more, and a number average major axis diameter of 50 times or more of the number average minor axis diameter. The refined cellulose fiber is subjected to a periodic acid treatment for introducing a reducing functional group corresponding to the carboxyl group amount of the refined cellulose fiber to the refined cellulose fiber into which the group is introduced. a step of introducing an aldehyde group is a functional group having a reducing property on the surface, using said reducing functional groups only on the surface of the fine cellulose fibers in solution selectively one or more And a step of forming a coating layer comprising the metal by reduction deposition of the metal, and a method for producing a metal / cellulose composite fine fiber.
The invention according to claim 2 includes a step of dispersing the finely divided cellulose fiber introduced with the aldehyde group in a solvent, and adding a silver ammonia complex and a protective colloid agent to the solvent at a temperature below the boiling point. characterized by comprising the step of heating or cooling, a method according to claim 1.
The invention according to claim 3 is a dispersion in which the metal / cellulose composite fine fiber produced by the method for producing metal / cellulose composite fine fiber according to claim 1 or 2 and a protective colloid agent are contained in a solvent. It is a manufacturing method .
The invention described in claim 4 is a transparent conductive layer comprising a step of applying a coating liquid comprising the dispersion produced by the method for producing a dispersion according to claim 3 and drying the coating liquid. It is a manufacturing method of an electrically conductive film.
本発明によれば、微細化されたセルロース繊維表面上に導入された還元性を有する官能基を足場にして、繊維表面上にのみ選択的に金属イオンを還元析出させることが可能であるため、添加する金属イオンの濃度を制御することによって、微細化されたセルロース繊維表面上を各種金属によって任意の厚みで被覆することが可能となる。すなわち、本発明によって得られる金属／セルロース複合化微細繊維は、テンプレートと成る微細化されたセルロースとして短軸径の短いものを選択することにより、従来では達成できなかった短軸径２０ｎｍ以下の金属ナノワイヤーを容易に作製することができる。この極細の金属／セルロース複合化微細繊維を用いることで、高透明性の導電膜を提供することが可能となった。 According to the present invention, it is possible to selectively reduce and precipitate metal ions only on the fiber surface using the reducing functional group introduced on the surface of the refined cellulose fiber as a scaffold. By controlling the concentration of the metal ions to be added, it becomes possible to coat the surface of the refined cellulose fiber with various thicknesses with various metals. That is, the metal / cellulose composite fine fiber obtained by the present invention is a metal having a short axis diameter of 20 nm or less, which could not be achieved in the past, by selecting finely divided cellulose as a template and having a short minor axis diameter. Nanowires can be easily produced. By using this ultrafine metal / cellulose composite fine fiber, it has become possible to provide a highly transparent conductive film.
また、本発明における金属の使用量は微細化されたセルロース繊維の被覆に必要な量だけで済むことから、従来の金属ナノワイヤーと比較して金属の総使用量を抑制できることになり、省資源化が達成される。さらには本発明により得られる透明導電材料はテンプレートとしてセルロースを用いているためバイオマス化度が高く、カーボンニュートラルな環境調和型材料としての特徴も併せ持つ高機能部材である。 In addition, since the amount of metal used in the present invention is only the amount necessary for the coating of finely divided cellulose fibers, the total amount of metal used can be suppressed as compared with conventional metal nanowires, thus saving resources. Is achieved. Furthermore, since the transparent conductive material obtained by the present invention uses cellulose as a template, it is a highly functional member that has a high degree of biomass conversion and has characteristics as a carbon neutral environment-friendly material.
以下、本発明の詳細を説明する。 Details of the present invention will be described below.
（微細化されたセルロース繊維とその製造方法）
本発明において用いる微細化されたセルロース繊維（以下、単に微細化セルロース繊維と言う）は、その繊維径が以下に示す範囲内にあればよく、その調製方法については特に限定されない。すなわち短軸径において数平均短軸径が１ｎｍ以上１００ｎｍ以下であればよく、好ましくは２ｎｍ以上５０ｎｍ以下、より好ましくは４ｎｍ以上２０ｎｍ以下である。数平均短軸径が１ｎｍ未満では高結晶性の剛直な微細化セルロース繊維構造をとることが出来ず、金属ナノワイヤー製造のためのテンプレートとして用いることができない。一方、１００ｎｍを超えると十分な透明性が得られない。また、長軸径においては数平均長軸径が１００ｎｍ以上、例えば５００ｎｍ以上、好ましくは１μｍ以上、より好ましくは２μｍ以上である。数平均長軸径が１００ｎｍ未満では繊維の絡み合いによるパーコレーション効果が低下し、薄膜を形成した際に十分な導電性を発揮することが出来ない。また、本発明の効果の観点から数平均長軸径が数平均短軸径の５０倍以上であることが好ましい。
(Miniaturized cellulose fiber and its production method)
The refined cellulose fiber used in the present invention (hereinafter simply referred to as refined cellulose fiber) may have a fiber diameter within the range shown below, and the preparation method is not particularly limited. That is, in the minor axis diameter, the number average minor axis diameter may be 1 nm or more and 100 nm or less, preferably 2 nm or more and 50 nm or less, more preferably 4 nm or more and 20 nm or less. If the number average minor axis diameter is less than 1 nm, a highly crystalline rigid and finely divided cellulose fiber structure cannot be obtained, and it cannot be used as a template for producing metal nanowires. On the other hand, if it exceeds 100 nm, sufficient transparency cannot be obtained. The major axis diameter has a number average major axis diameter of 100 nm or more, for example 500 nm or more, preferably 1 μm or more, more preferably 2 μm or more. When the number average major axis diameter is less than 100 nm, the percolation effect due to the entanglement of the fibers is lowered, and sufficient conductivity cannot be exhibited when a thin film is formed. From the viewpoint of the effect of the present invention, the number average major axis diameter is preferably 50 times or more than the number average minor axis diameter.
微細化セルロース繊維の原料として用いることが出来るセルロースの種類も特に限定されず、例えば木材系天然セルロースに加えて、コットンリンター、竹、麻、バガス、ケナフ、バクテリアセルロース、ホヤセルロース、バロニアセルロースといった非木材系天然セルロース、さらにはレーヨン繊維、キュプラ繊維に代表される再生セルロースを用いることが出来る。 The type of cellulose that can be used as a raw material for the finely divided cellulose fiber is not particularly limited. For example, in addition to wood-based natural cellulose, non-cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, squirt cellulose, valonia cellulose, etc. Wood-based natural cellulose, as well as regenerated cellulose represented by rayon fiber and cupra fiber can be used.
セルロース繊維の微細化方法もとくに限定されないが、前述の高圧ホモジナイザーによる機械処理、ＴＥＭＰＯ酸化処理等による化学処理の他、希酸加水分解処理や酵素処理などを用いても良い。また、バクテリアセルロースも微細化セルロース繊維として用いることが出来る。さらには各種天然セルロースを各種セルロース溶剤に溶解させたのち、電解紡糸することによって得られる微細再生セルロース繊維を用いても良い。 The method for refining cellulose fibers is not particularly limited, but dilute acid hydrolysis treatment, enzyme treatment, or the like may be used in addition to the above-described mechanical treatment using a high-pressure homogenizer and chemical treatment such as TEMPO oxidation treatment. Bacterial cellulose can also be used as finely divided cellulose fibers. Furthermore, finely regenerated cellulose fibers obtained by dissolving various natural celluloses in various cellulose solvents and then performing electrospinning may be used.
例えば特許文献６に記載の方法で木材セルロースをブレンダーあるいはグラインダーで繰り返し処理して微細化したセルロース繊維を金属で被覆した場合、繊維長は１μｍから１０ｍｍに達することから、超低抵抗を有する導電膜を容易に作製することができる。一方、繊維幅は１０〜５０ｎｍとなるため、透明性の達成が課題となる。特許文献７記載の木材ＣＳＮＦを用いた場合、短軸径が４ｎｍ程度であるため、金属で被覆して得られる導電性ナノワイヤーの短軸径を５ｎｍから１０ｎｍの範囲に制御することが可能である。また、木材ＣＳＮＦの長軸径はＴＥＭＰＯ酸化処理時のｐＨに依存するため、中性領域で酸化を行なえば長軸径を５μｍ程度に揃えることも可能であり、高透明性と導電性を両立する導電材料の設計が可能である。また、バクテリアセルロースは繊維幅が１０ｎｍ程度と木材ＣＳＮＦより太いものの、金属による被覆後の短軸長を２０ｎｍ以下に制御することは十分可能であり、長軸長は１ｍｍから十数ｍｍにも達するため、透明性に加えて超低抵抗の薄膜を形成することが可能となる。ブレンダーあるいはグラインダー処理により微細化したセルロース繊維、木材ＣＳＮＦ、バクテリアセルロースともに本発明において使用される微細化セルロースとしては好ましいが、透明性と導電性の両立、および材料の安定供給の面から、木材ＣＳＮＦがより好ましい。 For example, when a cellulose fiber, which is refined by repeatedly treating wood cellulose with a blender or grinder by the method described in Patent Document 6, is coated with a metal, the fiber length reaches from 1 μm to 10 mm. Can be easily manufactured. On the other hand, since the fiber width is 10 to 50 nm, achieving transparency is a problem. When wood CSNF described in Patent Document 7 is used, the minor axis diameter is about 4 nm, and therefore the minor axis diameter of the conductive nanowire obtained by coating with metal can be controlled in the range of 5 nm to 10 nm. is there. In addition, since the long axis diameter of wood CSNF depends on the pH during TEMPO oxidation treatment, it is possible to make the long axis diameter about 5 μm if oxidation is performed in the neutral region, achieving both high transparency and conductivity. It is possible to design a conductive material. In addition, although bacterial cellulose has a fiber width of about 10 nm and is thicker than wood CSNF, it is possible to control the minor axis length after coating with metal to 20 nm or less, and the major axis length reaches 1 mm to several tens of mm. Therefore, it is possible to form an ultra-low resistance thin film in addition to transparency. Cellulose fibers, wood CSNF, and bacterial cellulose refined by blender or grinder treatment are preferred as the refined cellulose used in the present invention. However, wood CSNF is preferred in terms of both transparency and conductivity and stable supply of materials. Is more preferable.
以下、木材ＣＳＮＦを製造する方法について説明する。 Hereinafter, a method for producing wood CSNF will be described.
本発明で用いられる木材ＣＳＮＦは、セルロースを酸化する工程と、微細化し分散液化する工程により得られる。また、酸化の際に導入されるカルボキシル基量は０．１ｍｍｏｌ／ｇ以上５．０ｍｍｏｌ／ｇ以下が好ましく、０．５ｍｍｏｌ／ｇ以上２．０ｍｍｏｌ／ｇ以下がより好ましい。カルボキシル基量が０．１ｍｍｏｌ／ｇ未満であると、静電的な反発が起こらずにセルロースを微細化して均一に分散させることは難しい。また、５．０ｍｍｏｌ／ｇを超えると、微細化セルロース繊維の分子量が低下し、金属被覆処理用のテンプレートとしての強度特性を損なうおそれがある。 Wood CSNF used in the present invention is obtained by a step of oxidizing cellulose and a step of pulverizing and dispersing it. Further, the amount of carboxyl groups introduced during oxidation is preferably 0.1 mmol / g or more and 5.0 mmol / g or less, and more preferably 0.5 mmol / g or more and 2.0 mmol / g or less. When the carboxyl group amount is less than 0.1 mmol / g, it is difficult to make the cellulose finely dispersed uniformly without causing electrostatic repulsion. Moreover, when it exceeds 5.0 mmol / g, there exists a possibility that the molecular weight of refined cellulose fiber may fall and the intensity | strength characteristic as a template for a metal coating process may be impaired.
（セルロースを酸化する工程）
酸化される木材セルロースの原料としては特に限定されないが、一般的には針葉樹パルプや広葉樹パルプ、古紙パルプ、などが用いられ、精製および微細化のしやすさから、針葉樹パルプを用いることが好ましい。
(Step of oxidizing cellulose)
Although it does not specifically limit as a raw material of the wood cellulose oxidized, A conifer pulp, a hardwood pulp, a waste paper pulp, etc. are generally used, and it is preferable to use a conifer pulp from the ease of refinement | purification and refinement | miniaturization.
木材セルロースの繊維表面を酸化しカルボキシル基を導入する方法としては、水系の比較的温和な条件で、可能な限り構造を保ちながら、アルコール性一級炭素の酸化に対する選択性が高い、ＴＥＭＰＯをはじめとするＮ−オキシル化合物の存在下、共酸化剤を用いた手法が望ましい。前記のＮ−オキシル化合物としては、ＴＥＭＰＯのほか、２，２，６，６−テトラメチル−４−ヒドロキシピペリジン−１−オキシル、４−メトキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−エトキシ−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、４−アセトアミド−２，２，６，６−テトラメチルピペリジン−Ｎ−オキシル、等が挙げられる。その中でも、ＴＥＭＰＯなどが好ましく用いられる。 As a method for oxidizing the fiber surface of wood cellulose and introducing a carboxyl group, it is possible to start with TEMPO, which has high selectivity to the oxidation of alcoholic primary carbon while maintaining the structure as much as possible under relatively mild conditions in water. A technique using a co-oxidant in the presence of the N-oxyl compound is desirable. Examples of the N-oxyl compound include TEMPO, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N. -Oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl, and the like. Among them, TEMPO is preferably used.
また、前記の共酸化剤としては、ハロゲン、次亜ハロゲン酸、亜ハロゲン酸や過ハロゲン酸、またはそれらの塩、ハロゲン酸化物、窒素酸化物、過酸化物など、酸化反応を推進することが可能であれば、いずれの酸化剤も用いることができる。入手の容易さや反応性から次亜塩素酸ナトリウムが好ましい。 The co-oxidant may promote an oxidation reaction such as halogen, hypohalous acid, halous acid or perhalogen acid, or a salt thereof, halogen oxide, nitrogen oxide, or peroxide. Any oxidant can be used if possible. Sodium hypochlorite is preferred because of its availability and reactivity.
さらに、臭化物やヨウ化物の共存下で行うと、酸化反応を円滑に進行させることができ、カルボキシル基の導入効率を改善することができる。 Furthermore, when carried out in the presence of bromide or iodide, the oxidation reaction can proceed smoothly, and the introduction efficiency of the carboxyl group can be improved.
Ｎ−オキシル化合物としてはＴＥＭＰＯが好ましく、触媒として機能する量があれば十分である。また臭化物としては臭化ナトリウムまたは臭化リチウムを用いた系が好ましく、コストや安定性から臭化ナトリウムがより好ましい。共酸化剤、臭化物またはヨウ化物の使用量は、酸化反応を促進することができる量があれば十分である。反応はｐＨ９〜１１がより望ましいが、酸化が進行するにつれて、カルボキシル基が生成されて系内のｐＨが低下してしまうため、系内をｐＨ９〜１１に保つ必要がある。 As the N-oxyl compound, TEMPO is preferable, and an amount that functions as a catalyst is sufficient. As the bromide, a system using sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable from the viewpoint of cost and stability. The amount of the co-oxidant, bromide or iodide used is sufficient if there is an amount capable of promoting the oxidation reaction. The reaction is more preferably pH 9 to 11, but as the oxidation proceeds, carboxyl groups are generated and the pH in the system is lowered, so the inside of the system needs to be maintained at pH 9 to 11.
系内をアルカリ性に保つためにはｐＨの低下に応じてアルカリ水溶液を添加していくことで調整することができる。アルカリ水溶液としては、水酸化ナトリウム、水酸化リチウム、水酸化カリウム、アンモニア水溶液、さらには水酸化テトラメチルアンモニウム、水酸化テトラエチルアンモニウム、水酸化テトラブチルアンモニウム、水酸化ベンジルトリメチルアンモニウムなどの有機アルカリなどが用いられるが、コストなどから水酸化ナトリウムが好ましい。 In order to keep the inside of the system alkaline, it can be adjusted by adding an alkaline aqueous solution as the pH decreases. Examples of the alkaline aqueous solution include sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia solution, and organic alkalis such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide. Although used, sodium hydroxide is preferred in view of cost.
酸化反応を終了させるためには系内のｐＨを保ちながら他のアルコールを添加し共酸化剤を完全に反応し終える必要がある。添加するアルコールとしては反応をすばやく終了させるためメタノール、エタノール、プロパノールなどの低分子量のアルコールが望ましいが、反応により生成される副産物の安全性などからエタノールがより好ましい。 In order to complete the oxidation reaction, it is necessary to add the other alcohol while maintaining the pH in the system and complete the reaction of the co-oxidant. The alcohol to be added is preferably a low molecular weight alcohol such as methanol, ethanol or propanol in order to quickly terminate the reaction, but ethanol is more preferable from the viewpoint of safety of by-products generated by the reaction.
酸化し終わった酸化パルプの洗浄方法としては、アルカリと塩を形成したまま洗浄する方法、酸を添加してカルボン酸にして洗浄する方法等がある。ハンドリング性や収率等から酸を添加してカルボン酸にして洗浄する方法が好ましい。なお洗浄溶媒としては水が好ましい。 As a method for washing oxidized pulp after oxidation, there are a method of washing while forming an alkali and a salt, a method of adding an acid to obtain a carboxylic acid, and the like. In view of handling properties and yield, a method of adding an acid to obtain a carboxylic acid and washing it is preferred. The washing solvent is preferably water.
（酸化セルロースを微細化し分散液化する工程）
酸化セルロースを微細化する方法としてはまず、酸化セルロースを水やアルコールをはじめとした各種有機溶媒やそれらの混合溶媒中に懸濁させる。必要とあれば、分散性を上げるために分散液のｐＨ調整を行ってもよい。ｐＨ調整に用いられるアルカリ水溶液としては、水酸化ナトリウム、水酸化リチウム、水酸化カリウム、アンモニア水溶液、さらには水酸化テトラメチルアンモニウム、水酸化テトラエチルアンモニウム、水酸化テトラブチルアンモニウム、水酸化ベンジルトリメチルアンモニウムなどの有機アルカリなどが挙げられる。コストや入手のしやすさなどから水酸化ナトリウムが好ましい。
(Step of making oxidized cellulose fine and dispersing liquid)
As a method for refining oxidized cellulose, first, oxidized cellulose is suspended in various organic solvents such as water and alcohol, or a mixed solvent thereof. If necessary, the pH of the dispersion may be adjusted to increase dispersibility. Examples of the alkaline aqueous solution used for pH adjustment include sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia aqueous solution, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, etc. And organic alkalis. Sodium hydroxide is preferred because of cost and availability.
続いて物理的に解繊する方法としては、高圧ホモジナイザー、超高圧ホモジナイザー、ボールミル、ロールミル、カッターミル、遊星ミル、ジェットミル、アトライター、グラインダー、ジューサーミキサー、ホモミキサー、超音波ホモジナイザー、ナノジナイザー、水中対向衝突などを用いることで微細化することができる。これらのような微細化処理を任意の時間や回数行うことで表面にカルボキシル基を有する微細化セルロース繊維の水分散液を得ることができる。このとき前記微細化セルロース繊維の数平均繊維幅は１ｎｍ以上１００ｎｍ以下が好ましく、繊維幅が１ｎｍより小さい場合、微細化セルロースの結晶性が失われてしまい、１００ｎｍより大きい場合、その分散液および積層体の透明性が損なわれてしまう。また、数平均繊維長は数平均繊維幅の５０倍以上であることが好ましく、５０倍未満では金属被覆後に導電材料として用いた際に繊維同士の接点が減少し、導電性が著しく低下する。 Subsequent physical defibrating methods include high pressure homogenizer, ultra high pressure homogenizer, ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer, underwater It can be miniaturized by using an opposing collision or the like. An aqueous dispersion of fine cellulose fibers having a carboxyl group on the surface can be obtained by performing such a fine treatment for an arbitrary time or number of times. At this time, the number average fiber width of the fine cellulose fibers is preferably 1 nm or more and 100 nm or less. If the fiber width is smaller than 1 nm, the crystallinity of the fine cellulose is lost. The transparency of the body is impaired. Further, the number average fiber length is preferably 50 times or more of the number average fiber width. When the number average fiber length is less than 50 times, the number of contact points between fibers decreases when used as a conductive material after metal coating, and the conductivity is remarkably lowered.
前記微細化セルロース繊維分散液は、必要に応じて、本発明の効果を損なわない範囲で、セルロースおよびｐＨ調整に用いた成分以外の他の成分を含有してもよい。該他の成分としては、特に限定されず、当該微細セルロースの用途等に応じて、公知の添加剤のなかから適宜選択できる。具体的には、アルコキシシラン等の有機金属化合物またはその加水分解物、無機層状化合物、無機針状鉱物、レベリング剤、消泡剤、水溶性高分子、合成高分子、無機系粒子、有機系粒子、潤滑剤、帯電防止剤、紫外線吸収剤、染料、顔料、安定剤、磁性粉、配向促進剤、可塑剤、架橋剤等が挙げられる。 The fine cellulose fiber dispersion may contain other components than cellulose and components used for pH adjustment, as long as the effects of the present invention are not impaired. The other components are not particularly limited, and can be appropriately selected from known additives according to the use of the fine cellulose. Specifically, organometallic compounds such as alkoxysilanes or hydrolysates thereof, inorganic layered compounds, inorganic needle minerals, leveling agents, antifoaming agents, water-soluble polymers, synthetic polymers, inorganic particles, organic particles , Lubricants, antistatic agents, ultraviolet absorbers, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, crosslinking agents and the like.
（微細化セルロース繊維表面を金属によって被覆する工程）
微細化セルロース繊維表面を被覆する金属種としては、特に限定しない。例えば、白金やパラジウム、ルテニウム、イリジウム、ロジウム、オスミウムの白金族元素の他、金、銀、鉄、鉛、銅、クロム、コバルト、ニッケル、マンガン、バナジウム、モリブデン、ガリウム、アルミニウムなどの金属、金属塩、金属錯体およびこれらの合金、または酸化物、複酸化物等が挙げられる。また、複数の金属種を用いても良い。導電材料としての使用が目的であるため、析出させる金属のうち少なくとも１種類は銀であることが好ましい。銀の還元を行う際に用いる物質は特に制限は無いが、銀錯体であることが好ましく、取り扱いおよび調製の簡便さから銀アンモニア錯体がより好ましい。
(Process of coating the surface of fine cellulose fiber with metal)
It does not specifically limit as a metal seed | species which coat | covers the micronized cellulose fiber surface. For example, in addition to platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium and osmium, metals such as gold, silver, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium and aluminum, metals Examples thereof include salts, metal complexes and alloys thereof, or oxides and double oxides. A plurality of metal species may be used. Since it is intended to be used as a conductive material, at least one of the deposited metals is preferably silver. Although there is no restriction | limiting in particular in the substance used when reduce | restoring silver, It is preferable that it is a silver complex and a silver ammonia complex is more preferable from the ease of handling and preparation.
微細化セルロース繊維表面を金属により被覆する方法としては特に限定しないが、微細化セルロース繊維表面上にのみ金属層を析出させるために、微細化セルロース繊維表面上に還元性の官能基を導入した状態で、前記金属塩とともに保護コロイド剤を添加し、溶媒の沸点以下の温度で加熱あるいは冷却しながら溶媒中に分散させて還元処理を行うことが好ましい。この状態で前記金属塩などに含まれる金属カチオンを還元し析出させることによって、微細化セルロース繊維表面を均一に金属層で被覆することが出来る。 The method for coating the surface of the fine cellulose fiber with a metal is not particularly limited, but a reducing functional group is introduced on the surface of the fine cellulose fiber in order to deposit a metal layer only on the surface of the fine cellulose fiber. Thus, it is preferable to carry out the reduction treatment by adding a protective colloid agent together with the metal salt and dispersing in a solvent while heating or cooling at a temperature below the boiling point of the solvent. By reducing and precipitating metal cations contained in the metal salt or the like in this state, the surface of the refined cellulose fiber can be uniformly coated with the metal layer.
前記微細化セルロース繊維表面上に導入する還元性の官能基については、対象となる金属種を還元できる官能基であれば特に制限は無いが、処理の簡便さから、過よう素酸ナトリウムを用いたアルデヒド基の導入が最も好ましい。この過よう素酸ナトリウム処理を用いることにより、微細化セルロース繊維の表面にのみアルデヒド基を導入することができる。
図１は、微細化セルロース繊維表面に１種類以上の金属から成る被覆層を形成する手段を説明するための図であり、微細化セルロース繊維に対し、上記のように例えば過よう素酸ナトリウムで処理し、表面にアルデヒド基を導入させ、金属カチオン、例えば銀イイオンを還元し析出させ、微細化セルロース繊維の表面に銀を付着させる。このようにして、微細化セルロース繊維表面に選択的に金属による被覆層を析出させることが可能となる。なお、金属から成る被覆層は、微細化セルロース繊維の表面全体に付着していることが好ましい。
The reducing functional group to be introduced onto the surface of the fine cellulose fiber is not particularly limited as long as it is a functional group capable of reducing the target metal species, but sodium periodate is used for ease of treatment. Most preferred is the introduction of aldehyde groups. By using this sodium periodate treatment, an aldehyde group can be introduced only on the surface of the refined cellulose fiber.
FIG. 1 is a view for explaining a means for forming a coating layer made of one or more kinds of metals on the surface of finely divided cellulose fibers. As described above, for example, sodium periodate is applied to the finely divided cellulose fibers. Treatment is performed to introduce aldehyde groups on the surface, and metal cations such as silver ions are reduced and deposited, and silver is adhered to the surface of the finely divided cellulose fibers. In this manner, a metal coating layer can be selectively deposited on the surface of the finely divided cellulose fiber. In addition, it is preferable that the coating layer which consists of metals adheres to the whole surface of micronized cellulose fiber.
前記溶媒とは５０％以上の水を含み、水以外の溶媒としては親水性溶媒が好ましい。水の割合が５０％以下になると微細化セルロース繊維の分散が阻害され、繊維表面を均一に金属で被覆することが難しくなる。親水性溶媒については特に制限は無いが、メタノール、エタノール、イソプロパノールなどのアルコール類；テトラヒドロフラン等の環状エーテル類が好ましい。 The solvent contains 50% or more of water, and a solvent other than water is preferably a hydrophilic solvent. When the water ratio is 50% or less, the dispersion of fine cellulose fibers is inhibited, and it becomes difficult to uniformly coat the fiber surface with metal. The hydrophilic solvent is not particularly limited, but alcohols such as methanol, ethanol and isopropanol; cyclic ethers such as tetrahydrofuran are preferred.
前記保護コロイド剤とは微細化セルロース繊維表面に析出した金属層同士の結合または凝集を防ぐ目的のために添加されるものである。前記の作用を有する化合物であれば特に制限は無く、各種親水性高分子、各種界面活性剤を使用することができ、例えばポリビニルピロリドン、ポリビニルアルコール、メチルセルロース、ヒドロキシプロピルセルロース、シクロデキストリンなどが好ましい。 The protective colloid agent is added for the purpose of preventing the bonding or aggregation of metal layers deposited on the surface of fine cellulose fibers. If it is a compound which has the said effect | action, there will be no restriction | limiting in particular, Various hydrophilic polymers and various surfactant can be used, For example, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, hydroxypropylcellulose, cyclodextrin etc. are preferable.
調製に用いる微細化セルロース繊維の濃度は特に限定しないが、０．０１％以上５％未満が好ましく、０．０１％未満では成形体形成用組成物としては溶媒過多となってしまい、５％を超えるとでは微細化セルロース繊維同士の絡み合いで粘度が上昇し、均一な攪拌が難しくなる。同様に用いる金属イオンを含む溶液の金属イオン濃度も限定しないが、金属イオンの濃度は析出する金属の被覆層の厚みに影響することがわかっており、この厚みは１ｎｍ以上１００ｎｍ以下であることが好ましく、１ｎｍ以上５０ｎｍ以下であることがさらに好ましく、１ｎｍ以上１０ｎｍ以下であることがより好ましい。１ｎｍ未満では微細化セルロース繊維の表面を金属層で均一に被覆することが出来ず導電性が低下してしまい、１００ｎｍを超えると被覆後の繊維の短軸長が大きくなってしまい、基材などに塗布して薄膜形成した際の透明性が損なわれてしまう。 The concentration of the finely divided cellulose fiber used for the preparation is not particularly limited, but is preferably 0.01% or more and less than 5%. If it is less than 0.01%, the composition for forming a molded body becomes excessive in solvent, and 5% If it exceeds, the viscosity increases due to the entanglement between the finely divided cellulose fibers, and uniform stirring becomes difficult. Similarly, the metal ion concentration of the solution containing metal ions to be used is not limited, but it is known that the metal ion concentration affects the thickness of the deposited metal coating layer, and this thickness is 1 nm to 100 nm. Preferably, it is 1 nm or more and 50 nm or less, more preferably 1 nm or more and 10 nm or less. If the thickness is less than 1 nm, the surface of the finely divided cellulose fiber cannot be uniformly coated with the metal layer, resulting in a decrease in conductivity. If the thickness exceeds 100 nm, the minor axis length of the coated fiber becomes large, and the substrate or the like. The transparency at the time of forming a thin film by applying to the film is impaired.
（金属／セルロース複合化微細繊維の分散体を乾燥し、成形体を作製する工程）
前記透明導電膜は金属／セルロース複合化微細繊維そのもの、あるいは各種溶媒中に金属／セルロース複合化微細繊維を分散させたものを塗液とし基材上に塗布したものを乾燥させることによって得ることが出来る。金属／セルロース複合化微細繊維を基材に塗布する際には公知の塗布方法を用いることができ、例えば、ロールコーター、リバースロールコーター、グラビアコーター、マイクログラビアコーター、ナイフコーター、バーコーター、ワイヤーバーコーター、ダイコーター、ディップコーター、スピンコーター等を用いることができる。以上の塗布方法を用いて、基材の少なくとも一方の面に塗布する。金属／セルロース複合化微細繊維を乾燥させる方法としては、特に限定しないが、乾燥する温度としては２０℃以上２００℃以下が好ましく、３０℃以上１５０℃以下がより好ましい。
(Process of drying a metal / cellulose composite fine fiber dispersion to produce a molded body)
The transparent conductive film can be obtained by drying a metal / cellulose composite fine fiber itself or a material obtained by dispersing a metal / cellulose composite fine fiber in various solvents and applying a coating liquid onto a substrate. I can do it. When applying metal / cellulose composite fine fibers to a substrate, known coating methods can be used, for example, roll coater, reverse roll coater, gravure coater, micro gravure coater, knife coater, bar coater, wire bar. A coater, a die coater, a dip coater, a spin coater or the like can be used. It applies to at least one surface of a substrate using the above application method. Although it does not specifically limit as a method of drying a metal / cellulose composite fine fiber, As a temperature to dry, 20 to 200 degreeC is preferable and 30 to 150 degreeC is more preferable.
用いることが出来る基材には特に制限は無く、種々の高分子組成物から成るプラスチックまたはガラス基板を用いることができる。例えば、ポリオレフィン系（ポリエチレン、ポリプロピレン等）、ポリエステル系（ポリエチレンテレフタレート、ポリエチレンナフタレート等）、セルロース系（トリアセチルセルロース、ジアセチルセルロース、セロファン等）、ポリアミド系（６−ナイロン、６，６−ナイロン等）、アクリル系（ポリメチルメタクリレート等）や、ポリスチレン、ポリ塩化ビニル、ポリイミド、ポリビニルアルコール、ポリカーボネート、エチレンビニルアルコール等からなるものが用いられる。また、前述のプラスチック材料の中から、少なくとも１種以上の成分を持つ、或いは共重合成分に持つ、或いはそれらの化学修飾体を成分に有する有機高分子材料も可能である。 The base material that can be used is not particularly limited, and plastic or glass substrates made of various polymer compositions can be used. For example, polyolefin (polyethylene, polypropylene, etc.), polyester (polyethylene terephthalate, polyethylene naphthalate, etc.), cellulose (triacetylcellulose, diacetylcellulose, cellophane, etc.), polyamide (6-nylon, 6,6-nylon, etc.) ), Acrylic (polymethyl methacrylate, etc.), polystyrene, polyvinyl chloride, polyimide, polyvinyl alcohol, polycarbonate, ethylene vinyl alcohol, etc. are used. In addition, organic polymer materials having at least one or more components from among the above-described plastic materials, having a copolymer component, or having a chemical modification thereof as a component are also possible.
また、環境への配慮から、用いる基材にも環境負荷の少ないものが求められる。そのため、基材として、例えば、ポリ乳酸、バイオポリオレフィンなど植物から化学合成されるバイオプラスチック、或いはヒドロキシアルカノエートなど微生物が生産するプラスチックを含む基材、更にはセルロース系材料を含む、紙、セロハン、アセチル化セルロース、セルロース誘導体、微細化セルロース繊維を含む基材も用いることができる。 In consideration of the environment, the substrate to be used is required to have a low environmental load. Therefore, as a base material, for example, a bioplastic chemically synthesized from a plant such as polylactic acid or biopolyolefin, or a base material containing a plastic produced by a microorganism such as hydroxyalkanoate, further including a cellulosic material, paper, cellophane, Substrates containing acetylated cellulose, cellulose derivatives, and finely divided cellulose fibers can also be used.
こうして得られた成形体は金属／セルロース複合化微細繊維の積層体であるため高い透明性と同時に導電性も有することから、新規バイオナノ素材由来の透明導電膜としての利用が期待できる。 Since the molded body thus obtained is a laminate of metal / cellulose composite fine fibers, it has high transparency as well as conductivity, so that it can be expected to be used as a transparent conductive film derived from a novel bio-nano material.
以下、本発明を実施例に基づいて詳細に説明するが、本発明の技術範囲はこれらの実施形態に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, the technical scope of this invention is not limited to these embodiment.
＜木材セルロースのＴＥＭＰＯ酸化＞
針葉樹クラフトパルプ７０ｇを蒸留水３５００ｇに懸濁し、蒸留水３５０ｇにＴＥＭＰＯを０．７ｇ、臭化ナトリウムを７ｇ溶解させた溶液を加え、２０℃まで冷却した。ここに２ｍｏｌ／Ｌ、密度１．１５ｇ／ｍＬの次亜塩素酸ナトリウム水溶液４５０ｇを滴下により添加し、酸化反応を開始した。系内の温度は常に２０℃に保ち、反応中のｐＨの低下は０．５Ｎの水酸化ナトリウム水溶液を添加することでｐＨ１０に保ち続けた。セルロースの質量に対して、水酸化ナトリウムが３．００ｍｍｏｌ／ｇになったと時点で、過剰量のエタノールを添加し反応を停止させた。その後、ガラスフィルターを用いて蒸留水によるろ過洗浄を繰り返し、酸化パルプを得た。
<TEMPO oxidation of wood cellulose>
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, and a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added and cooled to 20 ° C. 450 g of sodium hypochlorite aqueous solution having a concentration of 2 mol / L and a density of 1.15 g / mL was added dropwise thereto to initiate an oxidation reaction. The temperature in the system was always kept at 20 ° C., and the decrease in pH during the reaction was kept at pH 10 by adding a 0.5N aqueous sodium hydroxide solution. When sodium hydroxide reached 3.00 mmol / g based on the mass of cellulose, an excessive amount of ethanol was added to stop the reaction. Thereafter, filtration and washing with distilled water were repeated using a glass filter to obtain oxidized pulp.
＜酸化パルプのカルボキシル基量測定＞
上記ＴＥＭＰＯ酸化で得た酸化パルプおよび再酸化パルプを固形分重量で０．１ｇ量りとり、１％濃度で水に分散させ、塩酸を加えてｐＨを２．５とした。その後０．５Ｎ水酸化ナトリウム水溶液を用いた電導度滴定法により、カルボキシル基量（ｍｍｏｌ／ｇ）を求めた。結果は１．６ｍｍｏｌ／ｇであった。
<Measurement of carboxyl group content of oxidized pulp>
Oxidized pulp and re-oxidized pulp obtained by the TEMPO oxidation were weighed in an amount of 0.1 g by solid content, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. Thereafter, the carboxyl group amount (mmol / g) was determined by conductometric titration using a 0.5N aqueous sodium hydroxide solution. The result was 1.6 mmol / g.
＜酸化パルプの解繊処理＞
前記ＴＥＭＰＯ酸化で得た酸化パルプ１ｇを９９ｇの蒸留水に分散させ、ジューサーミキサーで３０分間微細化処理し、１％木材ＣＳＮＦ水分散液を得た。
<Oxidized pulp defibration treatment>
1 g of oxidized pulp obtained by the TEMPO oxidation was dispersed in 99 g of distilled water and refined with a juicer mixer for 30 minutes to obtain a 1% wood CSNF aqueous dispersion.
＜微細化セルロース繊維へのアルデヒド基導入＞
前記木材ＣＳＮＦ水分散液に対し、セルロース固形分に対して１．６ｍｍｏｌ／ｇに相当する過よう素酸ナトリウムを添加し、２０℃で２４時間攪拌したのち、透析による脱塩処理を行い、蒸留水で固形分を調整して０．１％表面アルデヒド化ＣＳＮＦ水分散液を得た。
<Introduction of aldehyde group into fine cellulose fiber>
Sodium periodate corresponding to 1.6 mmol / g of cellulose solid content is added to the wood CSNF aqueous dispersion and stirred at 20 ° C. for 24 hours, followed by desalting by dialysis and distillation. The solid content was adjusted with water to obtain a 0.1% surface aldehyded CSNF aqueous dispersion.
＜銀アンモニア錯体の調製＞
硝酸銀０．１ｇを純水１０ｍＬに溶解させたのち、１Ｍのアンモニア水を溶液が透明になるまで添加し、さらに蒸留水で全量を５０ｍＬとなるように調整し、銀アンモニア錯体を含む溶液として調製した。
<Preparation of silver ammonia complex>
After dissolving 0.1 g of silver nitrate in 10 mL of pure water, 1M ammonia water is added until the solution becomes transparent, and the total amount is adjusted to 50 mL with distilled water to prepare a solution containing a silver ammonia complex. did.
＜保護コロイド溶液の調製＞
ポリビニルピロリドン０．５ｇを純水５０ｍＬに溶解させ、保護コロイド溶液として調製した。
<Preparation of protective colloid solution>
Polyvinylpyrrolidone 0.5 g was dissolved in 50 mL of pure water to prepare a protective colloid solution.
＜銀／セルロース複合化微細繊維の作製＞
前記０．１％表面アルデヒド化ＣＳＮＦ水分散液１０ｍＬに対し、前記銀アンモニア錯体溶液を３５ｍＬ、保護コロイド溶液を３５ｍＬ添加し十分攪拌した。その後、６０℃の湯浴中で１２時間攪拌を続け、銀／セルロース複合化微細繊維の水分散体を得た。
<Production of silver / cellulose composite fine fiber>
35 mL of the silver ammonia complex solution and 35 mL of the protective colloid solution were added to 10 mL of the 0.1% surface aldehyde-modified CSNF aqueous dispersion and sufficiently stirred. Thereafter, stirring was continued for 12 hours in a 60 ° C. hot water bath to obtain an aqueous dispersion of silver / cellulose composite fine fibers.
＜銀／セルロース複合化微細繊維の形態観察＞
前記銀／セルロース複合化微細繊維を、走査型透過型電子顕微鏡（ＳＴＥＭ）を用いて観察した結果を図２に示す。この結果、厚さ１から５ｎｍ程度の銀による被覆層を有する微細化セルロース繊維の合成に成功したことが確認された。
<Form observation of silver / cellulose composite fine fiber>
The result of having observed the said silver / cellulose composite fine fiber using the scanning transmission electron microscope (STEM) is shown in FIG. As a result, it was confirmed that the fine cellulose fiber having a coating layer of silver having a thickness of about 1 to 5 nm was successfully synthesized.
＜銀／セルロース複合化微細繊維を用いた透明導電膜の作製＞
前記銀／セルロース複合化微細繊維水分散液を膜厚２５μｍのＰＥＴフィルム上にバーコーター＃１６を用いて塗布し、５０℃で１０分乾燥して前記銀／セルロース複合化微細繊維を含む層を有する積層体を作製した。
<Preparation of transparent conductive film using silver / cellulose composite fine fiber>
The silver / cellulose composite fine fiber aqueous dispersion was coated on a PET film having a film thickness of 25 μm using a bar coater # 16 and dried at 50 ° C. for 10 minutes to form a layer containing the silver / cellulose composite fine fibers. The laminated body which has was produced.
前記積層体に関して、分光光度計（ＵＶ−２４５０、ＳＨＩＭＡＤＺＵ）を用いて可視光線透過率を測定したところ、９２％の値を示した。また、抵抗率計（ロレスタＧＰＭＣＰ−Ｔ６1０型、三菱化学アナリティック）を用い前記積層体の表面抵抗値を測定したところ、８．１×１０２Ω／□ を示した。 When the visible light transmittance of the laminate was measured using a spectrophotometer (UV-2450, SHIMADZU), a value of 92% was shown. Moreover, when the surface resistance value of the said laminated body was measured using the resistivity meter (Loresta GPMCP-T610 type | mold, Mitsubishi Chemical Analytic), 8.1 * 10 < 2 > ohm / square was shown.
前項の結果から、微細化セルロース繊維上を均一に金属で被覆することによって金属／セルロース複合化微細繊維すなわちバイオナノ材料を用いた新規透明導電材料およびそれを基材に塗布することで透明導電膜を作製することに成功した。 From the results of the previous section, by coating the finely divided cellulose fiber uniformly with metal, a novel transparent conductive material using a metal / cellulose composite fine fiber, that is, a bio-nano material, and a transparent conductive film by applying it to a substrate Successfully produced.
＜ブレンダーを用いたセルロースナノファイバーの調製＞
特許文献６に記載の手法に従い、脱リグニン処理を施した木材セルロースを、ブレンダー（Ｖｉｔａ−Ｍｉｘ ＴＮＣ５２００）を用いて３７，０００ｒｐｍで６０分間処理しセルロースナノファイバーを得た。前記セルロースナノファイバーに対し、実施例１と同様の条件で銀／セルロース複合化微細繊維の水分散液を調製し、ＰＥＴフィルム上に塗工した積層体を得た。前記積層体に対して表面抵抗値を測定したところ、１．５×１０２Ω／□を示し、可視光線透過率を測定したところ、７５％の値を示した。機械処理のみで作製したセルロースナノファイバーはＣＳＮＦよりも長軸径が長いため、繊維同士の絡み合いによるパーコレーション効果が増大し、実施例１と比較して、より低抵抗の積層フィルムを作製可能であった。一方、短軸幅もＣＳＮＦと比較して長いことから、前記フィルムの透明性に関しては実施例１よりも低い値となった。
<Preparation of cellulose nanofiber using blender>
According to the method described in Patent Document 6, wood cellulose subjected to delignification treatment was treated at 37,000 rpm for 60 minutes using a blender (Vita-Mix TNC5200) to obtain cellulose nanofibers. An aqueous dispersion of silver / cellulose composite fine fibers was prepared on the cellulose nanofibers under the same conditions as in Example 1 to obtain a laminate coated on a PET film. When the surface resistance value of the laminate was measured, it was 1.5 × 10 2 Ω / □, and the visible light transmittance was measured to be 75%. Cellulose nanofibers produced only by mechanical treatment have a longer axis diameter than CSNF, so the percolation effect due to the entanglement of the fibers increases, and it is possible to produce a laminated film with lower resistance compared to Example 1. It was. On the other hand, since the short axis width is longer than that of CSNF, the transparency of the film was lower than that of Example 1.
＜バクテリアセルロースの調製＞
酢酸菌（Acetobacter xylinum）を４％のコーンスターチおよび４％スクロースを含む滅菌培地を用いて、28℃で１週間静置培養し、バクテリアセルロース（ＢＣ）ペリクルを得た。前記ＢＣペリクル１ｇに対し、亜塩素酸ナトリウム０．５ｇ、蒸留水５０mＬを加え、酢酸で溶液全体をｐＨ３に調整したのち６０℃で３時間漂白し、タンパク質を除去しＢＣを精製した。
<Preparation of bacterial cellulose>
Acetobacter xylinum was statically cultured at 28 ° C. for 1 week using a sterilized medium containing 4% corn starch and 4% sucrose to obtain a bacterial cellulose (BC) pellicle. To 1 g of the BC pellicle, 0.5 g of sodium chlorite and 50 mL of distilled water were added, the whole solution was adjusted to pH 3 with acetic acid, and then bleached at 60 ° C. for 3 hours to remove protein and purify BC.
＜バクテリアセルロースのＴＥＭＯ酸化＞
ＢＣを安定にナノ分散させるため、実施例１と同様の手法でＴＥＭＰＯ触媒酸化を行い、カルボキシル基量を測定した。カルボキシル基量の測定結果は１．０ｍｍｏｌ／ｇであった。
<TEMO oxidation of bacterial cellulose>
In order to stably nano-disperse BC, TEMPO catalytic oxidation was performed in the same manner as in Example 1, and the amount of carboxyl groups was measured. The measurement result of the amount of carboxyl groups was 1.0 mmol / g.
＜酸化バクテリアセルロースの解繊処理＞
前記ＴＥＭＰＯ酸化で得た酸化ＢＣ１ｇを９９ｇの蒸留水に分散させ、ジューサーミキサーで５分間処理し、１％ＢＣ分散液を得た。
<Defibration treatment of oxidized bacterial cellulose>
1 g of oxidized BC obtained by the TEMPO oxidation was dispersed in 99 g of distilled water and treated with a juicer mixer for 5 minutes to obtain a 1% BC dispersion.
＜バクテリアセルロース繊維へのアルデヒド基導入＞
前記ＢＣ水分散液に対し、セルロース固形分に対して１．０ｍｍｏｌ／ｇに相当する過よう素酸ナトリウムを添加し、２０℃で２４時間攪拌したのち透析による脱塩処理を行い、蒸留水で固形分を調整してアルデヒド化されたＢＣの０．１％水分散液を得た。
<Introduction of aldehyde groups into bacterial cellulose fibers>
To the BC aqueous dispersion, sodium periodate corresponding to 1.0 mmol / g with respect to the cellulose solid content was added, stirred at 20 ° C. for 24 hours, then desalted by dialysis, and then with distilled water. A 0.1% aqueous dispersion of aldehyded BC was obtained by adjusting the solid content.
＜銀／バクテリアセルロース複合化微細繊維と透明導電膜の作製＞
実施例１と同様の条件で前記アルデヒド基が導入されたバクテリアセルロースを銀で被覆して銀／バクテリアセルロース複合化微細繊維の水分散液を調製し、ＰＥＴフィルム上に塗工して積層体を得た。前記積層体に対して表面抵抗値を測定したところ、１．１×１０２Ω／□ を示し、可視光線透過率を測定したところ、８６％の値を示した。バクテリアセルロース繊維の短軸径は木材ＣＳＮＦよりも太いことから透明性が実施例１に比較して劣るものの、実施例２よりも良好であった。また、長軸径が木材ＣＳＮＦよりも長いため、繊維同士の絡み合いによるパーコレーション閾値の減少により、実施例１より低抵抗値を有する積層フィルムを作製可能であった。
<Preparation of silver / bacterial cellulose composite fine fiber and transparent conductive film>
Bacterial cellulose introduced with the aldehyde group was coated with silver under the same conditions as in Example 1 to prepare an aqueous dispersion of silver / bacterial cellulose composite fine fibers, and coated on a PET film to form a laminate. Obtained. When the surface resistance value was measured for the laminate, it was 1.1 × 10 2 Ω / □, and the visible light transmittance was measured to be 86%. Since the short axis diameter of the bacterial cellulose fiber was thicker than that of wood CSNF, the transparency was inferior to that of Example 1, but was better than that of Example 2. Moreover, since the major axis diameter was longer than that of wood CSNF, it was possible to produce a laminated film having a lower resistance value than that of Example 1 due to a decrease in percolation threshold due to entanglement of fibers.
[比較例１]
＜セルロースナノウィスカーの調製＞
針葉樹漂白クラフトパルプに対し、９６％濃硫酸を用いて３０℃、２４時間、酸加水分解を行い、得られた残渣をろ過洗浄してセルロースナノウィスカーを得た。透過型電子顕微鏡によって前記セルロースナノウィスカーを観察したところ、短軸径は１０ｎｍから２０ｎｍ、長軸径は２００ｎｍから４００ｎｍ程度であった。
[Comparative Example 1]
<Preparation of cellulose nanowhisker>
The conifer bleached kraft pulp was acid hydrolyzed with 96% concentrated sulfuric acid at 30 ° C. for 24 hours, and the resulting residue was filtered and washed to obtain cellulose nanowhiskers. When the cellulose nanowhisker was observed with a transmission electron microscope, the minor axis diameter was 10 nm to 20 nm, and the major axis diameter was about 200 nm to 400 nm.
＜銀／セルロースナノウィスカー複合化微細繊維と透明導電膜の作製＞
前記セルロースナノウィスカーに対し、実施例１と同様の条件で銀を析出させ銀／セルロース複合化微細繊維の水分散液を調製し、ＰＥＴフィルム上に塗工した積層体を得た。前記積層体に対して表面抵抗値を測定したところ、２．９×１０１０Ω／□ を示した。セルロースナノウィスカーを用いた場合、長軸径／短軸径のアスペクト比が小さくなることから、パーコレーション閾値が上昇し、導電性を発現できないと考えられる。
<Preparation of silver / cellulose nanowhisker composite fine fiber and transparent conductive film>
Silver was deposited on the cellulose nanowhiskers under the same conditions as in Example 1 to prepare an aqueous dispersion of silver / cellulose composite fine fibers, and a laminate coated on a PET film was obtained. When measuring the surface resistance value with respect to the laminate showed 2.9 × 10 10 Ω / □. When cellulose nanowhiskers are used, the aspect ratio of the major axis diameter / minor axis diameter decreases, so the percolation threshold rises, and it is considered that conductivity cannot be expressed.
本発明によればバイオマスを用いた低環境負荷プロセスにより高透明導電材料および透明導電膜を提供することが可能となり、カーボンニュートラルなＩＴＯ代替材料としてタッチパネル、電磁波シールド、電子ペーパー、太陽電池用電極、有機EL用電極といった様々な分野への応用が期待される。 According to the present invention, it becomes possible to provide a highly transparent conductive material and a transparent conductive film by a low environmental load process using biomass, and as a carbon neutral ITO substitute material, a touch panel, an electromagnetic wave shield, electronic paper, a solar cell electrode, Applications in various fields such as organic EL electrodes are expected.
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