JP4713274B2 - Method for producing polylactic acid resin foam - Google Patents
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本発明は、生分解性及び静菌性に優れたポリ乳酸系樹脂発泡体及びその製造方法に関する。 The present invention relates to a polylactic acid resin foam excellent in biodegradability and bacteriostatic properties and a method for producing the same.
ポリ乳酸系樹脂は、天然に存在する乳酸を重合されて得られた樹脂であり、自然界に存在する微生物によって分解可能な生分解性樹脂であると共に、常温での機械的特性についても優れていることから注目を集めている。 Polylactic acid resin is a resin obtained by polymerizing naturally occurring lactic acid, is a biodegradable resin that can be decomposed by microorganisms existing in nature, and has excellent mechanical properties at room temperature. It attracts attention.
ポリ乳酸系樹脂の原料となる乳酸は、分子中に不斉炭素原子を有するために光学活性を示し、Ｄ体、Ｌ体、及び、Ｄ体とＬ体とが等量混合してなるラセミ体の三種類が存在する。 Lactic acid, which is a raw material for polylactic acid-based resins, exhibits optical activity because it has an asymmetric carbon atom in the molecule, and racemates in which D-form, L-form, and D-form and L-form are mixed in equal amounts There are three types.
そのために、乳酸を重合させて得られるポリ乳酸系樹脂は、上記三種類の乳酸の混合割合と重合方法を調整することによって種々の性質を有するものとすることができ、現実に、ポリ乳酸には、結晶性のものから非結晶性のものまで多種多様存在し、融点又は軟化点も様々である。 Therefore, the polylactic acid-based resin obtained by polymerizing lactic acid can have various properties by adjusting the mixing ratio of the above three kinds of lactic acid and the polymerization method. Have a wide variety from crystalline to non-crystalline, and have various melting points or softening points.
そして、ポリ乳酸を用いた発泡体としては、特許文献１に、ポリ乳酸、又は、乳酸とヒドロキシカルボン酸とのコポリマーを主成分とする熱可塑性ポリマー組成物からなる緩衝材が提案されており、又、特許文献２に、ポリ乳酸系重合体を主成分とする熱可塑性重合体と、（メタ）アクリル酸エステル及び／又はグリシジルエーテルとを有機過酸化物の存在下に架橋反応させて得られる発泡用樹脂組成物を発泡成形した発泡体であって、密度が０．０４ｇ／ｃｍ3 以下である生分解性樹脂発泡体が提案されている。 As a foam using polylactic acid, Patent Document 1 proposes a buffer material made of a thermoplastic polymer composition mainly composed of polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid, Also obtained in Patent Document 2 is a cross-linking reaction between a thermoplastic polymer mainly composed of a polylactic acid polymer and (meth) acrylic acid ester and / or glycidyl ether in the presence of an organic peroxide. A biodegradable resin foam having a density of 0.04 g / cm 3 or less has been proposed, which is a foam obtained by foam-molding a foaming resin composition.
一方、近年、食品衛生及びその管理面の観点から、静菌性に優れ、野菜、果実などの食品の鮮度保持性に優れていると共に環境衛生に優れた食品用の包材となり得る発泡体が求められているが、上述した発泡体は、生分解性を有している点において環境衛生に優れているものの、静菌性に欠け、上述した要望を充分に満たすものではなかった。
本発明は、静菌性に優れており食品の鮮度保持性に優れ且つ生分解性を有し環境衛生にも優れたポリ乳酸系樹脂発泡体及びその製造方法を提供する。 The present invention provides a polylactic acid-based resin foam excellent in bacteriostatic properties, excellent in freshness retention of food, biodegradable and excellent in environmental sanitation, and a method for producing the same.
本発明のポリ乳酸系樹脂発泡体の製造方法で製造されるポリ乳酸系樹脂発泡体は、乳酸含有量が全重量に対して４０〜４００ｐｐｍである。このポリ乳酸系樹脂発泡体を構成するポリ乳酸系樹脂は、下記式３で示される。このポリ乳酸系樹脂は、Ｌ−乳酸及び／又はＤ−乳酸を重合させるか、或いは、Ｌ−ラクチド、Ｄ−ラクチド及びＤＬ−ラクチドからなる群より選ばれた一又は二以上のラクチドを開環重合させることによって得ることができ、何れのポリ乳酸系樹脂であってもよい。 Polylactic acid resin foam produced by the production method of the polylactic acid resin foam of the present invention, lactic acid content of at 40~400ppm relative to the total weight. The polylactic acid resin constituting the polylactic acid resin foam is represented by the following formula 3. This polylactic acid resin polymerizes L-lactic acid and / or D-lactic acid, or opens one or two or more lactides selected from the group consisting of L-lactide, D-lactide and DL-lactide. Any polylactic acid resin can be used.
ポリ乳酸系樹脂を製造するに際して、モノマーとしてＬ体とＤ体とを併用した場合において、Ｄ体又はＬ体の何れか少ない方の割合が５重量％以下である時は、得られるポリ乳酸系樹脂は、その結晶性が高くなる一方、Ｄ体又はＬ体の何れか少ない方の割合が５重量％を越えて増加するにしたがって、得られるポリ乳酸系樹脂は、その結晶性が低くなり、やがて非結晶となる。得られるポリ乳酸系樹脂発泡体の耐熱性や機械的強度が優れていることから、結晶性のポリ乳酸系樹脂を用いることが好ましい。 When the L-form and D-form are used in combination in the production of a polylactic acid-based resin and the ratio of the smaller of either the D-form or the L-form is 5% by weight or less, the resulting polylactic acid series While the resin has higher crystallinity, the polylactic acid resin obtained has lower crystallinity as the proportion of the smaller of D-form or L-form increases beyond 5% by weight. It will eventually become amorphous. Since the resulting polylactic acid resin foam has excellent heat resistance and mechanical strength, it is preferable to use a crystalline polylactic acid resin.
そして、ポリ乳酸系樹脂を製造するのに用いたモノマーが、Ｌ体とＤ体とを併用し、且つ、Ｄ体又はＬ体の何れか少ない方の割合が５重量％を越えている時は、得られるポリ乳酸系樹脂は、その結晶化速度が遅い。従って、ポリ乳酸系樹脂発泡体を押出発泡によって比較的容易に製造することができ、押出発泡時に押出温度、発泡剤の種類及び量、押出圧力などの押出発泡条件を制御することによって所望のポリ乳酸系樹脂発泡体を得ることができる。 And when the monomer used to produce the polylactic acid-based resin uses both L-form and D-form, and the ratio of the smaller of either D-form or L-form exceeds 5% by weight The resulting polylactic acid resin has a slow crystallization rate. Therefore, a polylactic acid-based resin foam can be produced relatively easily by extrusion foaming, and the desired foam can be controlled by controlling extrusion foaming conditions such as extrusion temperature, type and amount of foaming agent, and extrusion pressure during extrusion foaming. A lactic acid resin foam can be obtained.
一方、ポリ乳酸系樹脂を製造するのに用いたモノマーが、Ｌ体とＤ体とを併用し、且つ、Ｄ体又はＬ体の何れか少ない方の割合が５重量％以下である時は、得られるポリ乳酸系樹脂は、その結晶化速度が速い。従って、ポリ乳酸系樹脂発泡体を押出発泡によって製造する場合には、押出発泡に適したポリ乳酸系樹脂を選択することが好ましく、ポリ乳酸系樹脂を選択する際の目安として、ポリ乳酸系樹脂の動的粘弾性測定にて得られた貯蔵弾性率及び損失弾性率を挙げることができる。 On the other hand, when the monomer used to produce the polylactic acid-based resin uses the L-form and the D-form together, and the proportion of either the D-form or the L-form is less than 5% by weight, The resulting polylactic acid resin has a high crystallization rate. Therefore, when a polylactic acid resin foam is produced by extrusion foaming, it is preferable to select a polylactic acid resin suitable for extrusion foaming. As a guideline for selecting a polylactic acid resin, a polylactic acid resin is preferable. The storage elastic modulus and loss elastic modulus obtained by the dynamic viscoelasticity measurement can be mentioned.
ここで、動的粘弾性測定にて得られた貯蔵弾性率は、粘弾性において弾性的な性質を示す指標であって、発泡過程における気泡膜の弾性の大小を示す指標であり、発泡過程において、気泡膜の収縮力に抗して気泡を膨張させるのに必要な発泡圧の大小を示す指標である。 Here, the storage elastic modulus obtained by the dynamic viscoelasticity measurement is an index indicating elastic properties in the viscoelasticity, and is an index indicating the elasticity of the bubble film in the foaming process. This is an index indicating the magnitude of the foaming pressure required to expand the bubbles against the contraction force of the bubble film.
即ち、ポリ乳酸系樹脂の動的粘弾性測定にて得られた貯蔵弾性率が低いと、気泡膜が伸長された場合、気泡膜が伸長力に抗して収縮しようとする力が小さく、ポリ乳酸系樹脂発泡体の製造に必要とする発泡圧によって発泡膜が容易に伸長してしまう結果、気泡膜が過度に伸長してしまい破泡を生じる一方、ポリ乳酸系樹脂の動的粘弾性測定にて得られた貯蔵弾性率が高いと、気泡膜に伸長力が加わった場合、伸長に抗する気泡膜の収縮力が大きく、ポリ乳酸系樹脂発泡体の製造に必要とする発泡圧で一旦、気泡が膨張したとしても、温度低下などに起因する経時的な発泡圧の低下に伴って気泡が収縮してしまう。 That is, if the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is low, when the cell membrane is stretched, the force that the cell membrane attempts to contract against the stretching force is small. Dynamic foaming measurement of polylactic acid resin, while foam film easily stretches due to foaming pressure required for production of lactic acid resin foam, resulting in excessive expansion of bubble film and bubble breakage When the storage modulus obtained in (2) is high, when the expansion force is applied to the cell membrane, the cell membrane has a large shrinkage force against the expansion, and once the foam pressure required for the production of the polylactic acid resin foam is reached. Even if the bubbles expand, the bubbles contract as the foaming pressure decreases with time due to a temperature drop or the like.
又、動的粘弾性測定にて得られた損失弾性率は、粘弾性において粘性的な性質を示す指標であって、発泡過程における気泡膜の粘性を示す指標であり、発泡過程において、気泡膜をどの程度まで破れることなく伸長させることができるかの許容範囲を示す指標であると同時に、発泡圧によって所望大きさに気泡を膨張させた後、この膨張した気泡をその大きさに維持する能力を示す指標でもある。 Further, the loss modulus obtained by dynamic viscoelasticity measurement is an index indicating a viscous property in viscoelasticity, and is an index indicating the viscosity of the bubble film in the foaming process. This is an index indicating the allowable range of how much can be expanded without breaking, and at the same time, the ability to expand the bubbles to the desired size by the foaming pressure and then maintain the expanded bubbles at that size It is also an indicator that indicates.
即ち、ポリ乳酸系樹脂の動的粘弾性測定にて得られた損失弾性率が低いと、ポリ乳酸系樹脂発泡体の製造に必要とする発泡圧によって気泡膜が伸長された場合、気泡膜が容易に破れてしまう一方、ポリ乳酸系樹脂の動的粘弾性測定にて得られた損失弾性率が高いと、発泡力が気泡膜によって熱エネルギーに変換されてしまい、ポリ乳酸系樹脂発泡体の製造時に気泡膜を円滑に伸長させることができず、気泡を膨張させることができない。 That is, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is low, when the cell membrane is stretched by the foaming pressure required for the production of the polylactic acid-based resin foam, On the other hand, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid resin is high, the foaming force is converted into thermal energy by the cell membrane, and the polylactic acid resin foam The bubble membrane cannot be extended smoothly during production, and the bubbles cannot be expanded.
このように、ポリ乳酸系樹脂を発泡させてポリ乳酸系樹脂発泡体を製造するにあたっては、発泡過程において、ポリ乳酸系樹脂は、ポリ乳酸系樹脂発泡体を得るために必要とされる発泡圧によって気泡膜が破れることなく適度に伸長するための弾性力、即ち、貯蔵弾性率を有している必要があると共に、上記発泡圧によって気泡膜が破れることなく円滑に伸長し、所望大きさに膨張した気泡をその大きさに発泡圧の経時的な減少にかかわらず維持しておくための粘性力、即ち、損失弾性率を有している必要がある。 Thus, in producing a polylactic acid resin foam by foaming a polylactic acid resin, in the foaming process, the polylactic acid resin has a foaming pressure required to obtain a polylactic acid resin foam. It is necessary to have an elastic force for stretching the bubble film appropriately without breaking, i.e., a storage elastic modulus, and the bubble film can be smoothly stretched without breaking by the foaming pressure, to a desired size. It is necessary to have a viscous force, that is, a loss elastic modulus, for maintaining the expanded bubble in its size regardless of the decrease in the foaming pressure with time.
つまり、発泡工程において、ポリ乳酸系樹脂の貯蔵弾性率及び損失弾性率の双方が発泡に適した値を有している必要があり、このような発泡に適した貯蔵弾性率及び損失弾性率を発泡工程においてポリ乳酸系樹脂に付与するために、動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔとポリ乳酸系樹脂の融点（ｍｐ）とが、好ましくは下記式４を満たすように、より好ましくは式５を満たすように、特に好ましくは式６を満たすように調整することによって、ポリ乳酸系樹脂の貯蔵弾性率及び損失弾性率をそれらのバランスをとりながら発泡に適したものとしてポリ乳酸系樹脂の発泡性を良好なものとし、ポリ乳酸系樹脂発泡体を安定的に製造することができる。 That is, in the foaming process, both the storage elastic modulus and loss elastic modulus of the polylactic acid-based resin must have values suitable for foaming, and the storage elastic modulus and loss elastic modulus suitable for such foaming are set. In order to impart to the polylactic acid resin in the foaming step, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement and the melting point (mp) of the polylactic acid resin However, the storage elastic modulus and the loss elastic modulus of the polylactic acid resin are preferably adjusted so as to satisfy the following formula 4, more preferably the formula 5, and particularly preferably the formula 6. Therefore, it is possible to stably produce a polylactic acid-based resin foam by making the polylactic acid-based resin suitable for foaming while maintaining a good balance.
〔ポリ乳酸系樹脂の融点（ｍｐ）−４０℃〕
≦交点における温度Ｔ≦ポリ乳酸系樹脂の融点（ｍｐ）・・・式４
[Melting point of polylactic acid resin (mp) −40 ° C.]
≦ Temperature at the intersection T ≦ Melting point of polylactic acid resin (mp) Equation 4
〔ポリ乳酸系樹脂の融点（ｍｐ）−３５℃〕
≦交点における温度Ｔ≦〔ポリ乳酸系樹脂の融点（ｍｐ）−１０℃〕・・・式５
[Melting point of polylactic acid resin (mp) -35 ° C.]
≦ Temperature at the intersection T ≦ [melting point of polylactic acid resin (mp) −10 ° C.] Formula 5
〔ポリ乳酸系樹脂の融点（ｍｐ）−３０℃〕
≦交点における温度Ｔ≦〔ポリ乳酸系樹脂の融点（ｍｐ）−２０℃〕・・・式６
[Melting point of polylactic acid resin (mp) -30 ° C.]
≦ Temperature at the intersection T ≦ [melting point of polylactic acid resin (mp) −20 ° C.] Formula 6
更に、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔとポリ乳酸系樹脂の融点（ｍｐ）とが上記式４を満たすように調整することが好ましい理由を下記に詳述する。 Furthermore, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin and the melting point (mp) of the polylactic acid resin satisfy the above formula 4. The reason why it is preferable to make such adjustment will be described in detail below.
先ず、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔが、ポリ乳酸系樹脂の融点（ｍｐ）よりも４０℃を越えて低い場合には、押出発泡時におけるポリ乳酸系樹脂の損失弾性率が貯蔵弾性率に比して大き過ぎるために、損失弾性率と貯蔵弾性率とのバランスが崩れてしまう。 First, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement of the polylactic acid resin exceeds 40 ° C. than the melting point (mp) of the polylactic acid resin. If it is low, the loss elastic modulus of the polylactic acid resin at the time of extrusion foaming is too large compared with the storage elastic modulus, so that the balance between the loss elastic modulus and the storage elastic modulus is lost.
そこで、ポリ乳酸系樹脂の損失弾性率に適した発泡力、即ち、ポリ乳酸系樹脂の粘性に合わせた発泡力とすると、ポリ乳酸系樹脂の弾性力にとっては発泡力が大き過ぎてしまい、気泡膜が破れて破泡を生じて良好な発泡体を得ることができず、逆に、ポリ乳酸系樹脂の貯蔵弾性率に適した発泡力、即ち、ポリ乳酸系樹脂の弾性に合わせた発泡力とすると、ポリ乳酸系樹脂の粘性力にとっては発泡力が小さく、ポリ乳酸系樹脂が発泡しにくくなり、やはり良好な発泡体を得ることができない。 Therefore, if the foaming force suitable for the loss elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the viscosity of the polylactic acid-based resin, the foaming force is too large for the elastic force of the polylactic acid-based resin. The film breaks and foam breaks, and a good foam cannot be obtained. Conversely, the foaming force suitable for the storage elastic modulus of the polylactic acid resin, that is, the foaming force that matches the elasticity of the polylactic acid resin Then, the foaming force is small for the viscous force of the polylactic acid-based resin, and the polylactic acid-based resin is difficult to foam, and a good foam cannot be obtained.
又、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔが、ポリ乳酸系樹脂の融点（ｍｐ）よりも高いと、押出発泡時におけるポリ乳酸系樹脂の貯蔵弾性率が損失弾性率に比して大き過ぎるために、上述と同様に損失弾性率と貯蔵弾性率とのバランスが崩れてしまう。 Further, when the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin is higher than the melting point (mp) of the polylactic acid resin, Since the storage elastic modulus of the polylactic acid resin at the time of foaming is too large compared to the loss elastic modulus, the balance between the loss elastic modulus and the storage elastic modulus is lost as described above.
そこで、ポリ乳酸系樹脂の貯蔵弾性率に適した発泡力、即ち、ポリ乳酸系樹脂の弾性に合わせた発泡力とすると、ポリ乳酸系樹脂の粘性力にとっては発泡力が大き過ぎてしまい、気泡膜が破れて破泡を生じて良好な発泡体を得ることができず、逆に、ポリ乳酸系樹脂の損失弾性率に適した発泡力、即ち、ポリ乳酸系樹脂の粘性に合わせた発泡力とすると、ポリ乳酸系樹脂の弾性力にとっては発泡力が小さく、ポリ乳酸系樹脂が発泡力で一旦、発泡したとしても、経時的な発泡力の低下に伴って気泡が収縮してしまって、やはり良好な発泡体を得ることができない。 Therefore, if the foaming force suitable for the storage elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the elasticity of the polylactic acid-based resin, the foaming force is too large for the viscosity force of the polylactic acid-based resin, The film breaks and foam breaks, and a good foam cannot be obtained. Conversely, the foaming force suitable for the loss elastic modulus of the polylactic acid resin, that is, the foaming force that matches the viscosity of the polylactic acid resin Then, the foaming force is small for the elastic force of the polylactic acid-based resin, and even if the polylactic acid-based resin is once foamed by the foaming force, the bubbles shrink as the foaming force decreases over time, After all, a good foam cannot be obtained.
そして、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔと、ポリ乳酸系樹脂の融点（ｍｐ）とが上記式４を満たすように調整する方法としては、ポリ乳酸系樹脂の重量平均分子量が高くなるにしたがって、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔが高くなることから、ポリ乳酸系樹脂の重合時に反応時間或いは反応温度を調整することによって、得られるポリ乳酸系樹脂の重量平均分子量を調整する方法、押出発泡前に或いは押出発泡時にポリ乳酸系樹脂の重量平均分子量を増粘剤や架橋剤を用いて調整する方法が挙げられる。 And, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin and the melting point (mp) of the polylactic acid-based resin satisfy the above formula 4. As a method of adjusting so as to satisfy, as the weight average molecular weight of the polylactic acid resin increases, the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin Since the temperature T at the intersection becomes high, a method for adjusting the weight average molecular weight of the obtained polylactic acid resin by adjusting the reaction time or reaction temperature during polymerization of the polylactic acid resin, before extrusion foaming or extrusion foaming A method of adjusting the weight average molecular weight of the polylactic acid resin sometimes using a thickener or a crosslinking agent is mentioned.
このような観点から、ポリ乳酸系樹脂の重量平均分子量は、１４０，０００〜３００，０００が好ましく、１５０，０００〜２７０，０００がより好ましく、１６０，０００〜２５０，０００が特に好ましい。更に、ポリ乳酸系樹脂の分子量分布（重量平均分子量Ｍｗ／数平均分子量Ｍｎ）は、３．２〜１０が好ましく、３．４〜９がより好ましく、３．６〜８が特に好ましい。 From such a viewpoint, the weight average molecular weight of the polylactic acid-based resin is preferably 140,000 to 300,000, more preferably 150,000 to 270,000, and particularly preferably 160,000 to 250,000. Furthermore, the molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the polylactic acid-based resin is preferably 3.2 to 10, more preferably 3.4 to 9, and particularly preferably 3.6 to 8.
この他に、Ｌ体の比率がＤ体の比率に比して大きいモノマーから得られたポリ乳酸系樹脂の場合、Ｄ体の比率が増加するにつれてポリ乳酸系樹脂の融点（ｍｐ）が低下することから、モノマー中のＤ体の比率を調整することによってポリ乳酸系樹脂の融点（ｍｐ）を調整し、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔと、ポリ乳酸系樹脂の融点（ｍｐ）とが上記式４を満たすように調整する方法が挙げられる。 In addition, in the case of a polylactic acid resin obtained from a monomer in which the ratio of the L isomer is larger than that of the D isomer, the melting point (mp) of the polylactic acid resin decreases as the D isomer ratio increases. From the above, the storage modulus curve and loss obtained by adjusting the melting point (mp) of the polylactic acid resin by adjusting the ratio of D-form in the monomer and by measuring the dynamic viscoelasticity of the polylactic acid resin Examples include a method of adjusting the temperature T at the intersection with the elastic modulus curve and the melting point (mp) of the polylactic acid resin so as to satisfy the above formula 4.
ここで、ポリ乳酸系樹脂の融点（ｍｐ）は下記の要領で測定されたものをいう。即ち、ＪＩＳ Ｋ７１２１：１９８７に準拠してポリ乳酸系樹脂の示差走査熱量分析を行い、得られたＤＳＣ曲線における融解ピークの温度をポリ乳酸系樹脂の融点（ｍｐ）とする。なお、融解ピークの温度が複数個ある場合には、最も高い温度とする。 Here, the melting point (mp) of the polylactic acid resin is measured in the following manner. That is, the differential scanning calorimetry of the polylactic acid resin is performed in accordance with JIS K7121: 1987, and the melting peak temperature in the obtained DSC curve is defined as the melting point (mp) of the polylactic acid resin. When there are a plurality of melting peak temperatures, the highest temperature is set.
又、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔは下記の要領で測定されたものをいう。即ち、ポリ乳酸系樹脂を９．３３×１０4 Ｐａの減圧下にて８０℃で３時間に亘って乾燥する。このポリ乳酸系樹脂を該ポリ乳酸系樹脂の融点よりも４０〜５０℃だけ高い温度に加熱した測定プレート上に載置して窒素雰囲気下にて５分間に亘って放置し溶融させる。 Further, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin means that measured in the following manner. That is, the polylactic acid resin is dried at 80 ° C. for 3 hours under a reduced pressure of 9.33 × 10 4 Pa. This polylactic acid-based resin is placed on a measurement plate heated to a temperature higher by 40 to 50 ° C. than the melting point of the polylactic acid-based resin, and allowed to stand for 5 minutes in a nitrogen atmosphere to melt.
次に、直径が２５ｍｍの平面円形状の押圧板を用意し、この押圧板を用いて測定プレート上のポリ乳酸系樹脂を押圧板と測定プレートとの対向面間の間隔が１ｍｍとなるまで上下方向に押圧する。そして、押圧板の外周縁からはみ出したポリ乳酸系樹脂を除去した後、５分間に亘って放置する。 Next, a flat circular pressure plate having a diameter of 25 mm is prepared, and the polylactic acid resin on the measurement plate is moved up and down until the distance between the opposing surfaces of the pressure plate and the measurement plate becomes 1 mm. Press in the direction. And after removing the polylactic acid-type resin which protruded from the outer periphery of a press plate, it is left to stand for 5 minutes.
しかる後、歪み５％、周波数１ｒａｄ／秒、降温速度２℃／分、測定間隔３０秒の条件下にて、ポリ乳酸系樹脂の動的粘弾性測定を行って貯蔵弾性率及び損失弾性率を測定する。次に、横軸を温度とし、縦軸を貯蔵弾性率及び損失弾性率として、貯蔵弾性率曲線及び損失弾性率曲線を描く。なお、貯蔵弾性率曲線及び損失弾性率曲線を描くにあたっては、測定温度を基準として互いに隣接する測定値同士を直線で結ぶ。 Thereafter, the dynamic viscoelasticity measurement of the polylactic acid resin is performed under the conditions of 5% strain, frequency 1 rad / sec, temperature drop rate 2 ° C./min, and measurement interval 30 sec to determine the storage elastic modulus and loss elastic modulus. taking measurement. Next, a storage elastic modulus curve and a loss elastic modulus curve are drawn with the horizontal axis as temperature and the vertical axis as storage elastic modulus and loss elastic modulus. In drawing the storage elastic modulus curve and the loss elastic modulus curve, the measurement values adjacent to each other are connected with a straight line based on the measurement temperature.
そして、得られた貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔを上記グラフから読み取ることによって得ることができる。なお、貯蔵弾性率曲線と損失弾性率曲線とが複数箇所において互いに交差する場合は、貯蔵弾性率曲線と損失弾性率曲線との複数の交点における温度のうち最も高い温度を、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔとする。 And it can obtain by reading the temperature T in the intersection of the obtained storage elastic modulus curve and loss elastic modulus curve from the said graph. When the storage modulus curve and the loss modulus curve intersect each other at a plurality of locations, the highest temperature among the temperatures at the plurality of intersections of the storage modulus curve and the loss modulus curve is defined as the storage modulus curve. It is set as the temperature T in the intersection with a loss elastic modulus curve.
又、動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔは、Reologica Instruments A.B 社から商品名「DynAlyser DAR-100」 にて市販されている動的粘弾性測定装置を用いて測定することができる。 The temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement is a dynamic value commercially available from Reologica Instruments AB under the trade name “DynAlyser DAR-100”. It can be measured using a mechanical viscoelasticity measuring device.
ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔでの弾性率、即ち、貯蔵弾性率又は損失弾性率は、低いと、発泡中のポリ乳酸系樹脂の粘弾性が低くなり、気泡膜が発泡圧によって破れて破泡を生じることがある一方、高いと、発泡圧によって気泡膜を伸長させて気泡を所望大きさに膨張させることができず、発泡が不安定になることがあるので、１．０×１０3 〜１．０×１０5 Ｐａが好ましく、５．０×１０3 〜９．０×１０4 Ｐａがより好ましく、１．０×１０4 〜８．０×１０4 Ｐａが特に好ましい。 The elastic modulus at the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin, that is, the storage elastic modulus or the loss elastic modulus is low While the foamed polylactic acid resin has low viscoelasticity, the foam film may be broken by foaming pressure to cause foam breakage. On the other hand, when the foam is high, the foam film is expanded by the foaming pressure to expand the foam to the desired size. 1.0 × 10 3 to 1.0 × 10 5 Pa is preferable, and 5.0 × 10 3 to 9.0 × 10 4 Pa is more preferable. 1.0 × 10 4 to 8.0 × 10 4 Pa is particularly preferable.
なお、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔでの弾性率（貯蔵弾性率又は損失弾性率）は、ポリ乳酸系樹脂の重合時に反応時間或いは反応温度を調整することによって、ポリ乳酸系樹脂の重量平均分子量を調整する方法、押出発泡前に或いは押出発泡時にポリ乳酸系樹脂の重量平均分子量を増粘剤や架橋剤を用いて調整する方法が挙げられる。 The elastic modulus (storage elastic modulus or loss elastic modulus) at temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement of the polylactic acid resin is polylactic acid. A method of adjusting the weight average molecular weight of the polylactic acid resin by adjusting the reaction time or reaction temperature during polymerization of the resin, the viscosity average molecular weight of the polylactic acid resin before or during extrusion foaming The method of adjusting using a crosslinking agent is mentioned.
そして、本発明では、乳酸が有する静菌作用について着目し、乳酸を所定量だけ含有させることによって、ポリ乳酸系樹脂発泡体の機械的強度や耐熱性などの物理的特性を維持しつつ、ポリ乳酸系樹脂発泡体に優れた静菌性を付与して野菜や果物などの鮮度保持性に優れたものとしている。 And in this invention , paying attention to the bacteriostatic action which lactic acid has , by containing only a predetermined amount of lactic acid, while maintaining the physical properties such as mechanical strength and heat resistance of the polylactic acid resin foam, Bacteriostatic properties are imparted to the lactic acid-based resin foam to provide excellent freshness retention for vegetables and fruits.
具体的には、ポリ乳酸系樹脂発泡体中に含有されている乳酸含有量は、少ないと、ポリ乳酸系樹脂発泡体に優れた静菌性を付与することができない一方、多いと、ポリ乳酸系樹脂発泡体の気泡が粗大化して外観が低下し、良好なポリ乳酸系樹脂発泡体を得ることができないので、ポリ乳酸系樹脂発泡体の全重量に対して４０〜４００ｐｐｍに限定され、５０〜４００ｐｐｍが好ましく、６０〜４００ｐｐｍがより好ましい。 Specifically, if the content of lactic acid contained in the polylactic acid-based resin foam is small, excellent bacteriostatic properties cannot be imparted to the polylactic acid-based resin foam. The foam of the resin-based resin foam becomes coarse and the appearance is lowered, and a good polylactic acid-based resin foam cannot be obtained. Therefore, the amount is limited to 40 to 400 ppm with respect to the total weight of the polylactic acid-based resin foam. -400 ppm is preferable, and 60-400 ppm is more preferable.
次に、上記ポリ乳酸系樹脂発泡体の製造方法について説明する。ポリ乳酸系樹脂発泡体の製造方法としては、例えば、ポリ乳酸系樹脂を押出機に供給して発泡剤の存在下にて溶融混練した後、押出機から押出発泡させてポリ乳酸系樹脂発泡体を製造するにあたり、ポリ乳酸系樹脂を後述する要領で押出機内において加水分解及び／又は熱分解させて乳酸を生成させ、ポリ乳酸系樹脂発泡体中に含有される乳酸量をポリ乳酸系樹脂発泡体の全重量に対して４０〜４００ｐｐｍに調整する方法が挙げられる。 Next, the manufacturing method of the said polylactic acid-type resin foam is demonstrated. As a method for producing a polylactic acid-based resin foam, for example, a polylactic acid-based resin foam is obtained by supplying a polylactic acid-based resin to an extruder, melt-kneading in the presence of a foaming agent, and then extruding and foaming from the extruder. In producing the lactic acid, the polylactic acid resin is hydrolyzed and / or thermally decomposed in an extruder in the manner described later to produce lactic acid, and the amount of lactic acid contained in the polylactic acid resin foam is changed to the polylactic acid resin foam. The method of adjusting to 40-400 ppm with respect to the total weight of a body is mentioned.
なお、上記押出機としては、従来から汎用されている押出機であれば、特に限定されず、例えば、単軸押出機、二軸押出機、複数の押出機を連結させたタンデム型の押出機が挙げられ、タンデム型の押出機が好ましい。 The extruder is not particularly limited as long as it is a conventionally used extruder. For example, a single-screw extruder, a twin-screw extruder, and a tandem extruder in which a plurality of extruders are connected. A tandem type extruder is preferable.
又、上記発泡剤としては、従来から汎用されているものが用いられ、例えば、ノルマルブタン、イソブタン、ノルマルペンタン、イソペンタン、二酸化炭素、窒素などが挙げられ、ノルマルブタン、イソブタン、ジメチルエーテルが好ましい。 As the foaming agent, those conventionally used are used, and examples thereof include normal butane, isobutane, normal pentane, isopentane, carbon dioxide, nitrogen and the like, and normal butane, isobutane and dimethyl ether are preferable.
そして、押出機に供給される発泡剤量としては、少ないと、ポリ乳酸系樹脂発泡体の発泡倍率が低下して、低密度なポリ乳酸系樹脂発泡体を得ることができないことがある一方、多いと、ポリ乳酸系樹脂発泡体の製造時に金型内において内部発泡を生じていまい、良好なポリ乳酸系樹脂発泡体を製造することができないことがあるので、ポリ乳酸系樹脂１００重量部に対して０．１〜１０重量部が好ましく、０．２〜９重量部がより好ましく、０．３〜８重量部が特に好ましい。 And as the amount of the foaming agent supplied to the extruder, if the amount is small, the expansion ratio of the polylactic acid resin foam may be reduced, and a low density polylactic acid resin foam may not be obtained, If it is too large, internal foaming may not occur in the mold during the production of the polylactic acid resin foam, and a good polylactic acid resin foam may not be produced. In contrast, 0.1 to 10 parts by weight is preferable, 0.2 to 9 parts by weight is more preferable, and 0.3 to 8 parts by weight is particularly preferable.
なお、押出機には、気泡調整剤、結晶核剤、帯電防止剤、難燃剤、着色剤などの添加剤が供給されてもよい。上記気泡調整剤としては、例えば、ポリテトラフルオロエチレン粉末、アクリル樹脂で変性されたポリテトラフルオロエチレン粉末、タルク、炭酸カルシウム、硼砂、硼酸亜鉛、水酸化アルミニウム、シリカ、炭酸ナトリウム、重炭酸ナトリウム、炭酸リチウム、炭酸カリウムなどが挙げられ、ポリテトラフルオロエチレン粉末、アクリル樹脂で変性されたポリテトラフルオロエチレン粉末が好ましい。又、押出機に供給される気泡調整剤の量としては、ポリ乳酸系樹脂１００重量部に対して０．０１〜３重量部が好ましく、０．０５〜２重量部がより好ましく、０．１〜１重量部が特に好ましい。 The extruder may be supplied with additives such as a bubble adjusting agent, a crystal nucleating agent, an antistatic agent, a flame retardant, and a colorant. Examples of the air conditioner include polytetrafluoroethylene powder, polytetrafluoroethylene powder modified with an acrylic resin, talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, silica, sodium carbonate, sodium bicarbonate, Examples thereof include lithium carbonate and potassium carbonate, and polytetrafluoroethylene powder and polytetrafluoroethylene powder modified with an acrylic resin are preferable. The amount of the air conditioner supplied to the extruder is preferably 0.01 to 3 parts by weight, more preferably 0.05 to 2 parts by weight with respect to 100 parts by weight of the polylactic acid resin. -1 part by weight is particularly preferred.
そして、ポリ乳酸系樹脂はポリエステル系の樹脂であって分解し易い樹脂であることから、本発明では、上述のように、ポリ乳酸系樹脂の一部を押出機中にて分解（加水分解及び／又は熱分解）させることによって乳酸を生成させ、得られるポリ乳酸系樹脂発泡体中に所定量の乳酸が含有されるように調整している。 Since the polylactic acid-based resin is a polyester-based resin and easily decomposes, in the present invention, as described above, a part of the polylactic acid-based resin is decomposed (hydrolyzed and dehydrated) in the extruder. (Or thermal decomposition) to produce lactic acid, and the resulting polylactic acid resin foam is adjusted so that a predetermined amount of lactic acid is contained.
ポリ乳酸系樹脂を分解させて乳酸を生成させる方法としては、例えば、(1) 押出機中におけるポリ乳酸系樹脂の滞留時間を通常よりも長くすると共に、押出機におけるポリ乳酸系樹脂の加熱温度を通常よりも高くすることにより、ポリ乳酸系樹脂を押出機内において加熱し分解させて乳酸を生成させる方法、(2) 加熱によって水分を発生させる無機化合物を押出機中に供給し、発生した水分によってポリ乳酸系樹脂の分解を促進して乳酸を生成させる方法が挙げられ、上記(1) (2) の方法は単独で用いられても併用されてもよい。 Examples of a method for producing lactic acid by decomposing a polylactic acid-based resin include, for example, (1) increasing the residence time of the polylactic acid-based resin in the extruder longer than usual, and heating the polylactic acid-based resin in the extruder In which the polylactic acid resin is heated and decomposed in the extruder to produce lactic acid, and (2) an inorganic compound that generates moisture by heating is supplied into the extruder, and the generated moisture Can be used to promote the decomposition of the polylactic acid resin to produce lactic acid, and the above methods (1) and (2) may be used alone or in combination.
具体的には、押出機中におけるポリ乳酸系樹脂の滞留時間は、短いと、ポリ乳酸系樹脂の一部を分解させることができず、ポリ乳酸系樹脂発泡体中に所定範囲内の乳酸量を含有させることができないことがある一方、長いと、ポリ乳酸系樹脂の劣化が大きくなり、ポリ乳酸系樹脂の押出発泡に悪影響を与え、良好なポリ乳酸系樹脂発泡体を得ることができないばかりでなく、ポリ乳酸系樹脂発泡体の生産効率も低下することがあるので、２５０〜２１００秒が好ましく、２８０〜１８００秒がより好ましく、３００〜１２００秒が特に好ましい。 Specifically, if the residence time of the polylactic acid resin in the extruder is short, a part of the polylactic acid resin cannot be decomposed, and the amount of lactic acid within a predetermined range in the polylactic acid resin foam On the other hand, if it is too long, the deterioration of the polylactic acid-based resin will increase, adversely affect the extrusion foaming of the polylactic acid-based resin, and it will not be possible to obtain a good polylactic acid-based resin foam In addition, since the production efficiency of the polylactic acid-based resin foam may be lowered, 250 to 2100 seconds are preferable, 280 to 1800 seconds are more preferable, and 300 to 1200 seconds are particularly preferable.
ここで、押出機中におけるポリ乳酸系樹脂の滞留時間とは、ポリ乳酸系樹脂が押出機内にて滞留する平均時間（秒）をいい、押出機の樹脂通過部分の体積（ｃｍ3 ）を押出速度（ｃｍ3 ／秒）で除すことによって算出することができる。 Here, the residence time of the polylactic acid resin in the extruder means the average time (seconds) in which the polylactic acid resin stays in the extruder, and the volume (cm 3 ) of the resin passage portion of the extruder is extruded. It can be calculated by dividing by the speed (cm 3 / sec).
押出機の樹脂通過部分とは、押出機のシリンダー内の体積からスクリューの体積を引いて得られる体積をいい、タンデム型の押出機の場合には、押出機同士を連結している連結部内の体積を含めたものをいう。 The resin passage part of the extruder refers to the volume obtained by subtracting the volume of the screw from the volume in the cylinder of the extruder, and in the case of a tandem type extruder, the volume in the connecting part that connects the extruders. This includes the volume.
又、押出機内におけるポリ乳酸系樹脂の加熱温度の目安として押出機のバレル温度を挙げることができる。押出機は、供給部、圧縮部、計量部及び発泡剤混合部から構成されるが、バレル温度が高くなる、押出機の圧縮部及び計量部に着目する。押出機として、一段目の押出機と二段目の押出機とを連結部を介して連結してなるタンデム型の押出機を用いる場合であって、ポリ乳酸系樹脂が結晶性である時、一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔは、低いと、ポリ乳酸系樹脂を分解させることができず、ポリ乳酸系樹脂発泡体中の乳酸量を所定範囲内に含有させることができないことがあるので、式７を満たすことが好ましく、式８を満たすことがより好ましく、式９を満たすことが特に好ましい一方、一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度は、高すぎると、ポリ乳酸系樹脂の劣化が著しくなり、得られるポリ乳酸系樹脂発泡体に着色を生じることがあるので、式１０を満たすことが好ましい。なお、一段目の押出機の圧縮部と計量部のバレル温度が等しい場合は、何れか一方のバレル温度をいう。 Moreover, the barrel temperature of an extruder can be mentioned as a standard of the heating temperature of the polylactic acid-type resin in an extruder. Although an extruder is comprised from a supply part, a compression part, a measurement part, and a foaming agent mixing part, it pays attention to the compression part and measurement part of an extruder with which barrel temperature becomes high. When using a tandem-type extruder formed by connecting a first-stage extruder and a second-stage extruder via a connecting portion as an extruder, when the polylactic acid-based resin is crystalline, If the barrel temperature T, which is the higher of the barrel temperatures of the compression section or metering section of the first stage extruder, is low, the polylactic acid resin cannot be decomposed, and the amount of lactic acid in the polylactic acid resin foam However, it is preferable to satisfy the formula 7, more preferably the formula 8, more preferably the formula 9, while the compression section of the first-stage extruder. Alternatively, if the barrel temperature of the higher one of the barrel temperatures of the measuring section is too high, the polylactic acid resin will deteriorate significantly, and the resulting polylactic acid resin foam may be colored. It is preferable to satisfy. In addition, when the barrel temperature of the compression part of a 1st stage extruder and the measurement part is equal, one barrel temperature is said.
（一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔ）≧
〔ポリ乳酸系樹脂の融点（ｍｐ）＋５０℃〕・・・式７
(The higher barrel temperature T of the barrel temperatures of the compression section or the metering section of the first stage extruder) ≧
[Melting point of polylactic acid resin (mp) + 50 ° C.] Formula 7
（一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔ）≧
〔ポリ乳酸系樹脂の融点（ｍｐ）＋５５℃〕・・・式８
(The higher barrel temperature T of the barrel temperatures of the compression section or the metering section of the first stage extruder) ≧
[Melting point of polylactic acid resin (mp) + 55 ° C.] Formula 8
（一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔ）≧
〔ポリ乳酸系樹脂の融点（ｍｐ）＋６０℃〕・・・式９
(The higher barrel temperature T of the barrel temperatures of the compression section or the metering section of the first stage extruder) ≧
[Melting point of polylactic acid resin (mp) + 60 ° C.] Formula 9
（一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔ）≦
〔ポリ乳酸系樹脂の融点（ｍｐ）＋１００℃〕・・・式１０
(The higher barrel temperature T of the barrel temperatures of the compression section or the metering section of the first stage extruder) ≦
[Melting point of polylactic acid resin (mp) + 100 ° C.] Formula 10
又、押出機として、一段目の押出機と二段目の押出機とを連結部を介して連結してなるタンデム型の押出機を用いる場合であって、ポリ乳酸系樹脂が非結晶性である場合は、低いと、ポリ乳酸系樹脂を分解させることができず、ポリ乳酸系樹脂発泡体中に所定範囲内の乳酸量を含有させることができないことがある一方、高いと、ポリ乳酸系樹脂の劣化が著しくなり、得られるポリ乳酸系樹脂発泡体に着色を生じることがあるので、一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔは、式１１を満たすことが好ましい。
〔ポリ乳酸系樹脂のガラス転移温度（Ｔｇ）＋１００℃〕≦（一段目の押出機の圧縮部又は計量部のバレル温度のうちの高い方のバレル温度Ｔ）≦〔ポリ乳酸系樹脂のガラス転移温度（Ｔｇ）＋１７０℃〕・・・式１１
In the case of using a tandem type extruder in which a first-stage extruder and a second-stage extruder are connected via a connecting portion as an extruder, the polylactic acid resin is non-crystalline. In some cases, if low, the polylactic acid-based resin cannot be decomposed, and the polylactic acid-based resin foam may not contain the amount of lactic acid within a predetermined range. Since the deterioration of the resin becomes significant and the resulting polylactic acid-based resin foam may be colored, the higher barrel temperature T of the barrel temperature of the compression section or metering section of the first-stage extruder is expressed by the formula 11 is preferably satisfied.
[Glass transition temperature of polylactic acid resin (Tg) + 100 ° C.] ≦ (barrel temperature T of the higher one of the compression section or metering section of the first stage extruder) ≦ [glass transition of polylactic acid resin] Temperature (Tg) + 170 ° C.] Formula 11
なお、押出機の圧縮部及び計量部のバレル温度とは、バレル内周面から該バレル内周面に対して直交する方向に１５ｍｍだけ離間したバレル部分の温度をいう。 In addition, the barrel temperature of the compression section and the metering section of the extruder refers to the temperature of the barrel portion that is separated from the barrel inner peripheral surface by 15 mm in the direction orthogonal to the barrel inner peripheral surface.
又、ポリ乳酸系樹脂のガラス転移点Ｔｇは、下記の要領で測定したものをいう。示差走査熱量計装置を用い、測定容器に試料を１０〜２０ｍｇ充填し、窒素ガス流量３０ミリリットル／分のもと、試料を１０℃／分の昇温速度で樹脂の融解ピーク終了時より２０〜３０℃高い温度まで加熱溶融させ、その温度に１０分間保持し、次いで、試料を１０℃／分の降温速度で樹脂のガラス転移温度より少なくとも約５０℃低い温度まで降温する。再度、試料を１０℃／分の昇温速度で樹脂の融解ピーク終了時より２０〜３０℃高い温度まで昇温してガラス転移温度を測定し、ＪＩＳ Ｋ７１２１：１９８７に規定の補外ガラス転移開始温度をガラス転移温度Ｔｇとする。なお、上記示差走査熱量計装置としては、Ｔ．Ａ．Ｉｎｓｔｒｕｍｅｎｔｓ社から商品名「ＤＳＣ２０１０」で市販されているものを用いることができる。 Moreover, the glass transition point Tg of a polylactic acid-type resin means what was measured in the following way. Using a differential scanning calorimeter device, 10 to 20 mg of a sample is filled in a measurement container, and the sample is heated at a rate of 10 ° C./min from the end of the melting peak of the resin with a nitrogen gas flow rate of 30 ml / min. Heat and melt to 30 ° C higher temperature and hold at that temperature for 10 minutes, then cool the sample at a rate of 10 ° C / min to at least about 50 ° C below the glass transition temperature of the resin. Again, the sample was heated to a temperature 20-30 ° C. higher than that at the end of the melting peak of the resin at a rate of temperature increase of 10 ° C./min, and the glass transition temperature was measured. Extrapolated glass transition specified in JIS K7121: 1987 was started. Let the temperature be the glass transition temperature Tg. As the differential scanning calorimeter, the T.C. A. What is marketed with the brand name "DSC2010" from Instruments can be used.
又、上記では、ポリ乳酸系樹脂を押出機内において通常よりも長く且つ高い温度に加熱することによってポリ乳酸系樹脂を分解させて乳酸を生成していたが、押出機内に、加熱によって水分を発生させる無機化合物（以下、単に「無機化合物」ということがある）を供給し、発生した水分によってポリ乳酸系樹脂の分解が容易に進行するようにして乳酸の生成を行うようにしてもよい。 In the above, the polylactic acid resin was decomposed by heating the polylactic acid resin to a temperature longer and higher than usual in the extruder to generate lactic acid, but moisture was generated in the extruder by heating. Alternatively, an inorganic compound to be produced (hereinafter, sometimes simply referred to as “inorganic compound”) may be supplied, and lactic acid may be generated such that decomposition of the polylactic acid resin easily proceeds by the generated moisture.
加熱によって水分を発生させる無機化合物としては、熱分解によって水分を発生する無機化合物や、無機化合物の水和物であって加熱によって水分を発生させるものなどが挙げられる。 Examples of inorganic compounds that generate moisture by heating include inorganic compounds that generate moisture by thermal decomposition, and hydrates of inorganic compounds that generate moisture by heating.
熱分解によって水分を発生させる無機化合物としては、例えば、重炭酸ナトリウム、重炭酸カリウムなどが挙げられ、又、無機化合物の水和物であって加熱によって水分を発生させるものとしては、例えば、炭酸ナトリウムの水和物（Ｎａ2 ＣＯ3 ・Ｈ2 Ｏ、Ｎａ2 ＣＯ3 ・７Ｈ2 Ｏ、Ｎａ2 ＣＯ3 ・１０Ｈ2 Ｏ）、炭酸カリウムの水和物（Ｋ2 ＣＯ3 ・１．５Ｈ2 Ｏ）などが挙げられる。 Examples of inorganic compounds that generate moisture by thermal decomposition include sodium bicarbonate and potassium bicarbonate. Examples of inorganic compounds that generate moisture by heating include inorganic carbonates. Sodium hydrate (Na 2 CO 3 · H 2 O, Na 2 CO 3 · 7H 2 O, Na 2 CO 3 · 10H 2 O), potassium carbonate hydrate (K 2 CO 3 · 1.5H 2 O).
そして、押出機内に供給する無機化合物量としては、少ないと、ポリ乳酸系樹脂の分解を促進させることができず、得られるポリ乳酸系樹脂発泡体中に含有される乳酸量が必要とする量を下回る虞れがある一方、多いと、ポリ乳酸系樹脂の分解が進行し過ぎて、ポリ乳酸系樹脂の分子量が低下し、所望のポリ乳酸系樹脂発泡体が得られなかったり、或いは、得られるポリ乳酸系樹脂発泡体の強度が低下することがあるので、ポリ乳酸系樹脂１００重量部に対して０．０１〜０．５重量部が好ましく、０．０２〜０．４重量部がより好ましく、０．０３〜０．３重量部が特に好ましい。 And as an inorganic compound amount supplied in an extruder, when there is little, decomposition | disassembly of polylactic acid-type resin cannot be accelerated | stimulated, and the quantity which the amount of lactic acid contained in the obtained polylactic acid-type resin foam requires On the other hand, if it is too high, the decomposition of the polylactic acid resin proceeds excessively, the molecular weight of the polylactic acid resin decreases, and the desired polylactic acid resin foam cannot be obtained or obtained. Since the strength of the resulting polylactic acid resin foam may be reduced, 0.01 to 0.5 parts by weight is preferable with respect to 100 parts by weight of the polylactic acid resin, and 0.02 to 0.4 parts by weight is more preferable. Preferably, 0.03 to 0.3 parts by weight is particularly preferable.
又、押出機に供給する前のポリ乳酸系樹脂に含有されている乳酸量Ａと、ポリ乳酸系樹脂発泡体中に含有されている乳酸量Ｂとの比（乳酸量Ｂ／乳酸量Ａ）は、小さいと、ポリ乳酸系樹脂発泡体中に含有されている乳酸量が低下することがある一方、大きいと、ポリ乳酸系樹脂の分解が進行し過ぎて、ポリ乳酸系樹脂の分子量が低下し、得られるポリ乳酸系樹脂発泡体の強度が低下することがあるので、１．４〜３０となるように押出発泡させる。 Further, the ratio of the lactic acid amount A contained in the polylactic acid resin before being supplied to the extruder to the lactic acid amount B contained in the polylactic acid resin foam (lactic acid amount B / lactic acid amount A). If it is small, the amount of lactic acid contained in the polylactic acid resin foam may decrease. On the other hand, if it is large, the decomposition of the polylactic acid resin will proceed excessively and the molecular weight of the polylactic acid resin will decrease. However, since the strength of the resulting polylactic acid resin foam may be lowered, extrusion foaming is performed so that the strength becomes 1.4 to 30 .
そして、押出機内において、一部が分解されて乳酸を生成し且つ発泡剤と共に溶融混練されて発泡剤が均一に分散されたポリ乳酸系樹脂は、押出機の先端に取り付けられた金型から押出発泡され、所望形状を有するポリ乳酸系樹脂発泡体を得ることができる。なお、金型としては、従来から公知の金型が用いられ、サーキュラ金型、Ｔダイ、ノズルダイなどが挙げられ、ポリ乳酸系樹脂発泡シートを連続的に安定して製造するには、サーキュラ金型が好ましい。 In the extruder, a polylactic acid resin partially decomposed to produce lactic acid and melt-kneaded with the foaming agent to uniformly disperse the foaming agent is extruded from a mold attached to the tip of the extruder. A polylactic acid resin foam that is foamed and has a desired shape can be obtained. In addition, as a metal mold | die, a conventionally well-known metal mold | die is used, A circular mold, T die, a nozzle die etc. are mentioned, In order to manufacture a polylactic acid-type resin foam sheet continuously stably, a circular mold | die is mentioned. A mold is preferred.
金型としてサーキュラ金型を用いる場合には、サーキュラ金型の樹脂出口の口径よりも大きな径を有する冷却マンドレルを併用し、サーキュラ金型から押出発泡させて得られた円筒状発泡体を徐々に拡径した上で、この円筒状発泡体を冷却マンドレルに供給して冷却した後、円筒状発泡体をその内外周面間に亘って切断、展開することによってポリ乳酸系樹脂発泡シートを得ることができる。 When a circular mold is used as the mold, a cooling mandrel having a diameter larger than the diameter of the resin outlet of the circular mold is used in combination, and the cylindrical foam obtained by extrusion foaming from the circular mold is gradually added. After expanding the diameter, this cylindrical foam is supplied to a cooling mandrel and cooled, and then the cylindrical foam is cut and spread between the inner and outer peripheral surfaces to obtain a polylactic acid resin foam sheet. Can do.
このようにして得られたポリ乳酸系樹脂発泡体は所定量の乳酸を含有しており、この乳酸の有する静菌作用によって、野菜や果実などの鮮度保持性に優れ、食品容器や、野菜や果実の包装材として好適に用いることができる。 The polylactic acid-based resin foam thus obtained contains a predetermined amount of lactic acid. Due to the bacteriostatic action of this lactic acid, it has excellent freshness retention of vegetables, fruits, etc. It can be suitably used as a fruit packaging material.
本発明のポリ乳酸系樹脂発泡体の製造方法で製造されるポリ乳酸系樹脂発泡体は、乳酸含有量が全重量に対して４０〜４００ｐｐｍであるので、外観性に優れていると共に、優れた静菌性を有しており、果物や野菜などの鮮度保持性に優れている。 Polylactic acid resin foam produced by the production method of the polylactic acid resin foam of the present invention, the lactic acid content is 40~400ppm relative to the total weight, with an excellent appearance, excellent It has bacteriostatic properties and has excellent freshness retention for fruits and vegetables.
そして、本発明のポリ乳酸系樹脂発泡体を押出発泡によって製造するにあたって、ポリ乳酸系樹脂の押出機中における滞留時間を２５０〜２１００秒となるように調整している場合、又は、ポリ乳酸系樹脂が結晶性ポリ乳酸系樹脂であって、押出機の圧縮部又は軽量部のバレル温度のうちの高い方のバレル温度Ｔが所定条件を満たすように調整している場合には、ポリ乳酸系樹脂の一部を押出機内における加熱によって分解させて所定量の乳酸を生成させることができ、得られるポリ乳酸系樹脂発泡体は、所定量の乳酸を含有し、優れた静菌性を有しており、果物や野菜などの鮮度保持性に優れている。 And in producing the polylactic acid-based resin foam of the present invention by extrusion foaming, when the residence time in the extruder of the polylactic acid-based resin is adjusted to be 250 to 2100 seconds, or the polylactic acid-based If the resin is a crystalline polylactic acid-based resin and the barrel temperature T, which is the higher of the barrel temperatures of the compression section or lightweight section of the extruder, is adjusted so as to satisfy a predetermined condition, Part of the resin can be decomposed by heating in the extruder to produce a predetermined amount of lactic acid, and the resulting polylactic acid resin foam contains a predetermined amount of lactic acid and has excellent bacteriostatic properties It has excellent freshness retention for fruits and vegetables.
更に、本発明のポリ乳酸系樹脂発泡体を押出発泡によって製造するにあたって、加熱によって水分を発生させる無機化合物を押出機に供給している場合には、押出機内において、無機化合物から発生した水分の存在下にてポリ乳酸系樹脂を容易に分解させて乳酸を発生させることができ、得られるポリ乳酸系樹脂発泡体は、所定量の乳酸を含有し、優れた静菌性を有しており、果物や野菜などの鮮度保持性に優れている。 Furthermore, when the polylactic acid-based resin foam of the present invention is produced by extrusion foaming, when an inorganic compound that generates moisture by heating is supplied to the extruder, the moisture generated from the inorganic compound in the extruder is reduced. Polylactic acid resin can be easily decomposed in the presence to generate lactic acid, and the resulting polylactic acid resin foam contains a predetermined amount of lactic acid and has excellent bacteriostatic properties Excellent in keeping freshness of fruits and vegetables.
（実施例１）
結晶性のポリ乳酸系樹脂（ユニチカ社製 商品名「ＨＶ−６２００」、乳酸量：２０ｐｐｍ、融点：１６７．４℃、Ｄ体比率：１．５重量％、Ｌ体比率：９８．５重量％、動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点における温度Ｔ：１３９．５℃、動的粘弾性測定にて得られた、貯蔵弾性率曲線と損失弾性率曲線との交点の温度Ｔにおける弾性率（貯蔵弾性率又は損失弾性率）：４．２３×１０4 Ｐａ）を用意し、このポリ乳酸系樹脂を除湿乾燥機を用いて８０℃にて５時間に亘って乾燥した。なお、図１に、ポリ乳酸系樹脂の動的粘弾性測定にて得られた、貯蔵弾性率曲線及び損失弾性率曲線を示した。
Example 1
Crystalline polylactic acid resin (trade name “HV-6200” manufactured by Unitika Ltd.), lactic acid content: 20 ppm, melting point: 167.4 ° C., D-form ratio: 1.5 wt%, L-form ratio: 98.5 wt% The temperature at the intersection of the storage modulus curve and the loss modulus curve obtained by dynamic viscoelasticity measurement, T: 139.5 ° C., the storage modulus curve and loss obtained by dynamic viscoelasticity measurement Elastic modulus (storage elastic modulus or loss elastic modulus) at a temperature T at the intersection with the elastic modulus curve: 4.23 × 10 4 Pa), and this polylactic acid resin at 80 ° C. using a dehumidifying dryer Dried for 5 hours. In addition, in FIG. 1, the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of polylactic acid-type resin were shown.
一方、一段目となる口径５０ｍｍの単軸押出機と二段目となる口径６５ｍｍの単軸押出機とを接続管を介して接続してなるタンデム型の押出機を用意した。一段目の単軸押出機は、供給部（Ｌ／Ｄ：７）、圧縮部（Ｌ／Ｄ：７）、計量部（Ｌ／Ｄ：７）及び発泡剤混合部（Ｌ／Ｄ：７）からこの順序で構成されていた。 On the other hand, a tandem type extruder in which a first-stage single-screw extruder with a diameter of 50 mm and a second-stage single-screw extruder with a diameter of 65 mm were connected via a connecting pipe was prepared. The first-stage single-screw extruder has a supply unit (L / D: 7), a compression unit (L / D: 7), a metering unit (L / D: 7), and a blowing agent mixing unit (L / D: 7). It was composed in this order.
そして、一段目の押出機における供給部のバレル温度を１９０℃に、圧縮部及び計量部のバレル温度を２３０℃に、発泡剤混合部のバレル温度を２２０℃に調整する一方、上記結晶性のポリ乳酸系樹脂１００重量部及び気泡調整剤としてポリテトラフルオロエチレン粉末０．５重量部を予め均一に混合し、この混合物を、タンデム型の押出機の一段目の押出機にその供給部から供給して溶融混練した。 In the first stage extruder, the barrel temperature of the supply section is adjusted to 190 ° C., the barrel temperature of the compression section and the measurement section is adjusted to 230 ° C., and the barrel temperature of the foaming agent mixing section is adjusted to 220 ° C. 100 parts by weight of a polylactic acid resin and 0.5 parts by weight of a polytetrafluoroethylene powder as a foam control agent are uniformly mixed in advance, and this mixture is supplied from the supply unit to the first stage extruder of the tandem type extruder. And kneaded.
次に、一段目の押出機の発泡剤混合部にて、溶融状態のポリ乳酸系樹脂中にイソブタン１．１重量部を圧入して溶融混練して、ポリ乳酸系樹脂中にイソブタンを均一に分散させた。 Next, in the foaming agent mixing part of the first stage extruder, 1.1 parts by weight of isobutane is injected into the melted polylactic acid resin and melt-kneaded so that the isobutane is uniformly dispersed in the polylactic acid resin. Dispersed.
しかる後、この溶融状態のポリ乳酸系樹脂を連結部を介して二段目の押出機に連続的に供給し、二段目の押出機にて溶融状態のポリ乳酸系樹脂を１６７℃に冷却した後、二段目の押出機の先端に取り付けられたサーキュラダイ（サーキュラ金型のリップにおける内ダイの外径：６０ｍｍ、サーキュラ金型のリップにおける内外ダイ間の間隔：０．５ｍｍ）から１１ｃｍ3 ／秒の押出速度で円筒状に押出発泡した。なお、上記樹脂温度は、二段目の押出機とサーキュラダイとの間にブレーカープレートを挿入し、そのブレーカープレートの中心部に熱電対を挿入することにより測定した。 Thereafter, the molten polylactic acid resin is continuously supplied to the second stage extruder through the connecting portion, and the molten polylactic acid resin is cooled to 167 ° C. by the second stage extruder. 11 cm from the circular die (the outer diameter of the inner die at the lip of the circular mold: 60 mm, the distance between the inner and outer dies at the lip of the circular mold) attached to the tip of the second stage extruder. Extrusion foaming was performed in a cylindrical shape at an extrusion speed of 3 / sec. The resin temperature was measured by inserting a breaker plate between the second-stage extruder and the circular die, and inserting a thermocouple at the center of the breaker plate.
そして、上記円筒状発泡体を徐々に拡径した後、温度２０℃の冷却水で冷却され且つ長さ方向の全長に亘って一定の外径を有する円柱状の冷却用マンドレル（外径：２０５ｍｍ、長さ：４００ｍｍ）に上記円筒状発泡体を連続的に供給し冷却した上で、円筒状発泡体をその任意の部分において押出方向に連続的に内外周面間に亘って切断し展開することによってポリ乳酸系樹脂発泡シートを連続的に製造した。この長尺状のポリ乳酸系樹脂発泡シートを巻き取り機によってロール状に巻き取った。なお、ポリ乳酸系樹脂発泡シートは、その密度が０．２５ｇ／ｃｍ3 で且つ厚みが１．４ｍｍであった。 Then, after gradually expanding the diameter of the cylindrical foam, a cylindrical cooling mandrel (outer diameter: 205 mm) cooled with cooling water at a temperature of 20 ° C. and having a constant outer diameter over the entire length in the length direction. , Length: 400 mm), the cylindrical foam is continuously supplied and cooled, and then the cylindrical foam is continuously cut in the extruding direction between the inner and outer peripheral surfaces at an arbitrary portion thereof. Thus, a polylactic acid resin foam sheet was continuously produced. This long polylactic acid-based resin foam sheet was wound into a roll by a winder. The polylactic acid resin foamed sheet had a density of 0.25 g / cm 3 and a thickness of 1.4 mm.
一段目の押出機の樹脂通過部分の体積は７００ｃｍ3 で、二段目の押出機の樹脂通過部分の体積は３６８９ｃｍ3 で、連結部内の体積は１０３４ｃｍ3 であり、ポリ乳酸系樹脂の押出機中における滞留時間は、４９３秒であった。 By volume of resin passing portion of the extruder in the first stage is 700 cm 3, a volume of resin passing portion of the extruder in the second stage is 3689cm 3, the volume of the connecting portion is 1034cm 3, the extruder of the polylactic acid-based resin The residence time in it was 493 seconds.
（実施例２）
結晶性のポリ乳酸系樹脂１００重量部、気泡調整剤としてポリテトラフルオロエチレン粉末０．３重量部及び重炭酸ナトリウム０．２重量部を予め混合し、この混合物を一段目の押出機にその供給部から供給したこと以外は実施例１と同様にしてポリ乳酸系樹脂発泡シートを得た。
(Example 2)
100 parts by weight of a crystalline polylactic acid resin, 0.3 parts by weight of polytetrafluoroethylene powder and 0.2 parts by weight of sodium bicarbonate are mixed in advance as a foam regulator, and this mixture is supplied to the first-stage extruder. A polylactic acid resin foamed sheet was obtained in the same manner as in Example 1 except that it was supplied from the section.
（実施例３）
結晶性のポリ乳酸系樹脂（島津製作所社製 商品名「ＬＡＣＴＹ ９０３１」、乳酸量：２１ｐｐｍ、融点：１３２．９℃、Ｄ体比率：８．４重量％、Ｌ体比率：９１．６重量％）を用意し、このポリ乳酸系樹脂を除湿乾燥機を用いて８０℃にて５時間に亘って乾燥した。
(Example 3)
Crystalline polylactic acid resin (trade name “LACTY 9031” manufactured by Shimadzu Corporation), lactic acid content: 21 ppm, melting point: 132.9 ° C., D-form ratio: 8.4 wt%, L-form ratio: 91.6 wt% This polylactic acid resin was dried at 80 ° C. for 5 hours using a dehumidifying dryer.
一方、実施例１と同様のタンデム型の押出機を用意し、一段目の押出機における供給部のバレル温度を１３５℃に、圧縮部及び計量部のバレル温度を２００℃に、発泡剤混合部のバレル温度を１９０℃に調整する一方、上記結晶性のポリ乳酸系樹脂１００重量部、気泡調整剤としてポリテトラフルオロエチレン粉末０．５重量部、炭酸ナトリウムの水和物（Ｎａ2 ＣＯ3 ・Ｈ2 Ｏ）０．１重量部、及び、収縮防止剤としてステアリン酸モノグリセライドのマスターバッチ（上記ポリ乳酸系樹脂／ステアリン酸モノグリセライド（ステアリン酸モノグリセライド純度：９５重量％以上）（重量比）＝４）３重量部を予め均一に混合し、この混合物を、タンデム型の押出機の一段目の押出機に供給して溶融混練した。 On the other hand, the same tandem type extruder as in Example 1 was prepared, the barrel temperature of the supply section in the first stage extruder was 135 ° C., the barrel temperature of the compression section and the measurement section was 200 ° C., and the blowing agent mixing section While adjusting the barrel temperature to 190 ° C., 100 parts by weight of the crystalline polylactic acid-based resin, 0.5 parts by weight of polytetrafluoroethylene powder as a foam regulator, sodium carbonate hydrate (Na 2 CO 3. 0.1 part by weight of H 2 O and a master batch of stearic acid monoglyceride as a shrinkage inhibitor (the above polylactic acid resin / stearic acid monoglyceride (steric acid monoglyceride purity: 95 wt% or more) (weight ratio) = 4) 3 parts by weight were previously mixed uniformly, and this mixture was supplied to a first stage extruder of a tandem type extruder and melt-kneaded.
次に、一段目の押出機の発泡剤混合部にて、溶融状態のポリ乳酸系樹脂中にジメチルエーテル６重量部を圧入して溶融混練して、ポリ乳酸系樹脂中にジメチルエーテルを均一に分散させた。 Next, in the foaming agent mixing part of the first stage extruder, 6 parts by weight of dimethyl ether is pressed into the molten polylactic acid resin and melt-kneaded to uniformly disperse the dimethyl ether in the polylactic acid resin. It was.
しかる後、この溶融状態のポリ乳酸系樹脂を連結部を介して二段目の押出機に連続的に供給し、二段目の押出機にて溶融状態のポリ乳酸系樹脂を１１４℃に冷却した後、二段目の押出機の先端に取り付けられたサーキュラダイ（サーキュラ金型のリップにおける内ダイの外径：６０ｍｍ、サーキュラ金型のリップにおける内外ダイ間の間隔：０．５ｍｍ）から１１ｃｍ3 ／秒の押出速度で円筒状に押出発泡した。なお、上記樹脂温度は、二段目の押出機とサーキュラダイとの間にブレーカープレートを挿入し、そのブレーカープレートの中心部に熱電対を挿入することにより測定した。 Thereafter, the molten polylactic acid resin is continuously supplied to the second stage extruder through the connecting portion, and the molten polylactic acid resin is cooled to 114 ° C. by the second stage extruder. 11 cm from the circular die (the outer diameter of the inner die at the lip of the circular mold: 60 mm, the distance between the inner and outer dies at the lip of the circular mold) attached to the tip of the second stage extruder. Extrusion foaming was performed in a cylindrical shape at an extrusion speed of 3 / sec. The resin temperature was measured by inserting a breaker plate between the second-stage extruder and the circular die, and inserting a thermocouple at the center of the breaker plate.
そして、上記円筒状発泡体を徐々に拡径した後、温度２０℃の冷却水で冷却され且つ長さ方向の全長に亘って一定の外径を有する円柱状の冷却用マンドレル（外径：２０５ｍｍ、長さ：４００ｍｍ）に上記円筒状発泡体を連続的に供給し冷却した上で、円筒状発泡体をその任意の部分において押出方向に連続的に内外周面間に亘って切断し展開することによってポリ乳酸系樹脂発泡シートを連続的に製造した。この長尺状のポリ乳酸系樹脂発泡シートを巻き取り機によってロール状に巻き取った。なお、ポリ乳酸系樹脂発泡シートは、その密度が０．０６２ｇ／ｃｍ3 で且つ厚みが２．０ｍｍであった。 Then, after gradually expanding the diameter of the cylindrical foam, a cylindrical cooling mandrel (outer diameter: 205 mm) cooled with cooling water at a temperature of 20 ° C. and having a constant outer diameter over the entire length in the length direction. , Length: 400 mm), the cylindrical foam is continuously supplied and cooled, and then the cylindrical foam is continuously cut in the extruding direction between the inner and outer peripheral surfaces at an arbitrary portion thereof. Thus, a polylactic acid resin foam sheet was continuously produced. This long polylactic acid-based resin foam sheet was wound into a roll by a winder. The polylactic acid-based resin foam sheet had a density of 0.062 g / cm 3 and a thickness of 2.0 mm.
一段目の押出機の樹脂通過部分の体積は７００ｃｍ3 で、二段目の押出機の樹脂通過部分の体積は３６８９ｃｍ3 で、連結部内の体積は１０３４ｃｍ3 であり、ポリ乳酸系脂の押出機中における滞留時間は、４９３秒であった。 By volume of resin passing portion of the extruder in the first stage is 700 cm 3, a volume of resin passing portion of the extruder in the second stage is 3689cm 3, the volume of the connecting portion is 1034cm 3, polylactic acid extruder fat The residence time in it was 493 seconds.
（比較例１）
一段目の押出機における供給部のバレル温度を１９０℃に、圧縮部及び計量部のバレル温度を２１０℃に、発泡剤混合部のバレル温度を２００℃に調整したこと以外は実施例１と同様にしてポリ乳酸系樹脂発泡シートを得た。なお、ポリ乳酸系樹脂発泡シートは、その密度が０．２５ｇ／ｃｍ3 で且つ厚みが１．４ｍｍであった。
(Comparative Example 1)
Example 1 except that the barrel temperature of the supply section in the first stage extruder was adjusted to 190 ° C, the barrel temperature of the compression section and the measurement section was adjusted to 210 ° C, and the barrel temperature of the foaming agent mixing section was adjusted to 200 ° C. Thus, a polylactic acid resin foam sheet was obtained. The polylactic acid resin foamed sheet had a density of 0.25 g / cm 3 and a thickness of 1.4 mm.
（比較例２）
押出速度を１１ｃｍ3 ／秒の代わりに２４．２ｃｍ3 ／秒として、ポリ乳酸系樹脂の押出機中における滞留時間を２２４秒としたこと以外は、実施例１と同様にしてポリ乳酸系樹脂発泡シートを得た。なお、ポリ乳酸系樹脂発泡シートは、その密度が０．２５ｇ／ｃｍ3 で且つ厚みが１．４ｍｍであった。
(Comparative Example 2)
As 24.2cm 3 / sec instead of the extrusion rate 11cm 3 / sec, except that the residence time in the extruder of the polylactic acid resin was 224 seconds, similarly to the polylactic acid-based resin foam as in Example 1 A sheet was obtained. The polylactic acid resin foamed sheet had a density of 0.25 g / cm 3 and a thickness of 1.4 mm.
（比較例３）
結晶性のポリ乳酸系樹脂として、島津製作所社から商品名「ＬＡＣＴＹ ９０３１」で市販されているポリ乳酸系樹脂を用いたこと、一段目の押出機における供給部のバレル温度を１３５℃に、圧縮部及び計量部のバレル温度を２４０℃に、発泡剤混合部のバレル温度を２３０℃に調整したこと以外は実施例１と同様にしてポリ乳酸系樹脂発泡シートを製造しようとしたが、ポリ乳酸系樹脂の劣化による粘度低下が原因となってポリ乳酸系樹脂発泡シートを得ることができなかった。
(Comparative Example 3)
As the crystalline polylactic acid resin, a polylactic acid resin commercially available from Shimadzu Corporation under the trade name “LACTY 9031” was used, and the barrel temperature of the supply section in the first stage extruder was compressed to 135 ° C. An attempt was made to produce a polylactic acid-based resin foam sheet in the same manner as in Example 1 except that the barrel temperature of the part and the metering part was adjusted to 240 ° C. and the barrel temperature of the foaming agent mixing part was adjusted to 230 ° C. A polylactic acid resin foam sheet could not be obtained due to a decrease in viscosity due to deterioration of the resin.
ポリ乳酸系樹脂中におけるＤ体比率及びＬ体比率、ポリ乳酸系樹脂及びポリ乳酸系樹脂発泡シート中に含有される乳酸量、並びに、静菌性を下記に示した要領にて測定し、その結果を表１，２に示した。なお、表２中、ポリ乳酸系樹脂は単に「樹脂」と、ポリ乳酸系樹脂発泡シートは単に「発泡シート」と表記した。 The D-form ratio and L-form ratio in the polylactic acid-based resin, the amount of lactic acid contained in the polylactic acid-based resin and the polylactic acid-based resin foamed sheet, and the bacteriostatic properties were measured as described below. The results are shown in Tables 1 and 2. In Table 2, the polylactic acid resin is simply referred to as “resin”, and the polylactic acid resin foam sheet is simply referred to as “foam sheet”.
（ポリ乳酸系樹脂中におけるＤ体比率及びＬ体比率）
ポリ乳酸系樹脂０．２ｇをクロロホルムに完全に溶解させてポリ乳酸系樹脂溶液２０ミリリットルを作製した。次に、旋光計（日本分光社製 商品名「ＤＩＰ−３７０」）を用いて、２５℃、セルの層長１００ｍｍの条件下にてナトリウムスペクトルＤ線をポリ乳酸系樹脂溶液に照射して、ポリ乳酸系樹脂容器の旋光度を測定し、この旋光度から式１２に基づいて比旋光度を算出した。次に、この比旋光度から式１３及び式１４に基づいてポリ乳酸系樹脂中におけるＤ体比率及びＬ体比率を算出した。
(D-form ratio and L-form ratio in polylactic acid resin)
A polylactic acid resin 0.2 g was completely dissolved in chloroform to prepare 20 ml of a polylactic acid resin solution. Next, using a polarimeter (trade name “DIP-370” manufactured by JASCO Corporation), the polylactic acid resin solution was irradiated with sodium spectrum D-line under the conditions of 25 ° C. and cell layer length of 100 mm, The optical rotation of the polylactic acid resin container was measured, and the specific optical rotation was calculated from this optical rotation based on Equation 12. Next, the D-form ratio and the L-form ratio in the polylactic acid resin were calculated from the specific rotation based on the formulas 13 and 14.
比旋光度（°）＝１００×Ｘ／（Ｌ×ｃ）・・・式１２
Ｘ（°）：ポリ乳酸系樹脂溶液の旋光度
Ｌ（ｍｍ）：セルの層長
ｃ（ｇ／ミリリットル）：ポリ乳酸系樹脂溶液の濃度
Ｄ体比率（重量％）＝（比旋光度＋１５６）×１００／３１２・・・式１３
Ｌ体比率（重量％）＝１００−Ｄ体比率・・・式１４
Specific rotation (°) = 100 × X / (L × c) Equation 12
X (°): Optical rotation of polylactic acid-based resin solution L (mm): Cell layer length c (g / milliliter): Concentration of polylactic acid-based resin solution D-isomer ratio (% by weight) = (specific optical rotation + 156) × 100/312 ... Formula 13
L body ratio (% by weight) = 100-D body ratio Formula 14
（ポリ乳酸系樹脂及びポリ乳酸系樹脂発泡シート中に含有される乳酸量）
ポリ乳酸系樹脂又はポリ乳酸系樹脂発泡シートを０．５ｇ採取し、これを試験試料とした。この試験試料をクロロホルム２０ミリリットルに完全に溶解させて試験溶液を作製した。
(Amount of lactic acid contained in polylactic acid resin and polylactic acid resin foam sheet)
0.5 g of polylactic acid resin or polylactic acid resin foamed sheet was sampled and used as a test sample. This test sample was completely dissolved in 20 ml of chloroform to prepare a test solution.
次に、蒸留水にリン酸を溶解させてなる０．１重量％のリン酸水溶液１０ミリリットルを上記試験溶液中に加えた。しかる後、試験溶液を振とう機を用いて３０分間に亘って振とうさせた後、試験溶液を手動にて５０回に亘って振とうした。 Next, 10 ml of a 0.1 wt% aqueous phosphoric acid solution obtained by dissolving phosphoric acid in distilled water was added to the test solution. Thereafter, the test solution was shaken for 30 minutes using a shaker, and then the test solution was manually shaken 50 times.
続いて、試験溶液を５分間に亘って放置した後、１０ミリリットルの遠沈管に、試験溶液の上澄み液を試験液として５ミリリットル採取した。この試験液を毎分３０００回転の回転速度で１０分間に亘って遠心分離した後、試験液の上澄み液５０マイクロリットルを用いて下記条件下にて高速液体クロマトグラフにより分析を行い、試験試料１ｇ当たりに含まれる乳酸量を算出した。なお、乳酸標準品として、和光純薬工業社から市販されている乳酸試薬特級（乳酸：８５．０〜９２．０重量％）を用い、乳酸含有量を、最小値と最大値の中間値（８８．５重量％）として計算した。 Subsequently, after leaving the test solution for 5 minutes, 5 ml of the supernatant of the test solution was collected as a test solution in a 10 ml centrifuge tube. The test solution was centrifuged at 3000 rpm for 10 minutes and then analyzed by high performance liquid chromatograph under the following conditions using 50 microliters of the test solution supernatant. The amount of lactic acid contained per hit was calculated. In addition, as a lactic acid standard product, a lactic acid reagent special grade (lactic acid: 85.0 to 92.0% by weight) commercially available from Wako Pure Chemical Industries, Ltd. was used, and the lactic acid content was determined to be an intermediate value between the minimum value and the maximum value ( 88.5% by weight).
〔測定装置〕
高速液体クロマトグラフ：島津製作所社製 商品名「HPLC LC-10Avp」
分離カラム：ＧＬサイエンス社製 商品名「Inertsil ODS-3」
(内径:4.6ｍｍ×長さ250mm)
〔測定条件〕
カラム温度：４０℃
移動相：リン酸（試薬特級）１ｇとリン酸二水素カリウム（試薬特級）１．３６ｇとを
蒸留水１リットルに溶解させて得られた液
流速 ：０．７ミリリットル／分
注入量：５０マイクロリットル
検出器：ＵＶ２１０ｎｍ（３Ｄ）
〔measuring device〕
High performance liquid chromatograph: Shimadzu Corporation trade name “HPLC LC-10Avp”
Separation column: GL Sciences product name “Inertsil ODS-3”
(Inner diameter: 4.6mm x length 250mm)
〔Measurement condition〕
Column temperature: 40 ° C
Mobile phase: 1 g of phosphoric acid (special reagent grade) and 1.36 g of potassium dihydrogen phosphate (special grade reagent)
Liquid obtained by dissolving in 1 liter of distilled water Flow rate: 0.7 ml / min Injection volume: 50 microliters Detector: UV 210 nm (3D)
（静菌性）
１００℃に加熱された一対の加熱板間にポリ乳酸系樹脂発泡シートをその厚みが１．８ｍｍとなった状態に６秒間に亘って押圧した後、雌雄金型を用いて皿状容器に熱成形した。なお、皿状容器は、縦２００ｍｍ×横１５０ｍｍの平面長方形状の底面部の四方周縁から上方における斜め外方に向かって高さ２０ｍｍの周壁部が突設されていた。
(Bacteriostatic)
A polylactic acid resin foam sheet is pressed between the pair of heating plates heated to 100 ° C. for 6 seconds in a state where the thickness is 1.8 mm, and then heated in a dish-shaped container using male and female molds. Molded. The dish-like container had a peripheral wall portion with a height of 20 mm protruding from the four side periphery of the bottom surface of the flat rectangular shape of 200 mm long × 150 mm wide, obliquely outwardly upward.
次に、この皿状容器の底面部上に、中サイズ（１７ｇ±２ｇ）の苺果実（あすかルビー）４個を載置し、皿状容器の上端開口部をポリメチルペンテン製のフィルムで完全に閉止した。 Next, 4 medium-sized (17g ± 2g) strawberries (Asuka Ruby) are placed on the bottom of the dish-shaped container, and the upper end opening of the dish-shaped container is completely covered with a film made of polymethylpentene. Closed.
しかる後、２℃に保持された、冷蔵庫の冷蔵室内に上記皿状容器を１２日間に亘って放置した後、皿状容器内の苺果実の外観を目視にて観察すると共に、果実硬度計（木屋製作所社製 商品名「ＵＡ型−半球状針頭（φ１２ｍｍ、高さ１０ｍｍ）」）を用いて苺果実の果実硬度を測定した。 Then, after leaving the dish-shaped container in the refrigerator compartment kept at 2 ° C. for 12 days, the appearance of the strawberry fruit in the dish-shaped container is visually observed, and a fruit hardness meter ( The fruit hardness of the persimmon fruit was measured using a product name “UA type—semispherical needle head (φ12 mm, height 10 mm)” manufactured by Kiyama Seisakusho.
〔外観〕
○：カビが全くなかった。
△：少しカビが発生していた。
×：カビが大量に発生していた。
〔appearance〕
○: There was no mold at all.
Δ: A little mold was generated.
X: A large amount of mold was generated.
Claims (4)
１．４≦（乳酸量Ｂ／乳酸量Ａ）≦３０・・・式１ A method for producing a polylactic acid resin foam by supplying a polylactic acid resin to an extruder, melt-kneading in the presence of a foaming agent, and then extruding and foaming from the extruder, the polylactic acid resin The amount of lactic acid contained in the polylactic acid resin before being supplied to the extruder, while the amount of lactic acid contained in the foam is 40 to 400 ppm with respect to the total weight of the polylactic acid resin foam Production of polylactic acid-based resin foam , wherein the ratio of A to the amount of lactic acid B contained in the polylactic acid-based resin foam (lactic acid amount B / lactic acid amount A) satisfies the following formula 1. Method.
1.4 ≦ (lactic acid amount B / lactic acid amount A) ≦ 30 Formula 1
（ポリ乳酸系樹脂の融点＋50℃）≦バレル温度Ｔ≦（ポリ乳酸系樹脂の融点＋100℃）
・・・式２ The polylactic acid resin is a crystalline polylactic acid resin, and is adjusted so that the higher barrel temperature T of the barrel temperatures of the compression section or the metering section of the extruder satisfies the following formula 2. The manufacturing method of the polylactic acid-type resin foam of Claim 1 or Claim 2 to do.
(Melting point of polylactic acid resin + 50 ° C.) ≦ barrel temperature T ≦ (melting point of polylactic acid resin + 100 ° C.)
... Formula 2
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| JP4960122B2 (en) * | 2007-03-16 | 2012-06-27 | 積水化成品工業株式会社 | Method for producing foamed polylactic acid resin particles for in-mold foam molding |
| JP2010070711A (en) * | 2008-09-22 | 2010-04-02 | Toray Ind Inc | Polylactic acid foam and method for producing the same |
| JP2011093982A (en) * | 2009-10-28 | 2011-05-12 | Sekisui Plastics Co Ltd | Polylactic acid-based resin foamed sheet molding and method for producing the same |
| JP5695994B2 (en) * | 2011-03-24 | 2015-04-08 | 積水化成品工業株式会社 | Method for producing biodegradable aliphatic polyester resin foam sheet |
| CN103649165B (en) * | 2011-07-28 | 2015-08-12 | 东丽株式会社 | Polylactic resin and manufacture method thereof |
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| JPH05508669A (en) * | 1990-07-16 | 1993-12-02 | イー・アイ・デユポン・ドウ・ヌムール・アンド・カンパニー | degradable foam material |
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| WO2004026035A1 (en) * | 2002-09-08 | 2004-04-01 | Board Of Trustees Of The University Of Arkansas | Organic acids incorporated edible antimicrobial films |
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| JPH05508669A (en) * | 1990-07-16 | 1993-12-02 | イー・アイ・デユポン・ドウ・ヌムール・アンド・カンパニー | degradable foam material |
| JP2000248442A (en) * | 1999-03-03 | 2000-09-12 | Unitika Ltd | Antimicrobial interknitted fabric |
| JP2001270956A (en) * | 2000-03-24 | 2001-10-02 | Iwata Kagaku Kogyo Kk | Blowing agent and its composition |
| WO2004026035A1 (en) * | 2002-09-08 | 2004-04-01 | Board Of Trustees Of The University Of Arkansas | Organic acids incorporated edible antimicrobial films |
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| WO2023042024A1 (en) | 2021-09-16 | 2023-03-23 | Ricoh Company, Ltd. | Foamed polylactic acid sheet, and method for producing foamed polylactic acid sheet |
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