JP2005289069A - Biodegradable thermoforming sheet-shaped material and container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable thermoforming sheet-shaped material and a container which can be directly touched with foods or the like due to high hygienic properties and excel in a heat resistant property and an impact resistance property. <P>SOLUTION: In the biodegradable thermoforming sheet-shaped material, a layer which consists of a polylactic acid base polymer is prepared to at least one of the surface of a base substrate which makes as a principal component a resin composite in which 20 wt.% or more of an aliphatic polyester whose glass transition temperature is 0°C or lower and melting point 80°C or higher is blended with a polylactic acid base polymer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biodegradable thermoforming sheet and container, and more particularly, to a biodegradable thermoforming sheet and container having excellent heat resistance and impact resistance.

The problem of disposal of plastic products has been highlighted in recent years. Plastic materials such as polyethylene, polypropylene, and polyethylene terephthalate (PET) generate a large amount of heat during combustion, which may damage the combustion furnace during the combustion process. Polyvinyl chloride, which is still used in large quantities, is self-digesting. It cannot be burned. Plastic products, including such materials that cannot be incinerated, are often buried in the soil, but these remain chemically and are not biodegradable, so they remain and accumulate almost without being decomposed. As a result, the capacity of the waste disposal site is saturated in a short period of time.
Therefore, biodegradable materials that have low combustion heat and are safe for the human body and the like have been demanded, and many studies have been conducted. As one of them, polylactic acid is known. Polylactic acid has a calorific value less than half that of polyethylene, and is naturally hydrolyzed in soil and water, and then becomes a harmless decomposition product by microorganisms. Currently, development of containers (molded articles) such as films, sheets and bottles using polylactic acid has been actively conducted.
However, the polylactic acid film or sheet as it is is brittle and inferior in impact resistance, so its thermoformed product has limited applications. Aliphatic polyesters other than polylactic acid, on the other hand, pass the elution test that guarantees food hygiene, but the safety of the eluate that is eluted is not guaranteed, so it is suitable for applications that come into direct contact with food. There was a drawback of not.

  The present invention has been made to solve the above problems, and the object of the present invention is excellent in transparency, high safety to human bodies, etc., can be used in direct contact with foods, etc. An object of the present invention is to provide a biodegradable thermoforming sheet and a container excellent in heat resistance and impact resistance.

（式中、Ｒ^１およびＲ^２は、炭素数２〜１０のアルキレン基またはシクロアルキレン基である。ｎは、重量平均分子量が２万〜３０万となるのに必要な重合度である。ｎ個のＲ^１またはＲ^２は、それぞれ同一でも異なっていてもよい。また、式中には、エステル結合残基に代えて、ウレタン結合残基および／またはカーボネート結合残基を重量平均分子量の０〜５％含有する。）
また、前記脂肪族ポリエステルの重量平均分子量は１５万〜２５万であることが好ましい。
また、前記ポリ乳酸系重合体は、Ｄ−乳酸：Ｌ−乳酸＝１００：０〜９４：６または０：１００〜６：９４であることができる。
また、前記ポリ乳酸系重合体の重量平均分子量は１０万〜３０万であることができる。
本発明の容器は、上記生分解性熱成形用シート状物を熱成形して形成されたことを特徴とする。
本発明の食品用容器は、上記生分解性熱成形用シート状物を熱成形して形成されたことを特徴とする。 As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the biodegradable thermoforming sheet of the present invention comprises a resin composition in which a polylactic acid polymer is blended with 20% by weight or more of an aliphatic polyester having a glass transition temperature of 0 ° C. or lower and a melting point of 80 ° C. or higher. A layer made of a polylactic acid polymer is provided on at least one surface of a base substrate as a main component.
Here, the aliphatic polyester has a weight average molecular weight of 20,000 to 300,000 and may have a structure represented by the following general formula (1).

(In the formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. N is a degree of polymerization necessary for the weight average molecular weight to be 20,000 to 300,000. N. Each R ¹ or R ² may be the same or different, and in the formula, a urethane bond residue and / or a carbonate bond residue may be substituted with an ester bond residue with a weight average molecular weight of 0. Contain ~ 5%.)
The aliphatic polyester preferably has a weight average molecular weight of 150,000 to 250,000.
The polylactic acid polymer may be D-lactic acid: L-lactic acid = 100: 0 to 94: 6 or 0: 100 to 6:94.
The polylactic acid polymer may have a weight average molecular weight of 100,000 to 300,000.
The container of the present invention is characterized by being formed by thermoforming the biodegradable sheet for thermoforming.
The food container of the present invention is formed by thermoforming the biodegradable sheet for thermoforming.

  According to the present invention, there are provided a biodegradable sheet for thermoforming and a container that are highly safe, can be used in direct contact with foods, etc., and are excellent in heat resistance and impact resistance. be able to.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
The biodegradable thermoforming sheet of the present invention has a layer made of a polylactic acid polymer on at least one surface of a base substrate.
The base substrate in the present invention is blended with a polylactic acid polymer in an amount of 20% by weight or more of an aliphatic polyester (including an alicyclic group, the same applies hereinafter) having a glass transition temperature of 0 ° C. or lower and a melting point of 80 ° C. or higher. The resin composition is the main component. That is, a base substrate made of a resin composition containing 20% by weight or more of an aliphatic polyester in the total weight of the aliphatic polyester and the polylactic acid polymer may be used. Although depending on the production method, if the proportion of the aliphatic polyester is too small, the elongation of the sheet-like material is less than 10%, and it is fragile and not suitable for normal use. In order to improve the impact resistance, the proportion of the aliphatic polyester is required to be 20% or more by weight, and preferably 30% or more.

  Here, the sheet-like material means a sheet or a film. According to the definition in JIS, a sheet is a thin, generally flat product whose thickness is small compared to the length and width, and a film is extremely small compared to the length and width and has a maximum thickness. An arbitrarily limited thin flat product, usually supplied in the form of a roll (JIS K 6900). Therefore, it can be said that a particularly thin sheet is a film. However, since the boundary between the sheet and the film is not clear and it is difficult to distinguish clearly, in the present application, as described above, the term “sheet-like product” is used as a concept including both the sheet and the film. use.

The polylactic acid polymer of the base substrate used in the present invention and the polylactic acid polymer constituting the layer provided on at least one surface of the base substrate are poly (L -Lactic acid), poly (D-lactic acid) whose structural unit is D-lactic acid, poly (DL-lactic acid) whose structural unit is L-lactic acid and D-lactic acid, and a mixture thereof. . In the present invention, it may be a copolymer with other hydroxycarboxylic acid units described later, or may contain a small amount of a chain extender residue.
The polylactic acid is preferably D-lactic acid: L-lactic acid = 100: 0 to 94: 6 or 0: 100 to 6:94. Polylactic acid having a configuration outside this range has low crystallinity and poor heat resistance.
Examples of the other hydroxycarboxylic acid units copolymerized with polylactic acid include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3 2-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid, etc. Examples thereof include lactones such as functional aliphatic hydroxycarboxylic acids, caprolactone, butyrolactone, and valerolactone.

As a polymerization method for the polylactic acid polymer, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, a polylactic acid polymer having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid, or a mixture thereof.
In addition, in the ring-opening polymerization method (lactide method), a lactate which is a cyclic dimer of lactic acid is obtained by using a suitable catalyst while using a polymerization regulator or the like as necessary. Can do.

  The polylactic acid polymer used in the present invention preferably has a weight average molecular weight of 60,000 to 700,000, more preferably 80,000 to 400,000, and particularly preferably 100,000 to 300,000. If the molecular weight is too small, practical physical properties such as mechanical properties and heat resistance are hardly expressed, and if it is too large, the melt viscosity is too high and the molding processability is poor.

  When a dissolution test of a food hygiene test is performed using the polylactic acid polymer used in the present invention, lactide, an oligomer of lactic acid, and lactic acid are eluted in the test. Even when lactide is absorbed into the body, it immediately changes to lactic acid. Lactic acid and oligomers of lactic acid are used as food additives, respectively, and safety for the human body and the like is guaranteed.

The aliphatic polyester used in the present invention is an aliphatic polyester having a glass transition temperature (hereinafter abbreviated as “Tg”) of 0 ° C. or lower and a melting point (Tm) of 80 ° C. or higher. When the glass transition temperature (Tg) exceeds 0 ° C., the impact resistance improving effect of polylactic acid is lost, and when the melting point (Tm) is less than 80 ° C., the heat resistance is poor.
As said aliphatic polyester, the polymer which has an aliphatic dicarboxylic acid unit and an aliphatic diol unit as a main component is mentioned. In the present invention, it is preferable to use a biodegradable aliphatic polyester.
In order to adjust the aliphatic polyester, a known method such as a direct method or an indirect method can be employed. For example, the direct method is a method in which an aliphatic dicarboxylic acid unit and an aliphatic diol unit are directly polymerized to obtain a high molecular weight product while removing moisture contained in these components or moisture generated during polymerization. is there. The indirect method is an indirect production method in which the polymer is polymerized to the level of an oligomer and then increased in molecular weight using a small amount of chain extender, as in the case of the polylactic acid polymer.

  Examples of the aliphatic dicarboxylic acid unit include aliphatic dicarboxylic acids such as succinic acid, adipic acid, suberic acid, sebacic acid and dodecanedioic acid, and anhydrides and derivatives thereof. On the other hand, examples of the aliphatic diol unit include aliphatic diols such as ethylene glycol, butanediol, hexanediol, octanediol, cyclopentanediol, cyclohexanediol, and cyclohexanedimethanol, or derivatives thereof. As for an aliphatic dicarboxylic acid unit and an aliphatic diol unit, what has a bifunctional compound which has a C2-C10 alkylene group or a cycloalkylene group as a main component is preferable. Two or more of these aliphatic dicarboxylic acid units or aliphatic diol units may be used.

  In the present invention, the weight average molecular weight of the aliphatic polyester is preferably in the range of 20,000 to 300,000, more preferably 150,000 to 250,000. If the weight average molecular weight of the aliphatic polyester is too small, the properties as a polymer will be inferior. If it is too large, the melt viscosity will be too high, resulting in a decrease in miscibility with polylactic acid, or a sheet similar to polylactic acid. In some cases, the extrudability deteriorates.

（式中、Ｒ^１およびＲ^２は、炭素数２〜１０のアルキレン基またはシクロアルキレン基である。ｎは、重量平均分子量が２万〜３０万となるのに必要な重合度である。ｎ個のＲ^１またはＲ^２は、それぞれ同一でも異なっていてもよい。また、式中には、エステル結合残基に代えて、ウレタン結合残基および／またはカーボネート結合残基を重量平均分子量の０〜５％含有する。） In the present invention, an aliphatic polyester having the structure of the following general formula (1) can be preferably used.

(In the formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. N is a degree of polymerization necessary for the weight average molecular weight to be 20,000 to 300,000. N. Each R ¹ or R ² may be the same or different, and in the formula, a urethane bond residue and / or a carbonate bond residue may be substituted with an ester bond residue with a weight average molecular weight of 0. Contain ~ 5%.)

  Examples of the aliphatic polyester particularly preferably used in the present invention include polyethylene suberate, polyethylene sebacate, polyethylene decanedicarboxylate, polybutylene succinate, polybutylene adipate, polybutylene sebacate, polybutylene succinate adipate, These copolymers are mentioned.

  In order to improve the melt viscosity, tri- or higher functional carboxylic acid, alcohol or hydroxycarboxylic acid can be used for the purpose of providing branching to the aliphatic polyester. Specifically, a polyfunctional component such as malic acid, tartaric acid, citric acid, trimellitic acid, pyromellitic acid, pentaerythlit or trimethylolpropane can be used. When these polyfunctional components are used in a large amount, the resulting polyfunctional polyester has a cross-linked structure and is not thermoplastic, or even if it is thermoplastic, a microgel having a partially highly cross-linked structure is formed on the sheet. There is a risk of fish eyes. Accordingly, the proportion of these polyfunctional components contained in the aliphatic polyester needs to be very small, and is limited to such an extent that the chemical properties and physical properties of the polymer are not greatly affected.

  Further, if necessary, a non-aliphatic dicarboxylic acid such as terephthalic acid and / or a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A, lactic acid and / or a hydroxycarboxylic acid other than lactic acid may be used as a small amount copolymerization component. May be used.

  In the present invention, a block copolymer of a polylactic acid polymer and an aliphatic polyester (partly transesterified product, a small amount of chain extender) together with or in place of the aliphatic polyester. Including products containing residues, etc.). This block copolymer can be prepared by any method. For example, either a polylactic acid polymer or an aliphatic polyester is separately prepared as a polymer, and the other constituent monomer is polymerized in the presence of the polymer. Usually, a block copolymer of polylactic acid and aliphatic polyester is obtained by polymerizing lactide in the presence of an aliphatic polyester prepared in advance. Basically, polymerization can be carried out in the same manner as in the case of preparing a polylactic acid polymer by the lactide method, except that an aliphatic polyester is allowed to coexist. In this case, at the same time as the polymerization of lactide proceeds, an appropriate transesterification reaction occurs between polylactic acid and the aliphatic polyester, and a copolymer having relatively high randomness is obtained. When an aliphatic polyester urethane having a urethane bond is used as a starting material, ester-amide exchange is also generated.

  For the purpose of adjusting various physical properties, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment, and the like are added to each layer constituting the sheet-like material of the present invention. You can also

As a method for producing a multilayer sheet-like material of the present invention, ordinary multilayer T-die, I-die, and round die are used and melt-extruded at a temperature higher than the melting point of the resin, and the inside of the die and the die are discharged. The so-called co-extrusion method in which layers are laminated with each other, and dry lamination, wet lamination, and the like, which are separately melt-extruded and formed into a sheet and then laminated using an adhesive.
The thickness of the sheet is not particularly limited as long as it is a thickness that can be used for a normal thermoforming technique, and specifically, the total thickness is in the range of about 0.03 to 2.0 mm. Is preferred.

In the present invention, the biodegradable thermoforming sheet of the present invention can be preheated to the forming temperature with an infrared heater, a hot plate heater, hot air or the like and thermoformed to form a container or the like. Examples of the thermoforming method include a vacuum forming method, a plug assist forming method, a pressure forming method, a male / female forming method, and a method of expanding a forming male die after deforming a sheet along the forming male shape. In addition, the shape, size, and the like of the container are appropriately selected according to the application.
Since the front and back surfaces of the sheet-like material of the present invention are covered with a layer made of a polylactic acid polymer, the manufactured container is safe for the human body and can be used as a container for directly putting food.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
(Example 1)
Polylactic acid (trade name “EcoPLA4040D” manufactured by Cargill Co., Ltd.) and polybutylene succinate / adipate (Showa Polymer Co., Ltd.) as the aliphatic polyester according to the present invention using a small twin screw extruder in the same direction with a diameter of 25 mm. Manufactured and trade name “Bionore # 3003”, glass transition temperature −45 ° C.) was mixed and melted at a weight ratio of 70/30, and then extruded into a strand shape at 210 ° C. to produce pellets.
A single-screw extruder with a diameter of 65 mm was used as the extruder for the middle layer, and a single-screw extruder with a diameter of 40 mm and a multi-manifold die were used as the extruder for the surface layer. At 210 ° C., the prepared pellets are supplied to a 65 mm diameter middle layer extruder, and polylactic acid (trade name “EcoPLA4040D”, manufactured by Cargill Co., Ltd.) is supplied to a 40 mm diameter surface layer single screw extruder and extruded. The sheet was rapidly cooled with a casting roll to obtain a sheet-like material having a total thickness of 200 μm of 2 types and 3 layers with a middle layer thickness of 180 μm and a surface layer thickness of 10 μm.
Using the obtained sheet-like material, a container having a diameter of 100 mm and a depth of 30 mm was molded by a hot plate contact heating type pressure air forming machine manufactured by CKD under the conditions of a molding temperature of 100 ° C. and a molding pressure of 0.3 MPa. .
Since the surface of the obtained container is made of polylactic acid, even if it comes into direct contact with food, it is safe for human bodies and has no problem.
In addition, the middle base layer has 30% by weight of polybutylene succinate / adipate as an aliphatic polyester according to the present invention, so it has excellent impact resistance, and 100 cc of water is put in the obtained container. After sealing with a heat seal lid, it did not break even when dropped onto a concrete floor from a height of 1 m.
In addition, since the sheet-like material of this invention was excellent also in heat resistance, it turned out that it is suitable also for thermoforming.

(Comparative Example 1)
Using a polylactic acid similar to the polylactic acid used in Example 1, a single-layer sheet-like product having a thickness of 300 μm was obtained. In the same manner as in Example 1, the obtained sheet-like material was molded into a container having a diameter of 100 mm and a depth of 30 mm at a molding temperature of 100 ° C. and a molding pressure of 0.3 MPa.
Although the obtained container was secured to the human body and the like, a drop test was performed in the same manner as in Example 1, and the container was destroyed.

Claims (5)

  On at least one surface of a base substrate comprising as a main component a resin composition in which an aliphatic polyester having a glass transition temperature of 0 ° C. or lower and a melting point of 80 ° C. or higher is blended with a polylactic acid-based polymer at least on one side, A biodegradable sheet for thermoforming, characterized in that a layer comprising a lactic acid polymer is provided. 2. The biodegradable sheet for thermoforming according to claim 1, wherein the aliphatic polyester has a weight average molecular weight of 20,000 to 300,000 and a structure represented by the following general formula (1).

(In the formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. N is a degree of polymerization necessary for the weight average molecular weight to be 20,000 to 300,000. N. Each R ¹ or R ² may be the same or different, and in the formula, a urethane bond residue and / or a carbonate bond residue may be substituted with an ester bond residue with a weight average molecular weight of 0. Contain ~ 5%.)   3. The polylactic acid-based polymer is D-lactic acid: L-lactic acid = 100: 0 to 94: 6 or 0: 100 to 6:94, according to claim 1. A biodegradable sheet for thermoforming.   A container formed by thermoforming the sheet for biodegradable thermoforming according to any one of claims 1 to 3.   A food container formed by thermoforming the biodegradable thermoforming sheet according to any one of claims 1 to 3.