JPH05139435A - Foaming container - Google Patents

Abstract

PURPOSE:To provide foaming containers such as tray and lunch box which are made from a thermoplastic polymer composition consisting mainly of the copolymer of polylactic acid or lactic acid and hydroxycarboxylic acid so as to be made decomposable in a relatively short period of time in a natural environment. CONSTITUTION:Polystyrene or polyolefin foaming containers are widely used in the tray or lunch box. In this case, the foaming container is made from a thermoplastic polymer composition consisting mainly of the copolymer of polylactic acid or lactic acid and hydroxycarboxylic acid. Levo or dextro-lactic acid alone or the mixture thereof is used in the aforesaid lactic acid. Glycolic acid is used in the aforesaid hydroxycarboxylic acid. When the foaming container is disposed of by being buried under the ground or discarded into the sea or river, as in the case of paper or wood, the foaming container is decomposed into harmless water and carbon dioxide in a relatively short period of time in a natural environment.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a foam container. More specifically, the present invention relates to a foam container having a degradability in a natural environment, which is made of a thermoplastic polymer composition mainly containing lactic acid polymer.

[0002]

2. Description of the Related Art Conventionally, polystyrene-based or polyolefin-based foam containers have been widely used for trays, lunch boxes and the like. In particular, these foam containers are molded with a small amount of resin and are used as disposable containers and food containers. However, the foam container molded from such a resin,
In addition to being bulky and increasing the amount of garbage at the time of disposal, conventional materials have a very slow decomposition rate in the natural environment, so when they are buried, they remain in the ground semipermanently. In addition, the discarded plastics have caused problems such as damage to the landscape and the living environment of marine life. However, up to now, no foam container that is easily decomposed in a natural environment has been known.

On the other hand, polylactic acid or a copolymer of lactic acid is known as a degradable thermoplastic polymer.
This lactic acid-based polymer is degradable in a natural environment, and when placed in soil or seawater, it begins to decompose in a few weeks and disappears in about a year. The decomposition products are lactic acid, carbon dioxide and water, all of which are harmless. Lactic acid as a raw material is obtained from inexpensive fermentation such as corn starch and corn syrup, and is easily produced from petrochemical raw materials such as ethylene. The production of polylactic acid or a copolymer of lactic acid is disclosed in US Pat. No. 1,995,970 and is synthesized from a cyclic dimer of lactic acid commonly referred to as lactide. Because of its biocompatibility and degradability, this lactic acid-based polymer is used as a surgical suture and a medical sustained-release material, but its use as a cushioning material has not yet been known.

[0004]

The present invention is to provide a foam container that can be decomposed in a natural environment.

[0005]

Means for Solving the Problems The present inventors have focused on lactic acid-based polymers for the purpose of obtaining a foamable container that can be decomposed in a natural environment, and obtained a foamed sheet from a resin mainly containing lactic acid polymer. The present invention has been completed by succeeding in obtaining a container that does not impair the degradability of the polymer. That is, the present invention is a foam container made of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component. In the polylactic acid or the copolymer of lactic acid and hydroxycarboxylic acid used in the present invention, lactic acid or a lactide which is a cyclic dimer of lactic acid and further hydroxycarboxylic acid may be used as a raw material, or other monomer may be appropriately used depending on the case.
When lactic acid is used, dehydration condensation is used, but to obtain a high molecular weight product, ring-opening polymerization of lactide is preferable.
Lactide used for ring-opening polymerization is L-lactide or D-lactide.
Lactide, meso lactide, or a mixture thereof is used, but a mixture of D or L-lactide with the opposite optical activity is preferable. The mixing ratio is
D or L-lactide / optical antipode = 95/5 to 50
/ 50 is preferable.

The degree of polymerization of the lactic acid type polymer is 150 to 2
It is 10,000. If the degree of polymerization is lower than this, the strength of a molded product such as a film is small and it is not suitable for practical use. On the other hand, if the degree of polymerization is too high, the viscosity in the molten state during heating is high and the moldability is poor.

The polymerization method may be a method using a solvent or a method not using a solvent, but in view of the problem of recovery of the solvent, industrially bulk polymerization without a solvent is preferable. As the ring-opening polymerization catalyst, zinc, tin chloride, carboxylate or the like is generally used, but the catalyst is not particularly limited. Toxicities should be considered when used in biocompatible materials and food products. The lactic acid-based polymer according to the present invention may contain a plasticizer, a modifier and the like.

The foam container according to the present invention is manufactured from a thermoplastic polymer composition containing a lactic acid-based polymer as a main component. Usually, a foamed sheet is manufactured using the above-mentioned thermoplastic polymer, and the foamed sheet is used in an arbitrary shape. Used as a foam container. The production of the foamed sheet can be carried out using a usual method. Usually, it is preferable to use a so-called extrusion foaming method in which foaming is carried out simultaneously with extrusion from an extruder using a foaming agent. Examples of the foaming agent include evaporative foaming agents that are foamed by evaporation, such as hydrocarbons such as ethane, butane, pentane, hexane, heptane, ethylene, propylene, petroleum ether, methyl chloride, monochlorotrifluoromethane, dichlorodifluoromethane, dichlorotetramethane. Examples thereof include halogenated hydrocarbons such as fluoroethane, carbon dioxide gas, nitrogen gas, and water. The amount of these foaming agents added is preferably 0.1 to 30% by weight, and particularly preferably 0.5 to 10% by weight, based on the thermoplastic polymer composition.

If necessary, a decomposition type foaming agent which decomposes to generate gas when heated, for example, an inorganic foaming agent such as sodium bicarbonate, azodicarbonamide, N, N'-dinitropetamethylenetetramine, p, p'- Organic foaming agents such as oxybis (benzenesulfonylcarbazide), azobisisobutyronitrile, benzenesulfonylhydrazide, foaming aids or nucleating agents such as stearic acid, oxalic acid, salicylic acid, phthalic acid, benzoic acid, citric acid, tartaric acid An appropriate amount of an inorganic acid such as the above, a salt of the organic acid or the inorganic acid, a carbonate such as sodium carbonate, zinc oxide, calcium oxide, titanium oxide, silica, alumina, clay, kaolin, diatomaceous earth and the like may be added. For coloring or other modification of the foamed molded product, it is also possible to add an appropriate amount of pigment, flame retardant, filler or the like.

The extrusion temperature of the foamed sheet depends on the composition of the polymer, but the melt viscosity is usually 10,000 to 10
Perform at a temperature of 50,000 poise. If it is lower than this, the viscosity of the melted polymer is high, the formation of bubbles is slow, and the expansion ratio does not increase. On the other hand, if the viscosity of the polymer is too low at a temperature higher than this, bubbles cannot be retained, and a foamed sheet of uniform quality cannot be obtained. Although the expansion ratio depends on the container to be molded, it is preferably 1.5 to 15 times. The foamed container is reheated to soften the sheet, and then formed into a desired shape by thermoforming such as vacuum or pressure forming. The foam container is preferably one in which the skin layer on the outer surface is partially removed. To partially remove the skin layer on the outer surface of the foam container, for example, make a cut in the surface layer of the foam sheet before thermoforming and expand the cut by heating in an oven before molding the container. Or
Alternatively, a method of forming small holes after molding the container is used.

[0011]

The present invention will be described in detail below with reference to examples. Examples 1 to 3 0.5% by weight of talc was added as a cell regulator to a mixture of poly D, L-lactide and poly L-lactide having a molecular weight of about 100,000 shown in Table-I, and the temperature was 200 ° C. in an extruder of 50 mmΦ.
After melt-kneading at the temperature of, butane was injected under pressure at a ratio of 0.065 mol to 100 g of the resin. After the press-fitting, the cylinder temperature of the extruder was set to 140 to cool the resin mixture, and the resin mixture was discharged into the atmosphere through the slit to obtain a foamed sheet having a width of 650 mm. The thickness and apparent density of the obtained foamed sheet are shown in Table-I. A tray having a size of 200 × 100 mm and a depth of 15 mm was formed from these foamed sheets by a vacuum forming machine. Before entering the oven of the molding machine, the foamed sheet is passed through a roll having a 5 mm cross cut on the outer surface side of the container. The break is about 2 mm when passing through an oven at 150 ° C
Spread to. Then, it is inserted into the mold and shaped. The outer side of the obtained tray had a lattice-like skin layer removed, and there was no problem in using the tray.
This tray was embedded in soil having a temperature of 35 ° C. and a water content of 30% to carry out a decomposition test. The degradability was evaluated by the weight reduction rate. The results are also shown in Table-I.

Examples 4 to 6 A foamed sheet and a tray were formed in the same manner as in Example 1 except that the copolymer of L-lactide and oxycarboxylic acid shown in Table II was used. The thickness, apparent density and result of the decomposition test of the obtained foamed sheet are shown in Table-II.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

INDUSTRIAL APPLICABILITY The foam container mainly composed of the polymer containing lactic acid as a main component of the present invention is the same as a natural product such as paper or wood when it is buried in the ground as waste or dumped in the sea or river. It decomposes into harmless water and carbon dioxide within a relatively short period of time in the natural environment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08J 9/14 CFD 8927-4F C08L 67/04 LPM 8933-4J // B29B 17/00 8824-4F B29C 51/00 7421-4F B29K 105: 04 C08L 67:00 (72) Inventor Masanobu Amioka 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. A foam container made of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component. 2. The foam container according to claim 1, wherein the lactic acid is L-lactic acid, D-lactic acid or a mixture thereof. 3. The foam container according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid.