JP2000327031A - Biodegradable food tray - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the mechanical characteristics by setting a specified wt.% or higher of a constituent component to be a polylactic acid wherein the D-lactic acid component is a specified mol.% or lower, and at the same time, setting a hydrolysis coefficient of the resin at a specified relative viscosity or higher, a specified temperature and a specified RH, to be a specified value or lower. SOLUTION: 95% or higher of the constituent component of a resin constituting a food tray is made of a polylactic acid component. The polylactic acid comprises a mixture of an L-lactic acid and a D-lactic acid, and the mixture comprises a copolymer or a mixed body wherein the ratio of the D-lactic acid is 5 mol.% or lower. Then, the relative viscosity of the polylactic acid based resin at 20 deg.C, which is measured by using a 0.5 wt.% of a phenol/ tetrachlooethane =50/50 mixed liquid, is set to be 1.8 or higher. Also, the hydrolysis coefficient of the polylactic acid based resin at 50 deg.C, and 90% RH is set to be 0.05 or lower. By this constitution, a food tray having excellent mechanical characteristics, and biodegradability as well, and equipped with mildewproof property can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food tray manufactured using a biodegradable polymer containing polylactic acid as a main component as a raw material. The present invention relates to a food tray which does not generate any waste and does not accumulate in the natural environment even after disposal.

[0002]

2. Description of the Related Art In recent years, plastic trays for food have been widely used. As a raw material for these trays, a vinyl chloride resin, an olefin resin, and a styrene resin are mainly used. However, since these resins do not decompose in the natural environment or decompose at a very low rate, they can remain semi-permanently on the ground or in the ground when left unused or buried in soil after use. Become. Also, when dumped in the ocean, the landscape is damaged and the living environment of marine life is destroyed. Furthermore, when vinyl chloride resin is incinerated, harmful gases such as hydrogen chloride gas and dioxins are generated, not only polluting the atmosphere, but also promoting the deterioration of incinerators and discarding them together with the expansion of consumption. Disposal has become a social problem.

[0003] The garbage generated from Japanese households is about 5%.
It is said that the amount is up to 10 million tons / year, of which 60% by volume is made of plastic or the like. Plastic trays make up a significant portion of that. Conventionally, most of these household wastes have been disposed of by landfill or incineration. However, in recent years, as the amount of household waste has increased, it has become impossible to dispose of such household waste. Additional incinerators are being considered to increase the throughput, but equipment costs are increasing in order to suppress the generation of dioxins due to high-temperature incineration, making it impossible for small and medium-sized municipalities to construct. In recent years, particularly in urban areas, it has been promoted to treat some of the garbage by composting in order to solve these problems. Household garbage is processed by compost and reused as fertilizer.

On the other hand, in convenience stores and station lunch stores, disposal of unsold lunches has become a major problem.
In recent years, compost has been treated and composted as well as household waste for disposal, but it is necessary to separate the trays from the contents when putting them into compost, and to put only the contents. There was a lot of effort. In order to promote this composting, it is necessary that the raw material of the food tray is a biodegradable polymer. However, commercially available trays made from starch-based and petrified-based biodegradable resins have insufficient strength in performance and tend to grow mold, and are not suitable for food applications. Therefore, in reality, there is a need for a food tray having biodegradability, excellent mechanical properties, and antifungal properties.

[0005] With respect to containers made of polylactic acid, see, for example, JP-A-6-23828 and JP-A-6-1221.
48, JP-A-6-298236, JP-A-9
Japanese Patent Application Laid-Open Nos. 157359, 9-111107, 8-151440, etc., all have inferior mechanical properties and heat resistance.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a food tray having excellent mechanical properties, biodegradability, and antifungal properties.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a food tray made of a polylactic acid-based sheet has excellent mechanical properties, mildew resistance, and biodegradability. Having been found to be the most suitable material for the above-mentioned applications, and reached the present invention. That is, the gist of the present invention is a soil-degradable food tray in which 95% by weight or more of the constituent component is composed of polylactic acid having a D-lactic acid component of 5% by mole or less. The relative viscosity is 1.
A biodegradable food tray having a hydrolysis coefficient of 8 or more, 50 ° C. and 95% RH of 0.05 or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the resin constituting the food tray of the present invention, it is necessary that 95% by weight or more of the constituent component is a polylactic acid component. If the content of the polylactic acid component is less than 95% by weight, it is difficult to provide both biodegradability and strength required for a food tray, and it is not preferable because mold is generated.
The polylactic acid in the present invention is composed of a mixture of L-lactic acid and D-lactic acid, and it is necessary that the proportion of D-lactic acid is 5 mol% or less, preferably 3 mol% or less. . If the content of D-lactic acid exceeds 5 mol%, the crystallinity of the polylactic acid is reduced, and the tray obtained cannot have the necessary strength for practical use.

Further, a small amount of a copolymer component may be contained as long as the object of the present invention is not impaired. Examples of the copolymerization component include aromatic dicarboxylic acid components such as 5-sodium sulfoisophthalic acid, isophthalic acid, phthalic anhydride, and naphthalenedicarboxylic acid, aliphatic dicarboxylic acid components such as adipic acid and sebacic acid, ethylene glycol, diethylene glycol, and butylene. Glycol components such as glycol, 1,4-cyclohexanedimethanol, an alkylene oxide adduct of bisphenol A, an alkylene oxide adduct of bisphenol S, 4-hydroxybenzoic acid, ε
-Hydroxycarboxylic acid components such as caprolactone.

The polylactic acid resin which is a component of the biodegradable food tray of the present invention contains a lubricant, an antiblocking agent, an antistatic agent, and the like, as long as the object of the present invention is not impaired.
Additives such as flame retardants, light stabilizers and antifouling agents, matting agents, pigments and the like may be blended. In order to impart flexibility, an aliphatic polyester such as polybutylene succinate and polybutylene succinate adipate may be contained.

The relative viscosity of a polylactic acid-based resin, which is a component of the biodegradable food tray of the present invention, measured using a 0.5 wt% solution of a phenol / ethane tetrachloride = 50/50 mixture at 20 ° C. 1.8 or more, preferably 2.0
２．５2.5 is required. When the relative viscosity is less than 1.8, the polylactic acid is hydrolyzed when the food is added to the tray and sterilized by heating, or when the heated food is filled, and the strength is deteriorated in a short time, The tray breaks during transportation, which is not desirable.

It is necessary that the polylactic acid resin, which is a component of the biodegradable food tray of the present invention, has a hydrolysis coefficient at 50 ° C. and 95% RH of 0.05 or less. The hydrolysis coefficient refers to the slope of a straight line plotted with the change in relative viscosity when treated at 50 ° C. and 95% RH for 6 days on the vertical axis and the number of treatment days on the horizontal axis. If the hydrolysis coefficient is larger than 0.05, the strength is deteriorated when the food is heated and sterilized or when the food is heated to a high temperature, and the food is easily broken and broken during transportation. Since a tray for lunch, a container for natto, a tray for tofu, and the like are particularly required to have heat resistance and strength, it is necessary to maintain these characteristics.

The form of the food tray is not particularly limited, but it is preferable that the tray is deep drawn to a depth of 2 mm or more in order to fill the food. Although the thickness and width of the sheet are not particularly limited, the thickness is preferably 50 μm or more, and more preferably 150 μm or more and 500 μm or less in view of necessary strength.

As a method for forming a polylactic acid-based sheet used as a material for the biodegradable food tray of the present invention, for example, a method such as a melt casting method, a melt extrusion method, and a calendering method can be used. Industrially, the melt extrusion method is generally used. As the melt extrusion method, a known T
Die method can be applied. The extrusion temperature is 190-
It is in the range of 280C, preferably 200-250C. If the molding temperature is too low, molding becomes unstable, and it is easy to fall into overload, and if it is too high, the strength of the sheet obtained by decomposition of polylactic acid is reduced, and problems such as coloring occur. Further, the hydrolysis coefficient is undesirably large. When the polylactic acid-based sheet is deep-drawn into a tray, the deep-drawing temperature is preferably in the range from the glass transition point (Tg) of the lactic acid-based polymer to be used to (Tg + 50) ° C. or less. If the deep drawing temperature is lower than Tg, deep drawing is difficult, and if it exceeds (Tg + 50) ° C., improvement in strength by stretching may not be recognized.

[0015]

Next, the present invention will be described specifically with reference to examples.

Example 1 Chips containing 98% by weight of polylactic acid (ECOPLA4030D manufactured by Cargill) and 2% by weight of polybutylene succinate (Bionole 1903 manufactured by Showa Kogyo KK) having a D% of 1 mol% and a residual lactide of 0.18% were used as chips. The mixture was melted and extruded from a T-die at a temperature of 220 ° C. using an extruder to a thickness of 40 ° C.
An unstretched sheet of 0 μm was obtained. This unstretched sheet is
After heating to ° C., a lunch tray with a depth of 35 mm was prepared by vacuum forming. The obtained food tray is placed at 50 ° C, 95
After treating for 6 days under the condition of% RH, the hydrolysis coefficient was measured. High-temperature cooked rice and side dishes were placed in the obtained food tray, and a transportation test was conducted. As a result, no mold or the like was generated, and no damage occurred during transportation.

Examples 2-3, Comparative Example 1 An unstretched sheet was obtained in the same manner as in Example 1 except that the mixing ratio of polylactic acid and bionole was changed as shown in Table 1. Created. Table 1 shows the characteristic values of the obtained trays.

Example 4, Comparative Example 2 An unstretched sheet having a different relative viscosity was obtained in the same manner as in Example 1 except that polylactic acid having a small molecular weight was used, and a tray was prepared therefrom. Table 1 shows the characteristic values of the obtained trays.

Examples 5-6 Unstretched sheets were obtained in the same manner as in Example 1 except that a different polylactic acid of D% was used, and trays were prepared therefrom.
Table 1 shows the characteristic values of the obtained trays.

COMPARATIVE EXAMPLES 3-4 96% by weight of different polylactic acid of D% and Bionole 190
An unstretched sheet was obtained in the same manner as in Example 1 except that 4% by weight of Bionole 3020 was mixed instead of 3 to prepare a tray. Table 1 shows the characteristic values of the obtained trays.

Comparative Example 5 An unstretched sheet was obtained in the same manner as in Example 1 except that 10% by weight of a starch-based resin was mixed instead of Bionole 1903, and a tray was prepared therefrom. Table 1 shows the characteristic values of the obtained trays.

[0022]

[Table 1]

[0023]

According to the present invention, there is provided a food tray having excellent mechanical properties, biodegradability, and antifungal properties. This tray can be used for food applications such as bento, natto, and tofu, and when discarded, the food and the tray can be put into compost without separating them, reducing the amount of garbage and reusing it as fertilizer. Can be used.

Claims (5)

[Claims] 1. A soil-degradable food tray comprising 95% by weight or more of polylactic acid having a D-lactic acid component of 5% by mole or less, wherein the resin constituting the tray has a relative viscosity of 1. A biodegradable food tray having a hydrolysis coefficient of 8 or more and a hydrolysis coefficient at 50 ° C. and 95% RH of 0.05 or less. 2. The method according to claim 1, wherein 95% by weight or more of the constituent components are obtained by deep drawing of a sheet manufactured using a resin made of polylactic acid having a D-lactic acid component of 5 mol% or less as a raw material. Item 6. The biodegradable food tray according to Item 1. 3. The tray according to claim 1, wherein the food is a lunch box. 4. The tray according to claim 1, wherein the food is natto. 5. The tray according to claim 1, wherein the food is tofu.