STORAGE AND TRANSPORTATION METHOD AND PACKAGING MATERIAL FOR RICE

Abstract: A hermetically sealed package wherein the inside of the keeping-ownshape container is formed from a gas barrier plastic material into which an agricultural product such as rice is filled and sealed together with an inert gas provides an efficient storage and transportation system. Once the product is sealed in this package, it is handled in an integral manner from the packaging area to storage through the distribution channels to the final consumption site. A container formed from a high nitrile resin is suitable for applying the system. Keeping-ownshape characteristics is achieved by using a container formed from a gas barrier plastic material packed with an excess of an inert gas, with the amount of the inert gas adsorbed by the agricultural product taken into consideration, or by using a container made of a gas-barrier plastic material, with a smaller part of the wall being made of a film portion which is thinner than the remaining larger portion of the wall.

Description: The present invention relates to a storage and transportation system and a packaging material, packaging container, and package suitable for the storage and transportation of rice. In the long period strage of grains, including white rice, wheat, barley, oats, and rye, corn or varieties of beans, and tasted materials such as treated tea leaves and roasted coffee beans, there are many problems such as deterioration of freshness by oxidation, the loss of their taste and flavor, and decline of their quality by the generation of fungi. Normally, grains are packed in sacks such as hemp sacks, paper sacks, and plastic film bags. However, with these forms of packaging, the above-mentioned quality problems cannot be adequately prevented. There are commonly known a method for large volume warehouse storage, the so-called Controlled Atmosphere Storage (CAS), in which freshness is preserved by storage under gases for which the composition, temperature, and humidity are controlled therein, and vacuum storage methods in which a high degree of vacuum is provided therein. However, with these methods, the warehouse becomes large-scale, and the costs go up proportionally, and after the products are taken out of the warehouse and enter the distribution or consumers circuitry, the decrease in freshness and quality cannot be prevented. In addition, it has been proposed that for long distance transportation, the storage room is divided into small scale compartments, and the condition of preservation in each compartment is individually controlled. However, in this case, the preservation and transportation equipment becomes large-scale and after the products are taken out of the storage room, the decrease in its quality cannot be prevented. On the other hand, in usual packaging, large-sized metal containers and drums has been used. These are very costly, and a non-returnable system cannot be adopted in addition. Because these are not transparent, the contents cannot be seen, and the effect from the standpoint of design and appearance cannot be obtained. In this case of rice which is a representative grain, in the final distribution process and in the stores, this grain is packed in bags of polyethylene film or paper and is sold. In particular, in the case of the bags of polyethylene film, small apertures are made for preventing the burst of bags, and airing of the bags is keeping. Accordingly, in any case, the problem arises that when rice is stored for a long period, its taste and flavor are lost, and odd smell is arised. In order to provide good storage characteristics, consideration has been given to the use of aluminum deposited film, but this causes an increase in costs and because the film has a fairly thick aluminum layer, there is the inconvenience that the contents in the bag are invisible. Also, such bags are mostly soft, so their decorativeness in the store is destroyed. There is known a close contact dormancy packaging method that the rice, which has the property of adsorbing large quantities of carbon dioxide under the high concentrations of the gas, is placed in a bag made of a film which has the very poor permeability for carbon dioxide (for example, a lamination of simultaneous biaxially-oriented nylon film and polyethylene film), rice is packaged after the atmosphere is displaced with high purity carbon dioxide gas, and then the bag is sealed. With the close contact dormancy packaging method, in a short period after sealing the package, the rise is flowable, and after the period, the bag is drawing in the inside, and rugged surface configurations on the packaging bag may be constructed, viz., specifically, close contact dormancy packaging presents the same type of appearance as with the conventional vacuum packaging, and the flowing of the rice is prevented and it becomes hard clumps of hermetically sealed bags. In this way, when the outer surface of the bag takes on some creasy surface appearance, it is not possible to arrive at an effective design to take advantage of the transparency of the package. In addition, if there is some printing on the bag surface, a highly effective display is not possible, and an effective display in the stores is not obtainable. Also, when handling during transportation, storage, and display, some small cracks are formed in the rugged portion and there is some concern that the hermetical seal might be broken. It is therefore an object of the present invention is to provide a superior systematized storage and transportation method for preventing deterioration of freshness and quality of rice. Another object of the present invention is to provide a superior, inexpensive packaging material, container, and the package for rice, suitable for the use in a non-returnable package delivery method, and, all of which prevent deterioration of the freshness and quality of rice, and also provide an effective display. The first object of the present invention is achieved by a hermetically sealed package wherein the inside of the keeping-ownshape container is formed from a specific gas barrier plastic material, into which the rice is filled and hermetically sealed together with an inert gas. Once the rice is hermetically sealed in this package, it is handled in an integral manner from the packaging area to storage through the distribution channels to the final consumption site. The need for large-scale storage facilities and expensive containers is eliminated, while the loss of freshness and quality of the rice is effectively prevented. Handling is easily carried out, and there is possibility of adoption of a non-returnable container to provide an efficient storage and transportation system. The inventors of the present invention have searched for materials suitable as a gas barrier plastic material. As a result, it has been found that the storage and display effect can be improved through the use of a high nitrile resin as the packaging material, or by filling the rice into containers formed from a sheet of that resin. In the drawing, Fig. 1 is a partly sectional view of an example of a container according to the present invention. Fig. 2 is a partly sectional view of an example of a package according to the present invention. In the storage and transportation method of the present invention, the preparation of the hermetically sealed package is performed at the harvest site of rice, at the rice cleaning facilities, or at the loading location of the transportation terminal. Thereafter, the hermetically sealed packages are transported right up to the final consumption site or processing site, without being opened in the tight-sealed form, so that the rice can be transported or stored with its freshness fully maintained, without any necessity for particular transportation and preservation facilities such as refrigerating facilities. Also, because a plastic material is used, it is low priced, and suitable for use with non-returnable containers. The plastic material is superior in gas barrier properties, rigidity, workability, and air tightness when sealed, and transparency. The container for use in the present invention has good characteristics of keeping-ownshape. The container can have an external shape which is a cylinderical tube, a square tube, or box-shaped. The rice is filled into the container along with an inert gas Inert gases which are suitable for this application are carbon dioxide gas, nitrogen gas or mixtures of these gases. Filling an inert gas together with the product prevents flavor loss through oxidation and generation of bacteria, mold and insects. It is preferable that a deoxidant such as fine iron powder, sodium sulfate powder be additionally employed for removing oxygen remaining in the container. The same effect can also be obtained when air and such deoxidants are employed at the same time instead of using nitrogen gas. Carbon dioxide is especially desirable because it exhibits dormancy-forming and bacteriostatic characteristics. The size of the package used in this storage/transportation system depends on the objective of the application. Any suitable size can be used, but taking all things into consideration with respect to the efficiency of the transportation system, including the strength of the container, cost of transportation, and convenience in handling, the 10 to 50 Kg is preferable, and the 20 to 40 Kg is more preferable. Also, the sales unit at the final consumption site and the unit used in the household should be considered, so that a smaller unit, for example, less than 10 Kg could also be more suitable. The high nitrile resin is most preferable for packaging rice since it possesses gas barrier characteristics, transparency, and suitable strength, making it suitable as a packaging material for rice. High nitrile resins used in the present invention for the packaging material and the container material are copolymers comprising mainly unsaturated nitrite components such as acrylonitrile and methacrylonitrile, and other monomers such as styrene, butadiene, isoprene, methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, with the content of the unsaturated nitrite being 50 wt.% or more. One or more of these monomers can be polymerized with an unsaturated nitrile such as acrylonitrile. In addition, the high nitrite resins may be used in combination with a rubber-type polymer such as butadiene-acrylonitryl copolymer, isoprene-acrylonitryl copolymer, butadiene-styrene copolymer, polybutadiene, and polyisoprene. The high nitrile resin may be obtained by graft polymerisation of the unsaturated components and the above-mentioned monomers in the presence of these rubber-type polymers. As such high nitrile resins, BAREX® (made by Sohio Chemicals Co., Ltd.) and PANEX® (made by Kanegafuchi Chemical Industry Co., Ltd.) are commercially available. A sheet-shaped BAREX® is commercially available under the trade mark of ZEXLON® from Mitsui Toatsu Chemicals, Inc. BAREX® is an acrylonitrile thermoplastic resin which is excellent in gas barrier property, rigidity, transparency, and processability (for example, in deep-draw processing), so that there are no difficulties in forming the container. In addition, this material exhibits superior adhesion property, so that, after the filling, the hermetic sealing of the container is easily performed by heat sealing. When the high nitrile resin is employed for the packaging material of the present invention, the packing material can be obtained in sheet form by normal extrusion, calendering, and inflation molding processes. The thickness of the sheet is not restricted, but the 100 µm to 5000 µm is preferable. Also, the packaging container is prepared by forming the high nitrile resin into a sheet by the vacuum molding or by the pressure molding, or by the direct injection molding. Further, it is possible to use this material for bag packaging in the same way as conventional packaging by normal heat sealing of a multi-layered film laminated from the above-mentioned single films or laminated from the above-mentioned single films and films of polypropylene, polyethylene, polyester, nylon and the like. Also, it is possible to print on the surface. It is possible for the container cross-section to take various forms such as a circle, triangle, square forms, etc. The wall thickness of the container varies according to the amount of the contents, the required strength, etc., but usually about 100 to 800 µm is desirable. The strength of a container with a wall thickness of less than 100 µm may be inadequate. On the contrary, a thickness exceeding 800 µm may be acceptable, but the workability is unsatisfactory and the cost is increased. A lid or a top film of the container can be made of a film with high gas barrier properties such as a single layer of the above-mentioned high nitrile resin or vinylidene chloride resin, or a multi-layer film comprising a film made of a resin such as polypropylene, polyethylene, and nylon, which is overlaid on the above-mentioned single layer. Aluminum and steel can also be used for such lid or the top film. Fig. 1 is a sectional view of an example of a container of this type according to the present invention. A quantity of rice 19 is stored in a container body 11 made from a high nitrile resin sheet. On the top of the container body 11, a top film 17 is sealed to a flange section 13 formed on the container body 11. Further, a rib 15 is provided on the container body 11 with the effect of increasing the strength, or to improve the design. Fig. 2 is a partial sectional view of a package 21 in which rice is stored. The package 21 is formed from a container body 23 which is cylindrical or has a square cross section, a top cover 25 which seals an opening in the bottom of the container. In addition, as shown in Fig. 1, the container body 23 and the bottom plate 27 may also be integrally formed. The previously mentioned high nitrite resin may easily be processed into this kind of form because it has superior deep-drawing processing characteristics. Thus it is preferable to adopt such molding method. The top cover 25 may be created in advance to provide a pull top sealing means. In the package 21 after a predetermined amount of rice 29 has been stored, and after the air has been removed by means of a gas replacement method, high purity carbon dioxide gas, nitrogen gas used for food, or a mixture of carbon dioxide gas and nitrogen gas is filled under a predetermined pressure and sealed by means of the top cover 25. With reference to the following examples, the present invention will now be explained in detail. In the following embodiments, the evaluation of "the taste of white rice" and "flavor" was based on the judgement by the five (5) monitors. Example 1 By using a high nitrile resin containing about 70 wt.% acrylonitrile by analysis of nitrogen value, obtained by emulsion polymerization of 75 parts by weight of acrylonitrile and 25 parts by weight of methyl methacrrylate in the presence of 10 parts by weight of butadience - acrylonitryl rubber-type copolymer (containing 70 wt.% butadiene), a sheet having a thickness of 500 µm was obtained by extrusion. The thus obtained sheet was subjected to a vacuum forming process to provide a container having a depth of 5 cm with an inside volume of 500 ml. The container was filled with 400 g of white rice and charged with carbon dioxide gas. By using a separately fabricated film made of the above-mentioned high nitrile resin having a thickness of 40 µm, the container was subjected to heat sealing. After six (6) months the same taste of white rice was still present and there was no odd smell present at all. Example 2 Example 1 was repeated except that the high nitrile resin employed in Example 1 was replaced by the high nitrile resin prepared as follows, whereby a container according to the present invention was prepared. A high nitrile resin containing about 65 wt.% of acrylonitrile (by the analysis of the contained nitrogen) was prepared by polymerization of 70 parts by weight of acrylonitryl, 15 parts by weight of methyl methacrylate, and 5 parts by weight of styrene, in the presence of 10 parts by weight of butadiene acrylonitrile rubber-like copolymer. A check was made for the taste of the white rice and the presence of flavor in the same manner as in Example 1. After six (6) months, the taste of the white rice was still present and there was no odd smell present. Example 3 Through the blow molding process and by using the same resin as with Example 1, a container having an average wall thickness of 500 µm with the inside volume of 500 ml was prepared, and the same processings as given in Example 1 were repeated. Even after six (6) months, the taste of the white rice was still remaining and there was no odd smell. Example 4 The same resin as with Example 1 was used, and by the injection molding a container of an internal volume 500 ml and with an average wall thickness of 500 µm was prepared, with the repetitions of the processes given in Example 1 except for the replacement of the carbon dioxide with a mixture gas of carbon dioxide gas/nitrogen gas (1 : 1). Even after six (6) months, the taste of the white rice was still remaining and there was no odd smell. Comparative Example 1 Example 1 was repeated except that polyethylene was used as the resin, whereby a container was prepared. The container was subjected to the same tests as in Example 1. The result was that the container form was broken down from lack of strength, and in addition, after six (6) months the taste of the white rice was extremely decreased and odd smell was present.

Claims: A storage and transportation method for rice comprising the steps of: filling rice into a package keeping ownshape retention capability made of a gas-barrier plastic material which comprises a high nitrile resin comprising a copolymer of (i) an unsaturated nitrile component in an amount of 50 wt. % or more, and (ii) a monomer component which is capable of being copolymerised with said unsaturated nitrile component, together with an inert gas, tightly sealing said package, and storing and transporting said package in a tightly sealed state. The method as claimed in claim 1, wherein said inert gas is selected from nitrogen gas, carbon dioxide gas and a mixture thereof. The method as claimed in claim 1 or 2, wherein said high nitrile resin is a copolymer obtained by copolymerizing (i) acrylonitrile and (ii) a monomer component which is capable of being copolymerized with said acrylonitrile in the presence of a conjugated diene synthetic rubber. The method as claimed in claim 3, wherein said conjugated diene synthetic rubber is selected from butadiene-acrylonitrile copolymer, isoprene-acrylonitrile copolymer, butadiene-styrene copolymer, polybutadiene and polyisoprene. A packaging material for rice comprising a high nitrile resin comprising a copolymer of (i) an unsaturated nitrile component as the main component, and (ii) a monomer component capable of being copolymerized with said unsaturated nitrile component. The packaging material as claimed in claim 5, wherein said packaging material is in the form of a bag. The packaging material as claimed in claim 5, wherein said packaging material is in the form of a molded container. The packaging material as claimed in any one of claims 5 to 7, where said unsaturated nitrile component is in an amount of 50 wt. % or more. The packaging material as claimed in any one of claims 5 to 8, wherein said high nitrile resin is a copolymer obtained by copolymerizing (i) acrylonitrile and (ii) a monomer component which is capable of being copolymerized with said acrylonitrile in presence of a conjugated diene synthetic rubber. The packaging material as claimed in claim 9, wherein said conjugated diene synthetic rubber is selected from butadiene-acrylonitrile copolymer, isoprene-acrylonitrile copolymer, butadiene-styrene copolymer, polybutadiene and polyisoprene. The packaging material as claimed in any one of claims 5 to 10, wherein said unsaturated nitrile component is selected from acrylonitrile and methacrylonitrile. The packaging material as claimed in any one of claims 5 to 11, wherein said monomer component is selected from styrene, butadiene, isobutylene, methylacrylate, ethylacrylate, methylmethacrylate and ethylmethacrylate. The packaging material as claimed in claim 5, wherein said high nitrile resin is a mixture of said copolymer and a conjugated diene synthetic rubber. The packaging material as claimed in any one of claims 5 to 13, wherein said packaging material is in the shape of a sheet having a thickness ranging from 100 to 5000 µm. The packaging material as claimed in claim 7, wherein said container comprises a wall having a thickness ranging from 100 to 800 µm.

Inventors: FUJITA, MITSUNOBU, KONISHI, YOSHIYUKI, RYUNO, TOSHIRO, SHIBASAKI, KUNIHIRO, SHIMA, YOSHISUKE, YOSHIDA, HISAJI
Applicants: KOIKE CHEMICAL CO. LTD., KYOKUJITSU CO. LTD., MITSUI TOATSU CHEMICALS, INCORPORATED
Application year: 1987
Main classification: B65D81
IPC codes: B65B31, B65D79, B65D81, B65B25