Method for manufacturing additives to impart freshness preservation function, method for manufacturing packaging bags, masterbatch and packaging bag

Abstract

We have developed a technology to provide a simple and useful additive that can effectively impart freshness preservation properties to the raw materials for manufacturing plastic film packaging bags without compromising the strength of the film, thereby providing superior packaging bags that can maintain freshness for a longer period than products with freshness preservation properties added using conventional technologies. [Solution] A method for manufacturing an additive for imparting freshness preservation function to a plastic film, comprising: a step of preparing liquid A containing powdered rice husks and vegetable oil; a step of preparing liquid B containing powdered metal complex and vegetable oil; a step of introducing liquid A and liquid B into a supercritical fluid apparatus, and preparing an additive stock solution by heating and mixing and stirring liquid A and liquid B under pressurized conditions in the presence of a carbon dioxide supercritical fluid in the supercritical fluid apparatus; and a step of preparing a masterbatch by incorporating the additive stock solution prepared in the step in an amount of 0.2 to 0.5 parts per 100 parts of resin material; a method for manufacturing an additive; a method for manufacturing a packaging bag; a masterbatch; and a packaging bag.

Description

Technical Field

[0001] The present invention relates to a method for producing an additive for imparting a freshness retention function to a plastic film, a method for producing a packaging bag using the additive, a masterbatch, and a packaging bag. Specifically, in a plastic film packaging bag used for storing fresh foods such as vegetables and fruits such as lettuce, cabbage, and bananas, it is possible to keep the fresh foods stored in the bag in a fresh state for a longer period of time. The present invention relates to a technology for providing an additive for imparting an excellent freshness retention function to a plastic film, and further to a technology for simply and stably providing a packaging bag having an excellent freshness retention function that has never existed before and contains the additive.

Background Art

[0002] In recent years, as described below, various technologies have been proposed for products called "freshness retention bags", and a wide variety of products are commercially available and widely used. For example, in Patent Document 1, a freshness retention material for fresh foods such as a configuration in which a gas-permeable body, which is a synthetic resin having a three-dimensional network skeleton structure, is coated with a porous inorganic silicate compound such as oolite or hotsukite is proposed. In this proposal, the freshness retention material is obtained by coating or impregnating the surface of the gas-permeable body with a slurry composed of a porous inorganic silicate compound and water and then drying it. Patent Document 2 describes that the above-mentioned porous powder adsorbs and removes ethylene gas that is slightly generated during storage of vegetables, fruits, etc., and malodorous gases such as ammonia. And in Patent Document 2, a freshness retention resin composition in which 2 to 300 parts by weight of crushed Natsume stone powder is blended with 100 parts by weight of synthetic resin is proposed. By adding crushed Natsume stone powder, in addition to adsorbing ethylene gas and malodorous substances such as ammonia, the freshness of agricultural products or cut flowers is maintained for a long time by far infrared rays irradiated from the crushed Natsume stone powder. A freshness retention film / sheet formed using this is proposed.

[0003] Patent Document 3 proposes a multilayer packaging material comprising a thermoplastic resin layer containing a thermoplastic resin and a porous powder. Patent Document 4 proposes a fresh produce freshness-preserving packaging container made of a synthetic resin film having through-holes perforated by laser processing. Furthermore, many proposals have been made to appropriately adjust the oxygen and carbon dioxide permeability of the plastic film to enhance freshness preservation (see, for example, Patent Document 5). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-136956 [Patent Document 2] Japanese Patent Application Publication No. 9-202361 [Patent Document 3] Japanese Patent Application Publication No. 63-151451 [Patent Document 4] Patent No. 7326721 [Patent Document 5] Patent No. 7283473 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, according to the inventors' research, the packaging bag products that provide freshness preservation using the conventional technologies described above, while exhibiting freshness preservation, are not entirely sufficient. The inventors recognized that in order to effectively utilize resources such as agricultural products, there is a need for packaging bags with enhanced freshness preservation capabilities, particularly for vegetables, fruits, and cut flowers, that can maintain their freshness for a longer period. They also recognized that if this could be achieved with simple technology, the effect would be extremely significant.

[0006] Therefore, the ultimate objective of the present invention is to provide a superior packaging bag that has a longer freshness retention period than conventional packaging bag products that have been given freshness retention properties by prior art. A specific objective of the present invention is to find a technology that provides a useful additive that can effectively impart freshness retention properties to the raw materials for manufacturing packaging bags made of plastic film without impairing the strength of the film. Specifically, an objective of the present invention is to develop a technology that, by adding only a small amount to the raw materials for resin compositions for forming plastic films, enables packaging bags made of plastic film formed from said raw materials to retain the freshness of agricultural products and other foods for a longer period of time. An objective of the present invention is to develop a technology that provides a useful and novel additive that can effectively utilize rice husks, a natural resource that has been difficult to finely grind and uniformly incorporate into plastic films. [Means for solving the problem]

[0007] The above objective is achieved by the present invention as described below. That is, the present invention provides a method for manufacturing an additive for imparting the following freshness-preserving function. [1] A method for manufacturing an additive for imparting freshness preservation function to a plastic film, comprising the steps of: preparing a first stock solution (Solution A) containing powdered rice husks and vegetable oil; preparing a second stock solution (Solution B) containing powdered metal complex and vegetable oil; introducing the first stock solution (Solution A) and the second stock solution (Solution B) into a supercritical fluid apparatus, and preparing an additive stock solution by heating, mixing, and stirring the first stock solution (Solution A) and the second stock solution (Solution B) under pressurized conditions in the presence of a carbon dioxide supercritical fluid within the supercritical fluid apparatus; and preparing a masterbatch by incorporating the additive stock solution prepared in the step of preparing the additive stock solution in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material.

[0008] The following are preferred methods for manufacturing additives that provide the above-mentioned freshness-preserving function. [2] A method for producing the additive for imparting freshness preservation function described in [1] above, wherein the melting point of the vegetable oil is 70°C or higher and 85°C or lower. [3] A method for producing an additive for imparting freshness preservation function according to [1] or [2] above, wherein the resin constituting the resin material is selected from the group consisting of polyolefin resins, polyethylene terephthalate resins, and polystyrene resins, at least one of these. [4] A method for producing an additive for imparting freshness preservation function according to any one of [1] to [3] above, wherein the metal complex is selected from at least one of the group consisting of metal phthalocyanines, metal porphyrin complexes and metal carbonyl complexes.

[0009] As another embodiment of the present invention, the present invention provides a method for manufacturing the following packaging bags. [5] A method for manufacturing a packaging bag made of a plastic film that has been given freshness preservation function, comprising the steps of: preparing a first stock solution (Solution A) containing powdered rice husks and vegetable oil; preparing a second stock solution (Solution B) containing powdered metal complex and vegetable oil; introducing the first stock solution (Solution A) and the second stock solution (Solution B) into a supercritical apparatus, and preparing an additive stock solution by heating, mixing and stirring the first stock solution (Solution A) and the second stock solution (Solution B) under pressurized conditions in the presence of a carbon dioxide supercritical fluid within the supercritical apparatus; and preparing the additive stock solution A method for manufacturing a packaging bag, comprising the steps of: preparing a masterbatch by including the additive stock solution prepared in the manufacturing process in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material; preparing a resin composition by mixing the additive, which is a masterbatch for imparting freshness preservation function, prepared in the masterbatch preparation step, in an amount of 9 parts by mass or more and 12 parts by mass or less per 100 parts by mass of thermoplastic resin; and manufacturing a bag-shaped plastic film containing the additive for imparting freshness preservation function by molding the resin composition prepared in the step.

[0010] The following are examples of preferred methods for manufacturing the above-mentioned packaging bags. [6] The method for manufacturing a packaging bag according to [5], wherein the thermoplastic resin is selected from at least one of the group consisting of polyolefin resins, polystyrene resins, and polyethylene terephthalate resins. [7] The method for manufacturing a packaging bag according to [6] above, wherein the polyolefin resin is either a high-density polyethylene resin or polypropylene. [8] A method for manufacturing a packaging bag according to any one of [5] to [7] above, wherein the step of manufacturing the bag-shaped plastic film is inflation molding. [9] A method for manufacturing a packaging bag according to any one of [5] to [8] above, wherein the thickness of the plastic film is 8 μm or more and 50 μm or less.

[0011] The present invention provides the following masterbatch as another embodiment.

[10] A masterbatch used as an additive for imparting freshness preservation function to a plastic film, characterized in that, per 100 parts by mass of resin material, it contains 0.2 parts by mass or more and 0.5 parts by mass or less of a processed product comprising a first stock solution (Solution A) containing powdered rice husks and vegetable oil, and a second stock solution (Solution B) containing powdered metal complex and vegetable oil, in a supercritical apparatus under pressurized conditions in which a supercritical carbon dioxide fluid is present.

[0012] As described later, the distinguishing feature of the present invention is that the processed products of liquid A and liquid B, which are processed in a supercritical apparatus under pressurized conditions where supercritical carbon dioxide fluid is present, are used as additive stock solutions, and these additive stock solutions are used as constituent materials for the masterbatch. On the other hand, the processed products of liquid A and liquid B introduced into the supercritical apparatus in the presence of supercritical carbon dioxide fluid can only be identified by using this manufacturing method description. That is, the additive stock solutions obtained as processed products of liquid A and liquid B processed in the presence of supercritical carbon dioxide fluid exhibit completely different effects from liquid A and liquid B before they were introduced into the supercritical apparatus in the following respects, but it is impossible and impractical to identify them as products without specifying the manufacturing method. By being processed in the supercritical apparatus, the powdered rice husks in the processed product (additive stock solution) are finely ground, making it possible to incorporate the active ingredients of liquid A and liquid B into a resin material at a sufficient concentration, which was not possible in the past, and to create a masterbatch. When this masterbatch is incorporated into a general-purpose resin, it becomes possible to uniformly incorporate the active ingredients into the resin. There is no way to specify the invention of a masterbatch that can achieve these effects other than defining it as stipulated in claim 9, which states that "for every 100 parts by mass of resin material, it contains 0.2 parts by mass or more and 0.5 parts by mass or less of a processed product of a first stock solution (liquid A) containing powdered rice husks and vegetable oil, and a second stock solution (liquid B) containing powdered metal complex and vegetable oil, in a supercritical apparatus under pressurized conditions where a supercritical carbon dioxide fluid is present."

[0013] The present invention provides the following packaging bag as another embodiment.

[11] A packaging bag characterized by being made of a plastic film made of a resin composition comprising 100 parts by mass of a resin selected from the group consisting of polyolefin resins, polyethylene terephthalate resins, and polystyrene resins, and containing the masterbatch described in

[10] in an amount of 9 parts by mass or more and 12 parts by mass or less.

[0014] Preferred packaging bags include the following:

[12] The packaging bag according to

[11] , wherein the thickness of the plastic film is 8 μm or more and 50 μm or less.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a packaging bag that has a very useful practical meaning in that it has a longer freshness retention period than the packaging bag products provided with freshness retention properties obtained by the prior art. According to the present invention, by a simple method of adding only a small amount to raw materials such as resins when manufacturing a packaging bag made of a plastic film, it is possible to keep the freshness of agricultural products and the like stored in the bag for a longer period without impairing the strength of the packaging bag made of a plastic film formed from this manufacturing raw material, and it is possible to provide a useful additive that can achieve a high level of freshness retention performance that could not be achieved by the prior art. According to the present invention, as a result of realizing the development of a technology for obtaining, as a masterbatch, an additive for imparting a freshness retention function to a new, effective, and useful plastic film, it becomes possible to effectively utilize rice husks, which are natural resources that were difficult to uniformly disperse in the plastic film. Moreover, by adding it to the plastic film, it becomes possible to realize the provision of a new packaging bag product that can maintain the freshness of vegetables and the like stored in the bag for a longer period than conventional packaging bag products. According to the present invention, by simply preparing, as a masterbatch, an additive raw material obtained by the new, effective, and useful manufacturing method of the present invention and adding a small amount to the resin composition raw material for forming the plastic film, it is possible to provide a plastic film-based packaging bag that can achieve freshness retention of agricultural products and the like stored in the bag for a longer period without impairing the strength required for the packaging bag.

Brief Description of the Drawings

[0016] [Figure 1A] It is a diagram showing an outline of a manufacturing flow when forming an additive for imparting a freshness retention function to the plastic film of the present invention as a masterbatch. [Figure 1B]It is a diagram showing an outline of a manufacturing flow when producing a packaging bag using an additive obtained by the manufacturing method of the present invention formed from a masterbatch. [Figure 2A] It is a graph showing the results of a performance test on freshness retention over a long period, which was confirmed by the change in the area occupied by the green hue obtained by color decomposition of the photographic image of the cabbage, which was stored in the packaging bag FR of the example of the present invention and in two types of commercially available packaging bags A and B for freshness retention used for comparison. [Figure 2B] It is a graph showing the results of a performance test on freshness retention over a long period, which was confirmed by the change in the area occupied by the brown hue obtained by color decomposition of the photographic image of the cabbage, which was stored in the packaging bag FR of the example of the present invention and in two types of commercially available packaging bags A and B for freshness retention used for comparison. [Figure 2C] It is a graph showing the results of a performance test on freshness retention over a long period, which was confirmed by the change in the area occupied by the yellow hue obtained by color decomposition of the photographic image of the cabbage, which was stored in the packaging bag FR of the example of the present invention and in two types of commercially available packaging bags A and B for freshness retention used for comparison.

Mode for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described with reference to preferred embodiments, but the present invention is not limited to the following embodiments. The present inventors have earnestly studied to obtain a packaging bag that can maintain freshness for a longer period than conventional products by a simple means of adding an additive made into a masterbatch to a thermoplastic resin that has been conventionally widely used as a forming material for packaging bags made of plastic film. As a result, the present invention has been achieved.

[0018] The inventors first focused on rice husks, a natural resource whose usefulness is recognized but which is discarded in large quantities, as a material to be incorporated into plastic films, and investigated its potential use as an additive material to effectively impart freshness preservation functionality.

[0019] Rice hulls are composed mostly of recalcitrant organic substances such as cellulose and hemicellulose, and contain about 20% amorphous silica. The inventors anticipated that powdered rice hulls could be a promising material for imparting freshness-preserving functions to plastic films, and investigated the components from the perspective of imparting freshness-preserving functions. In addition to the organic substances mentioned above, rice hulls also contain lignin. During the investigation, the inventors discovered that lignin has freshness-preserving functions. Specifically, when the freshness-preserving effect was confirmed using only lignin on lettuce, it was found that the lettuce remained green for a longer period. From these results, the inventors recognized that using "rice hull powder" as a forming component of plastic films for making packaging bags may provide long-term freshness-preserving functions to plastic film packaging bags. Furthermore, they considered that using a plastic film made by adding a small amount of lignin powder to rice hull powder might allow for more stable imparting of freshness-preserving functions to plastic film packaging bags. Furthermore, in a study using lignin alone, the lettuce remained green for a longer period, but it ended up looking as if it had been steamed. From this, it was found that using lignin in its raw form on vegetables may diminish the value of the vegetables themselves and therefore cannot be used.

[0020] When powdered rice husks are used as a component of the plastic film, the inventors anticipated that, in addition to the freshness-preserving function of lignin discovered during their research, the cellulose and silica components, which are other components of the rice husks, would impart the following functions to the packaging bag. The inventors conducted a confirmation test on this point. As a result, they found that when the plastic film is used to make a packaging bag, the cellulose and silica components of the rice husks contribute to moisture regulation inside the bag and / or gas adsorption and moisture retention from vegetables inside the bag, and that using "rice husks" is desirable in this respect as well.

[0021] On the other hand, even if the incorporation of rice husk powder can impart freshness preservation functionality to plastic films, in order to more effectively and stably impart freshness preservation functionality to packaging bags without compromising the strength of the bags, it is necessary to ensure that the rice husk powder is uniformly distributed throughout the film. However, according to the inventors' research, even if pellets containing a high concentration of finely ground rice husk powder are produced and the resulting pellets are used as a masterbatch and incorporated into the resin for forming packaging bags, there is a technical challenge in that it is difficult to uniformly incorporate the rice husk powder into the formed plastic film. In addition, grinding rice husks with a mill is difficult, and fine grinding is extremely difficult, and there is also the problem of poor handling.

[0022] The inventors of this invention have diligently studied how to resolve the above-mentioned technical problems and realize a plastic film with higher freshness retention than conventional films, and have made the following new discoveries, leading to the present invention. First, in order to impart a high freshness retention function to a plastic film, the inventors have found that it is effective to use a resin composition containing rice husk powder in combination with a powdered metal complex and vegetable oil as additives, and to prepare a plastic film using this additive and make a packaging bag from this film. Furthermore, in order to uniformly and stably impart sufficient freshness retention function to the plastic film, it is preferable to use a masterbatch with a high concentration of active ingredients as the composition of the additive. In addition, the inventors have found that by applying a new method using a supercritical fluid apparatus when preparing the masterbatch, it is possible to include an active ingredient for imparting freshness retention function to the masterbatch at a sufficient concentration, and moreover, when the obtained masterbatch is incorporated into a general-purpose resin, it is possible to uniformly incorporate fine powdered rice husks into the resin, resulting in a useful additive stock solution (hereinafter referred to as the additive stock solution). Specifically, it was found that by using a supercritical apparatus under pressurized conditions containing supercritical carbon dioxide fluid to prepare the above-mentioned additive stock solution, it becomes possible to stably and uniformly incorporate the active ingredient, powdered rice husks, into the plastic film. It should be noted that among the processes performed using a supercritical apparatus, the process performed under pressurized conditions containing supercritical carbon dioxide fluid is sometimes referred to as a "carbon dioxide supercritical polymerization apparatus" to distinguish it from other processes.

[0023] More specifically, the inventors have discovered that the excellent effects of the present invention can be achieved by preparing a masterbatch, which serves as an additive for imparting freshness-preserving function to plastic films, as described below, and using it to manufacture packaging bags. First, as shown in Figure 1A, a first stock solution (hereinafter also referred to as solution A) containing powdered rice husks and vegetable oil, and a second stock solution (hereinafter also referred to as solution B) containing powdered metal complex and vegetable oil are prepared. Then, the prepared solutions A and B are introduced into a supercritical fluid apparatus. In the supercritical fluid apparatus into which solutions A and B have been introduced, solutions A and B are heated and mixed and stirred under pressure in the presence of a carbon dioxide supercritical fluid to prepare stock solutions that constitute the additive, which are liquid substances. The inventors have discovered that by treating liquids A and B in the presence of a supercritical carbon dioxide fluid as described above, an additive stock solution can be obtained in which powdered rice husks and powdered metal complexes are dispersed and compounded as nano-sized or near-nano-sized fine particles (nanocapsule-like particles) in vegetable oil. Furthermore, they have discovered that by incorporating this additive stock solution into a resin material at a sufficient concentration and pelletizing it, a useful additive for imparting freshness-preserving function to plastic films can be formed as a user-friendly masterbatch. Specifically, the method involves preparing a masterbatch by incorporating the additive stock solution prepared using the supercritical apparatus described above in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material. This yields a masterbatch containing powdered rice husks, powdered metal complexes, and vegetable oil at sufficient concentrations. Furthermore, it was found that by adding (blending) the obtained masterbatch to a general-purpose thermoplastic resin used in the manufacture of packaging bags, and using the resulting resin composition as a raw material composition for manufacturing plastic films by molding methods such as inflation molding, packaging bags can be prepared using the resin composition (see Figure 1B). The inventors have found that the above-described simple manufacturing method efficiently produces plastic films and packaging bags that exhibit an unprecedentedly high level of freshness preservation function, which is the objective of the present invention.

[0024] The additive for imparting the freshness-preserving function that characterizes the present invention is an additive used in the manufacture of a plastic film having a freshness-preserving function, and can be provided as a masterbatch, characterized in that the masterbatch contains a processed product of powdered rice husks, powdered metal complex, and vegetable oil at a sufficient concentration. The raw materials constituting the additive characterizing the present invention will now be described. For the powdered rice husks used in the present invention, it is preferable to use powder or fine powder obtained by directly processing rice husks of the grain into powder. Depending on the thickness of the plastic film used for the packaging bag to be prepared, the rice husks contained in the plastic film formed using the additive characterizing the present invention are preferably, for example, powdered rice husks with a number average particle size of about 3 μm to 50 μm, and more preferably powdered rice husks with a number average particle size of about 3 μm to 30 μm. If the particle size of the rice husks contained in the plastic film exceeds 50 μm, it may give a foreign body sensation or cause the film to tear easily, so this is undesirable. The particle size mentioned above is the number-average particle size, which is the 50% diameter known as the median diameter.

[0025] The additive for imparting freshness preservation function of the present invention comprises the above-mentioned powdered rice husks, a powdered metal complex, and vegetable oil. The metal complex constituting the additive of the present invention is preferably at least one selected from the group consisting of metal phthalocyanines, metal porphyrin complexes, and metal carbonyl complexes. Phthalocyanines are known to form complexes with a wide variety of metal elements. Examples of metals include copper, iron, zinc, cobalt, nickel, manganese, and aluminum. According to the inventors' studies, among these, metal phthalocyanine complexes are particularly preferred.

[0026] Metallic porphyrin complexes are a general term for colored metal complexes that use porphyrins and their derivatives as ligands. Porphyrins are also known to form complexes with a wide variety of metal elements. Examples of metals include iron, manganese, and cobalt. Metallic carbonyl complexes are a general term for coordination compounds formed when carbon monoxide coordinates to a fibrous metal. Examples of metals include iron, cobalt, and molybdenum.

[0027] The vegetable oil that constitutes the additive for imparting the freshness-preserving function of the present invention preferably has the following characteristics. When producing the additive stock solution that characterizes the present invention, a supercritical fluid is used to mix and stir liquid A, which contains powdered rice husks and vegetable oil, and liquid B, which contains powdered metal complex and vegetable oil, while heating under pressure. By using the processed material in this way, it becomes possible to prepare an additive stock solution in which the powdered rice husks and the powdered metal complex are dispersed and compounded in the vegetable oil as nano-sized or near-nano-sized fine particles (nanocapsules). The processing conditions when mixing and stirring liquid A and liquid B as described above under pressure using a supercritical fluid are preferably as follows: Raise the temperature to a pressure of 9 MPa / 90°C. After the processing is complete, it is necessary to slowly lower the temperature and release the carbon dioxide gas. For this reason, the vegetable oil that constitutes the additive of the present invention is suitable to be an oil that quickly forms a film when the temperature is lowered. Specifically, it is preferable to use a vegetable oil in this invention that has a melting point and exhibits the characteristic of forming a uniform film.

[0028] In addition to the above, since the additive for imparting freshness preservation function in the present invention is an additive for plastic films used in freshness preservation bags for food, it is desirable to use materials derived from natural products as much as possible for the raw materials. For this reason, the present invention uses vegetable oil. Examples of vegetable oils derived from natural products include olive oil, corn oil, sesame oil, rice oil, soybean oil, rapeseed oil, coconut oil, palm oil, sunflower oil, safflower oil, and cottonseed oil. In the present invention, among these, since the process of mixing and stirring liquids A and B described above in the presence of the carbon dioxide supercritical fluid is carried out at a temperature of about 90°C, it is preferable to use vegetable oils that become solid at room temperature with a melting point of about 70°C to 85°C. Examples of such oils include carnauba wax, rice wax, sunflower wax, rosin ester, and candelilla wax. Among these, it is preferable to use rice wax or a mixture of rice wax and other hydrogenated vegetable oils. Examples of hydrogenated vegetable oils include hydrogenated palm oil and hydrogenated rapeseed oil.

[0029] Rice wax, which can be suitably used as a vegetable oil constituting the additive of the present invention, is a natural plant-based wax unique to Japan. It is obtained by further de-oiling and refining the crude wax obtained in the process of refining rice bran oil extracted from rice bran. Rice wax is used, for example, as a mold release agent and lubricant. Rice wax has a high proportion of wax esters and high crystallinity. It also has a melting point of about 80°C and is suitable for the present invention because it melts and solidifies sharply when heated. In the present invention, it is preferable to use an oil with a melting point of 70°C to 85°C, preferably 73°C to 80°C, as the vegetable oil.

[0030] When preparing the additives for imparting the freshness-preserving function of the present invention, in addition to the materials described above, solvents, colorants, etc., may be used as appropriate. As for the solvent, it is desirable to use one that is low polar, has a low boiling point, and is capable of dissolving the vegetable oil that constitutes the present invention. Examples of such solvents include dichloromethane and bromopropane. As for the colorant, those used in conventional packaging bags may be used as appropriate.

[0031] As mentioned above, the additive for imparting the freshness-preserving function of the present invention, with the material composition described above, can be stably prepared as a raw additive solution by processing it using a supercritical fluid apparatus. Furthermore, by using a raw additive solution obtained by dispersing and compounding the resulting powdered rice husk and powdered metal complex as nano-sized or near-nano-sized fine particles (nanocapsule-like particles) in vegetable oil, it becomes possible to easily and stably produce a masterbatch containing sufficient active ingredients suitable for manufacturing the packaging bags of the present invention. As a result, it becomes possible to mass-produce the packaging bags of the present invention, which exhibit a longer-lasting freshness-preserving function than conventional bags, using the same manufacturing methods as conventional methods. This means that, according to the present invention, it is possible to economically provide the packaging bags of the present invention with superior freshness-preserving function.

[0032] The present invention provides a method for producing an additive for imparting freshness preservation function, comprising the steps of: preparing a first stock solution (Solution A) containing powdered rice husks and vegetable oil; preparing a second stock solution (Solution B) containing powdered metal complex and vegetable oil; introducing the prepared Solutions A and B into a supercritical fluid apparatus, and mixing and stirring the first stock solution (Solution A) and the second stock solution (Solution B) under pressurized conditions in the presence of carbon dioxide supercritical fluid while heating them to prepare a stock solution for the additive; and preparing a masterbatch by incorporating the stock solution for the additive prepared in the step of preparing the stock solution for the additive in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material. In the production method of the present invention, the method of introducing Solutions A and B into the supercritical fluid apparatus is not particularly limited, and any method is acceptable as long as it is possible to mix and stir Solutions A and B under pressurized conditions in the presence of carbon dioxide supercritical fluid while heating them.

[0033] As mentioned above, in the process of preparing the additive stock solution by sending (introducing) liquid A and liquid B into a supercritical fluid apparatus and mixing and stirring them while heating them under pressure in the presence of a carbon dioxide supercritical fluid, it is preferable to create a high-pressure, high-temperature environment in the supercritical fluid apparatus at 9 MPa / 90°C, and then slowly lower the temperature to room temperature. Furthermore, the inventors have found that in order to obtain an additive stock solution with good properties for imparting freshness preservation, it is desirable that, as the temperature is lowered, the powdered rice husks and / or powdered metal complexes constituting liquids A and B quickly penetrate into the vegetable oil used in liquids A and B, and be dispersed and compounded as nano-sized or near-nano-sized fine particles. The inventors then investigated oils having the above-mentioned properties and found that, given the requirements that the oil should be easily soluble during processing in the presence of a supercritical carbon dioxide fluid at 90°C, rapidly form a film when the temperature is lowered after the processing, and be a vegetable oil suitable for the purpose of the present invention, a vegetable oil with a melting point of about 70°C to 85°C, such as rice wax, is preferable and suitable for the manufacturing method of the present invention.

[0034] According to the inventors' studies, for example, using iron phthalocyanine as a representative example of metallic phthalocyanine and rice wax as a representative example of vegetable oil, liquid A, which contains powdered rice husks and rice wax and a solvent as needed, and liquid B, which contains powdered iron phthalocyanine and rice wax and a solvent as needed, are each sent into a supercritical apparatus, mixed and stirred while heated under pressure in the presence of carbon dioxide supercritical fluid in the supercritical apparatus, and then cooled, thereby easily obtaining an additive stock solution containing nanocapsules in which powdered rice husks and / or powdered iron phthalocyanine are encapsulated (coated) in a vegetable oil such as rice wax. The inventors believe that this is one of the factors that has enabled the excellent effects of the present invention. According to the inventors' studies, the stock solution obtained by introducing liquid A and liquid B into a supercritical apparatus and treating them under pressure in the presence of carbon dioxide supercritical fluid has the following characteristics. For example, the resulting additive stock solution, when solution B is used, contains nanocapsule-like particles with a median size of approximately 22 nm, encapsulating phthalocyanine iron. Although phthalocyanine iron is used as a representative example in the specification of this invention, the effects of this invention can be obtained with any metal complex similar to phthalocyanine iron.

[0035] In the present invention's method for producing additives, powdered rice husks used in combination with the powdered metal complex described above are also treated together with vegetable oils such as rice wax in a supercritical apparatus in the presence of a supercritical carbon dioxide fluid to prepare the additive stock solution. Similar to the case where metal complexes such as phthalocyanine iron are used as constituent materials, it can be inferred that the stock solution contains nanocapsules ranging in size from tens of nanometers to over a hundred nanometers, containing powdered rice husks. In this case, it is estimated that several tens of percent of the total rice husks are in the form of capsules. Supercritical water is known to dissolve organic matter better than ordinary water, and when powdered rice husks are treated in a supercritical apparatus under pressurized conditions in the presence of the supercritical carbon dioxide fluid described above, it is thought that the recalcitrant organic components other than the silica that make up the rice husks dissolve easily, resulting in the rice husks in the resulting additive stock solution being in the form of nanocapsules containing a larger proportion of finer-sized silica. The inventors have confirmed that when a stock solution obtained by processing powdered rice husks used as a raw material for an additive in a supercritical fluid apparatus is used as an additive in the manufacture of a plastic film, the powdered rice husks dispersed in the plastic film become significantly finer compared to the powdered rice husks used as the raw material. According to the inventors' studies, in the manufacturing method of the present invention, when preparing the additive stock solution of the present invention, the powdered rice husks used as the raw material can be micronized by processing them in a supercritical fluid apparatus. Therefore, relatively large rice husks with an average number of particles expressed by median diameter of about 30 μm to 90 μm can be used as the powdered rice husks used as the raw material. On the other hand, rice husks are hard and difficult to pulverize by mechanical grinding methods using mills, and are also difficult to handle. Therefore, being able to use relatively large rice husks as a raw material is a major industrial advantage.

[0036] The inventors of the present invention believe that the high level of freshness preservation achieved by using packaging bags containing the additive of the present invention is as follows. The mechanism by which the additive that can impart freshness preservation function of the present invention exerts its freshness preservation effect is not yet clear, but it can be inferred that the following actions, for example, contribute to it. It should be noted that the present invention is not limited to the actions described below. In the raw material of the additive of the present invention, powdered rice husks and powdered metal complexes are treated with vegetable oil under pressurized conditions in the presence of a carbon dioxide supercritical fluid, resulting in a structure in which nano-sized or near-nano-sized fine particles (nanocapsule-like) are dispersed and composited in the vegetable oil. It is inferred that this fine dispersion increases the specific surface area of ​​the siliceous components derived from rice husks and the metal complexes, and thus increases the frequency of contact with ethylene gas and other volatile components that are generated in trace amounts during the storage of vegetables and fruits and are present in the atmosphere inside the packaging bag. The silica of the rice husk powder constituting the additive can function as an adsorption site for ethylene gas, etc., and the powdered metal complex, such as the metal phthalocyanine complex used in combination, is thought to contribute to the chemical conversion or inactivation of ethylene gas and reactive oxygen species through oxidation-reduction reactions, etc. Furthermore, the vegetable oil functions as a matrix that effectively disperses the powdered rice husk and / or the powdered metal complex in a thermoplastic resin such as a polyolefin resin. In addition, by using a vegetable oil with a melting point of 70°C to 85°C, for example, it is presumed that the state of the fine particles (nanocapsules) of the additive is maintained during the thermal history of film molding, and as a result, a stable freshness preservation function is exhibited within the operating temperature range of the packaging bag. Thus, in the additive that characterizes the present invention, a system consisting of rice husk powder, a metal complex, and vegetable oil is dispersed and compounded as nano-sized or near-nano-sized fine particles (nanocapsule-like particles) by treatment with a carbon dioxide supercritical fluid. This allows for efficient adsorption, capture, or chemical conversion of ethylene gas and other components inside the packaging bag, and as a result, the freshness preservation of the packaged goods, such as fruits and vegetables, contained in the packaging bag is improved.It should be noted that the effects described above may manifest either individually or synergistically in combination. The present invention is not limited to the effects described above.

[0037] Furthermore, as described above, in the manufacturing method of the present invention, the rice husks in the additive stock solution produced become nanocapsule-like fine particles with a composition containing many fine-sized silica particles in a vegetable oil. This improves compatibility with thermoplastic resins such as polyolefin resins that form the base of the packaging bag, making it possible to uniformly incorporate powdered rice husks into the resin, which was previously difficult. This is also considered to be one of the reasons why a high level of freshness preservation has been achieved in packaging bags using the additive of the present invention.

[0038] According to the inventors' studies, the additive of the present invention, formed as a masterbatch using a stock solution with the above-described carbon dioxide supercritical fluid configuration, can be added to thermoplastic resins commonly used in the manufacture of plastic films to uniformly incorporate rice husks of a finer size than those used as raw materials into the resulting plastic film. This is considered to be a major factor in achieving excellent freshness preservation in plastic film packaging bags formed using the additive of the present invention.

[0039] According to the inventors' investigation, as described later, even when preparing a stock solution of additives using only solution A containing rice husk powder in the same manner, and manufacturing a packaging bag using the obtained additive, it was not possible to obtain the high level of freshness preservation function achieved by using the packaging bag of the present invention which also contains a powdered metal complex. From this fact, the inventors believe that the presence of powdered rice husks and metal complexes such as phthalocyanine iron, uniformly dispersed and compounded in the plastic film forming the packaging bag, combined with the synergistic effect of the environment in a cool, dark place (vegetable compartment of a refrigerator) where vegetables are stored, causes ethylene gas adsorption and inactivation of the vegetables that are the target of freshness preservation, thereby suppressing the rate of maturation.

[0040] In the method for producing the additive of the present invention, the resin used when preparing the masterbatch using the additive stock solution prepared as described above is not particularly limited. Considering subsequent applications such as packaging bags, a thermoplastic resin is preferred, and specifically, at least one selected from the group consisting of polyolefin resins, polyethylene terephthalate resins, and polystyrene resins is preferred.

[0041] According to the inventors' studies, when the masterbatch configured as described above is applied as an additive to the packaging bag of the present invention, a packaging bag with high freshness preservation capabilities can be easily prepared by configuring it as follows. Specifically, for example, a resin composition can be prepared by mixing 9 to 12 parts by mass of the masterbatch additive with 100 parts by mass of a thermoplastic resin such as a polyolefin resin, and then using this resin composition to produce a bag-shaped plastic film of the present invention with excellent freshness preservation properties by methods such as inflation molding or T-die molding. Considering the packaging bag, it is preferable to prepare the plastic film with a thickness of 8 μm to 50 μm. According to the present invention, excellent freshness preservation properties can be obtained regardless of the film thickness. Considering the strength of the packaging bag, although it depends on the application, it is more preferable that the thickness of the bag-shaped plastic film be around 20 μm to 35 μm.

[0042] The following describes the method for producing an additive for imparting freshness preservation function of the present invention, which involves liquid A containing powdered rice husks and rice wax, and liquid B containing a powdered metal complex and rice wax. Liquid A may contain the aforementioned powdered rice husks and, for example, a vegetable oil such as rice wax. In addition, other components such as liquid paraffin to impart fluidity to liquid A, or acetyl tributyl citrate to impart plasticity to the synthetic resin, may be included. Liquid B may also contain a metal complex and a vegetable oil such as rice wax, and may use the components mentioned above. Furthermore, other components such as a silicone resin to impart hydrophobicity to the synthetic resin to which the freshness preservation function is to be imparted by using the resulting stock solution as an additive may be included. In addition, an organic solvent may be used as appropriate as needed to provide suitable fluidity when sending (introducing) the solution into the supercritical fluid apparatus.

[0043] The additive of the present invention, which imparts freshness-preserving function to synthetic resins for the manufacture of packaging bags, is preferably formed as a masterbatch, as specified in the manufacturing method of the present invention. As described above, according to the manufacturing method of the present invention, a raw additive solution for forming a masterbatch can be easily prepared by using a supercritical apparatus to treat powdered rice husks and powdered metal complexes under pressure in the presence of a carbon dioxide supercritical fluid in combination with vegetable oil, thereby dispersing and compounding nanocapsules containing at least powdered metal complexes and nanocapsules containing at least powdered rice husks. The additive of the present invention, formed as a masterbatch containing the above-described raw additive solution at a sufficient concentration, mixes well with general-purpose synthetic resins conventionally used in the manufacture of packaging bags. As a result, when a plastic film is prepared using a resin composition containing the additive of the present invention, the powdered rice husks and powdered metal complexes, which are the active ingredients of the additive, can be uniformly contained in the prepared plastic film. The resin composition containing the additive of the present invention is a useful material for producing packaging bags using molding methods such as inflation molding and T-die molding. The packaging bags obtained in this way uniformly contain powdered rice husks and powdered metal complexes, which are the active ingredients of the additive of the present invention. As a result, the bags have higher freshness preservation properties, sufficient strength and other properties required for packaging bags, and a semi-transparent appearance similar to conventional products, making them highly practical and useful. Furthermore, they can be easily colored using colorants.

[0044] The additive of the present invention, which can achieve the above-described excellent effects, can be easily obtained, for example, as follows: The additive for imparting the freshness-preserving function characteristic of the present invention to a resin material, is easily obtained by adding the additive stock solution, for example, to a resin material containing a resin selected from polyolefin resins such as polyethylene and polypropylene, or thermoplastic resins such as polyethylene terephthalate resin and polystyrene resin, in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin. Preferably, the masterbatch contains the stock solution at a concentration of about 0.3 parts by mass. By using a masterbatch containing the stock solution with powdered rice husks at a sufficient concentration in the manufacture of a plastic film for forming a packaging bag, a plastic film in which fine powdered rice husks are distributed throughout the film can be prepared with a small amount of additive.

[0045] By using a masterbatch containing a high concentration of the additive stock solution for imparting the freshness-preserving function that characterizes the present invention, prepared as described above, the packaging bag of the present invention exhibiting high freshness-preserving properties can be easily prepared, as previously stated. Furthermore, the inventors have confirmed that even if only a small amount of additive is used in the preparation of the packaging bag, the packaging bag of the present invention can exhibit high freshness-preserving properties. Specifically, for example, when producing a packaging bag by inflation molding, it has been confirmed that a packaging bag with high freshness-preserving properties can be prepared by using a resin composition which is a mixture containing 10 parts by mass of the additive of the present invention formed as a masterbatch and 90 parts by mass of a thermoplastic resin such as a polyolefin resin. In contrast, as previously stated, the masterbatch described above contains 0.2 parts by mass or more and 0.5 parts by mass of the additive stock solution in 100 parts by mass of resin material. As described above, the additive stock solution that characterizes the present invention is a processed product obtained by sending (introducing) liquid A and liquid B into a supercritical fluid apparatus and treating them in the presence of a carbon dioxide supercritical fluid. For example, the additive stock solution contains 1 to 3 parts by mass of each active ingredient in liquid A and liquid B per 100 parts by mass of the additive stock solution. Therefore, the amount of liquid A and liquid B, which are the active ingredients of the additive of the present invention that make up the stock solution contained in 100 parts by mass of plastic film that constitutes the packaging bag, is extremely small, about 0.0005 to 0.0008 parts by mass. Furthermore, the amounts of active ingredients in liquid A and liquid B that make up the additive stock solution of the present invention should be approximately the same, or it is preferable to use a slightly smaller amount of liquid B, which contains a metal complex, compared to liquid A, which contains rice husks. For example, it is preferable to adjust the amount of active ingredient in liquid B to be 0.7 to 0.9, with the amount of active ingredient in liquid A being 1, and then send (introduce) them into the supercritical fluid apparatus.

[0046] When preparing the packaging bags, any thermoplastic resin commonly used in the preparation of packaging bags, such as polyolefin resins, polyethylene terephthalate resins, and polystyrene resins, can be used as the resin. For example, it is preferable to use polyolefin resins such as polyethylene or polypropylene. Using high-density polyethylene, also known as HDPE, is a more preferable embodiment. In other words, according to the inventors' research, by using HDPE as the main raw material for the bag, the resulting packaging bag can be made strong and resistant to tearing even when filled with heavy items. [Examples]

[0047] Further specific examples of the above-described embodiment will be explained below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. Unless otherwise specified, parts or % are based on mass.

[0048] [Example 1] As the base resin used in manufacturing packaging bags, high-density polyethylene pellets, which have been conventionally used in the manufacture of packaging bags, were used. Then, the additive of the present invention, which is formed as a masterbatch, was added to the high-density polyethylene pellets of the base resin to impart freshness-preserving function to the formed plastic film. The additive formed as a masterbatch was prepared by applying the manufacturing method of the present invention using the supercritical apparatus described above, to prepare an additive stock solution containing powdered rice husks, powdered metal complex, and vegetable oil, and the additive was prepared using this stock solution. When preparing the additive stock solution, the powdered rice husks used as raw materials had a number-average median diameter of about 50 μm to 60 μm. In addition, powdered phthalocyanine iron (manufactured by Tokyo Chemical Industry Co., Ltd.), which is sold as a pigment, was used as the powdered metal complex. In addition, rice wax with a melting point of about 75°C was used as the vegetable oil. These are all representative examples, and the additive of the present invention is not limited to these.

[0049] In the embodiments of the present invention, in order to smoothly supply (introduce) liquid A, which contains powdered rice husks and vegetable oil, and liquid B, which contains powdered metal complex and vegetable oil, to a supercritical fluid apparatus, the fluidity of liquid A and / or liquid B was adjusted by adding the above-mentioned components to liquid A and / or liquid B using an organic solvent or liquid paraffin. Then, liquid A and liquid B, which were sent (introduced) into the supercritical fluid apparatus, were mixed and stirred under pressure in the presence of carbon dioxide supercritical fluid at a pressure of 9 MPa / 90°C while being heated. After the treatment, the temperature was slowly lowered and the carbon dioxide gas was removed, and the treated material was taken out of the supercritical fluid apparatus to obtain the additive stock solution. As mentioned above, the vegetable oil used in the embodiments has a melting point of about 75°C, so when the temperature drops, the vegetable oil contained in the treated material (stock solution) solidifies rapidly, and as a result, the surface of the powdered rice husks and powdered metal complex in the treated material is quickly and uniformly coated, becoming fine particles (nanocapsule-like).

[0050] In the embodiments of the present invention, a masterbatch was prepared by sufficiently incorporating the additive stock solution specified in the present invention, prepared as described above, into a resin material. In the embodiments of the present invention, polyethylene was used as the resin material for incorporating the additive stock solution, considering that the final product would be a packaging bag made of high-density polyethylene. Furthermore, the masterbatch was prepared by incorporating the additive stock solution into the resin material so that its content was 0.3% by mass.

[0051] Using the masterbatch, which is an additive of the present invention as described above, a resin composition raw material for producing a packaging bag was prepared by adding and mixing it with pellets of high-density polyethylene, which is the base resin. In this case, 10 parts by mass of the masterbatch, which is an additive of the present invention prepared above, was used for 100 parts by mass of high-density polyethylene. In the example of the present invention, the obtained resin composition was used as a raw material and subjected to inflation molding to produce a polyethylene packaging bag with dimensions of approximately 40 cm in length, approximately 30 cm in width, and 25 μm in thickness. Upon visual observation, the obtained packaging bag was uniformly translucent. Furthermore, it did not tear under normal force when pulled by hand. In the additive stock solution used to produce the plastic film constituting the packaging bag of Example 1, the amount of active ingredients in solution A, which contains rice husks and vegetable oil, was 0.00075% by mass, and the amount of active ingredients in solution B, which contains a metal complex and vegetable oil, was 0.00058% by mass.

[0052] [Example 2] Except for replacing the base resin with polypropylene, a packaging bag for Example 2 was prepared in the same manner as in Example 1, and containing the same additives as used in Example 1. Visual inspection of the packaging bag for Example 2 revealed that the obtained packaging bag was uniformly translucent. Furthermore, it did not tear under normal force when pulled by hand.

[0053] [Comparative Example 1] In the comparative example, the preparation of the additive stock solution using the supercritical fluid apparatus as in Example 1 was carried out using only solution A, which contained powdered rice husks and vegetable oil. Then, a masterbatch was prepared using the stock solution obtained without using a metal complex. The packaging bag for the comparative example was prepared in the same manner as in Example 1. When the obtained packaging bag for Comparative Example 1 was visually observed, the resulting packaging bag was uniformly translucent. However, it was not possible to obtain the excellent freshness preservation function obtained with the packaging bags of Examples 1 and 2, which used a powdered metal complex in combination.

[0054] (Evaluation Result 1 - Evaluation by Visual Observation) The inventors of the present invention confirmed the freshness preservation performance of the plastic film packaging bag of Example 1 obtained as described above by placing vegetables inside. As a result, they found that the following excellent effects can be obtained. First, one cabbage was placed in the packaging bag of Example 1, and the bag containing the cabbage was placed in a refrigerator to begin storage, and storage continued for 41 days. During that time, the storage condition of the cabbage was examined by removing the cabbage from the packaging bag and visually observing it. The condition of the outer leaves (appearance) of the cabbage was observed by visual inspection and by touching with clean, gloved fingers after removing it from the packaging bag. In addition, the cabbage after 41 days from the start date was cut open and observed, including the condition of the inside.

[0055] As a result, initially, after 20 days from the start of storage, there was almost no change in the appearance of the cabbage. Then, after about 30 days from the start of storage, a slight yellow discoloration was observed on the cabbage leaves. After 41 days from the start of storage, the yellow area on the outer leaves of the cabbage had grown larger, but the core at the cut surface remained white, and although the yellow area on the outer leaves had grown larger, it was still possible to hold it without any problems. Furthermore, the difference in color of the core at the cut surface of a cabbage cut in half with a knife after 41 days, the feel of the hardness of the cabbage when cut with a knife, and the difference in the slimy feel when touching the outer leaves all confirmed that the freshness of the cabbage stored in the packaging bag of Example 1 was maintained in a remarkably good state. Furthermore, when lettuce, broccoli, Shine Muscat grapes, komatsuna (Japanese mustard spinach), cucumber, and cut vegetables were placed in the packaging bag of Example 1 and evaluated in the same way as with cabbage, the results showed excellent freshness retention, similar to that of cabbage.

[0056] In contrast, a comparative test was conducted using cabbages of the same freshness and size as those used in the examples, in the same manner as in the examples. In the comparative test, instead of the freshness-preserving bags used in the examples, commercially available freshness-preserving bags that are currently widely used were used. These commercially available freshness-preserving bags use Oya stone as a manufacturing material. One cabbage was placed in this freshness-preserving bag and stored for a long period of time in the same refrigerator as used in the examples, starting from the same date as in the examples. As a result, the condition of the stored cabbages was as follows. First, 14 days after the start of storage, a small yellow area was observed on the outer leaves of the cabbage. Then, 20 days after the start of storage, the yellow area on the outer leaves became larger, and by 41 days after the start of storage, the yellow area had spread to almost the entire outer leaf of the cabbage. Furthermore, by 41 days after the start of storage, the leaves below the outer leaves also had yellow areas, and the outer leaves felt slimy to the touch. In the comparative test, the cabbage stored in the conventional freshness-preserving bag for 41 days had a slightly brown core, and felt softer when cut with a knife compared to the cabbage stored in the packaging bag of the example for 41 days.

[0057] (Evaluation Result 2 - Evaluation based on color analysis of the image) In addition to the visual evaluation described above, to conduct a more objective evaluation, photographic images of the vegetables used as test subjects were used, and the information in the photographic images was color-separated to evaluate the state of freshness preservation. Specifically, a freshness preservation test was conducted using packaging bag FR, which was prepared in Example 1 and measures approximately 40 cm in length and 30 cm in width, a commercially available packaging bag A made from Oya stone and possessing freshness preservation properties of the same size, and a commercially available packaging bag B made from rice bran and possessing freshness preservation properties. Approximately the same size cabbages were placed in each of the three test bags: packaging bag FR from Example 1, and the commercially available packaging bags A and B used for comparison. Approximately the same size and condition of cabbages were placed in each bag, and the bags were stored for a long period in the vegetable compartment of the same refrigerator. For the three test subjects, photographs of the cabbages in each bag were taken under the same conditions from day 0 to day 41 of the test, and the freshness preservation properties were evaluated by image analysis using the obtained photographic images. Specifically, we performed hue analysis on the cabbage photographs obtained at each stage of development, and determined the amount of green, brown, and yellow regions in each photograph to evaluate them relatively. The evaluation method using color analysis of the cabbage photographs is described below.

[0058] The photographic images of the cabbage were formatted as BMP (bitmap) images, and these images were analyzed in detail. The colors were classified based on the RGB values ​​of red (R), green (G), and blue (B), and the number of pixels and the proportion of each color were quantified using Python. The classification criteria for green, yellow, and brown colors used to evaluate freshness were as follows.

[0059] (Color classification criteria) (1) Green: R-value: 0-100, G-value: 100-255, B-value: 0-100 (2) Yellow: R-value: 150-255 G-value: 150-255 B-value: 0-100 (3) Brown: R-value: 100-255, G-value: 50-150, B-value: 0-100

[0060] Next, the hue information was extracted by converting to the HSV color space, which consists of three components: hue, saturation, and lightness. Then, the pixels of green, yellow, and brown were counted. The freshness preservation was then evaluated using the number of green, yellow, and brown pixels obtained by counting the pixels of each color for photographic images of cabbage stored in a refrigerator for 0, 20, and 41 days. Specifically, considering the discoloration of the cabbage during storage, the total number of pixels of green, yellow, and brown was set to 100, and the proportion of each of the three colors' pixel counts was calculated. Cabbage with a smaller decrease in the proportion of green pixels was judged to have better freshness preservation. When evaluating using brown, a larger increase in the proportion of brown pixels indicated that the freshness had deteriorated. The following are the set values ​​for the hue ranges of the three colors green, yellow, and brown used in the above evaluation.

[0061] (Set the hue range) (1) Green area: [(35,50,50),(85,255,255)] (2) Yellow area: [(20,50,50),(30,255,255)] (3) Brown area: [(10,50,50),(20,255,255)]

[0062] Table 1 shows the results of a color analysis of photographic images of cabbage stored in the vegetable compartment of the same refrigerator using three different packaging bags, at various storage times. Specifically, Table 1 shows the percentage of the area occupied by green, with the total number of pixels of the three colors (green, yellow, and brown) set to 100, as analyzed for each photographic image of the stored cabbage. As shown in Table 1, when using packaging bag FR in the example, unlike when using commercially available packaging bags A and B, the cabbage placed in the bag retained significantly more green color even after 41 days, confirming that the bag has unprecedented freshness preservation capabilities. Figure 2A is a graph showing the evaluation results of freshness preservation based on the change in the green area of ​​the cabbage photographic images shown in Table 1 over time.

[0063] TIFF0007836542000002.tif42170

[0064] Table 2, similar to Table 1, shows the evaluation results of color analysis of photographic images of cabbage in the same refrigerator's vegetable compartment, using three different packaging bags, at various storage times. Specifically, Table 2 shows the percentage of the area occupied by brown, with the total number of pixels for the three colors (green, yellow, and brown) being set to 100, as analyzed for each photographic image of the stored cabbage. As shown in Table 2, when using packaging bag FR in the example, unlike when using commercially available packaging bags A and B, the area of ​​brown in the cabbage inside the bag was significantly smaller even after 41 days of storage, confirming that the bag exhibits good freshness preservation capabilities. Figure 2B is a graph of the evaluation results obtained by observing the change in the area of ​​brown in the photographic images of cabbage shown in Table 2 over time.

[0065] TIFF0007836542000003.tif40170

[0066] Table 3 shows the results of a color analysis of photographic images of cabbage stored in the vegetable compartment of the same refrigerator using three different packaging bags, at various storage times. Specifically, Table 3 shows the percentage of the area occupied by yellow, with the total number of pixels of the three colors (green, yellow, and brown) being set to 100, as analyzed for each photographic image of the stored cabbage. As shown in Table 3, when using packaging bag FR in the example, unlike when using commercially available packaging bags A and B, the increase in the yellow area of ​​the cabbage placed in the bag was small even after 41 days, confirming that the bag has superior freshness preservation capabilities that conventional products cannot achieve. Figure 2C is a graph showing the evaluation results of freshness preservation based on the change in the yellow area of ​​the cabbage photographic images shown in Table 3 over time.

[0067] TIFF0007836542000004.tif40170

[0068] (Evaluation Result 3 - Intensity Evaluation) The strength of the high-density polyethylene packaging bag of Example 1 and the polypropylene packaging bag of Example 2 was confirmed by pulling them in various directions with both hands. As a result, it was confirmed that both the bags of Example 1 and Example 2 had the same strength as commercially available packaging bags of similar thickness that were used as a comparison when the freshness preservation performance was evaluated earlier.

Claims

1. A method for manufacturing an additive for imparting freshness-preserving function to a plastic film, comprising the steps of: preparing a first stock solution (Solution A) containing powdered rice husks and vegetable oil; preparing a second stock solution (Solution B) containing powdered metal complex and vegetable oil; introducing the first stock solution (Solution A) and the second stock solution (Solution B) into a supercritical fluid apparatus, and preparing an additive stock solution by heating, mixing, and stirring the first stock solution (Solution A) and the second stock solution (Solution B) under pressurized conditions in the presence of a carbon dioxide supercritical fluid within the supercritical fluid apparatus; and preparing a masterbatch by incorporating the additive stock solution prepared in the step of preparing the additive stock solution in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material.

2. A method for producing an additive for imparting freshness preservation function according to claim 1, wherein the melting point of the vegetable oil is 70°C or higher and 85°C or lower.

3. A method for producing an additive for imparting freshness preservation function according to claim 1 or 2, wherein the resin constituting the resin material is selected from at least one of the group consisting of polyolefin resins, polyethylene terephthalate resins, and polystyrene resins.

4. A method for producing an additive for imparting freshness preservation function according to claim 1 or 2, wherein the metal complex is selected from at least one of the group consisting of metal phthalocyanines, metal porphyrin complexes, and metal carbonyl complexes.

5. A method for manufacturing a packaging bag made of plastic film with freshness-preserving properties, comprising the steps of: preparing a first stock solution (Solution A) containing powdered rice husks and vegetable oil; preparing a second stock solution (Solution B) containing powdered metal complex and vegetable oil; introducing the first stock solution (Solution A) and the second stock solution (Solution B) into a supercritical fluid apparatus, and preparing an additive stock solution by heating, mixing, and stirring the first stock solution (Solution A) and the second stock solution (Solution B) under pressurized conditions in the presence of a carbon dioxide supercritical fluid within the supercritical fluid apparatus; and preparing the additive stock solution A method for manufacturing a packaging bag, comprising the steps of: preparing a masterbatch by including the additive stock solution prepared in the step of preparing a resin material in an amount of 0.2 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of resin material; preparing a resin composition by mixing the additive, which is a masterbatch for imparting freshness preservation function prepared in the step of preparing the masterbatch, in an amount of 9 parts by mass or more and 12 parts by mass or less per 100 parts by mass of thermoplastic resin; and manufacturing a bag-shaped plastic film containing the additive for imparting freshness preservation function by molding the resin composition prepared in the step of preparing a bag.

6. The method for manufacturing a packaging bag according to claim 5, wherein the thermoplastic resin is selected from at least one of the group consisting of polyolefin resins, polystyrene resins, and polyethylene terephthalate resins.

7. The method for manufacturing a packaging bag according to claim 6, wherein the polyolefin resin is either a high-density polyethylene resin or polypropylene.

8. The method for manufacturing a packaging bag according to claim 5 or 6, wherein the step of manufacturing the bag-shaped plastic film is inflation molding.

9. The method for manufacturing a packaging bag according to claim 5 or 6, wherein the thickness of the plastic film is 8 μm or more and 50 μm or less.

10. A masterbatch used as an additive to impart freshness-preserving function to plastic film, characterized in that, per 100 parts by mass of resin material, it contains 0.2 parts by mass or more and 0.5 parts by mass or less of a processed product comprising a first stock solution (Solution A) containing powdered rice husks and vegetable oil, and a second stock solution (Solution B) containing powdered metal complex and vegetable oil, processed in a supercritical apparatus under pressurized conditions where a supercritical carbon dioxide fluid is present.

11. A packaging bag characterized by being made of a plastic film made from a resin composition comprising 100 parts by mass of a resin selected from the group consisting of polyolefin resins, polyethylene terephthalate resins, and polystyrene resins, and containing the masterbatch described in claim 10 in an amount of 9 parts by mass or more and 12 parts by mass or less.

12. The packaging bag according to claim 11, wherein the thickness of the plastic film is 8 μm or more and 50 μm or less.

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