Antibacterial packaging material that can extend the edibility of food.

Abstract

The problem that this invention aims to solve is to provide a food packaging material that can be manufactured at low cost using complex silver anion water, which can maintain the freshness and extend the shelf life of food by providing an antibacterial function that mimics the antibacterial function of artificial bamboo skin, or extend the edibility of food by providing a function that artificially mimics the safe antibacterial function of bamboo skin. [Solution] Aside from obtaining packaging material by coating cellulose-based nonwoven fabric with complex silver anion water, a packaging material can be obtained by coating synthetic fiber nonwoven fabric with a nonionic or anionic surfactant as a pretreatment and drying it, and then coating it with a liquid agent (silver ion water) that contains almost entirely complex silver anions. This allows the antibacterial function of silver anions to be utilized, and in both cases, it is possible to extend the freshness and edibility of food. Citric acid and silver are registered as food additives, and polyester complies with the revised Food Sanitation Law, so there are no safety concerns. A packaging material obtained by using a blended nonwoven fabric of 70% synthetic fiber and 30% cellulose fiber as a base material and mixing complex silver anion water with water-soluble polyester resin is sufficient to solve the problem.

Description

Technical Field

Background Art

[0001] Needless to say, not only fresh foods but also cooked foods are greatly affected by storage temperature for their extended lifespan, and oxygen in the air also oxidizes food and causes deterioration. In recent years, vacuum packaging technology has also been reused by cutting off oxygen involved in food spoilage and deterioration and taking advantage of its function of preventing the growth of aerobic bacteria.

[0002] Seasonings such as vinegar, salt, sugar, spices such as pepper and chili peppers have been used since ancient times to extend the edibility of all foods. These not only increase the flavor of food but also protect the food itself from spoilage-causing bacteria, suppress bacterial growth, and have a history of food culture of being used to extend the edibility of food.

[0003] Furthermore, in Japan, food has been wrapped with bamboo bark that has a safe antibacterial function to inhibit the growth of microorganisms other than those mentioned above for a long time. This is because the safe natural antibacterial agent contained in bamboo bark can reduce the activity of bacteria and inhibit growth. If artificial but safe and inexpensive food packaging materials and containers have such functions, food spoilage and deterioration can be reduced, and as a result, food loss can be reduced.

[0004] Not only food packaging materials, but also Patent Document 2, mentioned in the prior art documents below, describes a plastic food container manufactured by injection molding, which incorporates a flat pure silver-encapsulated powder in which a vapor-deposited pure silver layer is sandwiched between polyester resin. It is commercially available that, when the food is placed in the container, the moisture in the food causes silver cations to leach from the powder kneaded into the plastic resin, and if the food contains little cysteine ​​as a constituent component, or if cysteine ​​is not the sole protein in the food, the food's shelf life can be extended. In other words, if a silver-based antibacterial agent is incorporated into a polymer resin, and there is some moisture in the food, silver cations will leach out through the intermolecular structure of the resin, killing or inhibiting the growth of bacteria related to food spoilage through its antibacterial function, thereby extending the food's shelf life. In particular, if the silver ions are converted into silver anions, the reaction with thiol groups and their precursor methionine contained in cysteine ​​can be suppressed, although the amount may differ in all food ingredients.

[0005] The silver ion described in claim 1 is a complex silver anion, and the silver ion that can be encapsulated in the water-soluble polyester resin described in claim 2 but still eluted is also a complex silver anion. It does not react with the thiol group of cysteine ​​or the precursor methionine, and can extend the shelf life of food at a lower concentration than silver cations. Foods such as beef, pork, chicken, and fish are almost entirely composed of protein, some of which is amino acids. Almost all foods, whether vegetables or fruits, contain cysteine ​​to varying degrees, and both fresh and cooked foods contain negatively charged organic ions. Therefore, the complex silver anion does not react with organic ions and can exert antimicrobial function, thus extending the shelf life of cooked foods. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5988476 [Patent Document 2] Patent No. 4175486 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In short, the problem that this invention aims to solve is to obtain a food packaging material that has even greater antibacterial properties than those artificially mimicking the safe antibacterial properties of bamboo leaves, which can maintain the freshness of fresh produce and extend its shelf life.

[0008] A silver anion solution containing the complex silver anion is combined and blended with a water-soluble polyester resin liquid that can be used for food packaging materials to obtain a weakly viscous mixture of silver ion water and water-soluble polyester resin (hereinafter referred to as silver PET resin liquid or silver PET resin) that uniformly contains a silver anion concentration of 10 to 20 ppm. The hydrophobicity of the laminated polyester film having aluminum etc. sandwiched in the above-mentioned aluminum is considered to have little effect on adhesion as it is all polyester, but if the above-mentioned laminated film is coated so that the coated surface of the liquid comes into contact with cooked food, a laminated film for food packaging materials such as packaging bags and containers that can extend the freshness and edibility of food can be obtained as described above. The cooked food that will be inside is, so to speak, oil in the polyester film that makes up the laminated film and so to speak, water in the water-soluble polyester resin, but since it is the same polyester resin that has ester bonds, it is listed in the positive list as a raw material for packaging materials under the revised Food Sanitation Law, so there is no problem with safety and there is no problem with adhesion or bonding.

[0009] Furthermore, if a laminated film processed as described above is used in retort foods, which can have their edibility extended by adding preservatives to pre-cooked foods, it becomes possible to eliminate or reduce the addition of such preservatives, thereby reducing or eliminating the effect of preservatives on the flavor of the food, and also significantly reducing the odor emitted by the preservatives themselves. The contents of claim 2 have the following characteristics.

[0010] A weakly viscous silver PET solution is obtained by adjusting the concentration of silver anions in the silver PET resin to 10 to 20 ppm. The hydrophobicity of the laminated polyester film is almost completely destroyed by the additive using the coating method described above, and since both are polyester, there is almost no effect on the adhesive strength and adhesion. Similarly, if the coated surface of the laminated film described above is coated with the silver ion water so that it comes into contact with cooked food, and the laminated film is dried, a laminated film for food packaging materials such as three-dimensional packaging bags and containers that can extend the freshness and edibility of food as described above can be obtained.

[0011] Furthermore, while retort foods, which extend the edibility of cooked foods, usually contain preservatives, manufacturing packaging bags using this processed laminated film eliminates or reduces the need for such preservatives. This reduces or eliminates any impact on the flavor of the retort foods, and also significantly reduces or eliminates the odor produced by the preservatives themselves.

[0012] Fresh foods can be broadly classified into meats, fish and shellfish, vegetables, and fruits, and all of these fresh foods contain cysteine, an amino acid, to varying degrees. Furthermore, depending on the type of food, cysteine ​​has a thiol group, a functional group in which sulfur and hydrogen are bonded, although the amount may vary. Silver and citric acid are listed as food additives in the Food Sanitation Act, and polyester also meets the specifications suitable for inclusion in the positive list of food-contact plastics under the revised Food Sanitation Act. However, when silver ionizes, it becomes a silver cation, and the silver cation reacts with the thiol group to form silver sulfide, quickly losing its antibacterial function. Of course, the surfactants and water-soluble polyester resins used in the implementation of this invention must be suitable for use in food packaging materials, and are already listed in the positive list. The silver anion does not react with either the thiol group or organic ions and can fully perform its antibacterial function.

[0013] The silver ion water described in Patent Document 1 contains silver dissolved in a dilute citric acid solvent. The carboxyl groups that make up citric acid are ligands, and each group has a trivalent negative charge, so citric acid has three carboxyl groups. The silver ions in this silver ion water become negatively charged complex anions through coordination bonding with the carboxyl groups. Although silver cations are monovalent cations, the bidentate carboxyl groups form cyclic coordination bonds with the silver ions in the dilute citric acid solvent. Therefore, the silver anions contained in the silver ion water described in Patent Document 1 are chelated and the bond is strong. Even when adjusted to a suitable concentration with water, they can all complex and maintain a monovalent negative charge silver anion state up to a pH of approximately 2.5 to less than 9.0.

[0014] Since the thiol group mentioned above has a negative charge, it does not react with silver anions, allowing it to exert its antibacterial function against bacteria across a broad spectrum, as inherent to the silver ion, the central metal ion. Furthermore, since each of the above foods contains negatively charged organic ions, the silver anion does not react with these organic ions either, allowing it to exert its antibacterial function across a broad spectrum, similar to the above. Incidentally, silver cations are unstable, as they are affected by ultraviolet light, and can oxidize and lose their bactericidal function. They also react with the thiol groups and organic ions present in all foods, losing their antibacterial function.

[0015] However, whether it is silver cations or silver anions, when a liquid containing them is applied, it will be adsorbed onto cellulose fibers such as cotton, linen, and rayon. For example, even if a fabric or nonwoven made of cellulose fibers is gravure coated or dipped and then dried before packaging food, the silver ions will be adsorbed onto the nonwoven fabric and will not transfer to the food being packaged. While the nonwoven fabric or fabric itself may exhibit deodorizing properties due to its antibacterial function and antimicrobial properties, it will not kill bacteria present on the surface of the food. Furthermore, fresh food does not contain bacteria inside, only on the surface. If bacteria are present inside, the food may have already spoiled or deteriorated and should not be consumed. Meat inspections are conducted to stop shipment to the consumer market, except for pet food, if bacteria are found inside the meat.

[0016] Therefore, as the nonwoven fabric used in carrying out claim 1 of the present invention, and as the laminated film used for the film used for the retort food storage bag, a plastic film, especially polyester film, is optimal, and as the nonwoven fabric material, polyethylene and polypropylene are suitable, with polyester being the most suitable example. Furthermore, the complex silver anions directly embedded in the packaging material according to the present invention, or contained within the silver PET resin, exhibit strong antibacterial properties when they come into contact with moist food items. [Means for solving the problem]

[0017] First, to obtain the food packaging material described in claim 1, the synthetic fiber nonwoven fabric is first immersed in a solution containing slightly less than 1% of a nonionic or anionic surfactant to impart hydrophilicity to the synthetic fiber nonwoven fabric. This solution is then squeezed and dried. After that, the material is coated with silver ion water containing almost entirely silver anions using a well-known method such as gravure coating, or immersed in silver ion water, squeezed and dried, and then cut to a size suitable for the food to be packaged. Complexed silver anions break down into silver cations at around 200°C, but as described above, the water evaporating during drying after coating absorbs heat of vaporization, so the temperature does not reach a level where the silver anions on the coated nonwoven fabric are broken down into cations.

[0018] The water-soluble polyester resin (manufactured by Go-o Chemical Industry Co., Ltd.: product name Pluscoat) is an anionic aqueous solution with a polyester resin solid content of approximately 20% to 25% and ion-exchanged water of approximately 80% to 75%, and is in the weakly acidic range with a pH of around 4.0. This water-soluble polyester resin has a certain degree of viscosity. The silver ion water described in Patent Document 1 has a silver anion concentration of approximately 25 to 30 ppm after production. The silver anion concentration in the silver PET resin can be adjusted to 10 to 20 ppm using ion-exchanged water or purified water, and the aforementioned auxiliary agent can be applied to the food-contact side of the laminated film in the same manner as above to increase the adhesion and bonding between the film and the silver PET resin. However, since it is a polyester whether oil-based or water-based, there is no need to worry about adhesion or bonding. By applying well-known coatings such as gravure coating or fine dot printing and drying, a laminated film can be obtained in which the food-contact side exhibits antibacterial function.

[0019] Since the synthetic nonwoven fabric is highly hydrophobic, it is preferable to perform a pretreatment using a well-known coating method, which involves mixing a nonionic or anionic surfactant with slightly less than 1% water, immersing the fabric, and drying it. In this subsequent step, the silver anions coated using a well-known method remain on the nonwoven fabric and can transfer to the packaged food, thereby exhibiting antibacterial and germicidal functions. The surfactant used must be positively resistant and safe.

[0020] Perform the above pretreatment on the polyester film on the side that comes into contact with food, and then coat the silver PET resin by well-known methods such as gravure coating or dot printing. Print the product name, cooking method, ingredient list, etc. on the reverse side of the film, cut it, and apply heat pressing to the three end portions to form a bag shape to obtain a packaging material. Since the adhesiveness between the silver PET resin and the laminated polyester film used for the retort food packaging bag is good and the adhesion density is high, the constituent molecules of the silver PET resin containing silver anions coated on the polyester film in contact with food are immobilized and will not mix into the food. In the unlikely event that the silver PET resin containing silver anions peels off from the laminated polyester film, which is the basic packaging material, and is swallowed together with the food, the water-soluble polyester resin of the original silver PRE resin is harmless even when used in food, the silver anions are complexed by gastric juice, which is dilute hydrochloric acid, and changed into silver cations. The silver cations react with the chlorine in the dilute hydrochloric acid, which is gastric juice, to form insoluble silver chloride and are not absorbed into the body but excreted. Of course, food packaging materials are for packaging food and are not edible, which is self-evident.

[0021] The laminated film, which is the base material of the retort food packaging material as described above, has aluminum generally provided in a sandwich shape by vacuum deposition on two polyester films, and the product name, cooking method, content ingredients, etc. are printed on both the front and back of the packaging bag and ultraviolet rays are blocked. However, the side in contact with food is a polyester film without the above-mentioned printing or other processing. When the silver PET resin containing silver anions subjected to the above pretreatment is coated by a well-known method, the adhesiveness between the polyesters is strong, so the coated water-soluble plastic resin and the silver anions will not mix into the food into which they are enclosed, and the silver anions can elute, so it can be used. Retort foods are rarely solids, and the food itself moves inside the container, so the silver anions and the retort food itself come into contact evenly, and the bactericidal power of the silver anions can work.

Advantages of the Invention

[0022] It is natural that the packaging form of food varies depending on the food to be packaged. For example, simply wrapping the food with a two-dimensional packaging material and then further wrapping it with a wrapper, putting it in a packaging bag or container for refrigerated or frozen storage, or being able to store retort foods at room temperature for a long time. However, regardless of the packaging material, the ultimate goal is to prevent microbial contamination of the food, prevent deterioration of the food by ultraviolet rays, and prevent oxidation by oxygen in the air, either singly or in combination. The packaging form is used appropriately for the purpose of extending the shelf life of food. The packaging material according to the present invention can eliminate or at least reduce the amount of preservatives added to retort foods. In the present invention, regardless of the packaging form, the complex silver anion does not react with the thiol groups and organic ions that all foods possess more or less. The silver anion can effectively exert an antibacterial effect to maintain the freshness of the food and extend its lifespan, reduce food loss, and offset the economic loss caused by the loss.

[0023] In addition, citric acid and silver are also recognized as food additives, and polyethylene, polypropylene, polyester, and silver are listed in the positive list that can be used in food-contact plastics in the revised Food Hygiene Law according to the specifications of the monomers. When the complex silver anion is chewed in the stomach together with the food, the complex is broken by dilute hydrochloric acid, which is gastric acid, and changes into silver cations. The silver cations react with the chlorine in the dilute hydrochloric acid, which is gastric acid, and change into silver chloride, which is excreted as an insoluble substance. In short, neither silver cations nor complex silver anions are harmful to human health. This is also clear from the statement of the WHO in 2003 that drinking water containing 0.1 ppm of silver cations and anions is harmless even if only this water is consumed for 70 years.

Embodiments for Carrying out the Invention

[0024] First, a method for obtaining silver ion water using a dilute citrate solvent containing almost entirely complex silver anions is described below. Patent Document 1 states that a liquid containing silver ions can be obtained by vacuum deposition of pure silver onto an unprocessed polyester film with dilute citrate, cutting the silver surface without protection, and stirring the resulting fine silver-deposited film in a dilute citrate solvent. However, the silver ions in the liquid obtained by this method are complexed silver anions. It is common knowledge in coordination chemistry that the carboxyl group constituting citrate is a ligand with a negative charge. Furthermore, when the carboxyl group coordinates with the silver ion, it coordinates in a bidentate cyclic manner, thus forming a stable chelate.

[0025] First, a 50 nm thick pure silver vapor-deposited film is formed on a 9-12 micron thick polyester base film using vacuum deposition without any pretreatment. In vacuum deposition, the deposition vessel is brought to a near-vacuum state, and a block of pure silver is placed in an electric crucible inside the vessel. At a pressure considerably lower than normal atmospheric pressure (almost 0 atmospheres), the pure silver can be melted and vaporized with low-temperature heat, and each silver atom is individually deposited onto the polyester film. The film, which does not protect the vapor-deposited layer surface, is then cut into approximately 2 cm squares in preparation for stirring. At this time, the pure silver atoms accumulate individually, like powder snow, and the metallic bonds are weak, so when lightly rubbed, ultrafine silver powder is transferred to friction paper. In short, since the pure silver atoms form layers in an almost independent state, stirring the cut film with a dilute citric acid solvent of about 2% concentration yields silver ion water, which is almost entirely composed of complex silver anions. For example, the silver ion water is mixed with 130 L of a 2% dilute citric acid solvent, and the total area of ​​the above-mentioned cut film, which is approximately 2 cm square, is 120 m². 2 It can be obtained by adding and stirring. There is some loss in practice because the solvent is also taken out when the film is removed, but silver ion water is obtained in which almost all of the dissolved silver is complex silver anions. The stock solution after production is about 120 L, the silver anion concentration is 25-30 ppm, and the pH is about 2.6.

[0026] While inorganic acids such as nitric acid and dilute nitric acid, which are strong acids, can dissolve silver atoms even if the metallic bond has been restored, and even if the deposited silver has become a silver salt, stirring the film fragments will produce a liquid containing only silver cations. However, silver atoms with very weak metallic bonds, or those without restored metallic bonds, will dissolve in dilute citric acid at a concentration of about 2%, which is an organic acid and a weak acid, through intermittent stirring. The carboxyl groups that make up citric acid will then form bidentate coordinate bonds, and the dissolved silver ions will complex and become anions. In this way, silver ion water, in which almost all of the dissolved silver in dilute citric acid solvent is complex silver anions, can be obtained. Incidentally, the concentration of complex silver ions obtained by the above method is about 25-30 ppm, so it is sufficient to dilute it with deionized water to adjust the silver anion concentration according to the application.

[0027] The complex silver anions contained in the silver ion water obtained as described above have weak coordinate bonds, to the point that they normally revert to silver cations as the pH approaches neutral. However, the silver ions in the citric acid solvent complex and chelate, resulting in strong coordinate bonds. Therefore, the complexed anionic state can be maintained up to a pH of around 9.0, but metallic silver gradually precipitates as the pH rises further. It is important to maintain the pH below 6.0 when using this solution. In antibacterial tests of ordinary fabrics, nonwovens, and textile products, silver cations exhibit antibacterial properties across a broad spectrum. For example, in cotton textile products such as towels, the required concentration of eluted silver cations is said to be 5-10 ppb. However, complex silver anions can exhibit the same or even greater antibacterial properties as silver cations at a concentration of 2-5 ppb.

[0028] When gravure coating the nonwoven fabric using only the aforementioned complex silver anion water, applying a nonionic or anionic surfactant as a pretreatment, as described above, can break down the hydrophobicity of the hydrophobic synthetic nonwoven fabric and prevent the silver ion water from being repelled. Therefore, it is preferable to pretreat with a surfactant solution at a concentration of slightly less than 1%, but it is not necessary to apply a surfactant amount that would affect the silver anion concentration or pH; a very small amount of surfactant is sufficient. It is essential that the surfactant used is harmless even if ingested.

[0029] Water-soluble polyester resin has a low molecular weight of around 15,000 and is in liquid form consisting of 80% deionized water and 20% polyester resin solids. It is an anionic system, and the undiluted solution is weakly acidic with a pH of around 4.0. The silver ion water is also a liquid, and although the mixing of both liquids for coating nonwoven fabric will be described later, both liquids are anionic and have acidic pH ranges, making them very compatible.

[0030] Since the combined solution of both liquids described in the paragraph above contains a very large amount of water, the silver ion concentration should be calculated during the preparation process, taking into account the complex silver anion concentration and the solid content of the water-soluble polyester resin. In other words, the calculation should be such that the complex silver anion is contained in the solid content of the polyester resin after the water has evaporated. The solid content of the water-soluble polyester resin is 20% per liter of the stock solution, so assuming the specific gravity of the polyester resin is approximately 1.4, the solid content of the polyester resin in 1 liter of the stock solution will be 280g.

[0031] When preparing a silver PET resin solution using silver ion water containing complex silver anions with a silver ion concentration of 20 ppm, even if the water in the silver ion water evaporates when it dries, the silver anions can remain. Furthermore, even if the silver anions are dissolved in the silver ion water, and even if about 2% citric acid is dissolved, calculating the specific gravity as 1 will not be a major error. Since the water in 1 L of food-grade water-soluble polyester resin stock solution also evaporates, the amount of polyester resin dissolved in the water will be 280 g. To adjust the silver anion concentration to the appropriate blending amount, it is sufficient to calculate based on the aforementioned specific gravity, even if there is some error. Since a silver anion concentration of 10 ppm or higher is preferable, it is better if the error is slightly on the upward side. When adjusting the silver anion concentration to 10 ppm within the polyester resin in 1 L of silver PET resin solution, if silver ion water with a silver anion concentration of 20 ppm is used, as described above, both the water and the silver anions will evaporate, so it is sufficient to add 280 ml and stir well. It should be noted that the drip from meat and fish contains not only water and blood, but also vitamins and amino acids, which are very nutritious for bacteria involved in spoilage to multiply.

[0032] Furthermore, regardless of the silver anion concentration in the silver ion water, if storing silver ion water in a plastic container, you should shake the container well 5-6 times immediately before use. If the container is left standing during storage, the silver anions will get into the gaps between the plastic molecules that make up the container, causing the apparent concentration to decrease. Shaking it immediately before use, as described above, will restore the silver anion concentration to its original level.

[0033] As shown in the example below, when packaging food with a two-dimensional polyester and cellulose fiber blended nonwoven fabric (70-80% polyester, 30-20% cellulose) containing residual silver anions, a gap will inevitably form somewhere between the nonwoven fabric and the packaged food. Since the silver anions remaining on the nonwoven fabric cannot turn into a gas when they evaporate like water and therefore cannot come into contact with the food, care must be taken to ensure that they come into contact with the packaged food as much as possible. In other words, silver anions cannot move through the air in their silver anion state except when they are not contained in the solvent water. [Examples]

[0034] A comparative experiment was conducted to determine the disinfecting power of chopped vegetables (chopped green onions) by washing them with (A) an aqueous solution of sodium hypochlorite at a concentration of 200 ppm (hereinafter referred to as hypochlorite water) and (B) an aqueous solution of silver ion water with a silver anion concentration of 0.1 ppm. After washing the chopped green onions with both solutions (A) and (B) for 8 minutes at room temperature with agitation, they were further washed with well water to remove the solutions adhering to the chopped green onions sample (A) and (B). Hypochlorite water is a well-known disinfectant. Experimental Example 1

[0035] The initial bacterial count of the chopped green onions was approximately 4.0 on a logarithmic scale. However, both samples (A) and (B) showed a sterilization rate of nearly the same 99%, and the total bacterial count decreased to approximately 2.0 on a logarithmic scale. Since chopped green onions are stored at 10°C in retail stores, sample (B) was able to extend its edibility for at least two days, similar to conventional washing with hypochlorous acid water. Furthermore, if the total bacterial count after sterilization with hypochlorous acid water and then washing with well water is approximately 2 on a logarithmic scale, retail stores are permitted to sell the product for two days after arrival, up to a logarithmic scale of 5 for both bacterial counts. In other words, chopped green onions that have been in stock for two days are sometimes used in prepared foods sold in retail stores, but after three days of storage, the total bacterial count reaches approximately 6 on a logarithmic scale, making them unsaleable and requiring disposal. Based on these results, the silver anions from the food packaging material according to the present invention can transfer to the food being packaged, but some silver anions may not transfer to the food, so the target concentration was set at 10-20 ppm. Washing with hypochlorous acid water and subsequent disinfectant washing is not feasible on a daily basis in homes or retail stores selling chopped green onions. Washing with the silver ion water at a concentration of 0.1 ppm does not harm the silver ion water after washing, as described above, and the internal temperature of a typical household refrigerator is around 10°C, so washing with silver ion water that retains a slightly acidic taste is possible for home use. This example was applied to vegetables. Furthermore, 0.1 ppm silver ion water has been approved by the Ministry of Health, Labour and Welfare for use as a washing water for vegetables and fruits. [Example 2]

[0036] First, the basis weight of the 100% polyester spunbond nonwoven fabric that will serve as the base material for the packaging is 20 g / m². 2 The nonwoven fabric was cut into approximately 30 cm squares, and a silver PET resin solution was prepared so that there were 10 ppm of silver anions per gram of solid content of 120 g of water-soluble polyester resin. The 100% polyester nonwoven fabric, cut as described above, was immersed in a silver PET resin solution and squeezed with a prototype mangle, leaving slightly less than 3g of the liquid in a wet state on the nonwoven fabric. The nonwoven fabric was dried, and three 10cm square kitchen paper sheets were impregnated with 10ppm silver ion water and dried. Three of the same kitchen paper sheets were left unprocessed. First, two of the kitchen paper sheets were placed near the center of the processed nonwoven fabric, and approximately 65g of beef steak was placed on top. The nonwoven fabric was wrapped tightly around the beef, and then sealed with plastic wrap to prevent drying. This was n=3. Three unprocessed pieces of the same nonwoven fabric were prepared, and three pieces of kitchen paper were prepared in the same packaging without any processing. These were used as a comparison blank and stored in a refrigerator at a storage temperature of 10°C. Experimental Example 2

[0037] Three days (72 hours) after the start of storage as described above, sample n=3 and comparison blank n=3 were opened, and changes in color and odor were observed. <Sample> The meat that was in contact with the kitchen paper had a faint odor of decay. The beef that was in direct contact with the nonwoven fabric coated with silver PET resin liquid still had a beefy smell. The color was slightly brownish. <Blank>It had a putrid odor overall. The color was a darker brown than the sample.

[0038] In consideration, although this is a general overview, beef steak meat is frozen when it is processed from slaughter to carcass, thawed, and then commercialized as steak meat. It is sold in a frozen state at the store, and the water and blood that expand during freezing break down the cell membranes, causing water and nutrients (blood) to leak out as drip before cooking. This makes it very easy for bacteria involved in spoilage to multiply. Furthermore, the storage temperature of 10°C is not an ideal temperature for the growth of these bacteria, although meat and fish are usually stored frozen or at 5°C during distribution and at the store. As described in the above example, the storage temperature of 10°C was deliberately chosen to create conditions favorable to bacteria. We believed that if superiority could be confirmed under these conditions, it would increase the reliability of this packaging material at the final stage of distribution at the store. Although the storage temperature of a consumer's home refrigerator is 10°C, we anticipate the possibility of unfounded complaints, so this invention is not intended for general consumers, but rather for professional businesses that provide food, such as yakiniku restaurants, steak restaurants, sushi restaurants, hotels, and restaurants. [Example 3]

[0039] As described in claim 2, the basis weight of the blended nonwoven fabric of 70% polyester and 30% cotton fiber is 30 g / m². 2 The nonwoven fabric was prepared by mixing 1,000 ml of water-soluble polyester resin (product name: Pluscoat, manufactured by Go-o Chemical Industry Co., Ltd. in Uji City, Kyoto Prefecture), product number Z-730 (polyester solids content 25% = solids content 350 g) with 350 ml of silver ion water with a silver anion concentration of 20 ppm, stirring to prepare a silver PET resin solution. The nonwoven fabric was then cut into approximately 30 cm squares to prepare three pieces. Packaging material was obtained by coating approximately 6 g per piece using a prototype gravure coating machine and drying.

[0040] Three pieces of the same nonwoven fabric as above were cut in the same way and prepared. Without any further processing, these three pieces were used as blank packaging material. Six pieces of beef steak, each weighing approximately 65g, were prepared and tightly wrapped using three pieces each of the sample packaging material and blank packaging material. These were then further wrapped in plastic wrap. Since temperature fluctuations due to opening and closing the refrigerator were a concern, an incubator was used and set to 5°C for 3 days (72 hours) for storage. Experiment Example 3

[0041] After preservation as described above, we observed changes in odor and color between beef steaks wrapped in sample packaging material and beef steaks wrapped in blank packaging material. The results were as follows. <Steak meat in sample packaging> There was no change in smell whatsoever; it still had the characteristic odor of beef that had been left out before preservation began. There was almost no change in color, and it retained the color it had before preservation began. It is reasonable to assume that the cotton fibers, which are almost uniformly scattered in the nonwoven fabric at a 30% concentration, absorb small amounts of the drip from the beef steak, with 20 ppm of silver anions exhibiting a sterilizing function, and that the 20 ppm of silver anions contained in the silver PET resin coating the 70% polyester fibers exert a sterilizing effect on the drip remaining on the cotton fibers. <Steak meat in blank packaging> I noticed a slight change in the smell, but since it had been refrigerated at 5°C, it wasn't a rotten smell. There was a slight change in color, towards a brownish hue, but it was minimal, and this is likely due to the 5°C storage conditions.

[0042] In the examples, storage at 5°C was selected, and although no clear overall superiority was observed between the sample packaging material and the blank packaging material, it was possible to confirm that there was a slight advantage. Originally, the meat of four-legged animals is bled once after being cut into carcasses, mold is intentionally planted on the surface to preserve the inside of the meat, and then it is frozen. After that, the surface mold is scraped off, and in some cases it is frozen again before entering the meat distribution network and being divided into smaller portions at retail stores for display. The storage temperature at this time is refrigerated at 5°C as described above, but naturally blood and bodily fluids remain in the divided meat itself, and it is unavoidable that they will leak out as drip from the raw meat cells that are broken down when thawed. It is not feasible to absorb all of this drip in one place with a drip absorbent that has high antibacterial properties and suppress the growth of bacteria that are involved in spoilage by making the drip non-nutrient-rich in the bacteria that cause spoilage.

[0043] As shown in Example 3 and Experimental Example 3, the packaging paper with the nonwoven fabric coated with silver PET resin liquid as the base material has 30% cellulose fibers scattered throughout. The drip flowing from the beef is absorbed gradually over a wide area, and the diluted drip, both in quantity and concentration, allows the silver anions in the cellulose fibers to exert their bactericidal effect. Furthermore, since the polyester fibers of the nonwoven fabric base material are coated with silver PET resin liquid, as described in Reference 2, silver anions leach out from between the molecules of the solid components of the water-soluble polyester, killing and antibacterializing the deeply involved bacteria on the surface of the beef that is in direct contact with the packaging material, thus extending the shelf life associated with maintaining freshness. The next experiments and observations, which will be conducted in the future, will involve increasing the storage period to 6-7 days and increasing the number of tests to provide more observation opportunities. This will undoubtedly demonstrate the superiority of packaging materials coated with water-soluble polyester resin and silver anions compared to unprocessed packaging materials. [Industrial applicability]

[0044] The food packaging material utilizing the complex silver anion according to the present invention does not react with the thiol group of cysteine, an amino acid found in almost all fresh foods, and utilizes its effective antibacterial properties to help maintain and extend the freshness of food. This enables fresh food to be kept fresh and its shelf life extended in stores that provide food, thereby reducing food waste and food loss, lowering costs, and meeting the goals of SGGs.

[0045] In the embodiments of this application, beef steak was used as a representative example of fresh food, but drip also occurs in fish, and it is unlikely that the drip in beef contains as many nutrients as beef drip, which are involved in spoilage. Furthermore, vegetables and fruits are also fresh foods, and it is clear that the antibacterial packaging material according to the present invention, which can be manufactured and distributed at low cost, can extend the shelf life by maintaining freshness.

Claims

1. A pure silver vapor deposition layer is provided on at least one side of a polyester film, and when it is cut and dissolved in a dilute citric acid solvent, a complex anionized silver solution (hereinafter referred to as silver ion water) can be obtained. First, the silver anion concentration is adjusted to 10-20 ppm, and a surfactant is applied as a pretreatment to synthetic fiber nonwoven fabrics such as polyester, polyethylene, and polypropylene, followed by mangle squeezing and drying to give the nonwoven fabric hydrophilicity. Then, the silver ion water is applied, dried, and cut to obtain a food packaging material. This material can be used to package not only fresh foods but also cooked foods that do not contain excessive moisture. When wrapped with plastic wrap and stored in a refrigerator at a storage temperature of about 10°C, the freshness of the food can be maintained and its shelf life extended. Furthermore, if the fresh food is meat or fish, it is necessary to impregnate cellulose-based paper, such as kitchen paper, with silver anions at a concentration of 10 ppm to 20 ppm and dry it so that it can absorb the drip that occurs when cells break down due to repeated freezing and thawing, and to exhibit antibacterial properties. By using this method, it becomes possible to maintain freshness and extend the shelf life of fresh food by using a nonwoven fabric that has undergone the above processing and comes into direct contact with the fresh food.

2. If the silver anion water described in claim 1 is mixed with a nonwoven fabric (approximately 70% polyester and 30% cellulose fibers) made of a blend of polyester and cellulose fibers (such as cotton, rayon, or linen) as a base material, and silver ions are added at a concentration of 10 to 20 ppm per gram of solid content of water-soluble polyester resin, and this mixture is applied to the nonwoven fabric by gravure coating, and the coated surface is sealed so that it can come into contact with fresh food, and stored at a temperature range of 0°C to 5°C, a packaging material can be obtained that can maintain freshness and extend the edibility of the food. In this case, the role of impregnating and drying a cellulose-based paper with a silver anion concentration of approximately 10 ppm as described in claim 1 to absorb drip and provide antibacterial properties is fulfilled by the cellulose fibers blended as the raw material for the nonwoven fabric, and the polyester portion of the packaging material described in claim 1 directly contacts the surface of the fresh food, thereby providing antibacterial properties and maintaining the freshness of the food and extending its edibility.

3. By mixing the water-soluble polyester resin and silver ion water described in the claim at a concentration of 10 to 20 ppm relative to the polyester resin solid content, and applying this mixture to the food-contacting side of a form with an aluminum vapor-deposited layer for retort foods sandwiched between two polyester resins, a bag-shaped packaging material can be obtained. Since the food placed inside will move around, it becomes possible to reduce or eliminate the addition of preservatives, reduce the odor of preservatives, and extend the shelf life to a level comparable to existing similar packaging materials.