FRESHNESS PRESERVATIVE PACKING MATERIAL FOR FOODSTUFFS AND METHOD OF FIXING THE FRESHNESS PRESERVATIVE SUBSTANCE ONTO THE PACKING MATERIAL

Abstract: The present invention provides a packing material for packing boxes (1), packing bags and wrapping paper characterized in that over a surface of the packing materials, when packed, an air pervious tight coating (4) is formed partially or entirely between the contact surface of the wrapped contents, and the coating retains grains or minute perticles (2) of freshness preservative substance containing one or more of a far-infrared radioactive substance of about 3∼14 µm wave length at normal temperature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature. There is also disclosed a method of fixing the freshness preservative substance onto the packing material by printing, coating or spraying and then drying over a surface of the packing material that is to be contacted with the wrapped contents by a liquid dispersion wherein grains or minute particles of freshness preservative substance containing one or more of a far-infrared radioactive substance of about 3∼14 µm wave length at normal temperature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature are dispersed in a solution containing a coating formative substance.

Description: The present invention relates to a packing material capable of preserving freshness of foodstuffs, above all perishables, that may be formed into boxes, bags, wrapping paper, and the like and to a method of fixing the freshness preservative substance onto the said packing material by means of physical and/or chemical process to preserve freshness as long as possible. A wrapping film manufactured through the process of dispersing minute particles into the film material by crushing and graining a solid substance of emitting far-infrared rays of about 3∼14 µm at the normal temperature as, for example, far-infrared radioactive ceramics, and the products such as packing bags made of this film and packing boxes covered by this film are commercially available (Chemical Abstracts, vol. 109, 1988, page 66, abstract no. 171 883p). Vegetables, meat, fish and others in fresh condition wrapped by this film preserve their freshness longer as packed therein by virtue of an adsorption of the far-infrared rays radiated from the minute particles in the film. Further, such corrugated cardboard boxes are commercially available, the inside of which is covered by cristobalite processed thin paper that is manufactured by mixing the paper material with grained minute particles of cristobalite of gas adsorption nature. When packed by these corrugated cardboard boxes, the freshness of vegetables and fruit are preserved longer by virtue of the cristobalite minute particles which adsorb ethylene gas emitted from the fresh vegetables and fruit themselves. The mechanism is that when the fresh vegetables and fruit are put into contact with the ethylene gas that was once emitted from themselves, the gas quicken their breathing pace and thus more energy is exhausted and maturity is accelerated resulting in earlier decay. On the other hand, when the ethylene gas is adsorbed by an adsorptive substance and kept away from the vegetables and fruit, such a bad influence is eliminated and their freshness is better preserved. When such a substance as oxygen reactive at the normal temperature, such as iron, aluminium, copper and ascorbic acid is sealed up by a packing material together with foodstuffs, the decay of the foodstuffs inside is well suppressed as said substance takes up oxygen inside and thus resulting in longer preservation of the freshness (US-A-3 134 687). In order to disperse the far-infrared radioactive minute particles into the polyethylene film, it is necessary to mix the minute particles with the material resin liquid during the manufacturing process of the film; however, an achievement of an even and uniform dispersion of the minute particles overall is very hard and further, the manufacturing process of the film itself becomes time-consuming, and thus the manufacturing cost is inclined to be increased because of the presence of the minute particles. Moreover, when the film is used for packing boxes, it should always be put up over the inside surface and such processing costs may be further increased. Said cristobalite processed thin paper, on the other hand, requires another sort of bothersome processing procedure of paper making with the cristobalite minute particles, which is time-consuming, and further, it is also required for the cristobalite processed thin paper when applied to boxes to be put up over the inside surface of boxes,and therefore the manufacturing cost is liable to be increased. Further, this cristobalite processed thin paper has such a defect as the minute particles falling off. A purpose of the present invention is to provide a packing material, such as packing boxes, packing bags and wrapping paper, that retains a freshness preservative substance evenly, uniformly overall and hard to fall off from the surface in contact with the wrapped contents. Another purpose of the present invention is to propose a method to fix the freshness preservative substance onto a packing material at a lower cost. Another purpose of the present invention is to propose a method of fixing the freshness preservative substance onto the packing material more evenly, uniformly overall and hard to fall off. Other purposes of the present invention and advantages expectable therefrom will be explained in the following. According to the present invention, there is provided a packing material for packing boxes, packing bags and wrapping paper, wherein an air permeable tight coating, when packed, is formed over a surface of the packing material partially or entirely at the contact surface of the wrapped contents, and the said coating retains in a dispersive condition grains or minute particles of freshness preservative substance containing all of a far-infrared radioactive substance of about 3∼14 µm wave length at the normal temerature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature. According to another aspect of the invention, there is provided a method of fixing a freshness preservative substance onto a packing material, comprising printing, coating or spraying over wrapped contents a liquid dispersion with grains or minute particles of freshness preservative substance containing all of a far-infrared radioactive substance of about 3∼14 µm wave length at the normal temperature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature dispersed in a solution containing a coating formative substance and then removing a solvent in the solution by drying the resultant. By mixing the minute particles of freshness preservative substance with the solution of coating formative substance, the liquid dispersion with the said minute particles evenly and uniformly dispersed therein is obtained, then the liquid dispersion is printed, coated or sprayed over a surface of the packing material to which the contents packed is to be contacted, and then dried. Thus said coating formative substance is solidified over the surface wherein the minute particles or grains of freshness preservative substance are evenly and uniformly dispersed overall to form a coating. This coating, formed tightly contacting onto the packing material, is hard to fall off of the surface and has an air permeability with little gas-barrier nature. As such a process is not required as inside lining of the packing material over the surface of a box, much less cost than ever is good enough to fix the freshness preservative substance over the packing material. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which Fig. 1 is a perspective view showing an embodiment of a packing box, the inside of which is fixed with the freshness preservative substance through the process as disclosed by the present invention; Fig. 2 is an enlarged sectional view of a part of the said packing box, and Fig. 3 is an enlarged sectional view of a sheet of wrapping paper whereover the freshness preservative substance is fixed in accordance with the present invention. The far-infrared radioactive substance, as a freshness preservative substance, is, for example, a mineral such as Zirconium, zirconia, zirconium compound, etc. or fine ceramics and the like manufactured through crushing and graining, mixing and calcining several kinds of the said mineral. However, any can be the substance as far as it radiates at the normal temperature the far-infrared rays of said wave length as above. By crushing and graining the fine ceramics, or calcining at a high temperature and crushing one of several kinds of said minerals, the minute particles of the far-infrared radioactive substance at the normal temperature of said wave length can be obtained. Another typical embodiment of the gas adsorptive substance as another kind of the freshness preservative substance is, for example, a porosity mineral such as cristobalite, sepiolite, zeolite, composite zeolite and the like or silica gel, etc. However, any can be the substance as far as it adsorbs gas. Another embodiment of the oxygen reactive substance at the normal temperature as another kind of the freshness preservative substance is, for example, an easily oxidizable metal such as iron, aluminium, copper, etc. in terms of cost and other ready accessibility and also ascorbic acid, sodium ascorbate, etc. However, any can be the substance as far as it reacts to oxygen at the normal temperature. The ascorbic acid and sodium ascorbate can be used, after melted into water, by having them adsorbed into the powder of porosity adsorptive substance. The most suitable fineness or particulate size of the minute particles of one or several kinds of freshness preservative substance will be decided on the nature of the packing material, the nature of the contents packed, the layer thickness of the coating or fixation of the freshness preservative substance over the packing material, the kind of solvent used and other various conditions. Generally speaking, it is preferable to have the minute particles of about 0.1∼5 µm. These grained freshness preservative substance is mixed with and dispersed into a solution containing a coating formative substance. A solvent of the solution of coating formative substance can either be water, an organic solvent or a mixture of water and an organic solvent. The best suitable kind of solvent is decided from among the said kinds depending on the nature and/or kind of the freshness preservative substance, the nature of the contents packed and other various conditions. For example, when minute particles of a metal chemically reactive to oxygen at the normal temperature is used, an organic solvent must be selected as the particles when mixed with a solution containing water will be rapidly oxidized. When water is selected as solvent for the solution of coating formative substance, it is preferred to mix a small amount of emulsifying stabilizer and/or thickener such as adhesive polysaccharides including xanthan gum, etc. and sepiolite etc., and in case where the said emulsifying stabilizer and/or thickener have or has a corrosiveness and/or fungicness, to add a very small amount of antiseptic. When an organic solvent is selected as as solvent for the said solution, it is preferred to select an organic solvent having a volatility so that the removal and recovery from the surface of packing material is quickly and certainly taken place. For such an organic solvent, any of the following will be preferably used: Ethanol, limonene, toluene, ethyle acetate, xylene, carbinol, benzene, methanol, isopropyl alcohol, butanol, methylene-chloraide, ethylene-chloraide, methyl acetate, ethyl acetate, butyl acetate, methyl cellosolve, aceton, methyl ethyl ketone, cyclohexane, etc. Any can be the coating formative substance as far as it be meltable to a solvent and solidifiable when removed by drying the solvent; however, such high polymer compound is preferred as ethylene cellulose, hydroxy-propyl-cellulose, acrylic resin, polyvinyl pyridine (PVP), etc. The fixation to a packing material of the liquid dispersion wherein the minute particles of freshness preservative substance dispersed therein is attained by such a step as printing, coating or spraying, etc. The coating may be done using a rollers or brushes, etc., while the printing by screening, flexgraphy and any other steps available. The fixation onto a packing material of the liquid dispersion with the minute particles of the freshness preservative substance dispersed therein can as well be done effectively onto a part thereof not necessarily onto the entire surface to be contacted by the packed contents. As for the layer thickness of the coating that is formed over a packing material with the liquid dispersion with the minute particles of the freshness preservative substance dispersed therein, any can be chosen; however, it is preferable to have it that is thinner than 50 µm. After fixation of the said liquid dispersion onto a packing material, the solvent therein is removed through a drying process. In case where an organic solvent is used, it is preferable to volatilize and recover the same. Thus a coating of minute particles of the freshness preservative substance that are evenly dispersed therein is formed over a packing material onto where the liquid dispersion has been fixed as above mentioned. The coating formative substance, under a solidified condition after the solvent being removed through the drying process, has little gas-barrierness and therefore has an air permeability to an extent. By supplying a gas under pressure to the liquid dispersion or by using a blowing agent before printing, coating or spraying the said liquid dispersion over a packing material, and thus foam the liquid dispersion as minute as a few microns, a number of minute stomata are formed overall the coating over the packing material. By deciding any average size of the foam at the said blowing process, that is, by chosing an average diameter of the numerous stomata formed overall the coating, the effectiveness of minute particles of the freshness preservative substance that is contained in the coating itself can be controlled fast or slow, especially when it is a gas adsorptive substance or an oxygen reactive substance at the normal temperature. A packing box, an embodiment of the packing material, may be manufactured by coating or spraying the liquid dispersion for fixation onto the entire or partial inside surface of a box after assembly; however, it is more effective and economical to have thick paper or corrugated cardboard, the packing material, cut into a box shape and then print, coat or spray the said liquid dispersion onto the desired surface of the packing material for fixation and assemble after having it dried, or to fix the liquid dispersion onto a desired surface of the packing material before cutting by printing, coating or spraying and then cut and assemble it after having it dried. A packing bag, another embodiment of the packing material, may be manufactured by coating or spraying the liquid dispersion for fixation onto the inside surface of the bag after shaping into a bag through assembly of a cut sheet; however, it is more effective and economical to manufacture into a bag shape after printing, coating or spraying the liquid dispersion onto a desired surface of the material and having it dried. Hereunder a few preferred embodiments of the present invention are described in more detail with some preferable embodiments of the liquid dispersion containing grains and/or minute particles of the freshness preservative substance. Example 1 Acrylic resin 500 parts by weight Water 244 parts by weight Adhesive polysaccharide xanthan gum 5 parts by weight Defoaming agent and antiseptic 1 part by weight each The above components were mixed together to prepare a solution of the coating formative substance, namely acrylic resin, with the water solvent. Oxidized aluminium 125 parts by weight Zirconia 57 parts by weight Dioxidized silicon 67 parts by weight The above said freshness preservative substances were minutely grained into an average particulate diameter of about 0.5 µm, and then mixed with the said solution in an evenly dispersed condition to make a liquid dispersion. Then the said liquid dispersion with the minute particles of the fresh preservation substance in a dispersed condition was fixed onto the inside surface of a cut material of a packing box, a corrugated cardboard box, by a process of screen printing into the average layer thickness of 30 µm, which after naturally dried was assembled into a box 1 as shown in Fig. 1, the inside surface of which has the minute particles 2 of the said three kinds of freshness preservative substance fixed evenly thereoverall. A coating 4 having air permeability with an average layer thickness of 17 µm was formed overall the inside surface of a packing box 1, which contained the minute particles 2 composed of the above said three kinds of freshness preservative substance (Fig. 2), thus the minute particles 2 were fixed overall the inside surface of the packing box 1 in a substantially evenly dispersed condition. Moreover, the coating 4 containing the minute particles 2 of the freshness preservative substance was firmly fixed thereonto in such a condition as hard to fall off even when directly contacted with other things. Example 2 Hydroxypropylcellulose 250 parts by weight Ethanol 500 parts by weight Antiseptic 1 parts by weight Above were mixed with an organic solvent and a solution of coating formative substance was prepared. Oxidized aluminium 125 parts by weight Zirconia 57 parts by weight Dioxidized silicon 67 parts by weight After grained into an average particulate diameter of 0.5 µm, the above freshness preservative substance was added in the above said solution and mixed to manufacture a liquid dispersion in an evenly dispersed condition. This liquid dispersion, which was manufactured by dispersing the minute particles of the freshness preservative substance, was fixed onto the inside surface of a packing box unassembled (corrugated cardboard box) with an average layer thickness of 25 µm through the screen printing process and then assembled into a packing box 1 after removing and recovering ethanol within the liquid dispersion and then naturally drying. A coating 4 with an average layer thickness of 14 µm with air permeability containing the minute particles 2 of the above said three kinds of freshness preservative substance was formed overall the inside surface of the packing box 1, thus fixing the minute particles 2 substantially evenly onto the inside surface of the packing box 1. Moreover, the coating 4 containing the minute particles of freshness preservative substance was firmly fixed to such an extent as hard to fall off even when contacted with other things. Example 3 Ethylene cellulose 250 parts by weight Limonene 500 parts by weight By mixing the above, a solution of coating formative substance with an organic solvent was prepared. Sepiolite 125 parts by weight Zirconia 57 parts by weight Dioxidized silicon 67 parts by weight The above freshness preservative substance was minutely grained into an average particulate diameter of 0.5 µm and then mixed with the above mentioned solution to manufacture a liquid dispersion evenly dispersed with the said minute particles, then air was pumped by a compressor into the said liquid dispersion to foam therein a number of air bubble of an average diameter of 1µm. The said liquid dispersion of the minute particles of the freshness preservative substance dispersed therein was fixed evenly onto a wrapping sheet 3, which is composed of a polyethylene sheet 31 laminated by paper 32 as shown in Fig. 3, in other words onto the surface of the paper 32, by the screen printing process with an average layer thickness of 10 µm, and then limonene was dried by evaporation and recovery so that a coating 4 with air permeability containing the minute particles 2 of freshness preservative substance evenly dispersed overall the surface is formed, thus manufacturing the wrapping sheet 3. The layer thickness of the coating 4 containing the minute particles 2 was about 6 µm on an average, and on this coating 4 a number of minute stomata were formed overall. The minute particles 2 were evenly and firmly fixed overall the wrapping sheet 3 to such an extent as hard to fall off. Example 4 Polyvinylalcohol 250 parts by weight Ethanol 500 parts by weight Minutely grained sepiolite 5 parts by weight The above were mixed to prepare a solution with an organic solvent of a coating formative substance. Iron powder 125 parts by weight Zirconia 57 parts by weight Dioxidized silicon 67 parts by weight The above freshness preservative substances were minutely grained into an average particulate diameter of 1 µm and then mixed with and evenly dispersed in a solution prepared by the same process as mentioned above. The liquid dispersion with the minute particles of freshness preservation substance dispersed therein was fixed onto a surface of cut but unassembled packing box 1 in the same process as mentioned in Example 1 so that the layer thickness thereof becomes about 10 µm on an average, and then ethanol in the liquid dispersion was evaporated, recovered and naturally dried and then finally assembled into a box. The coating 4, which average layer thickness was 6 µm, containing the minute particles 2 of freshness preservative substance was fixed evenly over the inside surface of the packing box 1 and as firmly as hard for the minute particles to fall off. The packing box 1 of this example can preserve the freshness of packed green vegetables and fruit longer through the oxidation of the iron within the coating by taking up the oxygen in the box. When the liquid dispersion with the minute particles of freshness preservative substance dispersed therein is to be fixed onto the inside surface of packing box 1, which is already assembled, brushes or rollers will be used for painting or sprayers for spraying, and then it is dried. The drying process can either be that by heater and other available process as well as natural drying. To manufacture a packing bag, it is preferred first to fix the liquid dispersion with the minute particles of freshness preservative substance dispersed therein by either printing, coating or spraying thereonto and then remove the solvent through drying, etc. and finally cut and assemble into a box. Thus the minute particles of freshness preservative substance can be fixed over the packing materials evenly, uniformly and firmly as hard for the minute particles to fall off. Moreover, the process is very simple and uncostly.

Claims: A packing material for packing boxes, packing bags and wrapping paper, wherein over a surface of the packing material , when packed, an air pervious tight coating is formed partially or entirely at the contact surface of the wrapped contents, and the coating retains grains or minute particles of freshness preservative substance containing all of a far-infrared radioactive substance of about 3-14 µm wave length at the normal temperature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature. A packing material as claimed in claim 1, characterized in that the coating has a number of minute stomata. A method of fixing a freshness preservative substance onto a packing material, comprising printing, coating or spraying over and then drying the resultant over a surface of the packing material that is to be contacted with the wrapped contents by a liquid dispersion, wherein grains or minute particles of freshness preservative substance containing all of a far-infrared radioactive substance of about 3-14 µm wave length at the normal temperature, a gas adsorptive substance and an oxygen reactive substance at the normal temperature are dispersed in a solution containing a coating formative substance. A method as claimed in claim 3, characterized in that the solvent of the solution containing a coating formative substance is water. A method as claimed in claim 3, characterized in that the solvent of the solution containing a coating formative substance is either an organic solvent or a mixture of an organic solvent and water. A method as claimed in any of claims 3 - 5, characterized in that the liquid dispersion is minutely foamed before printing, coating or spraying it over a surface of the packing material.

Inventors: HANIOKA, MIKIO, YOKOHAMA, YOSHIMASA
Applicants: NIPPON DANBOHRU CO.,LTD., YOKOYAMA, YOSHIMASA
Application year: 1989
Main classification: B65D81
IPC codes: B65D5, B65D81