JPS633588B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing canned goods, and more specifically, by heating and sterilizing canned goods with microwaves,
This invention relates to a method for efficiently manufacturing high-quality canned goods. Conventionally, in the production of canned cans, after filling the metal can body with the contents, the can body and metal can lid are sealed by means such as double seaming, and the canned cans are retort sterilized. A process is adopted in which the product is charged into a device, sterilized using hot water, hot steam, or the like as a heat medium, and then cooled. In this heat sterilization of canned products, the heat sterilization effect is determined by the combination of the temperature and time that the slowest point of heat conduction, that is, the center of the canned product, actually receives. As a result, the required heating sterilization time is quite long, and furthermore, heating up time (coming up time) and cooling down time (coming down) are required before and after this, so the canning can of the retort sterilizer has a significantly high internal pressure. You will receive it for a long time. For this reason, problems such as leakage from the sealed part, buckling, and shell breakage are likely to occur.Therefore, in the known manufacturing method of canning, the occurrence of the above-mentioned problems is prevented by applying high pressure inside the retort sterilization chamber. ing. As described above, in the conventional canned manufacturing method, the contents tend to undergo deterioration due to long-term heating, such as deterioration of the structure due to overcooking, disintegration of pigments and vitamins, and browning, resulting in unsatisfactory quality. Along with being a thing,
Actual sterilization operations are still unsatisfactory, such as requiring high pressure. In recent years, attempts have been made to apply microwave heating to heat sterilization of packaged foods. Microwaves have the characteristic of passing through packaging materials with low dielectric loss, such as plastics, with little heating. Rotational vibrations of dipoles occur in response to changes, and heat is generated by the friction of molecules, so foods with large dielectric loss can be efficiently heated from the inside. Due to this feature, microwaves are widely used in the food industry, and have been put into practical use for drying foods, thawing frozen foods, and sterilizing them. For example, heat sterilization
Application examples include sterilization of ham sausages, prevention of mold growth in pastries, and sterilization of squid delicacies to prevent mold. However, in these known methods, the microorganisms to be sterilized have extremely low heat resistance and can be completely killed at 80 to 90°C in about 10 to 20 minutes. However, some of the microorganisms that spoil packaged foods have a high heat resistance that cannot be killed by heating below 100℃, and many canned foods require sterilization at temperatures higher than 100℃. Become. According to the present invention, a canned container made of a plastic material that is transparent to microwaves is filled with contents, and the canned container and a metal can lid are sealed with a sealant. There is provided a method for producing a canned product, characterized in that the canned material is subjected to microwave irradiation at normal pressure and sterilized at a temperature higher than 100°C. The present invention will be described in detail below based on specific examples shown in the accompanying drawings. The manufacturing process of canned goods according to the present invention is described in 1-A to 1-1.
In Fig. 1-D, first, a canning container 1 made of a plastic material that is transparent to microwaves is prepared (Fig. 1-A). This canned container 1 is
It consists of a body part 2 and a bottom part 3, and a flange part 4 for seaming is formed at the upper end of the body part 2 and a can lid 3 (see Figure 1-C). In the specific example shown in Figures 1-A to 1-D, the body 2, the bottom 3, and the flange 4 are integrally formed of plastic material, and there is a seam at the boundary between the body 2 and the bottom 3. does not exist. Next, in the filling process shown in Figure 1-B,
The contents 5 are filled into the canning container 1 through the filling nozzle 6. It is desirable that the filling of the contents 5 be carried out hot, but it may of course be carried out cold. In the sealing process shown in Figure 1-C, the contents 5
A metal can lid 7 is placed over the container 1 filled with
The container flange portion 4 and the lid 7 are wound together with a sealant 8 interposed therebetween. At the time of this seaming, the air in the container head space can be removed in advance by means such as steam injection or nitrogen displacement deaeration. Finally, in the sterilization process shown in Figure 1-D,
The obtained canned product 10 is subjected to microwave irradiation from the microwave waveguide outlet 11 in a normal pressure atmosphere and sterilized at a temperature higher than 100° C. to obtain a sterilized packed product. An important feature of the present invention is that even when a plastic container is used, the can lid is made of metal, and if microwaves are used as the heat source for sterilization, it can be used at normal pressure. It is based on the surprising finding that it is possible to heat sterilize contents at temperatures higher than 100°C in an atmosphere. First, whether a container made of a certain material can withstand heat sterilization depends on the pressure generated by the contents, that is, the vapor pressure, the influence of residual air pressure in the head space, and the influence of temperature on the mechanical properties of the material. It is necessary to consider this from two aspects. Plastic materials have the desirable property of allowing microwaves to pass through the canned contents, but on the other hand, their mechanical strength is lower than that of metal materials, and their mechanical strength is particularly low at high temperatures. It has the above drawbacks. Despite these deficiencies of plastic materials, the present invention is capable of sterilizing the contents in an atmosphere of normal pressure and at temperatures higher than 100° C., which is believed to be due to the following reasons. First, in microwave heating, the wall of a plastic container only transmits microwaves, and the food contained therein is efficiently heated from inside within a very short time due to its dielectric loss. That is, in microwave heating, unlike heat sterilization using normal heat transfer, the food contents are always maintained at a higher temperature than the container wall. Moreover, this temperature difference between the food contents and the container wall is due to the very short microwave heating time, the relatively low thermal conductivity of the plastic material, and the fact that the container wall is cooled from the outside. It will be quite large.
Thus, according to the present invention, the thermal deterioration of the mechanical properties of plastic materials can be suppressed to a considerably lower level than in the case of heat sterilization by conventional heat transfer. Moreover, in the sterilization process according to the present invention, the plastic material is present in the form of a container body with a circumferential horizontal cross section, and therefore, this packaging has a strong structure against internal pressure in the horizontal direction. ,
The direction that is weak against internal pressure is the vertical direction. In the present invention, by providing a metal can lid in this axial direction, the pressure resistance in this axial direction is increased, and damage to the canned container due to internal pressure during sterilization is effectively prevented. In the present invention, in a normal pressure atmosphere and at 100°C
Another basis for the possibility of sterilization at higher temperatures can be found in the fact that the sterilization time is significantly shorter. Damage due to internal pressure of a canned container is related to creep or fatigue, and therefore it is significantly affected not only by the absolute value of the internal pressure applied to the canned container, but also by the amount of time this internal pressure continues to be applied. be done. In the present invention, since the sterilization time is significantly shortened by microwave heating, damage due to internal pressure can be more reliably prevented. The can lid used in the present invention is made of metal and has the property of reflecting microwaves. however,
In the present invention, the contents of the canned food are surrounded by a plastic material wall over 360 degrees, so that
Microwave penetration into the food contents is almost complete, with almost no substantial reduction in heating efficiency. According to the present invention, it is possible to perform sterilization in an atmosphere of normal pressure and at a temperature higher than 100°C, which provides extremely significant advantages over conventional methods in terms of sterilization operations and sterilization equipment. is achieved. That is,
According to the present invention, there is no need for a retort sterilizer with a pressure-resistant structure, and there is no need for any operation to pressurize the inside of the device during sterilization. This advantage is particularly noticeable when heat sterilization is performed continuously. In the conventional continuous sterilization method, access to and from the sterilizer is a problem. For example, seal valves such as rotary valves and gauge valves are required to enter and exit the can from a normal pressure atmosphere to a pressurized atmosphere or vice versa. However, according to the method of the present invention, there is an advantage that successive entry and exit into heat sterilization can be carried out very easily without such trouble. In addition, in the conventional method, the heat sterilization of the canned food was carried out in a wet manner, that is, with the outer surface of the canned material being wet, but according to the present invention, the heat sterilization of the canned material was carried out in a dry manner, that is, the outer surface of the canned material was wet. It has the distinct advantage that it can be done without wetting. Furthermore, according to the present invention, it is possible to heat sterilize in a short time, thereby preventing deterioration of food tissue due to overcooking.
The disintegration or browning of pigments and vitamins is prevented, making it possible to provide canned products of high quality and excellent content preservation at a relatively low cost. The canned containers used in the present invention include those in which the bottom and body are integrally made of plastic material (so-called two-piece can) as shown in FIG. 1-A, as well as those shown in FIG. Body part 2a made of plastic material and can bottom part 3a made of metal material
and may be connected via the seaming part 13 (so-called three-piece can). In the present invention, a can body of any shape made of a plastic material that is transparent to microwaves is used as the canned container to be filled with the contents. Of course, this plastic material is one that can withstand the above-mentioned heat sterilization temperature, and is preferably made of thermoplastic resin from the viewpoint of moldability into the can body. Examples of suitable plastic materials include, but are not limited to: Low-, medium- or high-density polyethylene, crosslinked polyethylene, isotactic polypropylene, crystalline propylene-ethylene copolymer, crystalline ethylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl Olefin resins such as alcohol copolymers and ionically crosslinked olefin copolymers (ionomers); vinyl chloride resins such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinylidene chloride copolymers; polystyrene, Thermoplastic styrene-butadiene copolymer, thermoplastic styrene-isoprene copolymer, acrylonitrile-butadiene-styrene copolymer; polyethylene terephthalate, polyethylene terephthalate/isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene diene Polyester resins such as methylene terephthalate; poly-dioxydiphenyl methane carbonate, poly-dioxydiphenyl ethane carbonate, poly-dioxydiphenyl-2,2-propane carbonate, poly-P-xylylene glycol biscarbonate, etc. Polycarbonate; acetal resin known as Delson (DuPont), etc. In the present invention, these resins or these resins and at least one other resin can be used as a material for the can body in the form of a polymer blend. It can be used as a material for can bodies in the form of a laminate. A suitable can body material is one made of a laminate of an oxygen barrier resin and a moisture resistant resin, and this laminate plastic material suppresses the permeation of oxygen and water vapor through the container wall to an extremely low level. It has the advantage of particularly excellent preservability of the contents. As an oxygen barrier resin, relative humidity is 0%,
The oxygen permeability coefficient at a temperature of 37℃ is 5×10 ^-11 cc・
cm/ ^cm2・sec・cmHg or less, suitable examples include, in order of importance, ethylene-vinyl alcohol copolymers, polyamides,
They are vinylidene chloride resin, vinyl chloride resin, and high nitrile resin. Examples of ethylene-vinyl alcohol copolymers include saponified ethylene-vinyl acetate copolymers with an ethylene content of 20 to 60 mol%, especially 25 to 50 mol%, and a saponification degree of 95% or more, especially 96% or more. is used. As polyamide,
nylon 6, nylon 6,6, nylon 6,10,
Nylon 6/nylon 6,6 copolyamide, polyparaxylylene adipamide, etc. are used. Vinylidene chloride resins include vinylidene chloride/vinyl chloride copolymers, vinylidene chloride/acrylamide copolymers, vinylidene chloride/methyl acrylate copolymers, etc. with a vinylidene chloride content of 50 mol% or more; Homopolymers of vinyl chloride are preferably used. Examples of high nitrile resins include copolymers of nitrile monomers containing acrylonitrile and methacrylonitrile in a range of 40 to 97 mol% and other monomers, such as acrylonitrile/butadiene/acrylate copolymers. used. As a moisture-resistant thermoplastic resin, the moisture permeability is 100×
10 ^-12 g·cm/cm ² ·sec·cmHg or less, particularly olefin resins such as polyethylene and polypropylene are preferably used. The plastic laminate material that forms the can body has an oxygen barrier resin as the middle layer, and a moisture-resistant resin as the inner layer.
Preferably, it is present as an outer surface layer. If there is no adhesiveness between these resin layers, an adhesive layer known per se may be interposed between both layers. Examples of such adhesives include olefinic resins graft-modified with ethylenically unsaturated carboxylic acids such as acrylic acid, maleic acid, and maleic anhydride or their anhydrides. Moreover, instead of interposing an adhesive between the two, for example, as disclosed in Japanese Patent Publication No. 11263/1983,
At least one of the moisture-resistant resin layer and the oxygen barrier resin layer may contain a carbonyl (C=0) group-containing thermoplastic polymer to improve the adhesion between the two. In the present invention, the plastic material forming the canned container can contain various reinforcing agents or fillers in order to reinforce it and increase its weight. As a reinforcing agent, carbon black,
Powder reinforcing agent such as white carbon; glass fiber,
Fiber reinforcing agents such as rock wool, pulp fibers, linters, and aromatic polyamides; flaky reinforcing agents such as mica and flaky glass are used. Fillers include light to heavy calcium carbonate, various silicas, magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium silicate, magnesium silicate, talc, asbestos powder, kaolin, calcined kaolin, bentonite, anhydrite, etc. can be mentioned. These fillers or reinforcing agents can be used alone or in combination of two or more,
It is used in amounts of 5 to 500 parts by weight, especially 10 to 200 parts by weight per 100 parts by weight of plastic. In connection with the present invention, in conjunction with microwave sterilization at atmospheric pressure and temperatures above 100° C., it is often desirable to include reinforcing agents in the plastic material. The reinforcing agent may be present in the form of a blend with the resin or may be inserted between the resin layers in the form of a sandwich. As this latter type of reinforcing agent, various natural, synthetic or inorganic fibers can be used in the form of paper sheets, non-woven fabrics, or woven fabrics. The molding of the canned container can be carried out using the above-mentioned plastic materials by molding means known per se. For example, a cylindrical can body is made of plastic material,
Either by extruding a tube through a circular die, stretching it if desired, and then cutting it to length, or by rolling a sheet of plastic material into a tube and heat-sealing opposite edges. It is formed by Further, a can body in which the body and the bottom are integrated can be easily manufactured by injection molding, blow molding, stretch blow molding, or the like. For example, a single-layer or multi-layer canned container can be obtained by injecting molten resin into a mold having a cavity in the form of a can body, and carrying out the injection in multiple stages if necessary. In addition, by melt-extruding a single resin or a combination of resins mentioned above into a parison, supporting the extruded parison in a split mold, and blowing fluid into the mold, wide-mouth bottles can be easily manufactured. It is possible to obtain a can body in the shape of . In addition, a parison or preform is produced in advance by melt extrusion or injection molding, and this parison or preform is stretched in the axial direction at a temperature lower than its melting point and circumferentially by blowing fluid. The plastic can body can be stretched and have biaxial molecular orientation on the walls. In addition, by manufacturing a single-layer or multi-layer plastic sheet in advance and subjecting this sheet to vacuum forming, pressure forming, plugger assist forming, stretch forming, press forming, etc., seamless plastic cans with flanges can be made. It can be molded into a body.
At this time, if the sheet is subjected to pressure forming, plug assist forming, press forming, etc. at a temperature that allows stretching, it is possible to impart monoaxial or biaxial molecular orientation to the container wall. The plastic can body used in the present invention generally has a thickness of 0.3 mm or more, particularly 0.5 mm or more, in order to withstand the above-mentioned autogenous pressure from the canned contents, and has a yield point stress of 200 kg / It is desirable that the weight is at least 250 kg/cm ² , particularly at least 250 kg/cm ² . In the present invention, the metal material constituting the can lid or, in the case of a three-piece can, the can bottom, is a metal material conventionally used for this type of can filling, such as a light metal plate such as aluminum, or a tin plated steel plate ( tin plate), aluminum plated steel plate,
Chrome plated steel sheets, phosphoric acid and/or chromium oxide chemically treated steel sheets, electrolytic chromic acid treated steel sheets (TFS), etc. are used. Of course, the inner and outer surfaces of these metal can lids may be provided with a resin protective coating, which is known per se. In order to withstand the internal pressure during sterilization, these metal materials are generally
It is desirable to have a thickness of 0.15 to 0.6 mm, particularly 0.2 to 0.5 mm. The can lid and the can body are sealed by means such as double seaming or heat sealing. At this time, as a sealant for double seaming, a sealant made of an elastomer such as styrene-butadiene rubber, optionally mixed with a tackifier such as rosin, and a filler such as calcium carbonate, is used. As the sealant, heat-sealable sealants that can withstand the above-mentioned sterilization temperature, such as various polyamides or copolyamides, copolyesters, acid- or acid anhydride-modified olefin resins, etc., are used. From the viewpoint of heat resistance of the sealing joint, sealing by double seaming is desirable. From the perspective of preventing an abnormal increase in internal pressure during sterilization, the air in the head space inside the canner is removed by means such as steam injection or deaeration, and the temperature at room temperature (25°C) is maintained at the time of final packaging. It is desirable that the degree of vacuum inside the can be 20 cmHg or less, especially 30 cmHg or less. In the present invention, heat sterilization using microwaves can be performed by any method. The microwaves have frequencies of 915 and 2450 MHz, but electromagnetic waves with other frequencies can of course also be used. Microwave irradiation is easily performed by introducing microwaves into the sterilization chamber from a microwave generator such as a magnetron through a waveguide.
At this time, in order to uniformly irradiate the microwave into the sterilization chamber, a fan may be provided at the waveguide outlet or at an appropriate position in the sterilization chamber. The output of microwaves varies significantly depending on the amount of heat required for sterilization, but in general, the output is set so that sterilization of one package by microwave irradiation is completed in 30 seconds to 10 minutes. It is desirable to specify. At this time, if the atmosphere is kept cool, heating for about 30 minutes is possible. Of course, the microwave irradiation may be performed continuously or intermittently to keep the product temperature within a certain range. Microwave irradiation can be carried out continuously or batchwise. In the case of a continuous type, the packed cans are placed on a conveyor belt or other transport mechanism and sent continuously or intermittently into a sterilization chamber under microwave irradiation; in the case of a batch type, a predetermined amount is placed in a sterilization chamber under microwave irradiation. It is best to pack it in cans and irradiate it with microwaves. In the present invention, it is desirable that the canned material introduced into the microwave sterilization chamber be preheated in advance in order to shorten the time required to raise the temperature to the sterilization temperature.
Generally, it is convenient for this purpose to maintain the temperature of the sealed package at 60 to 90°C. For this purpose, hot filling of the contents and preheating with hot air or hot steam are used. In the present invention, it is desirable that the canned product after the microwave irradiation is forcibly cooled in order to prevent quality deterioration and damage to the canned product due to so-called overcooking of the contents. This cooling can be performed using, for example, a cooling medium such as cold air or cold water. Generally, it is preferable to cool the product to a temperature of 50°C or less within a period of 4 to 10 minutes. The invention is illustrated by the following example. Example 1 The ethylene content is 30 mol%, the vinyl alcohol content is 70 mol%, the oxygen permeability coefficient at a temperature of 37°C and a relative humidity of 0% is 7×10 ^-14 cc・cm/cm ²・sec・cm
The intermediate layer is an ethylene-vinyl alcohol copolymer of Hg, and isotactic polypropylene with a density of ^0.90 g/cc and a moisture permeability of ^4.1 The inner and outer layers are made of maleic anhydride-modified polypropylene as the adhesive between the intermediate layer and the outermost layer, and a full-flight screw with a diameter of 95 mm and an effective length of 2090 mm is built-in.
The extruder for the outermost layer is equipped with a melt channel that branches into two flow paths, and has a diameter of 40 mm and an effective length.
Adhesive layer extruder equipped with a built-in 880mm full-flight screw and a melt channel branched into two flow paths, with a diameter of 65mm and an effective length of 1430 mm.
A symmetrical five-layer sheet with a thickness of 0.7 mm and a width of 450 mm is produced using a sheet forming machine that combines an extruder for intermediate layer equipped with a full-flight type screw of mm, a multi-layer 5-layer adapter, a T die, and a sheet take-off machine. Molded. The layer composition ratio of the molded sheet is the thickness ratio of each layer: outermost layer: adhesive layer: middle layer = 100:
Sheet molding was carried out by adjusting the extrusion rate of the three extruders by adjusting the screw rotation speed so that the ratio was as close as possible to 1:2. Next, from this sheet,
A body blank with a length of 170.5 mm and a length of 136.2 mm was made, and both ends of the body blank in the width direction were treated with ultrasonic waves.
Immediately after heating to 200°C, body forcing (cylindrical formation) was performed so that the overlap at both ends was 3.1 mm wide, and a can body with an inner diameter of 52.3 mm was formed. Next, maleic anhydride-modified polypropylene with a melt index of 100 was applied in a molten state to the inner surface of the side seam portion to correct the inner surface. After the side seam inner surface correction agent has cooled, both ends of the can body are locally heated to approximately 170℃ using an infrared heater.
A flange forming tool was inserted into both ends to form a flange at the opening of the can body. Next, an aluminum easy-open lid coated with a sealing compound using SBR latex as the main component was double-sealed to one end of the can body. The can thus obtained was hot-filled with 250 g of coffee drink at 90°C, and the other end of the can body was double-sealed with a lid made of stainless steel to complete the can. At this time, the ratio of the volume of the head space to the filled volume was approximately 8%. The canned product obtained in this way was sterilized using a microwave sterilizer (manufactured by Toyo Seikan Co., Ltd., model H40-C-40M/W).
Microwave heat sterilization was performed in a normal pressure atmosphere using an output of 800 W and a frequency of 2450 MHz. It was irradiated with microwaves for 4 minutes and 30 seconds, and then immersed in a refrigerant for 3 minutes to cool it down. At this time, a good temperature-time curve with a maximum temperature of 130°C was confirmed using a fluorescent temperature sensor. On the other hand, as a comparative example, the above-mentioned canning was carried out at 115℃ using a batch type pressurized steam retort pot.
Retort sterilization was performed for 20 minutes. "F" obtained by integrating the temperature-time curves obtained by both sterilization methods
Almost the same values were obtained. The two types of cans thus obtained were stored for one year in an atmosphere of 25° C. and 40% relative humidity. After storage, the contents of the two types of canned products did not deteriorate, and no changes were observed in taste or color. Example 2 A plastic can with an inner diameter of 65.3 mm and a top and bottom seam height of 121 mm was made from the symmetrical five-layer sheet of polypropylene/ethylene-vinyl alcohol copolymer molded in Example 1, except that a tin lid was double-sealed. , molded in the same manner as in Example 1. This plastic can was filled with boiled carrots, lotus roots, and tuna, and then double-sealed with an ordinary tin lid to obtain a canned product. The packaged product thus obtained was irradiated with microwaves for 4 minutes and 30 seconds in a normal pressure atmosphere using the microwave sterilizer used in Example 1, and then immersed in a refrigerant for 4 minutes. The maximum temperature reached
A good temperature-time curve of 130°C was obtained.
Immediately after microwave irradiation, the temperature of the polypropylene outermost layer of the can body was measured with a thermolabel and was found to be approximately 50°C, which was significantly lower than the maximum temperature inside the can of 130°C. As a comparative example, using the same batch-type pressurized steam retort pot as in Example 1,
Retort sterilization was also performed at 105°C for 60 minutes. The two types of canned products were stored in an atmosphere of 25° C. and 60% relative humidity for one year. After one year of storage, the contents remained unchanged and the taste remained unchanged. Example 3 Isotactic polypropylene with a tensile strength at yield point of 420 kg/cm ² at 50°C, hard polyvinyl chloride with a yield strength of 425 kg/cm ² described above, and soft polyvinyl chloride with a tensile strength at yield strength of 188 kg/cm ² described above. vinyl chloride,
Three types of thermoplastic resins were used to form sheets with thicknesses of 0.25, 0.28, 0.3,
Molded six types of sheets of 0.4, 0.5 and 0.6mm. total
All 18 types of sheets were used to form cans in the same manner as in Example 1, having an inner diameter of 52.3 mm, a top and bottom seam height of 132.8 mm, and an aluminum easy-open lid double-sealed at one end of the can body. Coffee drinks in every can
Hot filling of 250g was carried out at 90°C, and the other end of the can body was double-sealed with a stain-free steel lid to complete the can. The packaged product thus obtained was subjected to microwave heat sterilization in a normal pressure atmosphere using the same microwave sterilizer as in Example 1. microwave 4
The sample was irradiated for 30 seconds and then immersed in a refrigerant for 3 minutes to cool it down. At this time, a good temperature-time curve with a maximum temperature of 130°C was obtained. The maximum pressure inside the can during sterilization was approximately 2.4 Kg/cm ² (gauge pressure). Table 1 shows the deformation of the can after sterilization and the maximum temperature reached on the surface of the can body.

[Table] As is clear from Table 1, microwave sterilization
Since the contents are efficiently heated from the inside within a short period of time, the temperature of the can body is suppressed to a significantly lower temperature than the temperature inside the can, making sterilization possible under normal pressure. Moreover, the can which is mainly composed of a plastic material having a yield point strength according to the present invention and has a can body thickness can be used at normal pressure.
It is found that it can withstand microwave sterilization at temperatures of 100℃ or higher. Example 4 The cans formed in Example 1 were filled with 250 g of coffee drink at each temperature shown in Table 2, and the lids made of stainless steel were double-sealed to seal the cans. The thus obtained canned product was immediately subjected to microwave heat sterilization in a normal pressure atmosphere using the microwave sterilizer used in Example 1.
Table 2 shows the observation results of the pressure inside the can and the shape retention of the can body after microwave irradiation for 4 minutes and 30 seconds.

【table】 [Brief explanation of the drawing]

Figures 1-A to 1-D show the manufacturing process of canning according to the present invention, and Figure 1-A shows a canned container (two-piece can) whose body and bottom are integrally molded;
Figure 1-B shows the filling process, Figure 1-C shows the sealing process, and Figure 1-D shows the sterilization process. FIG. 2 shows a canned container (three-piece can) having a body made of plastic material and both ends of which are sealed with lids made of metal material. 1...2 piece can, 2...can body, 3...can bottom, 4...flange, 5...contents, 6...filling nozzle, 7...lid, 8...sealant, 9 ... Lifter plate, 10 ... Canning, 11 ... Microwave waveguide outlet, 12 ... Conveyor, 13 ... Sealing section, 2
a... 3-piece can body, 3a... 3-piece can bottom.

Claims (1)

[Scope of Claims] 1. A canned container body made of a plastic material that is transparent to microwaves is filled with the contents, and the container body and a metal can lid are sealed with a sealing agent. A method for producing a canned product characterized by subjecting the canned product to microwave irradiation at normal pressure and sterilizing it at a temperature higher than 100°C. 2. The method according to claim 1, wherein sterilization is carried out in a state where the temperature of the contents is higher than the temperature of the sealed container. 3. The method according to claim 1, wherein the canned container body is made of a plastic material having a thickness of at least 0.3 mm and a yield point strength of at least 200 kg/cm ² at 50°C. 4. The method according to claim 1, wherein the contents are hot-filled into the canned container at a temperature of 50 to 96°C. 5. The method according to claim 1, wherein air in the canning head space is removed by steam injection or degassing prior to sealing. 6. The method according to claim 5, wherein air is removed so that the degree of vacuum during canning at room temperature is 20 mmHg or less. 7. The method according to claim 1, wherein the canned container body is a seamless container comprising a body and a bottom integrally formed of a plastic material. 8. The method according to claim 1, wherein the canned container body comprises a body made of a plastic material and a bottom made of metal joined to the body by seaming.