Microwave oven heating package provided with heat-generating ink and high-luminance ink, and method for manufacturing same

Abstract

Provided is a microwave oven heating package which is provided with a high-luminance ink layer and an electroconductive heat-generating layer, and in which a steam passage port can be formed through dielectric breakdown and heat generation during microwave oven cooking.　A microwave oven heating package (100) comprises a first sheet member (11) in which a base material layer (12), a sealant layer (13), and an automatic steam-passing mechanism (5) are formed. A high-luminance ink layer (15) and an electroconductive heat-generating layer (16) are formed on the automatic steam-passing mechanism (5) in a superimposed manner. The high-luminance ink layer (15) is made of an ink composition containing a thin-plate flake-like vapor-deposited aluminum pigment in which the aspect ratio of thickness and length is 100-3000. The high-luminance ink layer (15) has formed therein a plurality of non-spark parts configured from island parts, and a spark part configured from a gap part separating the non-spark parts from each other or a bridge part narrower than the island parts. The electroconductive heat-generating layer (16) contains an electroconductive material comprising an organic compound and is layered on at least one of the upper and lower sides of the high-luminance ink layer (15) so as to cover the spark part in plan view.

Description

Microwave heating packaging with heat-generating ink and high-brightness ink, and manufacturing method thereof

[0001] The present invention relates to a package for microwave heating, and more particularly to a package for microwave heating with heat-generating ink and high-brightness ink, and a method for manufacturing the same.

[0002] Supermarkets, convenience stores, and other stores display foods completely sealed in plastic packaging, some of which are intended to be cooked in a microwave oven. When cooking in a microwave oven, the food inside the packaging heats up and generates steam, so various technologies have been proposed to allow this steam to escape safely, and many of these technologies are now available on the market.

[0003] (Top-seal packaging) In recent years, in response to demands for resource reduction, there has been a trend toward changing from the conventional inlaid lid to a form in which a thinner (approximately 50 to 80 μm) plastic composite film is used to seal (heat seal) the outer edge of the top opening of the container (hereinafter also referred to as "top-seal packaging").

[0004] This top-seal packaging has a high level of sealing for food, and it can also be filled with an inert gas instead of air, which has the advantage of extending the expiration date of food. For example, if the expiration dates of boxed lunches and prepared meals, which were previously only about one day after the date of manufacture, could be extended by several days or more, food waste could be significantly reduced. Therefore, this top-seal packaging technology is already being adopted by convenience stores to package salads and some prepared meals, and is becoming increasingly popular.

[0005] (Issues with packaging for microwave heating (top-seal packaging)) Foods (such as boxed lunches) covered with conventional fitted lids have perforations on the surface of the lid, and because the steam from the food escapes through the perforations when heated, consumers and store staff can place the food in a microwave oven and heat it without any effort.

[0006] However, in the case of top-sealed packages with enhanced sealing properties, no through-holes are pre-drilled, so a steam vent must be prepared before heating in the microwave, for example by peeling back a small edge of the lid (film).

[0007] Furthermore, when heating top-seal packaging at a convenience store, the store clerk must peel off part of the film, and as part of infection control measures, they must also disinfect their hands beforehand. Not only does this increase the amount of work required for peeling and disinfecting, but it also necessitates a manual to ensure that all store clerks perform these tasks correctly. On the other hand, when consumers take the food (packaged product) home to heat it rather than at a convenience store, they must open part of the lid (film) before using the microwave. Forgetting to do this can lead to accidents such as the packaging bursting or food spilling.

[0008] For these reasons, there is a demand for top-sealed packaging that has an "automatic steaming mechanism" that allows steam to escape automatically during microwave cooking without the need to peel off the film before microwave cooking, while maintaining the food's airtightness.

[0009] (Prior Art (Patent Document 1: Heat-Generating Ink)) In response to the above demand for top-sealed packaging, the inventors of the present application have already proposed a technology in which a conductive heat-generating layer containing a conductive material (also called "heat-generating ink") that generates heat when exposed to microwaves from a microwave oven is printed on a film (Patent Document 1). By printing this heat-generating ink partially within the "heat seal area" between the tray (container) and the film (lid), the conductive heat-generating layer is heated and weakened during microwave cooking, and the steam pressure generated by the contents causes the heat seal in the weakened area to peel off, opening the film and allowing steam inside the tray to be safely released.

[0010] (Problems of Patent Document 1) However, the package of Patent Document 1 requires the formation of a conductive heating layer (i.e., a weakened portion) in the heat-sealed area where the container and lid come into contact, but because the lid is typically heat-sealed along the outer periphery of the top opening of the container, the location of the weakened portion (steaming opening) is limited to the outer periphery of the lid. When a liquid food such as soup or noodles is packaged in a package with a steaming opening formed on the outer periphery of the lid as in Patent Document 1, there is a risk that the liquid will spill out of the steaming opening even if the package is tilted even slightly after cooking in a microwave. Furthermore, if the package is heated at a convenience store, great care must be taken to avoid spilling the hot water when taking it home.

[0011] (Prior Art (Patent Document 2: Tearable Label)) Patent Document 2 also discloses a tearable label that can form a desired cut in the lid film of a package by irradiating it with microwaves (see in particular Figure 9 of the document).

[0012] (Problems of Patent Document 2) However, to realize the package of Patent Document 2, a process of individually and additionally attaching a tear label to the lid film is required, which is unsuitable for manufacturing sites that mass-produce packages by gravure printing, and reduces productivity. Furthermore, if the tear label is not securely attached to the surface of the lid film, the effect of forming the cut cannot be achieved, so a label inspection process would also be necessary.

[0013] (Prior Art (Patent Document 3: Metal Vapor Deposited Layer)) Patent Document 3 also discloses a package in which a lid film surface is patterned so that a plurality of metal films each having a triangular or rectangular shape in plan view are arranged side by side. It is described that this patterning is preferably achieved by vapor-depositing a metal vapor-deposited layer on the film surface.

[0014] (Problems of Patent Document 3) However, the manufacturing method of laminating a metal film (metal foil) onto the surface of a lid film as in Patent Document 3 is technically difficult and cannot be realized in a mass production process of gravure printing that is normally used in manufacturing packages. While it is possible to vapor-deposit a metal vapor-deposited layer onto the film surface in advance, this is by no means an inexpensive method to manufacture, and the inventors of the present application believe that there have been no examples of packages to which such a metal film has been attached that have actually been commercialized.

[0015] Japanese Patent No. 6709931 Japanese Patent Application Laid-Open No. 2012-176805 Japanese Patent Application Laid-Open No. 2011-046419

[0016] The present invention has been proposed in light of the above circumstances, and aims to provide a package for microwave heating in which a steam vent can be formed at any position on the lid (for example, in the center of the lid surface of a top-seal package), which opens due to insulation breakdown (spark) when microwaves are irradiated during microwave cooking, and a method for manufacturing the same.

[0017] (Invention and Use of High-Brightness Ink Layer) The present inventors have discovered that by forming a high-brightness ink layer inside a package using an ink composition containing a specially shaped vapor-deposited aluminum pigment, and by applying (printing patterning) this high-brightness ink layer so that it has non-sparking areas and sparking areas that have a higher electrical resistance value when irradiated with microwaves than the non-sparking areas, insulation breakdown (opening) is more likely to occur when irradiated with microwaves.

[0018] (Risks when using only a high-brightness ink layer) However, with an automatic vaporization mechanism formed with a high-brightness ink layer, if the microwave irradiation energy is set low or the content of the food (the absorber of the above energy) inside the package is large (in other words, if the environmental conditions change when heating in the microwave), there is a risk that sufficient energy will not be irradiated to the spark part, and the opening will not be able to occur reliably.

[0019] (Additional Use of a Conductive Heat-Generating Layer) Therefore, the inventors discovered that by additionally using a conductive heat-generating layer containing the heat-generating ink of Patent Document 1 described above and overlaying it on the spark section of the high-brightness ink layer to form an automatic vaporization mechanism, a stable opening phenomenon can be achieved regardless of the set value of microwave irradiation energy or the type and content of food (the absorber of the above energy).

[0020] In short, by providing an automatic steaming mechanism that combines high-brightness ink and heat-generating ink, we have come up with the idea of ​​providing a microwave heating package that not only can be formed anywhere on the lid surface, but also has an automatic steaming mechanism that exhibits stable opening performance.

[0021] That is, the present invention employs, for example, the following configurations and features: (Aspect 1) A package for microwave heating comprising a first sheet member having a base layer, a sealant layer, and an automatic steaming mechanism formed thereon, wherein a high-brightness ink layer and a conductive heat generating layer are formed in superimposed relation on the automatic steaming mechanism, the high-brightness ink layer is an ink composition containing a vapor-deposited aluminum pigment in the form of thin flakes having an aspect ratio of average thickness to average length of 100 to 3000, the high-brightness ink layer is formed with a plurality of non-spark portions each composed of islands, and spark portions each composed of gaps separating the non-spark portions or bridge portions narrower than the islands, and the conductive heat generating layer comprises a conductive material made of an organic compound, and is laminated on at least one side of the high-brightness ink layer so as to cover the spark portions in a planar view. (Aspect 2) A package for microwave heating according to Aspect 1, wherein the high-brightness ink layer has a film thickness of 0.1 to 3 μm, and the high-brightness ink layer is laminated with the vapor-deposited aluminum pigment having a plate thickness of 10 to 50 nm. (Aspect 3) A package for microwave heating according to Aspect 1 or 2, wherein the island portion is circular, elliptical, or polygonal in plan view (where n is the number of vertices, and n is 3 or greater), or the gap of the void portion varies. (Aspect 4) A package for microwave heating according to Aspect 1 or 2, wherein a dividing layer made of ink or film is formed between the high-brightness ink layer and the conductive heat generating layer. (Aspect 5) The microwave oven heating package according to Aspect 1 or 2, characterized in that the substrate layer includes first and second substrate layers, and either the high-brightness ink layer or the conductive heat-generating layer is formed between the first substrate layer and the second substrate layer, and the other is formed between the second substrate layer and the sealant layer.(Aspect 6) A method for producing a package for microwave heating, comprising: a first step of preparing a first sheet member; a second step of preparing a second sheet member or a tray container; and a step of heat-sealing the first sheet member and the second sheet member or the tray container, wherein the first step comprises: a step 1a of preparing a film to serve as a base layer; a step 1b of applying a high brightness ink composition containing a vapor-deposited aluminum pigment to the interior or inner surface of the base layer to partially form a high brightness ink layer; a step 1c of applying a conductive material made of an organic compound to at least one of the top and bottom of the high brightness ink layer to form a conductive heat-generating layer; and a step 1d of preparing a film to serve as a sealant layer, and further adhering and laminating the film to the inner surface of the base layer, wherein in step 1b, thin flake-shaped vapor-deposited aluminum pigment having an aspect ratio of average thickness to average length of 100 to 3000 is used as the vapor-deposited aluminum pigment, A method for producing a package for microwave heating using a high brightness ink, characterized in that in step 1b, the ink composition is applied to the high brightness ink layer so as to form a plurality of non-spark portions composed of island portions and spark portions composed of gaps separating the non-spark portions or bridge portions narrower than the island portions, and in step 1c, the conductive heat generating layer is laminated in a superimposed manner so as to cover the spark portions in a planar view. (Aspect 7) A method for producing a package for microwave heating according to Aspect 6, characterized in that in step 1b, the high brightness ink layer has a film thickness of 0.1 to 3 μm, and the vapor-deposited aluminum pigment has a plate thickness of 10 to 50 nm. (Aspect 8) The method for producing a package for microwave heating according to Aspect 6 or 7, wherein in step 1b, the ink composition is applied so that the island portion has a circular, elliptical or polygonal shape in plan view (where n is the number of vertices, and n is 3 or more), or so that the gap of the void portion varies. (Aspect 9) The method for producing a package for microwave heating according to Aspect 6 or 7, wherein step 1 further includes step 1e of applying ink or laminating a film so that a dividing layer is formed between the high-brightness ink layer and the conductive heat-generating layer.(Aspect 10) A method for producing a package for microwave heating according to Aspect 6 or 7, characterized in that in step 1a, two films are prepared to form the first and second base layers; if the high-brightness ink layer is formed between the first and second base layers in step 1b, then in step 1c, the conductive heat-generating layer is laminated between the second base layer and the sealant layer; and if the high-brightness ink layer is formed between the second base layer and the sealant layer in step 1b, then the conductive heat-generating layer is laminated between the first and second base layers in step 1c.

[0022] In the microwave heating package of the present invention, a high-brightness ink layer having the above-described configuration is formed within the film (first sheet member). Therefore, when microwaves are irradiated onto the package, the thin flake-shaped vapor-deposited aluminum pigments stacked in large numbers within the ink layer become charged, creating a potential difference between adjacent pigments, and an electric current flows within the ink layer, generating Joule heat.

[0023] Furthermore, since the high-brightness ink layer is printed so as to form spark portions and non-spark portions of the above-described configuration, when microwaves are continuously irradiated, insulation breakdown occurs in the spark portions, through which current does not easily flow, and a vapor vent (vapor escape port) is formed that penetrates the first sheet member.

[0024] In the packaging for microwave heating of the present invention, the conductive heating layer is laminated so as to cover the spark portion of the high-brightness ink layer. Therefore, even if the environmental conditions during microwave heating change (for example, the food inside the packaging is large and irradiated energy is absorbed by the food), making it difficult for insulation breakdown to occur in the spark portion, the heat generated by the conductive heating layer melts and weakens the spark portion, ensuring the reliable and stable formation of a steam vent (steam release port).

[0025] Furthermore, in a preferred embodiment of the packaging of the present invention, a dividing layer made of ink or film is inserted between the high-brightness ink layer and the conductive heat-generating layer, forming a coupling structure in which the layers are close to each other but not in contact with each other. This reduces problems that can occur when the two layers come into direct contact (for example, insulation breakdown due to a decrease in resistance, or poor coating of one layer that is superimposed on the other), and makes it possible to create a base that is easy to form a vapor vent.

[0026] In addition, the coupling structure not only has excellent microwave power transmission properties, but also allows the power required for the steam vent operation to be distributed and supplied to the high-brightness ink layer and the conductive heat generating layer due to the presence of the separating layer, and prevents damage to the contacts when they are directly superimposed.

[0027] 1 is a perspective view and a cross-sectional view showing the overall structure of the packaging body of the present invention (Example 1), and a partially enlarged cross-sectional view showing the structure of a part thereof (the automatic steaming mechanism at the upper center); 2 is a partially enlarged cross-sectional view showing a modified example of the stacking arrangement of the first sheet member (laminate layer), and a schematic cross-sectional view showing the bridge portion and gap portion of the spark portion; 3 is a schematic view illustrating the shape of the vapor-deposited aluminum pigment of the present invention and the shape of a conventional pigment, in comparison; and 4 is a diagram illustrating the printing pattern (P １ ~P ６ 1 is a diagram illustrating an example of a method for manufacturing a package according to the present invention. FIG. 2 is a flowchart illustrating each step in the manufacturing method of a package according to the present invention. FIG. 3 is a diagram illustrating detailed steps in the process of forming a high-brightness ink layer. FIG. 4 is an image illustrating the results of a confirmation test (whether or not a steam vent hole is formed in the packages of the example and comparative examples 1 and 2).

[0028] The present invention will be described below based on the embodiments shown in the drawings, but the present invention is not limited to the specific embodiments described below. In addition, the same reference numerals are used in each drawing to designate the same or corresponding parts.

[0029] As described above, the microwave oven heating package of the present invention is characterized by the provision of an automatic vaporization mechanism that combines a layer containing a novel high-brightness ink and a layer containing a heat-generating ink (see Patent Document 1). Each ink material is described in detail below.

[0030] (Material for the Conductive Heating Layer) The material for the conductive heating layer 16 (hereinafter also referred to as "conductive material" or "heat-generating ink") can be, for example, inorganic materials such as indium oxide, aluminum, tin, nickel, or carbon, or conductive organic compounds such as polyanilines or polypyrroles, but is not necessarily limited to these, and any known conductive material that is commonly used in microwave cooking and generates heat when irradiated with microwaves will suffice. However, from the experience of the present inventors, organic compound-based conductive materials are preferred from the perspective of achieving favorable releasability of the sealant layer 13.

[0031] (High-Brightness Ink) In the present invention, a novel ink composition (high-brightness ink) is used to form the steam vent (automatic steam vent mechanism) of a package for microwave heating. This ink composition contains vapor-deposited aluminum pigment 15b (see FIG. 3(b)), thermoplastic resin 15a (see FIG. 3(a)), and a solvent (preferably an organic solvent). The presence of this vapor-deposited aluminum pigment 15b gives the ink composition a silver color.

[0032] The vapor-deposited aluminum pigment 15b is preferably contained in the ink composition at 0.5 to 15% by mass. If the content is less than the lower limit (0.5% by mass), the pigments 15b in the ink composition are less likely to come into contact with each other, and the effects of the present invention (electric charging and dielectric breakdown during microwave irradiation, as described below) are not fully achieved. On the other hand, if the content is more than the upper limit (15% by mass), the ink composition contains an excess of pigment 15b, which not only reduces the fluidity of the ink composition during production of the ink composition and during subsequent production of the package 100 (when applying the high-brightness ink layer 15, as described below), but also increases production costs.

[0033] (Vapor-deposited aluminum pigment) Here, the vapor-deposited aluminum pigment 15b is an aluminum powder that is "thin flake-shaped (scale-shaped)" in cross section, as shown in Figures 3(a) and 3(b). More specifically, the average thickness t ｐ and average length L ｐ The aspect ratio (AR = L ｐ / tp) is formed to be AR=100 to 3000.ｐ The average thickness t is preferably 10 to 50 nm. ｐ When is 10 nm, the corresponding average length L ｐ is 1 to 30 μm, and the average thickness t ｐ When is 50 nm, the corresponding average length L ｐ is 5 to 150 μm.

[0034] The pigment 15b has an extremely high aspect ratio AR compared to a conventional pigment of the same type (aluminum paste) described below, and therefore each pigment 15b is likely to be oriented so as to line up orderly in the same direction in the ink layer 15 after printing on the film (substrate layer 12). The pigments 15b lined up orderly in the same direction have more contact points (larger contact area) and are more uniformly packed, so that when microwaves are applied, current tends to flow uniformly through the pigments 15b (the ink layer 15 containing them).

[0035] (Conventional Pigment) Meanwhile, the shape of a conventional pigment (e.g., aluminum paste) is shown in FIG. 3(c) as reference numeral 150b. Reference numeral 150a denotes a resin surrounding the pigment 150b. This conventional pigment 150b is used when producing ordinary aluminum paste-like silver ink. This pigment 150b is clumped compared to the pigment 15b of the present invention, and has a corresponding aspect ratio AR of 100 or less. As a result, it is difficult for each pigment 150b to be oriented in the same direction within the ink layer 150 after film printing, resulting in a non-uniform pigment loading state, which makes it difficult for current to flow uniformly through the pigment 150b (or the ink layer 150 containing the pigment 150b) when exposed to microwaves.

[0036] (Resin) Examples of the thermoplastic resin 15a include resins used in ordinary gravure printing inks, but are more preferably at least one resin selected from among shellac resins, rosins, urethane resins, acrylic resins, polyvinylidene chloride resins, polyester resins, fibrous resins such as nitrocellulose, vinyl chloride-vinyl acetate copolymer resins, polyamide resins, and chlorinated olefin resins, and gravure printing inks or flexographic printing inks containing one or a combination of two or more of these resins may also be used.

[0037] (Solvent) The ink composition of the present invention may contain a solvent. In particular, in the case of gravure printing ink or flexographic printing ink, the solvent may be any solvent that dissolves or disperses the thermoplastic resin 15a in the solvent. Examples of the solvent include the following organic solvents and / or water that are commonly used in gravure printing ink or flexographic printing ink.

[0038] Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as hexane, cyclohexane, methylcyclohexane and ethylcyclohexane, alcohol solvents such as methanol, ethanol, isopropyl alcohol, normal propyl alcohol, 1-butanol, 2-butanol, isobutanol and tert-butanol, ester solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate and tert-butyl acetate, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether and propylene glycol monobutyl ether, and esters thereof.

[0039] Fig. 1(a) is a perspective view showing a package 100 for microwave heating according to Example 1. Fig. 1(b) is a schematic cross-sectional view of the package 100. Fig. 1(c) is a partially enlarged cross-sectional view showing the portion surrounded by circle C (broken line) in Fig. 1(b).

[0040] (Outline of Top-Seal Package (Tray Pack) According to Example 1) The package 100 shown in Example 1 is in the form of a tray pack including a first sheet member 1 and a tray container 2. The first sheet member 1 and the tray container 2 are heat-sealed to each other at their peripheral edges 11, 21 to form an internal space 4 in which foodstuffs 3 and the like are enclosed.

[0041] (Cross-sectional structure of first sheet member) Fig. 1(c) shows an enlarged cross-sectional structure of a portion having the automatic steam passage mechanism 5 (5A). The first sheet member 1 includes a heat-resistant film-like base material layer 12, a film-like sealant layer 13, an adhesive layer 14 that connects the base material layer 12 and the sealant layer 13 with an adhesive, and a printed layer (not shown). From the perspective of product sales, the base material layer 12 may be formed of multiple layers (for example, first and second base material layers 12a and 12b as shown).

[0042] Before the base material layer 12 is bonded to the sealant layer 13, a printing layer, a conductive heat-generating layer 16, and a high-brightness ink layer 15 (not shown) are applied to one side of the base material layer 12 (the inner side facing the sealant layer 13).

[0043] 1(c), before the first substrate layer 12a and the second substrate layer 12b are connected by the adhesive layer 14', a printing layer (not shown) and a conductive heat-generating layer 16 are applied (printed) in advance on the inner surface side (on the film) of the first substrate layer 12a, and high-brightness ink layers 15, 15 are applied (printed) in advance on the inner surface side (on the film) of the second substrate layer 12b so as to be spaced apart from each other. The first and second substrate layers 12a, 12b thus integrated are connected to a sealant layer 13 by an adhesive (adhesive layer 14) to form a final laminate of multiple layers.

[0044] That is, the base material layer 12 is integral with these multiple layers and connected to the sealant layer 13 via the adhesive layer 14. A laminate of films 12 and 13 made of different materials in this way is also called a "multilayer laminate film" or simply a "laminate layer."

[0045] (Material of Base Layer) It is desirable to use a stretched film material such as nylon, polypropylene, polyethylene terephthalate, polybutylene terephthalate, or transparent vapor-deposited PET as the material for the above-mentioned base layer 12 (12a, 12b), but this is not limited to these.

[0046] (Sealant Layer Material) Furthermore, it is desirable to use a non-stretched film material such as non-stretched polypropylene as the material for the sealant layer 13, but the material is not necessarily limited to this.

[0047] (Modifications Related to the Lamination Arrangement of the Conductive Heat-Generating Layer and the High-Brightness Ink Layer) The layer structure of the automatic vaporization mechanism 5 for the high-brightness ink layer 15 is not limited to the example (5A) shown in FIG. 1( c). Only one film (layer) serving as the substrate layer 12 may be prepared, and various layers may be formed between this substrate layer 12 and the sealant layer 13. For example, as shown in modification 5 (5B) of FIG. 2( a), before bonding the substrate layer 12 (12 a) to the sealant layer 13 with the adhesive layer 14, the high-brightness ink layer 15 and a printed layer (not shown) may be applied to the inner surface of the substrate layer 12 a (the surface facing the sealant layer 13), and then a third ink layer 17 may be applied using a known ink, followed by the application of the conductive heat-generating layer 16. The example shown in FIG. 2( a) is not limited to this, and the high-brightness ink layer 15 and the conductive heat-generating layer 16 may be applied in reverse.

[0048] (Outline of High-Brightness Ink Layer) As described above, it should be noted that in this embodiment, the high-brightness ink layer 15 is formed in the center of the first sheet member 1 in a plan view (between the base layer 12 and the sealant layer 13 in a cross-sectional view). Here, the high-brightness ink layer 15 is an ink composition containing a vapor-deposited aluminum pigment (hereinafter also simply referred to as "pigment") 15b in a thermoplastic resin 15a, as shown in Figure 3(a). Note that the ink composition is prepared by blending the thermoplastic resin 15a (e.g., shellac resin) and an organic solvent (e.g., toluene) in addition to this pigment 15b.

[0049] (Thin flake pigment) In addition, the vapor-deposited aluminum pigment 15b of the present invention has an average thickness t ｐ and average length L ｐ The aspect ratio (AR = L ｐ / t ｐ It should be noted that the high brightness ink layer 15 is formed in the form of a thin flake with an AR of 100 to 3000. ｉ The ink layer 15 has a thickness t of 10 to 50 nm. ｐ It is preferable that vapor-deposited aluminum pigment particles 15b having the above structure are laminated.

[0050] (Formation of Spark and Non-Spark Portions) The high-brightness ink layer 15 is printed (preferably by gravure printing) to form a plurality of non-spark portions NSP and spark portions SP that connect these non-spark portions NSP, NSP. The spark portions SP are formed to form bridge portions 151 (see FIGS. 2(b) and 4(b)) with reduced vapor-deposited aluminum pigment 15b (in other words, a cross-sectional area in a direction perpendicular to the connection (coupling) direction between the non-spark portions NSP) compared to the non-spark portions NSP, or void portions 152 (no connection between the non-spark portions NSP, see FIG. 2(c)). Note that this results in the spark portions SP having a higher electrical resistance when irradiated with microwaves than the non-spark portions NSP.

[0051] (Shape and Arrangement of Non-Spark Portions and Spark Portions) The non-spark portions NSP of the high-brightness ink layer 15 may be island-shaped objects (island portions) containing pigment 15b in a plan view, and may be selected from shapes such as circles, ellipses, polygons such as triangles and rectangles (where n is the number of vertices, n is 3 or more), as shown in Figures 4(a) to 4(d), or rectangles with partially curved surfaces (see Figure 4(e)). The non-spark portions NSP are multiple islands spaced apart from each other and sandwiching one spark portion SP, but are not limited to the example of two, and three or more may be arranged as shown in Figure 4(f), and the number of spark portions SP is also not limited to one, but multiple may be arranged.

[0052] According to the inventors' experience through trial and error, it is preferable that the distance between the non-spark portions NSP (in other words, the gap of the gap portion 152 or the width of the bridge portion 151) varies rather than being constant, and it is even more preferable that it varies so as to have a minimum value (see P in FIG. 4(d)). ４ Printing pattern P other than １ ~P ３ , P ５ ~P ６ As a result, highs and lows in the electrical resistance occur within the gap 152, and a spark is reliably generated at a point with a higher electrical resistance (i.e., a more specific point), and the vapor port can be expanded from that point.

[0053] (Principle of charging and heat generation in high-brightness ink layer) In the packaging body 100 of the present invention (this embodiment), the high-brightness ink layer 15 of the above-described configuration is formed within the first sheet member 1, so when microwaves are irradiated onto the packaging body 100, the thin flake-shaped pigments 15b stacked in large numbers within the ink layer 15 become charged, creating a potential difference between adjacent pigments 15b, 15b, and causing an electric current to flow within the high-brightness ink layer 15, generating Joule heat.

[0054] (Dielectric breakdown at spark portions) Furthermore, since the high-brightness ink layer 15 is printed to form the spark portions SP and non-spark portions NSP of the above-described configuration, when microwaves are continuously irradiated onto the package 100 by heating in the microwave oven, dielectric breakdown occurs at the spark portions SP, where current does not easily flow, and a steam hole (steam escape hole) is formed that penetrates the first sheet member 1.

[0055] (Arrangement of conductive heating layer on spark portion) In addition, it should be noted that in the present invention, the conductive heating layer 16 is arranged so that, in a plan view, it is projected onto the spark portion SP of the high-brightness ink layer 15. As a result, when microwaves are irradiated, the conductive heating layer 16 generates heat, which softens the spark portion SP in the vicinity, making it easier for the steam opening to open.

[0056] It is preferable that an intervening material (separating layer) made of ink or film is formed between the high-brightness ink layer 15 and the conductive heat-generating layer 16. In the embodiment shown in FIG. 1(c), the film of the second base material layer 12b is interposed so as to separate the layers 15, 16. On the other hand, in the modified example shown in FIG. 2, instead of using a film as in the embodiment, a separating layer (third ink layer 17) is formed by applying a separate ink (a known ink that can be used for gravure printing on packaging (for example, but not limited to, white ink (LAMITECC 630 R White B manufactured by Tokyo Ink Co., Ltd.))).

[0057] (Advantages of Inserting a Dividing Layer) By inserting such a dividing layer 17, a "coupling structure" is formed in which the layers 15, 16 are close to each other but not in contact with each other. This reduces problems that can occur when the layers 15, 16 are in direct contact with each other (for example, insulation breakdown at the spark portion SP due to a decrease in resistance (difficulty in current flow), and coating defects of one layer 16 that is superimposed on the other layer 15), making it possible to create a base material that is easy to form a vapor vent hole.

[0058] In addition, the coupling structure not only has excellent microwave power transmission properties, but also, due to the presence of the separating layer 17, the power required for the steam vent operation can be distributed and supplied to the high-brightness ink layer 15 and the conductive heat generating layer 16, and damage to the contacts that can occur when the two are directly superimposed on each other can be prevented.

[0059] (Overview of Manufacturing Method of Package) FIG. 5 is a flowchart showing the steps constituting the manufacturing method of the package 100 of the present invention. First, a first sheet member 1, which will form one side (e.g., the front side) of the package 100, is prepared (first step S1). Then, as shown in steps S2 to S4 on the left side of FIG. 5, a tray container 2 is prepared on the other side (e.g., the back side) of the package 100 (step S2). Next, food ingredients 3 are packed into the tray container 2 (packing step S3). Thereafter, the peripheral edge 11 of the first sheet member 1 is thermally welded to the peripheral edge 21 of the tray container 2, thereby completely sealing the food ingredients 3 within the package 100 (sealing step S4). When carrying out steps S1, S2, S4, etc., it is preferable to use a known gravure printing technique.

[0060] On the other hand, when manufacturing a package (not shown) that uses a second sheet member (not shown) instead of the tray container 2, after the first step S1 is completed, the process proceeds to steps S2a, S2b, S3a, and S4a shown on the right side of Fig. 5. Specifically, a regular second sheet member (not shown) made of a laminate layer is prepared (step S2a), and the peripheral edge 11 of the first sheet member 1 and a part of the peripheral edge of the second sheet member are heat-sealed (step S2b).

[0061] After step S2b is completed, a package is produced in which a portion of the periphery (e.g., three sides) is heat-sealed. The desired ingredients are then stuffed into the interior space of the package through the remaining open periphery (e.g., one side) (loading step S3a). After the ingredients have been packed, the remaining periphery is also heat-sealed to completely seal the ingredients within the interior space of the package (sealing step S4a).

[0062] The method for producing the package 100 of the present invention is characterized by the treatment in the first step S1 as shown in FIG. 5, and will be described in detail below.

[0063] (Formation of Substrate Layer, Conductive Heat-Generating Layer, and High-Brightness Ink Layer) Here, in the first step S1, first, a stretched film that will become the aforementioned substrate layer 12 is prepared (step S11). One layer (e.g., layer 16) of the conductive heat-generating layer 16 or the high-brightness ink layer 15 is formed on the inner surface side of this substrate layer 12 (i.e., the sealant layer 13 side) (step S12). In the former case, a heat-generating ink is applied to the inner surface side of the substrate layer 12 (film), and in the latter case, a high-brightness ink is applied to the inner surface side of the substrate layer 12 (film).

[0064] (Formation of Dividing Layer) Thereafter, a film or ink is superimposed on the inner surface of the base material layer 12 to further form a dividing layer (step S13). More specifically, the second base material layer 12b may be used as the dividing layer film and adhered to the base material layer 12 so as to sandwich one of the layers. Alternatively, a known film applicable to packaging materials may be used. The ink used in step S13 may be a known ink that can be printed on packaging materials (for example, the white ink described above).

[0065] In addition, the other of the conductive heat generating layer 16 and the high brightness ink layer 15 (the other layer for the one layer selected in step S12) is formed on the inner surface of the dividing layer (step S14). For example, in the case of the cross-sectional configuration shown in Figure 1(a), the conductive heat generating layer 16 is formed in step S12, so the high brightness ink layer 15 is formed in step S14.

[0066] (Preparation of Sealant Layer) Furthermore, an unstretched film that will become the sealant layer 13 is prepared and adhered to and laminated on the inner surface of the base material layer 12 (step S15). This forms a laminate layer (first sheet member 1) that incorporates the high-brightness ink layer 15. Note that adhesive layers 14, 14' made of adhesive or a printed layer (not shown) that will become the package surface may be inserted (laminated) between the base material layer 12, the dividing layer (in the case of a film such as the second base material layer 12b), and the sealant layer 13.

[0067] (Details of the High-Brightness Ink Layer Forming Step) The step S5 of forming the high-brightness ink layer 15 in the above-mentioned step S12 or S14 will be described in further detail with reference to FIG. 6. An ink composition containing vapor-deposited aluminum pigment 15b is applied to a part of the inner surface side (see FIGS. 1(c) and 2(a)) of the substrate layer 12 (12a) to partially form the high-brightness ink layer 15. The ink composition applied in this step contains a vapor-deposited aluminum pigment 15b having a thickness t of 10 to 50 nm. ｐ It is preferable to use a vapor-deposited aluminum pigment 15b having the following structure.

[0068] (Use of Special Pigment) The pigment to be added to the ink composition is a pigment having an average thickness t ｐ and average length L ｐ The aspect ratio (AR = L ｐ / t ｐ It should be noted that thin flake vapor-deposited aluminum pigments 15b (see also FIG. 3(b)) having an AR of 100 to 3000 are used (step S51). As a result, when the package 100 is heated in a microwave oven and the ink layer 15 is also irradiated with microwaves, the thin flake vapor-deposited aluminum pigments 15b become charged, creating a potential difference between adjacent pigments 15b, 15b, and causing a current to flow within the high-brightness ink layer 15, generating Joule heat.

[0069] (Application in a special printing pattern) Furthermore, in step S5, when forming the high brightness ink layer 15, it should be noted that the ink composition is applied so as to form a plurality of non-spark portions NSP and spark portions SP connecting the non-spark portions NSP, NSP (step S52) (each printing pattern P shown in FIG. 4 １ ~P６ (See Fig. 1). Such a print pattern P １ ~P ６ When microwaves are continuously irradiated onto the high-brightness ink layer 15, insulation breakdown occurs at the spark portion SP where current does not easily flow, and a vapor vent hole (vapor escape hole) is formed that penetrates the first sheet member 1 (i.e., the laminate layer).

[0070] (Formation of Spark and Non-Spark Portions) Note that the ink composition is applied to the non-spark portions NSP so as to form multiple islands, while the ink composition is applied to the spark portions SP so as to form bridge portions 151 with reduced vapor-deposited aluminum pigment 15b (in other words, the cross-sectional area in the direction perpendicular to the connecting direction between the non-spark portions NSP) compared to the non-spark portions NSP, or void portions 152 with no pigment 15b at all (step S53). This reliably increases the electrical resistance in the spark portions SP, ultimately causing dielectric breakdown.

[0071] In addition, it is preferable to form the islands so that the gaps between the non-spark portions NSP (the width of the spark portions SP) change (preferably gradually change to a very small width) (step S53a). For example, in the case of the print pattern P shown in FIG. １ ~P ３ , P ５ , P ６ In this way, the high-brightness ink layer 15 can be printed (laminated) on the base material layer 12. This causes high and low electrical resistance values ​​to occur even within the gap 152, ensuring that sparks are generated at locations with higher electrical resistance values ​​(i.e., more specific points), and the steam vent can be expanded from these points as base points.

[0072] Furthermore, when observing the package 100 in a plan view, it is preferable to position the spark portion SP so that it overlaps (is projected onto) the conductive heating layer 16 (step S54). As a result, when the conductive heating layer 16 generates heat during microwave irradiation, the spark portion SP arranged nearby also becomes soft, making it easier for the steam opening to open in the event of insulation breakdown at the spark portion SP.

[0073] (Confirmation test for the formation of steam vent holes) The present inventors used a high-intensity ink layer 15 and a conductive heat generating layer 16 to form a cross-sectional structure shown in FIG. 1(c) and a print pattern P shown in FIG. １ An automatic steaming mechanism 5 having the above structure was fabricated as this example (see FIG. 7(a)). Note that the ink composition was applied so that the high brightness ink layer 15 was composed of only circular non-sparking parts NSP without sparking parts SP, and a conductive heat generating layer 16 was formed on the outside of the non-sparking parts NSP, which was prepared as Comparative Example 1 (see FIG. 7(b)). Furthermore, in the same manner as in the above example, the high brightness ink layer 15 was coated with a printing pattern P １ However, the conductive heat generating layer 16 was superimposed on the non-spark portion NSP instead of the spark portion SP, to prepare a comparative example 2 (see FIG. 7(c)).

[0074] The comparative example and example packages prepared in this manner were heated in a microwave oven to confirm the presence or absence of a steam vent. Figures 7(a)-(c) show images of each sample before heating, and Figures 7(d)-(f) show images of the corresponding samples after heating. As shown in Figure 7(d), in the example sample, a steam vent was clearly formed along the overlapping portion between the spark portion SP and the conductive heating layer 16. On the other hand, in the comparative example 1 and example 2 samples shown in Figures 7(e) and 7(f), no steam vent was observed.

[0075] In this way, the packaging body 100 of the present invention combines the characteristics of the high brightness ink layer 15 (dielectric breakdown) and the characteristics of the conductive heat generating layer 16 (heat generation) so as to exhibit their full potential.

[0076] Although the embodiments and examples of the present invention have been described above with reference to the drawings, the scope of application of the present invention is not limited to the packaging form of the top-sealed package shown in the drawings. The same advantages can be obtained even if the above-described automatic steaming mechanism is formed in other packaging forms (for example, pillow packaging film, back-sealed bags, standing pouches, three-side sealed bags).

[0077] In the microwave heating package of the present invention, a high-brightness ink layer having the above-described configuration is formed within the film (first sheet member). Therefore, when microwaves are irradiated onto the package, the thin flake-shaped vapor-deposited aluminum pigments stacked in large numbers within the ink layer become charged, creating a potential difference between adjacent pigments, and an electric current flows within the ink layer, generating Joule heat.

[0078] Furthermore, since the high-brightness ink layer is printed so as to form spark portions and non-spark portions of the above-described configuration, when microwaves are continuously irradiated, insulation breakdown occurs in the spark portions, through which current does not easily flow, and a vapor vent (vapor escape port) is formed that penetrates the first sheet member.

[0079] In the package of the present invention, in particular, the conductive heating layer is laminated so as to cover the spark portion of the high-brightness ink layer. Therefore, even if the environmental conditions change during microwave heating (for example, the food inside the package is large and the irradiated energy is absorbed by the food), making it difficult for insulation breakdown to occur in the spark portion, the heat generated by the conductive heating layer melts and weakens the spark portion, and a steam vent (steam release port) is formed reliably and stably.

[0080] The packaging material and its manufacturing method of the present invention, which exhibit such remarkable effects, are not found in the packaging industry or on the market, and have extremely high industrial value and applicability.

[0081] 1 First sheet member 2 Tray container 3 Food material 4 Internal space 5, 5A, 5B Automatic steaming mechanism 11, 21 Periphery 12, 12a, 12b Base material layer (first and second base material layers) 13 Sealant layer 14, 14' Adhesive layer 15, 15a, 15b High-brightness ink layer, resin, vapor-deposited aluminum pigment 16 Conductive heat generating layer 17 Third ink layer 100 Package 150, 150a, 150b Conventional ink layer, resin, pigment 151, 152 Bridge portion, gap portion AR, L ｐ , t ｐ Pigment aspect ratio, average length, average thickness NSP, SP Non-spark part, spark part P １ , P ２ , P３ , P ４ , P ５ , P ６ Printing pattern when printing ink composition t ｉ High-brightness ink layer thickness

Claims

1. A package for microwave heating comprising a first sheet member having a base layer, a sealant layer, and an automatic steaming mechanism formed thereon, wherein a high-brightness ink layer and a conductive heat generating layer are formed in a superimposed manner on the automatic steaming mechanism, wherein the high-brightness ink layer is an ink composition containing a thin flake-shaped vapor-deposited aluminum pigment with an aspect ratio of average thickness to average length of 100 to 3000, and wherein the high-brightness ink layer is formed with a plurality of non-sparking portions composed of islands, and sparking portions composed of gaps separating the non-sparking portions or bridge portions narrower than the islands, and wherein the conductive heat generating layer comprises a conductive material made of an organic compound, and is laminated on at least one side of the high-brightness ink layer so as to cover the sparking portions in a plan view.

2. The microwave oven packaging according to claim 1, characterized in that the high brightness ink layer has a film thickness of 0.1 to 3 μm, and the vapor-deposited aluminum pigment having a plate thickness of 10 to 50 nm is laminated on the high brightness ink layer.

3. A package for microwave heating according to claim 1 or 2, characterized in that the island portion is circular, elliptical or polygonal in plan view (where n is the number of vertices, n is 3 or greater), or the gap of the gap portion varies.

4. A package for microwave heating according to claim 1 or 2, characterized in that a dividing layer made of ink or film is formed between the high brightness ink layer and the conductive heat generating layer.

5. The package for microwave heating according to claim 1 or 2, characterized in that the base layer comprises first and second base layers, and either the high-brightness ink layer or the conductive heat-generating layer is formed between the first base layer and the second base layer, and the other is formed between the second base layer and the sealant layer.

6. A method for manufacturing a package for microwave heating, comprising: a first step of preparing a first sheet member; a second step of preparing a second sheet member or a tray container; and a step of heat-sealing the first sheet member and the second sheet member or the tray container, wherein the first step comprises: a step 1a of preparing a film to serve as a base layer; a step 1b of applying a high-brightness ink composition containing a vapor-deposited aluminum pigment to the interior or inner surface of the base layer to partially form a high-brightness ink layer; a step 1c of applying a conductive material made of an organic compound to at least one of the top and bottom of the high-brightness ink layer to form a conductive heat-generating layer; and a step 1d of preparing a film to serve as a sealant layer, and further adhering and laminating the film to the inner surface of the base layer; wherein in step 1b, thin flake-shaped vapor-deposited aluminum pigment having an aspect ratio of average thickness to average length of 100 to 3000 is used as the vapor-deposited aluminum pigment, a step 1b of applying the ink composition to the high-brightness ink layer so as to form a plurality of non-spark portions composed of island portions and spark portions composed of gap portions separating the non-spark portions or bridge portions narrower than the island portions; and a step 1c of laminating the conductive heat generating layer in a superimposed manner so as to cover the spark portions in a plan view.

7. The method for manufacturing a package for microwave heating according to claim 6, characterized in that in step 1b, the high-brightness ink layer has a film thickness of 0.1 to 3 μm, and the vapor-deposited aluminum pigment has a plate thickness of 10 to 50 nm.

8. The method for manufacturing a package for microwave heating according to claim 6 or 7, characterized in that in step 1b, the ink composition is applied so that the island portion forms a circle, ellipse or polygon in plan view (where n is the number of vertices, and n is 3 or more), or so that the gap of the void portion changes.

9. The method for manufacturing a package for microwave heating according to claim 6 or 7, characterized in that the first step further includes step 1e of applying ink or laminating a film so as to form a dividing layer between the high brightness ink layer and the conductive heat generating layer.

10. A method for producing a package for microwave heating as claimed in claim 6 or 7, characterized in that in step 1a, two films are prepared as first and second base layers, and if the high-brightness ink layer is formed between the first and second base layers in step 1b, then in step 1c, the conductive heat-generating layer is laminated between the second base layer and the sealant layer, and if the high-brightness ink layer is formed between the second base layer and the sealant layer in step 1b, then the conductive heat-generating layer is laminated between the first and second base layers in step 1c.

Images