JP2022124281A - Microwave oven heating package with foaming ink and method for manufacturing the same - Google Patents

Abstract

To provide a microwave oven heating package that has an internal pressure adjustment function that automatically discharges water vapor when an internal pressure rises, and that can be used for various purposes such as boiling sterilization and hot water cooking.SOLUTION: A microwave oven heating package 100 includes at least a first sheet member 1. The first sheet member 1 is formed with a substrate layer 12, a sealant layer 13, and a weak adhesion layer 14 between the substrate layer 12 and the sealant layer 13, which is coated with foaming ink. The foaming ink contains thermally expandable microcapsules. A surface 14s of the weak adhesion layer 14 is an uneven surface in which the thermally expandable microcapsules are foamed. When the package 100 is heated, one layer of the substrate layer 12 or the sealant layer 13 adjacent to the surface 14s of the weak adhesion layer 14 is partially peeled from the other layer to form a vapor vent on the weak adhesion layer 14.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a package for microwave heating, and more specifically to a package for microwave heating provided with foaming ink and a method for producing the same.

(Issues related to package for microwave oven heating)
When foods sealed in a plastic package are cooked in a microwave oven or a steamer, the internal pressure of the package rises due to the expansion of water vapor generated by the heating of the food inside the package. As a result, problems such as deformation or bursting of the package may occur. In order to prevent such problems, when the pressure inside the package rises, part of the sealed part is broken to allow communication between the inside and the outside of the package, and the steam that causes the increase in internal pressure is automatically discharged. A package with an internal pressure adjustment function is required.

As a conventional technique for manufacturing a package having such an internal pressure adjusting function, it is known to partially reduce the heat seal strength at a portion to which the internal pressure is applied, as shown in Patent Documents 1 to 3, for example. It is

In the package disclosed in Patent Document 1, a substance that inhibits adhesion is applied to one of the front and back sealant layers and thermally welded to each other, so that the front and back sealant layers (that is, the front and back laminated films face each other) A weak adhesion layer is formed on a part of the thermally welded interface. Examples of substances that inhibit adhesiveness include silicon and inorganic substances such as silicon-based release agents.

However, in the prior art disclosed in Patent Document 1, there is a possibility that a substance inhibiting adhesiveness applied to the interface between the front and back laminated films facing each other may come into direct contact with, be exposed to, or be mixed into the inside of the package. , Cannot be used when the contents (sealed ingredients) are liquid.

In addition, in the package disclosed in Patent Document 2, only a portion of the sealed portion is heat-sealed at a lower temperature than the other portions without using a special substance to obtain a weak adhesive layer. This lowers the adhesive strength of the portion.

However, in the prior art disclosed in Patent Document 2, it is necessary to strictly control the heat-sealing temperature during the manufacture of the package, and changes occur in the production speed of the package (film feeding speed) and the environmental temperature of the production equipment. In such a case, there is a danger that the heat welding temperature to be applied to the weakly bonded portion, and thus the sealing strength, cannot be maintained at a desired value.

On the other hand, in the package disclosed in Patent Document 3, between the outer layer (base layer) and the inner layer (sealant layer) of the laminated film on one side, a resin having a melting point of 60 to 90 ° C. is used to adjust the laminate strength. forming layers. In other words, this package reduces the adhesive strength by causing cohesive peeling to occur in the laminate strength adjusting layer by heating with a microwave oven, and removes water vapor generated inside. Examples of resins having a melting point of 60 to 90° C. include polyamide-nitrocellulose resins.

However, the conventional technology disclosed in Patent Document 3 has the disadvantage that it cannot be used at temperatures exceeding the melting point of the resin constituting the laminate strength adjustment layer (for example, for applications such as boiling sterilization and hot water cooking).

JP 2007-284103 A JP-A-09-142541 JP 2007-217050 A JP 2020-082586 A

In this way, it is possible to handle both liquid and solid contents, and the seal strength is not easily affected by changes in the environmental temperature and production speed during the manufacture of the package. The inventors of the present invention have realized that there is a need for a package for microwave heating that can be used for various purposes such as cooking.

In other words, an object of the present invention is to provide a package for heating in a microwave oven, which has an internal pressure adjustment function that automatically discharges steam when the internal pressure rises, and which can be used for various purposes such as boiling sterilization and hot water cooking. is.

Another object of the present invention is to be able to package contents regardless of whether they are solid or liquid, and to provide a desired seal strength without being affected by changes in environmental temperature or production speed during manufacturing. An object of the present invention is to provide a package for heating in a microwave oven.

By the way, one of the applicants of the present application has already developed a non-slip package in which a foaming ink containing thermally expandable microcapsules is applied to the outermost surface of a laminated film (specifically, an outer layer (substrate layer)). proposed (see Patent Document 4). In the package of Patent Document 4, the thermally expandable microcapsules in the anti-slip layer are foamed by heat-treating (heat-sealing) the non-slip layer coated with foamable ink during the manufacture of the package. As a result, an uneven surface is formed on the non-slip layer, which is part of the outermost surface.

The non-slip package disclosed in Patent Document 4 is intended for products (for example, applications such as detergent refill pouches) that require easy gripping of a part of the package (for example, an extraction opening and an opening). It is created. In other words, in this package, since a non-slip layer (that is, uneven foam) is formed on the surface of the part to be gripped, even if you touch the gripping margin with a wet hand (Even if approached), it is possible to securely grip or open the relevant part without slipping.

The inventors of the present invention have found that the internal pressure automatic adjustment technology required for microwave oven heating packaging is achieved by relocating the foaming ink used for anti-slip technology on the surface of refill pouches as an internal structural member of the packaging. The inventors have found that this can also be used as a (steam venting technique), and have completed the present invention.

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,
The first sheet member includes a base material layer, a sealant layer, and a weakly adhesive layer formed by applying a foaming ink between the base material layer and the sealant layer,
The foamable ink contains thermally expandable microcapsules,
The surface of the weak adhesion layer forms an uneven surface in which the thermally expandable microcapsules are foamed,
The weak adhesive layer causes one layer of the base material layer or the sealant layer adjacent to the surface of the weak adhesive layer to be partially peeled off from the other layer when the package is heated. forming a steam vent,
A microwave oven heating package characterized by:
(Aspect 2)
The package for microwave heating further comprises a second sheet member or a tray container,
The sealant layer of the first sheet member is thermally welded to the peripheral edge of the second sheet member or the peripheral edge of the tray container,
The weak adhesion layer is provided by laminating a part of the heat-sealed sealant layer so that the part is used as a steam vent planned part,
The microwave oven heating package according to aspect 1, characterized by:
(Aspect 3)
An ink-unprinted portion to which the foamable ink is not applied is formed in the weak adhesion layer,
The ink-unprinted portion extends from the inner edge toward the outer edge of the weak adhesive layer so as to divide the planar area of the weak adhesive layer.
The package for microwave heating according to mode 1 or 2, characterized by:
(Aspect 4)
A first step of preparing a first sheet member;
a second step of providing a second sheet member or tray container;
a third step of heat-sealing the first sheet member and the second sheet member or the tray container;
A method for manufacturing a microwave oven heating package containing
The first step is
A step of preparing a film that serves as a base layer;
a step of partially forming a weak adhesion layer by applying foaming ink containing thermally expandable microcapsules to the inner surface side of the base material layer;
A step of preparing a film to be a sealant layer and further bonding and laminating it on the inner surface side of the base material layer;
including
The third step is
heat-sealing the sealant layer of the first sheet member to the peripheral edge of the second sheet member or the peripheral edge of the tray container;
a step of foaming the thermally expandable microcapsules during the thermal welding to form an irregular surface on the surface of the weak adhesion layer to weaken the seal strength in the vicinity of the weak adhesion layer;
and
The weak adhesion layer is provided by laminating a part of the heat-sealed sealant layer so as to serve as a steam vent planned part,
A method for manufacturing a package for heating in a microwave oven, characterized by:
(Aspect 5)
In the step of applying the foaming ink, the liquid containing 1 to 50% by mass of the thermally expandable microcapsules, 1 to 25% by mass of the thermoplastic resin, and 45 to 95% by mass of the solvent is used as the used as foaming ink,
A method for manufacturing a microwave oven heating package according to aspect 4, characterized in that:

In the package for microwave heating of the present invention, the foamable ink is applied to the inner surface of the laminate layer, and the thermally expandable microcapsules in the foamable ink are foamed by thermal welding to form an uneven surface. A weak bond layer is formed within the laminate layer (between the base layer and the sealant layer). As a result, the contents in the package are heated, steam is generated, and when the internal pressure of the accommodation space rises to a predetermined pressure, the weak adhesive layer having an uneven surface (that is, low seal strength) and its adjacent portion The stress difference of the shear force becomes remarkable at the boundary. Then, with this boundary portion as a base point, the weak adhesive layer begins to peel from the upper and lower laminate layers, and the laminate layer is also broken or peeled, and the accommodation space-sealant layer-weak adhesive layer-base layer-external space is communicated. A steam vent (communication path) is automatically formed to allow steam to escape to the outside of the package.

In the package for microwave heating of the present invention, the weak adhesive layer is printed on the inner layer that does not directly touch the contents (that is, between the base layer and the sealant layer), so the inner side of the sealant layer Contents (eg, foodstuffs) contained in the container usually do not come into contact with this weakly adhesive layer. Therefore, the package of the present invention can handle both liquid and solid contents.

Furthermore, according to the manufacturing method of the present invention, a weak adhesion layer containing foamable ink can be formed under a normal manufacturing environment (thermal welding process and thermal welding temperature), so that the seal strength is reduced to the environmental temperature at the time of production. It is possible to enjoy the benefits of being less susceptible to changes in packaging production speed.

In addition, since the melting point of the weak adhesive layer is at least higher than the normal heat welding temperature (110 to 160 ° C.), the package of the present invention can be used for various purposes such as boiling sterilization and hot water cooking. can also enjoy

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing and top view which showed the structure of the whole package of this invention (Example 1), and the enlarged sectional view which showed the structure of the one part (periphery part). It is a top view of the package of this invention (modification of Example 1), and the figure explaining arrangement|positioning of the ink printing part in a weak adhesion layer. 4 is a flow chart showing each step constituting the method for manufacturing the package of the present invention. It is a figure explaining the mechanism of peeling until the water vapor|steam generate|occur|produces in a package and escapes to the exterior. (a) and (b) are images showing the states of foamable ink before and after foaming, and (c) is an enlarged image of a portion (microcapsules) of FIG. 5(b). 4 is a graph showing the relationship between heat welding temperature and peel strength (Examples and Comparative Examples). It is sectional drawing and the top view which showed the structure of the whole package of this invention (Example 2), and the enlarged sectional view which showed the structure of the one part (periphery part).

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the embodiments shown in the drawings, but the present invention is not limited to the following specific embodiments. In addition, the same code|symbol is used for the member which is the same or respond|corresponds in each figure.

(Detailed description of each referenced drawing)
FIG. 1(a) is a schematic cross-sectional view showing a microwave oven heating package 100 (100A) (hereinafter also simply referred to as "package") according to Example 1. FIG. FIG.1(b) is the figure which showed the schematic plan view of 100 A of packages. FIG. 1(c) is a partially enlarged view showing a portion surrounded by a circle C (broken line) in FIG. 1(a). FIG. 2(a) is a schematic plan view of a packaging body 100B according to a modification of Example 1, and FIGS. It is a figure explaining. FIG. 3 is a flow chart showing each step constituting the method for manufacturing the package 100A of the present invention. FIGS. 4(a) to 4(e) are diagrams for explaining the peeling mechanism from the generation of water vapor ST in the package 100A to its escape to the outside. 5(a) and (b) are images showing the state of the foamable ink 15 before and after foaming, and FIG. 5(c) is an enlarged view of a portion (microcapsules 16) of FIG. 5(b). This is the image shown. FIG. 6 is a graph showing the relationship between the heat welding temperature TS and the peel strength PS.

(Outline of package (flat bag) according to Example 1)
A package 100A shown in Example 1 is in the form of a flat bag including a first sheet member 1 and a second sheet member 2. As shown in FIG. The first and second sheet members 1 and 2 are thermally welded (heat-sealed) at their peripheral edges 11 and 21 to form an internal space 4 in which the foodstuff 3 and the like are enclosed. In order to reliably enclose the foodstuff 3 in the package 100A, first, the package 100A forming a three-sided seal bag in which the three sides 11b to 11d of the peripheral portions 11 and 21 are heat-sealed is used. After stuffing the food material 3 into the internal space 4 from one side (for example, the upper side 11a described later) that is not heat-sealed, it is preferable to heat-seal this one side 11a (heat welding in FIG. 1(c) See weld surface HS).

(Formation of scheduled steam vent)
The peripheral edge portion 11 of the first sheet member 1 consists of four sides (that is, a top side 11a, a bottom side 11b, and left and right sides 11c and 11d). Of these, a part of the upper side 11a (central portion in the drawing) is formed with a planned steam vent portion 5 (see FIG. 1(b)).

(Cross-sectional structure of first sheet member)
FIG. 1(c) shows an enlarged view of the cross-sectional structure of the part having the planned steam vent 5. As shown in FIG. The first sheet member 1 includes a base layer 12 having heat resistance, a sealant layer 13 , and an adhesive layer (not shown) connecting the base layer 12 and the sealant layer 13 . Such laminated films made of different materials are also called multi-layer laminated films or laminated layers 12 and 13 . From the point of view of product sales, the substrate layer 12 may be formed of a plurality of layers (first and second substrate layers not shown). An adhesive layer or a printed layer may be further provided.

(Sectional structure of second sheet member)
The second sheet member 2 also has the same configuration as the first sheet member 1, and includes a base layer 22 having heat resistance, a sealant layer 23, and a base layer 22 and a sealant layer 23 (not shown) that connect the base layer 22 and the sealant layer 23. and an adhesive layer. From the viewpoint of product sales, the substrate layer 22 may be formed of a plurality of layers (first and second substrate layers not shown). An adhesive layer or a printed layer may be further provided.

(Weak adhesive layer provided on the first sheet member)
In this embodiment, only the first sheet member 1 has an adhesive layer (not shown) between the base layer 12 made of a stretched film and the sealant layer 13 made of a non-stretched film. Note that a weak adhesion layer 14 is also formed. When the multilayer laminate films 12 and 13 made of such different materials are stretched, between the base layer 12 that is a stretched film that is difficult to stretch and the sealant layer 13 that is a non-stretched film that is stretchable (specifically , a shear stress due to the difference in elongation occurs at the boundary line BL (see FIG. 1(c))). As in the present invention, by applying the weak adhesion layer 14 to a part of the boundary line BL where this stress difference occurs, the boundary B between the part where the weak adhesion layer 14 is not applied and the part where it is not applied A strong stress difference occurs at , and the upper and lower laminate layers 12 and 13 are likely to break (peel off) from the vicinity of the boundary B as a base point.

The weak adhesion layer 14 is provided on at least a portion of the peripheral portion 11 to be thermally welded. In particular, when the package 100A expands with steam during heating in a microwave oven, a weak adhesive layer is applied to a portion where a strong tensile stress is applied (for example, in the case of a three-sided seal bag, the center of one of the sides 11a to 11d of the peripheral portion 11). 14 is preferred. 1(b) shows an example in which the weak adhesive layer 14 is arranged only on one side 11a of the peripheral portion 11, but in the package 100B of FIG. 2(a), all of the peripheral portion 11 A modification is shown in which the weak adhesive layers 14 are arranged on the sides 11a to 11d, respectively.

2B to 2F are diagrams showing a printing area 15A of the foaming ink 15 (hereinafter also referred to as "ink printing part" or simply "printing part"), which is a component of the weak adhesion layer 14. FIG. be. FIG. 2B shows the case where the foaming ink 15 is applied all over the flat area of the weak adhesion layer 14 . Not limited to this example, when the weak adhesion layer 14 is observed in a plan view, a region where the foaming ink 15 is not applied so as to divide the plane area of the weak adhesion layer 14 (hereinafter referred to as an “ink unprinted portion” or simply It is preferable to arrange NPs (also called "unprinted areas") (see FIG. 2(c)). As a result, compared to the case where the foaming ink 15 shown in FIG. The length of the boundary B between 15A and the absent portion NP can be doubled, and as will be described later, locations where separation (communication between the internal space 4 and the external space) tend to occur when the internal pressure rises (exfoliation promotion locations). can be increased.

Specifically, as shown in FIG. 2(c), it is preferable to form an ink-unprinted portion NP having a lateral width W of 1 to 2 mm in the center of the ink-printed portion 15A in the horizontal direction. In this example, both the printed portion 15A and the unprinted portion NP extend over the entire width Ws (from the inner edge to the outer edge) of the thermally welded portion (peripheral edge portion 11). As a result, the length of the exfoliation-promoting portion is doubled.

However, the present invention is not limited to this example. For example, as shown in FIG. 2(d), the unprinted portion NP may be stretched halfway from the inner edge to the outer edge. The length of the exfoliation-promoting portion, which is the boundary B between the unprinted portion NP and the printed portion 15A, increases approximately 1 to 2 times (in the case of FIG. 2(d), approximately 1.5 times longer). The stretched length of the unprinted portion NP may be set within a range of 1 to 100% of the total width Ws of the thermally welded portion (peripheral portion 11). Moreover, the unprinted portion NP is not limited to one place, and may be arranged in a plurality of places as long as the print portion 15A can be divided in the horizontal direction (see also FIGS. 2(e) and 2(f)). As a result, the number of exfoliation-promoting locations can be further doubled.

Although the weak adhesive layer 14 having various embodiments described above is arranged on the first sheet member 1, the configuration is not limited to the above-described embodiments. For example, the weak adhesive layer 14 may also be formed on the second sheet member 2 side (that is, on both front and back sides).

As described above, the weak adhesion layer 14 can be formed by applying the foaming ink 15 to a portion of the peripheral portion 11 to be thermally welded. The weak adhesion layer 14 is preferably placed at a location where a strong tensile stress is applied when the food material 3 in the packaging body 100 is warmed and the packaging body 100 expands due to the pressure of the generated steam ST (Fig. 2(a) )).

(Material of base material layer)
As the material for the base material layers 12 and 22, it is desirable to use stretched film materials such as nylon, polypropylene, polyethylene terephthalate, and polybutylene terephthalate, but the materials are not limited to these.

(Material of sealant layer)
As the material of the sealant layers 13 and 23, it is desirable to use, for example, a non-stretched film material such as non-stretched polypropylene, but the material is not necessarily limited to this. In the present invention, the base layers 12, 22 and the sealant layers 13, 23, which constitute the laminate layers, have different elastic moduli (Young's moduli), respectively. A shear stress occurs at the line BL.

(Material of weak adhesion layer)
The weak adhesion layer 14 is a layer coated (printed) with foaming ink 15 . This foaming ink 15 is characterized by containing thermally expandable microcapsules 16 (hereinafter also simply referred to as "microcapsules"). Specifically, the foaming ink 15 is a liquid containing 1 to 50% by mass of the thermally expandable microcapsules 16, 1 to 25% by mass of the thermoplastic resin, and 45 to 95% by mass of the solvent. It is preferred to use

(Distribution ratio of thermally expandable microcapsules)
The thermally expandable microcapsules 16 preferably contain 1 to 50% by mass, more preferably 3 to 40% by mass. If the amount is less than the lower limit of 1% by mass, the foaming property (concavo-convex moldability) at the time of thermal welding is lowered, while if the upper limit of 50% by mass is exceeded, the adhesion to the substrate is deteriorated.

(Composition of thermally expandable microcapsules)
Thermally expandable microcapsules 16 are microcapsules made of thermoplastic resin such as vinyl chloride resin, ethylene vinyl acetate resin, acrylic resin, etc., and aliphatic carbonization such as isobutane, butane, isopentane, n-pentane. The microcapsules 16 contain hydrogen, and the contained aliphatic hydrocarbons are vaporized by heating to expand the microcapsules 16 . It is preferable that the microcapsules 16 have a particle diameter of 3 to 20 μm and an expansion ratio of 4 to 10 times.

(Change in shape of microcapsules after thermal welding)
Specifically, the microcapsules 16 are heated and expanded during heat welding in the manufacturing method of the package 100 to be described later, and the surface 14s of the weakly adhesive layer 14 containing the microcapsules 16 (the adjacent laminate layer 12, 13) is formed in an uneven shape.

(Allocation ratio of thermoplastic resin)
The thermoplastic resin content is preferably 1 to 25% by mass, more preferably 5 to 20% by mass. If the amount is less than the lower limit of 1% by mass, the adhesion to the substrate will be poor, while if the upper limit of 25% by mass is exceeded, the fluidity of the ink will be poor and the ink manufacturing suitability will be poor.

(Composition of thermoplastic resin)
Thermoplastic resins include, for example, nitrocellulose, cellulose acetylpropionate, polyamide resins, vinyl chloride-vinyl acetate copolymers, polyester resins, chlorinated polypropylene resins, (meth)acrylic resins, urethane resins, acrylic emulsions, urethane Although system emulsions and the like are preferred, they are not necessarily limited to these, and these resins may be used singly or in combination of two or more.

(Solvent distribution ratio)
The solvent content is preferably 45 to 95% by mass, more preferably 50 to 90% by mass. If the content is less than the lower limit of 45% by mass, the fluidity of the ink will be poor and the suitability for ink production will be inferior, while if the upper limit of 95% by mass is exceeded, the ink film thickness will be locally uneven, and the ink will not be formed on the printing surface. Amorphous shading (swimming phenomenon) may occur.

(Solvent composition)
The solvent is for dispersing the microcapsules 16 and the thermoplastic resin in the solvent. As this solvent, a known organic solvent type solvent can be used. preferable. These can be used alone or in combination of two or more.

(Method for manufacturing package)
FIG. 3 is a flow chart showing each step constituting the manufacturing method of the package 100A (100B) of the present invention. First, the first sheet member 1 that forms one side (for example, the surface) of the package 100A is prepared (first step S1). Also, a second sheet member 2 that forms the other side (for example, the back side) of the package 100A is prepared (second step S2). When the members 1 and 2 are prepared, the first sheet member 1 and the second sheet member 2 are laminated (heat-sealed) (third step S3). In another modification (see FIG. 7), the second sheet member 2 may be a tray container 6. FIG.

(Detailed description of the first step)
Here, in the first step S1, a stretched film to be the substrate layer 12 is prepared (step S11). In addition, the substrate layer 12 may be composed not only of a single layer made of a single film, but also of a multilayer (for example, two layers) in which a plurality of films are laminated. An inner layer (lamination) may be provided with an adhesive layer or a printed layer that serves as the package surface.

Microcapsules 16 are included on the inner surface side of the base material layer 12 (that is, the side close to the internal space 4 containing the food material 3 when the first and second sheet members 1 and 2 are heat-sealed). A foaming ink 15 is applied to partially form the weak adhesion layer 14 (step S12). Further, a non-stretched film to be the sealant layer 13 is prepared and laminated by adhering to the inner surface side of the base material layer 12 (step S13).

In the step S12 of applying the foamable ink 15, a liquid containing 1 to 50% by mass of the microcapsules 16, 1 to 25% by mass of the thermoplastic resin, and 45 to 95% by mass of the solvent is foamed. It is preferably used as ink 15 .

(Description of the second step)
The second sheet member 2 can also be manufactured in steps S21 to S23 similar to the steps S11 to S13 described above for manufacturing the first sheet member 1, so detailed description thereof will be omitted. Here, if there is no need to provide the weak adhesive layer 14 on the second sheet member 2 side, step S22 corresponding to step S12 may not be performed.

(Detailed explanation of the third step)
Here, in the third step S3, the peripheral edge portion 11 of the sealant layer 13 of the first sheet member 1 is thermally welded to the peripheral edge portion 21 of the sealant layer 23 of the second sheet member 2 (step S31). Then, in the thermal welding step S31, the microcapsules 16 are foamed to form the uneven surface 14s of the weak adhesion layer 14, thereby weakening (reducing) the sealing strength in the vicinity of the weak adhesion layer 14. (Step S32). At this time, the weak adhesion layer 14 is laminated on a part of the laminated layers 12 and 13 thermally welded to the upper and lower sides so as to form the part 5 intended for the steam vent.

When the third step S3 is finished, the package 100A is manufactured with the three sides 11b to 11d heat-sealed. After that, the desired foodstuff 3 is stuffed into the internal space 4 of the package 100A from the side 11a of the remaining open side (step S4). After the stuffing of the foodstuffs 3 is completed, the remaining sides 11a are also thermally welded to completely seal the internal space 4 (the foodstuffs 3 inside) of the package 100A (step S5).

(Peeling mechanism)
Next, the heating of the package 100A with a microwave oven is started, and the peeling mechanism from the generation of steam ST in the package 100A to its escape will be described with reference to FIG.

First, when the package 100A shown in FIG. 4(a) starts to be heated using a microwave oven, the food material 3 in the internal space 4 of the package 100A is warmed, and water vapor ST is generated as shown in FIG. 4(b). Then, the internal pressure of the internal space 4 increases. Naturally, this internal pressure is also applied to the thermally welded portion where the front and back first and second sheet members 1 and 2 are connected, as indicated by the arrows in FIG. 4(b). Since the base material layer 12 and the sealant layer 13 are made of different materials, their modulus of elasticity (Young's modulus) during tension is also different. Therefore, when the internal pressure increases and tensile stress is applied to each layer 12, 13, shear stress based on the tensile stress difference is generated between the laminate layers 12, 13 (boundary line BL).

Focusing on the interlayer (boundary line BL) between the base material layer 12 and the sealant layer 13, a weak adhesion layer 14 containing a foaming ink 15 is additionally applied (printed) to a part of these thermally welded portions. Therefore, even in the same interlayer BL, the portion with the weak adhesion layer 14 (ink printed portion 15A) has a higher adhesive strength with the upper and lower base layers 12 or sealant layers 13 than the portion without this (ink unprinted portion NP). is low, the weakly adhesive layer 14 begins to peel off from at least one of the laminate layers 12 and 13 with the boundary B as a starting point when subjected to the shearing force described above. That is, when the internal pressure of the internal space 4 increases, a gap G (peeling) occurs between the base material layer 12 and the sealant layer 13 near the weak adhesion layer 14 (see FIG. 4(c)).

On the other hand, even in the thermally welded portion, since the seal strength is relatively high in the ink-unprinted portion NP without the weak adhesive layer 14, separation between the base material layer 12 and the sealant layer 13 above and below hardly occurs. Therefore, a large stress change occurs at the boundary B between the ink-printed portion 15A and the ink-unprinted portion NP. enter. 4(d) indicates _a cut portion of the sealant layer 13. As shown in FIG.

The base material layer 12 immediately adjacent to the gap G also gradually becomes unable to withstand its own tensile strength alone and is cut or peeled off. Reference numeral _C2 in FIG. 4E indicates a cut portion (peeling portion) of the base layer 12 . Therefore, finally, the path CP formed by the cut portions C ₁ and C ₂ formed in the layers 12 and 13 and the gap G communicates the internal space 4 with the outside. Vapor ST in the internal space 4 escapes to the outside through the communication path CP.

(Prototype of weak adhesion layer and observation of microcapsules before and after foaming)
100 A of packages of this invention were produced by performing the above-mentioned manufacturing method. 5(a) and (b) are images showing the state of the foamable ink 15 before and after the thermal welding step S31 (foaming), and FIG. 5(c) is a part of FIG. 5(b). This is an enlarged image. As shown in FIG. 5(c), it can be observed that each of the microcapsules 16 is foamed over one surface (surface 14s of the weak adhesion layer 14) due to the heat welding described above. As a result, the surface 14s of the weak adhesion layer 14 forms an uneven surface in which a large number of spheres are randomly arranged. (also referred to as "seal strength") can be weakened compared to the seal strength of the portion where the weak adhesive layer 14 is not applied (ink-unprinted portion NP).

(Conventional package and package of the present invention)
Next, both the package 100A of the present invention (Example) and the conventional package (Comparative Example) were produced. At this time, the thermal welding temperature TS (also called "sealing temperature") set in the thermal welding step S31 is changed (every 5°C within the range of 110 to 160°C) to prepare samples of each package. I tried to. Also in the case of the examples and comparative examples, at least three bags were prepared as test samples under each temperature TS condition. The package of the comparative example differs from the package 100A of the embodiment only in that the weak adhesive layer 14 is not provided between the laminate layers 12 and 13, and the other configurations (bag shape, size, material, etc.) It is the same as the example.

After that, the peel strength PS of the packages of Examples and Comparative Examples heat-sealed at each sealing temperature TS was measured. Specifically, a tensile force was applied so as to separate the thermally welded surfaces HS of the first and second sheet members 1 and 2 from each other, and the tensile strength leading to peeling was recorded as the peel strength PS. The results are shown in Table 1 below and FIG. Each value shown in Table 1 is an average value of measured values obtained from a plurality of samples under the same temperature TS conditions.

Observing these peel strengths PS, in the conventional package (comparative example), the sample made at the heat welding temperature TS of 110 ° C. has a low peel strength PS of 1.43 kgf / 15 mm, but the temperature TS is further increased. The peel strength PS of the samples produced at a high setting rises sharply as the temperature setting increases, and settles at about 7 kgf/15 mm for the samples produced at a temperature TS of 130° C. or higher.

On the other hand, in the package 100A (weak adhesive layer 14) of the example, the sample made at the heat welding temperature TS of 110°C has a slightly low peel strength PS of 1.34 kgf/15 mm, but the peel strength PS is 115°C or higher. The peel strength PS is about 2 kgf/15 mm for the sample 100A manufactured under the heat welding temperature TS, and it can be seen that the peel strength PS remains constant over a wide temperature range.

From these measurement results, (1) even if the package 100A of the present invention is manufactured by changing the thermal welding temperature TS conditions by nearly 50° C., it is found that the peel strength PS remains constant with little change. rice field. As a result, even if the environmental temperature, the heat welding temperature, and the film feeding speed cannot be strictly controlled at the package manufacturing site, the package 100A (weak adhesive layer 14) of the present invention to be manufactured can be obtained by these factors. It can be said that the desired peel strength (automatic adjustment function of internal pressure) is always provided (exhibited) without being affected by

Also, when these measurement results are quantitatively observed, (2) the weak adhesion layer 14 of the present invention produced by setting the thermal welding temperature TS to 115° C. or higher does not adhere to conventional products (ordinary laminate layer adhesion). It has become clear that the peel strength PS can be suppressed to less than 30% compared to . It should be noted that the lower the peel strength PS, the better. Since there is a concern that the steam generated in the internal space 4 may not sufficiently steam the food 3, the peel strength PS indicated by the experimental results is considered desirable (just right) from the viewpoint of steaming the food 3 as well.

Furthermore, (3) the weak adhesion layer 14 of the present invention was found to be stably formed in the laminate layers 12 and 13 without melting even at a heat-sealing temperature TS of 160°C or lower. In other words, it was found that the melting point of the weak adhesion layer 14 is at least higher than the normal thermal welding temperature TS. For this reason, the packaging body 100A of the present invention can be used without problems in applications such as boiling sterilization and hot water cooking, which are placed in a high-temperature environment.

Thus, in the packaging body 100A of the present invention, the low peel strength PS is always exhibited in the vicinity of the weak adhesive layer 14, and the adhesive strength of the heat-sealed portions other than this portion remains as high as in the conventional product. Therefore, it can be said that when the internal pressure rises due to heating in a microwave oven, steam can always escape from the vicinity of the weak adhesion layer 14 . Therefore, by simply selecting the application of the weak adhesive layer 14, the vapor vent can be placed at the desired location.

FIG. 7(a) is a schematic cross-sectional view showing a microwave oven heating package 100 (100C) according to Example 2. FIG. FIG.7(b) is the figure which showed the schematic plan view of 100 C of packaging bodies. FIG. 7(c) is a partially enlarged view showing a portion surrounded by a circle C (broken line) in FIG. 7(a).

(Outline of package (tray pack) according to Example 2)
A packaging body 100C shown in the second embodiment is in the form of a tray pack including the first sheet member 1 and the tray container 6 as shown in the first embodiment. The configuration of Example 2 differs only in that a tray container 6 is used in place of the second sheet member 2 of Example 1, and other configurations are substantially the same as those of Example 1. Description of the part is omitted.

In this second embodiment, the first sheet member 1 and the tray container 6 are thermally welded (heat-sealed) at their peripheral edge portions 11 and 61 to form an internal space 4 in which the foodstuff 3 and the like are enclosed. The peripheral edge portion 11 of the first sheet member 1 also consists of four sides (that is, a top side 11a, a bottom side 11b, and left and right sides 11c and 11d) as in the first embodiment. Of these, a part of the upper side 11a (central part in the drawing) is formed with a planned steam vent portion 5 through which a steam vent is generated during microwave cooking. That is, the sealant layer 13 of the peripheral edge portion 11 of the first seal member 1 is heat-sealed to the upper surface of the peripheral edge portion 61 of the tray container 6 (see the heat-sealed surface HS in FIG. 7(c)), but the weak adhesive layer The region of the laminate layers 12 and 13 near 14 becomes the steam vent planned portion 5, and when heated in a microwave oven, the vicinity of the weak adhesive layer 14 (specifically, the boundary B), which has a relatively low peel strength, is used as a base point, The region 5 is peeled off to form a vapor vent (communication path).

(Other Modifications of Seal Form of Package)
As described above, the package 100 of the present invention has been described based on the first and second embodiments shown in the drawings, but the present invention is not necessarily limited to these examples without departing from the scope of the present invention. In Examples 1 and 2, the packaging bodies 100A, 100B, and 100C of flat bags and tray packs were used. A weak adhesion layer 14 (foamable ink 15) can be formed.

In the microwave oven heating package of the present invention, the foaming ink is applied to the inner surface of the laminate layer, and the thermally expandable microcapsules in the foaming ink are foamed by thermal welding to form an uneven surface. A weak bond layer is formed within the laminate layer (between the base layer and the sealant layer). As a result, the contents in the package are heated, steam is generated, and when the internal pressure of the accommodation space rises to a predetermined pressure, the weak adhesive layer having an uneven surface (that is, low seal strength) and its adjacent portion The stress difference of the shear force becomes remarkable at the boundary. Then, with this boundary portion as a base point, the weak adhesion layer begins to peel from the upper and lower laminate layers, and the laminate layer is also broken or peeled, and the accommodation space-sealant layer-weak adhesion layer-base layer-external space is communicated. A steam vent (communication path) is automatically formed to allow steam to escape to the outside of the package.

In the package for microwave heating of the present invention, the weak adhesive layer is printed on the inner layer that does not directly touch the contents (that is, between the base layer and the sealant layer), so the inner side of the sealant layer Contents (eg, foodstuffs) contained in the container usually do not come into contact with this weakly adhesive layer. Therefore, the package of the present invention can handle both liquid and solid contents.

Furthermore, according to the manufacturing method of the present invention, a weak adhesion layer containing foamable ink can be formed under a normal manufacturing environment (thermal welding process and thermal welding temperature), so that the seal strength is reduced to the environmental temperature at the time of production. It is possible to enjoy the benefits of being less susceptible to changes in packaging production speed.

In addition, since the melting point of the weak adhesive layer is at least higher than the normal heat welding temperature (110 to 160 ° C.), the package of the present invention can be used for various purposes such as boiling sterilization and hot water cooking. can also enjoy

The package and its manufacturing method of the present invention exhibiting such remarkable effects cannot be found in the package industry or market, and have very high industrial utility value and industrial applicability.

REFERENCE SIGNS LIST 1 first sheet member 2 second sheet member 3 foodstuff 4 internal space 5 planned steam vent 6 tray container 11, 11a, 11b, 11c, 11d, peripheral edge of first sheet member 12 base layer of first sheet member (one of the laminate layers)
13 Sealant layer of the first sheet member (one of the laminate layers)
14, 14s Weak adhesion layer, surface of weak adhesion layer 15, 15A Foaming ink, ink-printed portion 16 Thermally expandable microcapsules 21 Peripheral portion of second sheet member 22 Base layer of second sheet member (one of laminate layers one)
23 Sealant layer of the second sheet member (one of the laminate layers)
61 Peripheral portion of tray container 100, 100A, 100B, 100C Package body of the present invention (example) HS Heat-welded surface B Boundary between the weakly adhesive layer in the heat-welded portion and the other unprinted portion BL Laminate layer (base Boundary line between material layer and sealant layer) C ₁ , C ₂ sealant layer cut part, base layer cut part (peeling part)
CP Passage that communicates between the inner space and the outside of the package G Gap generated between the laminate layers when peeled HS Heat-sealed surface NP Unprinted area PS Peel strength (seal strength)
ST Water vapor TS Thermal welding temperature (sealing temperature)
W Width of unprinted area Ws Full width of heat-sealed area (periphery)

Claims (5)

A package for microwave heating comprising a first sheet member,
The first sheet member includes a base material layer, a sealant layer, and a weakly adhesive layer formed by applying a foaming ink between the base material layer and the sealant layer,
The foamable ink contains thermally expandable microcapsules,
The surface of the weak adhesion layer forms an uneven surface in which the thermally expandable microcapsules are foamed,
The weak adhesive layer causes one layer of the base material layer or the sealant layer adjacent to the surface of the weak adhesive layer to be partially peeled off from the other layer when the package is heated. forming a steam vent,
A microwave oven heating package characterized by: The package for microwave heating further comprises a second sheet member or a tray container,
The sealant layer of the first sheet member is thermally welded to the peripheral edge of the second sheet member or the peripheral edge of the tray container,
The weak adhesion layer is provided by laminating a part of the heat-sealed sealant layer so that the part is used as a steam vent planned part,
The microwave oven heating package according to claim 1, characterized in that: An ink-unprinted portion to which the foamable ink is not applied is formed in the weak adhesion layer,
The ink-unprinted portion extends from the inner edge toward the outer edge of the weak adhesive layer so as to divide the planar area of the weak adhesive layer.
The microwave oven heating package according to claim 1 or 2, characterized in that: A first step of preparing a first sheet member;
a second step of providing a second sheet member or tray container;
a third step of heat-sealing the first sheet member and the second sheet member or the tray container;
A method for manufacturing a microwave oven heating package containing
The first step is
A step of preparing a film that serves as a base layer;
a step of partially forming a weak adhesion layer by applying foaming ink containing thermally expandable microcapsules to the inner surface side of the base material layer;
A step of preparing a film to be a sealant layer and further bonding and laminating it on the inner surface side of the base material layer;
including
The third step is
heat-sealing the sealant layer of the first sheet member to the peripheral edge of the second sheet member or the peripheral edge of the tray container;
a step of foaming the thermally expansible microcapsules during the thermal welding to form an uneven surface on the surface of the weak adhesion layer to weaken the seal strength in the vicinity of the weak adhesion layer;
and
The weak adhesion layer is provided by laminating a part of the heat-sealed sealant layer so that the part is used as a steam vent planned part,
A method for manufacturing a package for heating in a microwave oven, characterized by: In the step of applying the foaming ink, a liquid containing 1 to 50% by mass of the thermally expandable microcapsules, 1 to 25% by mass of the thermoplastic resin, and 45 to 95% by mass of the solvent is used. used as foaming ink,
5. The method for producing a package for microwave heating according to claim 4, characterized in that:

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