JP7429014B2 - Microwave heating package with foamable ink and manufacturing method thereof - Google Patents

Description

The present invention relates to a package for heating in a microwave oven, and more specifically to a package for heating in a microwave oven provided with foamable ink and a method for manufacturing the same.

(Issues with microwave heating packaging)
When food sealed in a plastic package is cooked in a microwave oven, a steamer, etc., the internal pressure of the package increases due to the expansion of water vapor generated when the food inside the package warms. This causes problems such as the package being deformed or bursting. In order to prevent these problems, when the pressure inside the package increases, a part of the seal is broken to connect the inside and outside of the package, and the water vapor that causes the increase in internal pressure is automatically discharged. A packaging body with an internal pressure adjustment function is required.

As a conventional technique for manufacturing a package body having such an internal pressure adjustment function, for example, as shown in Patent Documents 1 to 3, it is known that the heat sealing strength is partially reduced at locations where internal pressure is applied. It is being

In the package disclosed in Patent Document 1, by applying a substance that inhibits adhesion to either the front or back sealant layers and thermally welding them to each other, the gap between the front and back sealant layers (in other words, the front and back laminated films are facing each other) is created. A weak adhesive layer is formed on a part of the thermally welded interface. Note that silicon such as a silicon-based mold release agent, inorganic substances, and the like are exemplified as substances that inhibit adhesion.

However, in the conventional technology disclosed in Patent Document 1, there is a possibility that a substance that inhibits adhesion 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 if the contents (sealed food) are liquid.

In addition, in the package disclosed in Patent Document 2, without using a special substance to obtain a weak adhesive layer, only a part of the sealed area is thermally welded at a lower temperature than other parts. The adhesive strength of this part is lowered.

However, in the conventional technology disclosed in Patent Document 2, it is necessary to strictly control the thermal welding temperature during the production of the package, which causes changes in the production rate (film feeding speed) of the package and the environmental temperature of the production equipment. In such a case, there is a risk that the heat welding temperature and seal strength that should be applied to weakly bonded areas cannot be maintained at desired values.

On the other hand, in the package disclosed in Patent Document 3, between the outer layer (base material layer) and inner layer (sealant layer) of the laminated film on one side, there is a laminate strength adjusting layer made of a resin having a melting point of 60 to 90°C. forming layers. In other words, this package is heated in a microwave oven to cause cohesive peeling in the laminate strength adjusting layer, thereby reducing the adhesive strength and removing the water vapor generated inside. Note that examples of resins having a melting point of 60 to 90°C include polyamide-nitrified cotton-based resins.

However, the conventional technique 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 purposes such as boiling sterilization and hot water cooking).

Japanese Patent Application Publication No. 2007-284103 Japanese Patent Application Publication No. 09-142541 Japanese Patent Application Publication No. 2007-217050 JP2020-082586A

In this way, it can handle both liquid and solid contents, and its sealing strength is less affected by changes in the environmental temperature and production speed during package manufacturing, and it can be sterilized by boiling or boiling in hot water. The inventors of the present invention have realized that there is a need for a microwave heating package that can be used for various purposes such as cooking.

That is, an object of the present invention is to provide a microwave heating package that has an internal pressure adjustment function that automatically discharges water vapor when the internal pressure rises, and that can be used for various purposes such as boil sterilization and hot water cooking. It 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 desired sealing 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 has already developed an anti-slip package in which a foamable ink containing thermally expandable microcapsules is applied to the outermost surface of a laminated film (specifically, the outer layer (base layer)). (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 (thermally welding) the anti-slip layer coated with foamable ink during manufacturing of the package. As a result, an uneven surface is formed on the anti-slip layer, which is a portion of the outermost surface.

The anti-slip package disclosed in Patent Document 4 is intended for products (for example, applications such as detergent refill pouches) that require easy grip of a part of the package (for example, the extraction opening or opening). It was created. In other words, this package has an anti-slip layer (i.e., textured foam) formed on the surface of the area where the grip area should be, so even if you touch the grip area with wet hands. (Even when approached), the part can be reliably grasped or opened without slipping.

The present inventors have discovered that if the foaming ink used for anti-slip technology on the surface of refill pouches is relocated as an internal structural member of the package, the internal pressure automatic adjustment technology required for microwave heating packages can be achieved. We have discovered that this can also be used as a (steam release technique), and have completed the present invention.

That is, the present invention employs, for example, the following configurations and features.
(Aspect 1)
A microwave oven heating package including a first sheet member,
A base material layer, a sealant layer, and a weak adhesive layer coated with foamable ink between the base material layer and the sealant layer are formed on the first sheet member,
The foamable ink includes thermally expandable microcapsules,
The surface of the weak adhesive layer forms an uneven surface in which the thermally expandable microcapsules are foamed by thermal welding ,
When the package is heated, the weak adhesive layer partially covers one of the base layer or the sealant layer adjacent to the surface of the weak adhesive layer, starting from the uneven surface. peeling off from the other layer to form a vapor vent;
A package for heating in a microwave oven, characterized by:
(Aspect 2)
The microwave heating package further includes 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 adhesive layer is provided by being laminated on a part of the heat-welded sealant layer so that the part is a planned steam outlet part.
The microwave heating package according to aspect 1, characterized in that:
(Aspect 3)
An ink-unprinted area where the foamable ink is not applied is formed in the weak adhesive layer,
The unprinted ink portion extends from the inner edge of the weak adhesive layer toward the outer edge so as to divide the planar area of the weak adhesive layer.
The microwave heating package according to aspect 1 or 2, characterized in that:
(Aspect 4)
A first step of preparing a first sheet member;
A second step of preparing a second sheet member or a tray container;
a third step of thermally welding the first sheet member and the second sheet member or the tray container;
A method for producing a package for heating in a microwave oven, the method comprising:
The first step is
A step of preparing a film to serve as a base layer;
partially forming a weak adhesive layer by applying foaming ink containing thermally expandable microcapsules to the inner surface of the base layer;
a step of preparing a film to serve as a sealant layer and further adhering and laminating it on the inner surface side of the base layer;
including;
The third step is
thermally welding 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;
during the thermal welding, foaming the thermally expandable microcapsules to form the surface of the weak adhesive layer into an uneven surface to weaken the seal strength near the weak adhesive layer;
including, and
The weak adhesive layer is provided by being laminated on a part of the heat-welded sealant layer so that the part is a planned steam outlet part.
A method for producing a package for heating in a microwave oven, characterized in that:
(Aspect 5)
In the step of applying the foamable 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 added to the liquid. used as foaming ink,
The method for producing a package for heating in a microwave oven according to aspect 4.

In the microwave oven heating package 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, thereby forming an uneven surface. A weak adhesive layer is formed within the laminate layer (between the base layer and the sealant layer). As a result, the contents inside the package are heated, water vapor is generated, and the internal pressure of the storage space rises to a predetermined pressure. At the boundary, the stress difference in shear force becomes significant. Then, starting from this boundary, the weak adhesive layer begins to peel off from the upper and lower laminate layers, and the laminate layer also breaks or peels off, creating communication between the housing space, the sealant layer, the weak adhesive layer, the base material layer, and the external space. A steam vent (communication path) is automatically formed to allow steam to escape to the outside of the package.

In the microwave heating package of the present invention, the weak adhesive layer is printed on the inner layer that does not come into direct contact with the contents (that is, between the base layer and the sealant layer), so it is further inside than the sealant layer. The contents contained therein (for example, foodstuffs) do not normally come into contact with this weakly adhesive layer. Therefore, the package of the present invention can accommodate either liquid or solid contents.

Furthermore, according to the manufacturing method of the present invention, a weak adhesive layer containing foamable ink can be formed under the normal manufacturing environment (thermal welding process and thermal welding temperature), so that the seal strength is lower than the environmental temperature at the time of manufacturing. This provides the benefit 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. You can also enjoy it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view and a plan view showing the structure of the entire package of the present invention (Example 1), and an enlarged cross-sectional view showing the structure of a part (periphery) thereof. FIG. 2 is a plan view of a package according to the present invention (a modification of Example 1), and a diagram illustrating the arrangement of ink-printed parts within a weak adhesive layer. 1 is a flowchart showing each step constituting the method for manufacturing a package according to the present invention. FIG. 3 is a diagram illustrating a peeling mechanism in which water vapor inside the package is generated and escapes to the outside. (a) and (b) are images showing the state of the foamable ink before and after foaming, and (c) is an enlarged image of a part (microcapsule) of FIG. 5(b). It is a graph showing the relationship between thermal welding temperature and peel strength (Examples and Comparative Examples). They are a sectional view and a plan view showing the structure of the entire package of the present invention (Example 2), and an enlarged sectional view showing the structure of a part (periphery) thereof.

The present invention will be described below based on embodiments shown in the drawings, but the present invention is not limited to the specific embodiments described below. Note that the same reference numerals are used for the same or corresponding members in each figure.

(Detailed explanation of each drawing to be referred to)
FIG. 1A is a schematic cross-sectional view showing a microwave heating package 100 (100A) (hereinafter also simply referred to as a "package") according to Example 1. FIG. 1(b) is a diagram showing a schematic plan view of the package 100A. 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 package 100B according to a modification of Example 1, and FIGS. 2(b) to 2(f) show the arrangement of an ink-printed portion 15A within a weak adhesive layer 14, which will be described later. FIG. FIG. 3 is a flowchart showing each step of the method for manufacturing the package 100A of the present invention. FIGS. 4A to 4E are diagrams illustrating a peeling mechanism in which water vapor ST within the package 100A is generated and escapes 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 part (microcapsules 16) of FIG. 5(b). This is the image shown. FIG. 6 is a graph showing the relationship between thermal welding temperature TS and peel strength PS.

(Outline of the package (flat bag) according to Example 1)
The 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. 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 food 3 and the like are sealed. In order to reliably enclose the foodstuff 3 in the package 100A, first use the package 100A which forms a three-sided sealed bag in which three sides 11b to 11d of the peripheral edges 11 and 21 are heat-welded. , it is preferable to heat-weld (seal) this side 11a after stuffing the food 3 into the internal space 4 from one side that is not heat-welded (for example, the upper side 11a described later) (the heat-welded side 11a in FIG. 1(c) (See welding surface HS).

(Formation of planned steam outlet)
The peripheral portion 11 of the first sheet member 1 consists of four sides (namely, the top side 11a, the bottom side 11b, and the left and right sides 11c, 11d). Of these, a portion of the upper side 11a (the central portion in the figure) is formed with a planned steam vent portion 5, which serves as a vent through which the steam ST inside the package 100A escapes to the outside during microwave cooking (see the figure). 1(b)).

(Cross-sectional structure of first sheet member)
FIG. 1(c) shows an enlarged cross-sectional structure of a portion having this planned steam outlet portion 5. As shown in FIG. The first sheet member 1 includes a base material layer 12 having heat resistance, a sealant layer 13, and an adhesive layer (not shown) connecting the base material layer 12 and the sealant layer 13. A film in which films made of different materials are laminated in this manner is also called a multilayer laminate film or laminate layers 12 and 13. In addition, from the viewpoint of product sales, the base material layer 12 may be formed of a plurality of layers (first and second base material layers not shown), and between the first and second base material layers, An adhesive layer or a printed layer may be further provided.

(Cross-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 heat-resistant base material layer 22, a sealant layer 23, and a layer (not shown) that connects the base material layer 22 and the sealant layer 23. An adhesive layer. In addition, from the viewpoint of product sales, the base material layer 22 may be formed of a plurality of layers (first and second base material layers not shown), and between the first and second base material layers, An adhesive layer or a printed layer may be further provided.

(Weak adhesive layer installed on the first sheet member)
In addition, in this embodiment, only in the first sheet member 1, in addition to an adhesive layer (not shown), there is provided a layer 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 adhesive layer 14 is also formed. When the multilayer laminate films 12 and 13 made of such different materials are stretched, there is a gap between the base layer 12, which is a stretched film that does not stretch easily, and the sealant layer 13, which is an unstretched film that stretches easily (specifically, , shear stress is generated on the boundary line BL (see FIG. 1(c)) due to the difference in elongation. As in the present invention, by applying the weak adhesive layer 14 to a part of the boundary line BL where this stress difference occurs, the boundary B between the part where the weak adhesive layer 14 is not applied and the part where the weak adhesive layer 14 is not applied is formed. A strong stress difference occurs, and the upper and lower laminate layers 12 and 13 tend to break (separate) starting from the vicinity of this boundary B.

The weak adhesive layer 14 is provided on at least a portion of the peripheral portion 11 to be thermally welded. Particularly, when the package 100A is expanded by water vapor during heating in a microwave oven, a weak adhesive layer is applied to a place where a strong tensile stress is applied (for example, in the case of a three-sided sealed bag, the center of any side 11a to 11d of the peripheral edge 11). It is preferable to arrange 14. Although the package 100A in FIG. 1(b) shows an example in which the weak adhesive layer 14 is arranged only on one side 11a of the peripheral edge 11, in the package 100B in FIG. A modification example is shown in which weak adhesive layers 14 are arranged on the sides 11a to 11d, respectively.

FIGS. 2(b) to 2(f) are diagrams showing a printing area 15A (hereinafter also referred to as an "ink printing section" or simply "printing section") of the foamable ink 15, which is a component of the weak adhesive layer 14. be. FIG. 2(b) shows a case where the foamable ink 15 is applied all over the entire planar area of the weak adhesive layer 14. Not limited to this example, when observing the weak adhesive layer 14 in a plan view, areas where the foamable ink 15 is not applied (hereinafter referred to as "unprinted ink areas" or simply It is preferable to arrange NP (also referred to as "unprinted part") (see FIG. 2(c)). As a result, compared to the case where the foamable ink 15 is applied solidly as shown in FIG. The length of the boundary B between 15A and the missing part NP can be doubled, and as will be described later, a location where peeling (communication between the internal space 4 and the external space) is likely to occur when internal pressure increases (a location where peeling is promoted) can be increased.

Specifically, as shown in FIG. 2(c), it is preferable to form an ink-unprinted portion NP having a width W of 1 to 2 mm at the center in the left-right direction of the ink-printed portion 15A. In this example, both the printed portion 15A and the unprinted portion NP extend over the entire width Ws of the heat-welded portion (periphery portion 11) (from the inner edge to the outer edge). As a result, the length of the area where peeling is promoted is doubled.

However, the present invention is not limited to this example, and for example, as shown in FIG. 2D, the stretching of the unprinted portion NP may end on the way from the inner edge to the outer edge. The length of the area where peeling is promoted, which is the boundary B between the unprinted area NP and the printed area 15A, increases by about 1 to 2 times (about 1.5 times or more in the case of FIG. 2(d)). Note that the stretched length of the unprinted portion NP may be set within a range of 1 to 100% with respect to the full width Ws of the heat-welded portion (peripheral portion 11). Further, the unprinted portion NP may be arranged not only at one location but at multiple locations as long as the printing section 15A can be divided in the horizontal direction (see also FIGS. 2(e) and 2(f)). Thereby, the number of locations where peeling is promoted can be further doubled.

Although it has been shown that the weak adhesive layer 14 having various embodiments is disposed on the first sheet member 1, the structure is not limited to the above embodiments. For example, the weak adhesive layer 14 may also be formed on the second sheet member 2 side (that is, on both the front and back sides).

As described above, this weak adhesive layer 14 can be formed by applying foamable ink 15 to a part of the peripheral edge 11 to be thermally welded. The weak adhesive layer 14 is preferably arranged at a location where tensile stress is strongly applied when the food material 3 inside the package 100 is heated and the package 100 expands under the pressure of the generated water vapor ST (see FIG. 2(a) ).

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

(Material of sealant layer)
Further, as the material for 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 thereto. In the present invention, the base material layers 12, 22 and the sealant layers 13, 23, which constitute the laminate layer, have different elastic modulus (Young's modulus), and due to the difference in elastic modulus, the boundary between them when the internal pressure increases A shear stress is generated in the line BL.

(Material of weak adhesive layer)
Furthermore, the weak adhesive layer 14 is a layer coated (printed) with foamable ink 15. This foamable ink 15 is characterized in that it contains thermally expandable microcapsules 16 (hereinafter also simply referred to as "microcapsules"). Specifically, the foamable ink 15 is a liquid containing 1 to 50% by mass of thermally expandable microcapsules 16, 1 to 25% by mass of a thermoplastic resin, and 45 to 95% by mass of a solvent. It is preferable 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. This is because if the content is less than the lower limit of 1% by mass, the foamability during heat welding (concave-convex formability) will be reduced, while if it exceeds the upper limit of 50% by mass, the adhesion to the substrate will be poor.

(Composition of thermally expandable microcapsules)
Thermal expandable microcapsules 16 are microcapsules made of thermoplastic resin such as vinyl chloride resin, ethylene vinyl acetate resin, or acrylic resin, and carbonized aliphatic resin such as isobutane, butane, isopentane, n-pentane, etc. The microcapsules 16 are encapsulated with hydrogen, and when heated, the encapsulated aliphatic hydrocarbons are vaporized and the microcapsules 16 are expanded. The particle size of the microcapsules 16 is preferably 3 to 20 μm, and the expansion ratio is preferably 4 to 10 times.

(Change in shape of microcapsules after heat welding)
Specifically, the microcapsules 16 are heated and expanded during thermal welding in the manufacturing method of the package 100 described below, and the surface 14s of the weak 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 is preferably contained in an amount of 1 to 25% by mass, more preferably 5 to 20% by mass. If it is less than the lower limit of 1% by mass, the adhesion to the substrate will be poor, while if it exceeds the upper limit of 25% by mass, the fluidity of the ink will be poor and the suitability for ink production will be poor.

(Composition of thermoplastic resin)
Examples of thermoplastic resins include nitrified cotton, cellulose acetyl propionate, polyamide resin, vinyl chloride-vinyl acetate copolymer, polyester resin, chlorinated polypropylene resin, (meth)acrylic resin, urethane resin, acrylic emulsion, and urethane. Although emulsions and the like are preferred, these resins are not necessarily limited to these, and these resins may be used alone or in combination of two or more types.

(Solvent distribution ratio)
The content of the solvent is preferably 45 to 95% by mass, more preferably 50 to 90% by mass. If it is less than the lower limit of 45% by mass, the fluidity of the ink will deteriorate and the suitability for ink production will be poor, while if it exceeds the upper limit of 95% by mass, the ink film thickness will become locally non-uniform and the ink will become uneven on the printing surface. There is a risk that irregularly shaped shading (swimming phenomenon) may occur.

(Solvent composition)
The solvent is one in which the above-mentioned microcapsules 16 and thermoplastic resin are dispersed. As this solvent, known organic solvent type solvents can be used, but from the viewpoint of printability and versatility, for example, toluene, ethyl acetate, n-propyl acetate, isopropyl alcohol, propylene glycol monomethyl ether, methyl ethyl ketone, etc. are preferred. preferable. These can be used alone or in combination of two or more.

(Method for manufacturing packaging)
FIG. 3 is a flowchart showing each step of the method for manufacturing the package 100A (100B) of the present invention. First, the first sheet member 1 that will constitute one side (for example, the front surface) of the package 100A is prepared (first step S1). Further, the second sheet member 2 that will constitute the other surface (for example, the back surface) of the package 100A is prepared (second step S2). When each member 1, 2 is ready, the first sheet member 1 and the second sheet member 2 are laminated (thermally welded) (third step S3). Note that in another modification (see FIG. 7), the second sheet member 2 may be a tray container 6.

(Detailed explanation of the first step)
Here, in the first step S1, a stretched film that will become the above-mentioned base material layer 12 is prepared (step S11). Note that the base material layer 12 may be composed of not only a single layer made of a single film but also a multilayer (for example, two layers) made by laminating a plurality of films, and an adhesive made of adhesive is used between the layers. An adhesive layer or a printed layer serving as the package surface may be an inner layer (laminated).

Microcapsules 16 are contained on the inner surface side of this 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-welded). A foaming ink 15 is applied to partially form a weak adhesive layer 14 (step S12). Furthermore, an unstretched film that will become the sealant layer 13 is prepared, and is adhered and laminated on the inner surface side of the base material layer 12 (step S13).

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

(Explanation of the second step)
Note that the second sheet member 2 can also be manufactured in the same steps S21 to S23 as the above-described steps S11 to S13 for manufacturing the first sheet member 1, so a detailed explanation will be omitted. Here, if there is no need to provide the weak adhesive layer 14 on the side of the second sheet member 2, it is not necessary to perform step S22 corresponding to the above step S12.

(Detailed explanation of the third step)
Here, in the third step S3, the peripheral edge 11 of the sealant layer 13 of the first sheet member 1 is thermally welded to the peripheral edge 21 of the sealant layer 23 of the second sheet member 2 (step S31). Then, during the thermal welding step S31, the microcapsules 16 are foamed to form the surface 14s of the weak adhesive layer 14 into an uneven surface, thereby weakening (reducing) the seal strength near the weak adhesive layer 14. (Step S32). At this time, the weak adhesive layer 14 is provided so as to be laminated on a portion of the upper and lower heat-welded laminate layers 12 and 13 so as to serve as the intended steam outlet portion 5 .

When this third step S3 is completed, a package 100A having three sides 11b to 11d thermally welded is manufactured. Thereafter, the desired food material 3 is stuffed into the internal space 4 of the package 100A from the remaining open side 11a (step S4). After the packing of the foodstuff 3 is completed, the remaining sides 11a are also thermally welded to completely seal the internal space 4 (the foodstuff 3 inside) of the package 100A (step S5).

(Peeling mechanism)
Next, heating of the package 100A is started in a microwave oven, water vapor ST is generated in the package 100A, and the mechanism of peeling until it escapes will be explained with reference to FIG. 4.

First, when heating the package 100A shown in FIG. 4(a) using a microwave oven, the food 3 in the internal space 4 of the package 100A is heated, and water vapor ST is generated as shown in FIG. 4(b). However, the internal pressure of the internal space 4 increases. Naturally, this internal pressure is also applied to the heat-welded portion where the first and second sheet members 1 and 2 on the front and back sides are connected, as shown by the arrow in FIG. 4(b). Since the base material layer 12 and the sealant layer 13 are made of different materials, their elastic modulus (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 is generated between the laminate layers 12, 13 (boundary line BL) based on the difference in tensile stress.

Focusing on the interlayer (boundary line BL) between the base material layer 12 and the sealant layer 13, a weak adhesive layer 14 containing foamable ink 15 is additionally applied (printed) to a part of these heat-welded parts. Therefore, even with the same interlayer BL, the adhesive strength between the upper and lower base material layers 12 or the sealant layer 13 is lower in the area where the weak adhesive layer 14 is present (the ink printed area 15A) than in the area without it (the non-ink printed area NP). Since the weak adhesive layer 14 is subjected to the above-mentioned shearing force, the weak adhesive layer 14 starts to peel off from at least one of the laminate layers 12 and 13 starting from the boundary B. In other words, when the internal pressure of the internal space 4 increases, a gap G (separation) occurs between the base material layer 12 and the sealant layer 13 near the weak adhesive layer 14 (see FIG. 4(c)).

On the other hand, even in the heat-welded portion, the sealing strength is relatively high in the ink-unprinted portion NP where the weak adhesive layer 14 is absent, so that peeling between the base material layer 12 and the sealant layer 13 located above and below is difficult to occur. Therefore, a large stress change occurs at the boundary B between the ink-printed area 15A and the non-ink-printed area NP, and normally the sealant layer 13, which is relatively easy to stretch, is cut first, and the gap G created near the weak adhesive layer 14 is Get into it. Here, the symbol C ₁ in FIG. 4(d) indicates a cut portion of the sealant layer 13.

Then, 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. 4(e) indicates a cut portion (peeling portion) of the base material layer 12. Therefore, ultimately, a path CP composed of the cut portions C ₁ and C ₂ formed in each layer 12 and 13 and the gap G communicates the internal space 4 with the outside. The water vapor ST in the internal space 4 escapes to the outside through this communication path CP.

(Prototype production of weak adhesive layer and observation of microcapsules before and after foaming)
A package 100A of the present invention was produced by carrying out the above-mentioned production method. 5(a) and (b) are images showing the state of the foamable ink 15 before and after the heat welding step S31 (foaming), and FIG. 5(c) shows a part of FIG. 5(b). This is an enlarged image. As shown in FIG. 5(c), it is observed that each of the microcapsules 16 is foamed over the entire surface (surface 14s of the weak adhesive layer 14) due to the above-described thermal welding. As a result, the surface 14s of the weak adhesive layer 14 forms an uneven surface in which a large number of spheres are arranged randomly, so that the adhesive strength between the base material layer 12 and the sealant layer 13 laminated on the weak adhesive layer 14 ( The seal strength (also referred to as "seal strength") can be made weaker than the seal strength of a portion to which the weak adhesive layer 14 is not applied (the non-ink printed portion NP).

(Conventional packaging and packaging of the present invention)
Next, both a package 100A of the present invention (Example) and a conventional package (Comparative Example) were produced. At this time, samples of each package were prepared by changing the thermal welding temperature TS (also called "sealing temperature") set during the thermal welding step S31 (every 5 degrees Celsius within the range of 110 to 160 degrees Celsius). I tried to. In the case of Examples and Comparative Examples, at least three bags were produced as test samples under each temperature TS condition. The package of the comparative example differs from the package 100A of the example only in that the weak adhesive layer 14 is not provided between the laminate layers 12 and 13, and the other configurations (bag shape, dimensions, material, etc.) are the same. This is similar to the example.

Thereafter, the peel strength PS of the packages of Examples and Comparative Examples that were thermally welded under each sealing temperature TS was measured. Specifically, a tensile force was applied so as to separate the heat-welded surfaces HS of the first and second sheet members 1 and 2 from each other, and the tensile strength that led to peeling was recorded as the peel strength PS. The results are shown in Table 1 and FIG. 6 below. Note that each value shown in Table 1 is an average value of measured values obtained from a plurality of samples under the same temperature TS condition.

Observing these peel strengths PS, in the conventional packaging (comparative example), the peel strength PS was as low as 1.43 kgf/15 mm in the sample made at the heat welding temperature TS of 110°C, but when the temperature TS was further increased For samples manufactured at a high setting temperature, the peel strength PS increases rapidly each time the set temperature is increased, and for samples manufactured at a temperature TS of 130° C. or higher, it settles at about 7 kgf/15 mm.

On the other hand, in the package 100A (weak adhesive layer 14) of the example, the peel strength PS of the sample made at the thermal welding temperature TS of 110°C is 1.34 kgf/15 mm, which is slightly low, but For sample 100A produced under the thermal welding temperature TS, the peel strength PS was about 2 kgf/15 mm, and it can be seen that the peel strength PS remains constant over a wide temperature range with almost no change.

From these measurement results, (1) it was found that in the package 100A of the present invention, even if the thermal welding temperature TS condition was greatly changed by nearly 50°C, the peel strength PS remained constant with almost no change. Ta. As a result, even if the environmental temperature, thermal welding temperature, and film feed speed are not strictly controlled at the packaging manufacturing site, the manufactured packaging 100A (weak adhesive layer 14) of the present invention will be able to comply with 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 the

In addition, when these measurement results are quantitatively observed, (2) the weak adhesive layer 14 of the present invention, which was produced by setting the heat welding temperature TS to 115°C or higher, was superior to the conventional product (adhesion of a normal laminate layer). It has become clear that the peel strength PS can be suppressed to less than 30% compared to the above. In addition, it seems that the lower the peel strength PS is, the better, but if it is too low (for example, the PS value of the example is less than 10% of the PS value of the comparative example), it may be difficult to heat it in a microwave oven. Since there is a concern that the steaming of the food material 3 by the water vapor generated in the internal space 4 may be insufficient, the peel strength PS shown in the experimental results is considered to be desirable (just right) from the viewpoint of steaming the food material 3.

Furthermore, (3) it was found that the weak adhesive layer 14 of the present invention did not melt even when the thermal welding temperature TS was below 160° C., and was stably formed within the laminate layers 12 and 13. In other words, it was found that the melting point of the weak adhesive layer 14 was higher than at least the normal thermal welding temperature TS. For this reason, the package 100A of the present invention can be used without problems in applications that are placed in high-temperature environments such as boil sterilization and hot water bath cooking.

In this way, in the package 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-welded parts other than this region remains high, no different from that of conventional products. Therefore, it can be said that when the internal pressure increases due to heating in a microwave oven, steam can always escape from a location near the weak adhesive layer 14. Therefore, simply by selecting the application of the weak adhesive layer 14, the vapor vent can be placed at a desired position.

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

(Outline of package (tray pack) according to Example 2)
A package 100C shown in Example 2 is in the form of a tray pack including the first sheet member 1 as shown in Example 1 and a tray container 6. The configuration of Example 2 differs only in that a tray container 6 is used instead of the second sheet member 2 of Example 1, and the other configurations are substantially the same as those of Example 1, so they are common. The explanation of the parts will be omitted.

In this second embodiment, the first sheet member 1 and the tray container 6 are heat-sealed at their peripheral edges 11 and 61 to form an internal space 4 in which the food 3 and the like are sealed. The peripheral edge 11 of the first sheet member 1 also consists of four sides (namely, the top side 11a, the bottom side 11b, and the left and right sides 11c and 11d), similarly to the first embodiment. Among these, a portion 5 of the upper side 11a (the central portion in the drawing) is formed with a predetermined steam vent portion 5 where a steam vent will be formed during microwave cooking. That is, although the sealant layer 13 on the peripheral edge 11 of the first sealing member 1 is thermally welded to the upper surface of the peripheral edge 61 of the tray container 6 (see the heat welding surface HS in FIG. 7(c)), the weak adhesive layer The area of the laminate layers 12 and 13 near 14 becomes the planned steam vent area 5, and when heating in a microwave oven, from the vicinity of weak adhesive layer 14 (specifically, boundary B) with relatively low peel strength, The region 5 is peeled off and a vapor vent (communication path) is formed.

(Other variations of the seal form of the package)
Although the package 100 of the present invention has been described above based on Examples 1 and 2 shown in the drawings, the present invention is not necessarily limited to these examples without departing from the spirit of the present invention. In Examples 1 and 2, flat bags and tray packs 100A, 100B, and 100C were used, but the present invention can be applied to various forms of packaging such as deep-draw packaging, pillow packaging, standing pouches, and envelope pasting. A weak adhesive layer 14 (foamable ink 15) can be formed.

In the microwave oven heating package 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, thereby forming an uneven surface. A weak adhesive layer is formed within the laminate layer (between the base layer and the sealant layer). As a result, the contents inside the package are heated, water vapor is generated, and the internal pressure of the storage space rises to a predetermined pressure. At the boundary, the stress difference in shear force becomes significant. Then, starting from this boundary, the weak adhesive layer begins to peel off from the upper and lower laminate layers, and the laminate layer also breaks or peels off, creating communication between the housing space, the sealant layer, the weak adhesive layer, the base material layer, and the external space. A steam vent (communication path) is automatically formed to allow steam to escape to the outside of the package.

In the microwave heating package of the present invention, the weak adhesive layer is printed on the inner layer that does not come into direct contact with the contents (that is, between the base layer and the sealant layer), so it is further inside than the sealant layer. The contents contained therein (for example, foodstuffs) do not normally come into contact with this weakly adhesive layer. Therefore, the package of the present invention can accommodate either liquid or solid contents.

Furthermore, according to the manufacturing method of the present invention, a weak adhesive layer containing foamable ink can be formed under the normal manufacturing environment (thermal welding process and thermal welding temperature), so that the seal strength is lower than the environmental temperature at the time of manufacturing. This provides the benefit 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. You can also enjoy it.

The packaging body and the manufacturing method thereof of the present invention that exhibit such remarkable effects are not found in the packaging body industry or market, and have very high industrial value and industrial applicability.

1 1st sheet member 2 2nd sheet member 3 Foodstuff 4 Internal space 5 Steam outlet planned portion 6 Tray container 11, 11a, 11b, 11c, 11d, Peripheral portion of first sheet member 12 Base material layer of first sheet member (One of the laminate layers)
13 Sealant layer of first sheet member (one of the laminate layers)
14, 14s Weak adhesion layer, surface of weak adhesion layer 15, 15A Foaming ink, ink printing part 16 Thermally expandable microcapsules 21 Periphery of second sheet member 22 Base material layer of second sheet member (one of the laminate layers) )
23 Sealant layer of second sheet member (one of the laminate layers)
61 Peripheral part of tray container 100, 100A, 100B, 100C Packaging body of the present invention (example) HS Heat-welded surface B Boundary between the weak adhesive layer in the heat-welded part and other ink-unprinted areas BL Laminate layer (base Boundary line between C ₁ and C ₂ sealant layer (material layer and sealant layer) Cutting part of sealant layer, cutting part of base material layer (peeling part)
CP Path that communicates the internal space of the package with the outside G Gap created between laminate layers when peeled HS Heat-welded surface NP Unprinted area PS Peel strength (seal strength)
ST Steam TS Thermal welding temperature (sealing temperature)
W Width of unprinted area Ws Total width of heat-welded area (periphery)

Claims (5)

A microwave oven heating package including a first sheet member,
A base material layer, a sealant layer, and a weak adhesive layer coated with foamable ink between the base material layer and the sealant layer are formed on the first sheet member,
The foamable ink includes thermally expandable microcapsules,
The surface of the weak adhesive layer forms an uneven surface in which the thermally expandable microcapsules are foamed by thermal welding ,
When the package is heated, the weak adhesive layer partially covers one of the base layer or the sealant layer adjacent to the surface of the weak adhesive layer, starting from the uneven surface. peeling off from the other layer to form a vapor vent;
A package for heating in a microwave oven, characterized by: The microwave heating package further includes 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 adhesive layer is provided by being laminated on a part of the heat-welded sealant layer so that the part is a planned steam outlet part.
The package for heating in a microwave oven according to claim 1. An ink-unprinted area where the foamable ink is not applied is formed in the weak adhesive layer,
The unprinted ink portion extends from the inner edge of the weak adhesive layer toward the outer edge so as to divide the planar area of the weak adhesive layer.
The package for heating in a microwave oven according to claim 1 or 2. A first step of preparing a first sheet member;
A second step of preparing a second sheet member or a tray container;
a third step of thermally welding the first sheet member and the second sheet member or the tray container;
A method for producing a package for heating in a microwave oven, the method comprising:
The first step is
A step of preparing a film to serve as a base layer;
partially forming a weak adhesive layer by applying foaming ink containing thermally expandable microcapsules to the inner surface of the base layer;
a step of preparing a film to serve as a sealant layer and further adhering and laminating it on the inner surface side of the base layer;
including;
The third step is
thermally welding 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;
during the thermal welding, foaming the thermally expandable microcapsules to form the surface of the weak adhesive layer into an uneven surface to weaken the seal strength near the weak adhesive layer;
including, and
The weak adhesive layer is provided by being laminated on a part of the heat-welded sealant layer so that the part is a planned steam outlet part.
A method for producing a package for heating in a microwave oven, characterized in that: In the step of applying the foamable 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 added to the liquid. used as foaming ink,
The method for manufacturing a package for heating in a microwave oven according to claim 4.

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