JP2020104882A - Paper-made container and method for manufacturing the same - Google Patents

Abstract

To provide a paper-made container which is suitably applicable to microwave heating and can be efficiently manufactured.SOLUTION: The paper-made container comprises a container body formed by bending a blank 1 made of a sheet-like material. The container body includes a bottom surface, a plurality of side surfaces rising from the bottom surface, a joined part formed between the side surfaces, a flange extending from the side surfaces to a peripheral edge of the container body, and an auxiliary flange extending from a part of the joined part to the peripheral edge of the container body. The sheet-like material includes a paper-made base material 2, a sealant layer 4 formed on a first surface 2a side of the base material and mainly containing polypropylene, and a heat seal layer 5 formed in at least a part on a second surface 2b opposite to the first surface and containing acid-modified polypropylene in the flange, and the melting point of the polypropylene in the heat seal layer is 100°C or higher.SELECTED DRAWING: Figure 3

Description

The present invention relates to a paper container, and more particularly to a paper container whose contents can be heated in a microwave oven and a method for manufacturing the paper container.

As a packaging container for frozen foods, the paper container described in Patent Document 1 is known. This paper container is formed by bending a sheet of paper blank and adhering predetermined surfaces to each other.

Japanese Patent No. 3687396

The paper container described in Patent Document 1 is excellent as a container for food and drink that is not heated, such as ice cream, but is still a container for food that is heated in a microwave oven and then served. There is room for improvement.
For example, Patent Document 1 describes that a polyethylene layer is provided on one surface of a blank that is an inner surface of a container in order to enhance waterproofness. However, when this is heated in a microwave oven, a polyethylene layer is formed. Foaming can result in pinholes, and food ingredients can pass through the polyethylene layer and soak into the paper.

Further, as will be described later in detail, as a countermeasure against this problem, simply forming the inner layer with a resin having a high melting point causes a problem that the production efficiency of the paper container is significantly reduced.

In view of the above circumstances, it is an object of the present invention to provide a paper container and a method for manufacturing the same, which are suitable for microwave oven heating and can be manufactured efficiently.

A first aspect of the present invention is a paper container provided with a container body formed by bending a blank made of a sheet material.
The container body includes a bottom surface portion, a plurality of side surface portions rising from the bottom surface portion, a joint portion formed between the side surface portions, a flange portion extending from the side surface portion to the peripheral edge of the container body, and a portion of the joint portion. And an auxiliary flange extending to the peripheral edge of the.
The sheet-like material is a paper base material, a sealant layer formed on the first surface side of the base material and having polypropylene as a main component, and at least a second surface of the flange portion opposite to the first surface. And a heat-sealing layer containing an acid-modified polypropylene.

A second aspect of the present invention is a method of manufacturing a paper container for manufacturing the paper container of the present invention.
This method includes a step A of arranging the blank above the female mold, a step B of arranging hot air supply units having jet nozzles at the four corners of the blank, and a part of the hot air supply unit is covered with a cover to surround the jet nozzle. A step C of forming a closed space in the closed space, a step D of supplying hot air into the closed space to melt a part of the sealant layer and softening the heat seal layer, and pressing the blank toward the female mold to form a blank. While bending, a part of the sealant layer is made to face and be joined, and a step E is also made in which the auxiliary flange is brought into contact with the heat seal layer and joined to the flange portion.

According to the present invention, it is possible to provide a paper container and a method for manufacturing the same, which is suitable for microwave heating and can be manufactured efficiently.

It is a figure which shows the blank of the paper-made container which concerns on one Embodiment of this invention. It is a schematic cross section of the same blank. It is a schematic cross section of a part of flange part in the same blank. It is a figure which shows one process of manufacture of the same paper-made container. It is a figure which shows one process of manufacture of the same paper-made container. It is a figure which shows one process of manufacture of the same paper-made container. It is a figure which shows one process of manufacture of the same paper-made container. It is a figure which shows the container main body of the same paper-made container. It is a figure which shows the same container main body to which the lid material was joined.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9.
The paper container of the present embodiment is composed of a container body formed by punching a sheet-shaped material and heat-bonding it while bending the blank, and a lid member attached to the container body. The sheet material is mainly paper.

FIG. 1 shows the shape of the blank 1 in this embodiment. The blank 1 has a substantially rectangular shape, and a plurality of bending lines are formed by embossing or the like. A quadrangular bottom portion 10 that constitutes the bottom surface of the paper container is provided at the center of the fold line having four sides. Around the bottom surface portion 10, four quadrangular side surface portions 11, 12, 13, 14 are provided so as to share one of the four sides with the bottom surface portion 10. Joining portions 21, 22, 23, and 24 that are joined by heat fusion are provided between the adjacent side surface portions. Each of the joints has two substantially triangular shapes that are line-symmetric.

Flange portions 31, 32, 33, 34 having substantially constant widths are provided on the sides of the side surface portions 11, 12, 13, 14 opposite to the bottom surface portion 10, respectively. Auxiliary flanges 21a, 22a, 23a, 24a having the same width as the flange portion are formed on one triangular shape of each joint.
Each flange portion and each auxiliary flange are located so as to extend along the peripheral edge of the container body in the completed container body.

FIG. 2 shows the layer structure of the blank 1. The blank 1 includes a base material 2 made of paper, an anchor layer 3 formed on the first surface 2 a of the base material 2, and a sealant layer 4 formed on the anchor layer 3. The layer structure of the blank 1 is the same as the layer structure of the sheet material.
The lid material may be made of a material different from that of the blank 1, but if it is made of the same sheet-shaped material as that of the blank 1, the entire paper container can be discarded as combustible waste after use, and separation is unnecessary. In this case, the sheet-shaped material forming the lid material may not have a heat seal layer described later.

As the base material 2, various paperboards such as coated balls, coated Manila, and ivory can be used. Various printings may be applied to one or both surfaces of the base material 2 for the purpose of improving the design and posting information.

The sealant layer 4 is mainly composed of homopolymer type polypropylene. This polypropylene has a melting point of at least 135° C. or higher so that it can sufficiently withstand the heat applied in the manufacturing process described later. The melting point is preferably 150°C or higher.
The thickness of the sealant layer 4 is 20 μm or more and less than 60 μm.

The anchor layer 3 enhances the adhesiveness between the base material 2 and the sealant layer 4. The material of the anchor layer 3 can be appropriately selected, but a material containing an acid-modified polypropylene resin aqueous dispersion as a main component is preferable. In this case, the polypropylene contained in the anchor layer 3 has a melting point of at least 120° C. or more so that it can sufficiently withstand the heat applied in the manufacturing process described later. The melting point is preferably 150°C or higher.

FIG. 3 shows the layer structure of the flange portion 31. At both ends in the longitudinal direction of the flange portion 31, the heat seal layer 5 is provided on the second surface 2b opposite to the first surface 2a. Also in the flange portion 33 facing the flange portion 31 with the bottom surface portion 10 interposed therebetween, the heat seal layer 5 is provided in the same manner at both end portions in the longitudinal direction (see FIG. 1 ).

The heat seal layer 5 is formed of a heat seal agent containing an acid-modified polypropylene resin aqueous dispersion. The melting point of polypropylene constituting the acid-modified polypropylene resin aqueous dispersion is 100° C. or higher, preferably 150° C. or higher.

The sheet-shaped material used as the material of the blank 1 configured as described above is coated with a varnish or the like serving as an anchor layer on the first surface 2a of the base material 2 to form the anchor layer 3 and then with the sealant layer. The resulting molten resin is laminated on the anchor layer 3 by extrusion lamination. Further, it can be manufactured by applying a heat-sealing agent which becomes the heat-sealing layer 5 to a predetermined portion of the second surface 2b. The blank 1 is completed by punching this sheet material into a predetermined shape.

A method for manufacturing the paper container of the present embodiment using the blank 1 will be described.
First, the blank 1 is placed on a female mold having a shape corresponding to the outer shape of the paper container with the surface on which the sealant layer 4 is formed facing upward (step A). The placement can be performed by a vacuum pad, a chuck, or the like.

Next, as shown in FIG. 4, the hot air supply units 101 are arranged at the four corners of the blank 1 (step B), and the four corners of the blank 1 are supported by the hot air supply unit 101. The hot air supply unit 101 prevents the blank 1 from warping before box making. The female mold is below the blank 1 and therefore not shown.
Each hot air supply unit 101 has an ejection hole (not shown). Hot air of several hundred degrees Celsius can be supplied from the jet port. The spouts are directed to the joints 21, 22, 23, 24 at the four corners of the blank 1 in the process B.

Next, as shown in FIG. 5, a part of each hot air supply unit 101 is covered with a cover 102 (step C). In each hot-air supply unit 101, a cover 102 seals the periphery of the ejection port, and a closed space into which hot air flows is formed so as to cover each joint and its periphery.

Next, hot air is ejected from the ejection port. At least a part of the sealant layer 4 is melted by the hot air in each of the joint portions 21, 22, 23, 24, and is brought into a state capable of heat fusion. (Step D) In the present embodiment, the sealant layer 4 of the auxiliary flanges 21a, 22a, 23a, 24a is also melted, and the heat seal layer 5 formed on the back side of the flange portions 31 and 33 is also softened.
The hot air generally stays in the closed space formed by the cover 102, and the temperature of the hot air leaking out of the closed space rapidly decreases with diffusion, so that the sealant layer 4 separated from the joint does not melt.

Next, the cover 102 is retracted, and the male die having a shape corresponding to the inner shape of the paper container approaches the blank 1 from above the blank 1. The male mold contacts the blank 1 and presses the blank 1 toward the female mold. (Process E).

The pressed blank 1 is bent along a bending line as shown in FIG. At this time, the joint portions 21, 22, 23, 24 are bent along the bending line between the two substantially triangular shapes. As a result, the two substantially triangular sealant layers 4 approach each other and are joined together.

Furthermore, the joined joint portions 21, 22, 23, 24 are bent along the side surface portion 11 or 13 among the side surface portions 11, 12, 13, 14 rising from the bottom surface portion by bending. Along with this movement, the melted sealant layer 4 of each of the auxiliary flanges 21a, 22a, 23a, 24a approaches the back side of the flange portion 31 or 33 provided on the side surface portion along which the joint portion extends, and the heat seal layer 5 is formed. Contact with. Since the heat seal layer 5 is made of a polypropylene material, the heat seal layer 5 is preferably joined to the sealant layer 4 of each auxiliary flange.

After the end of the process E, the male mold and the hot air supply unit 101 are retracted. By the procedure up to this point, the primary box making of the container body is completed, and as shown in FIG. 7, the basic shape 50A of the container body is formed.
After that, when each flange portion is bent in parallel with the bottom surface portion by another male mold or the like, the container body 50 is completed as shown in FIG.

The completed container body 50 is carried to the next step, and the internal space is filled with the contents. Finally, as shown in FIG. 9, the upper opening of the container body 50 is covered with the lid member 60, and the peripheral edge of the lid member 60 and the flange portion of the container body 50 are joined over the entire circumference, so that the contents are filled. The package is completed. After filling the contents, the contents may be subjected to a predetermined process such as freezing or drying at an appropriate timing.

In the paper container, a part of the sealant layer formed on the blank constitutes the innermost surface of the paper container. When the sealant layer is made of polyethylene, it has poor heat resistance, and thus foams when heated in a microwave oven, which easily causes pinholes. When pinholes occur, the seasoning components of foods, oils, etc. permeate the base material, greatly impairing the appearance.

When the sealant layer is made of a polyester resin such as polyethylene terephthalate (PET) or polyethylene butylene terephthalate (PBT) and a resin material having a high melting point such as polymethylpentene (PMP), the possibility of pinholes is reduced. Can However, since the sealant layer formed of these materials has a too high melting point, it may not be sufficiently melted even if hot air is applied in the above-mentioned step D, resulting in a marked decrease in manufacturing efficiency. Increasing the temperature of the hot air to ensure melting may cause charring on the substrate. Further, even when melted, the resin material flows due to the high temperature, moves to a region other than the joint portion, impairs the external appearance, and causes a phenomenon that stable seal strength cannot be obtained.

Polypropylene (PP) is known as another resin for forming the sealant layer. However, when the sealant layer is formed of PP, there is no problem when the sealant layers are opposed to each other and fused, but the sealant layer and the paper. In the flange portion where the base material made of steel was joined, it was observed that the joining was not sufficient.

The inventors have made various studies under the above circumstances. As a result, they have found that the heat-sealing layer containing the acid-modified polypropylene resin aqueous dispersion is provided on the back side of the flange portion to which the sealant layer of the auxiliary flange is joined, whereby the flange portion can be strongly joined. Further, by setting the melting point of polypropylene contained in the acid-modified polypropylene resin aqueous dispersion to a predetermined value or more, a structure was established in which the joint strength of the flange portion did not decrease even when heated in a microwave oven after box making. In the paper container according to the present embodiment, both reduction of pinholes and the like on the inner surface and improvement of manufacturing efficiency due to reliable joining of the flange portions are compatible.
Hereinafter, some of the examination data showing the effect of each configuration of the present invention will be shown.

(Study 1: Examination of flange joint strength during box making)
A sheet-like material for study was formed using the following materials.
Base material: base paper for paper cup, (basis weight 320 g/m ² ).
Sealant layer material: homopolymer type PP (melting point 160° C., MFR20, density 0.9 g/cm ² )
The sealant layer material was laminated on one surface of the base material by extrusion lamination to obtain a sheet-like material having a sealant layer having a thickness of 40 μm. With respect to this sheet-shaped material, three patterns having different flange configurations were prepared as follows.
Experimental Example 1: No heat seal layer (base material exposed on the second surface)
Experimental example 2: A polyethyleneimine heat sealant is applied to form a heat seal layer (application amount: solid content 0.5 g/cm ² ).
Experimental Example 3: An acid-modified polypropylene resin aqueous dispersion-containing heat-sealing agent (polypropylene melting point 120°C) was applied to form a heat-sealing layer (application amount: solid content 0.5 g/cm ² ).

Using a blank obtained by punching out a sheet-shaped material of each pattern, a paper container of each experimental example was produced by the above-described production procedure (hot air temperature 520° C., air flow rate 430 ml/min, box making speed 50 pieces/min).
The following two points were evaluated for the paper container of each experimental example.
(Measurement of peel strength between flange and auxiliary flange)
A test piece was prepared using each paper container, and the flange portion and the auxiliary flange were gripped and 180° peeling was performed to measure.
(Visual observation of peeling site)
The state of the peeling interface was visually confirmed.
The results of Study 1 are shown in Table 1.

As shown in Table 1, only the paper container of Experimental Example 3 had sufficient peel strength, and in Experimental Examples 1 and 2, the peel strength was small.
"Paper peeling" in Table 1 means a phenomenon in which a part of one of the paper base materials is peeled off from the rest of the paper base material while being in close contact with the sealant layer. That is, it can be said that in a paper container in which paper peeling has occurred, the adhesion between the flange portion and the auxiliary flange is high.
In the paper containers of Experimental Examples 1 and 2, the base material of the flange portion was interfacially separated from the sealant layer of the auxiliary flange, and no paper peeling occurred, whereas in the paper container of Experimental Example 3, paper peeling occurred. ..
From the above, it was shown that the auxiliary flange having the PP sealant layer and the flange portion can be firmly joined at the time of box making by forming the heat seal layer with the acid-modified polypropylene resin aqueous dispersion on the flange portion.

(Study 2: Examination of joint strength of flange by heating in microwave oven)
The following materials were used to form the study sheet material.
Base material: base paper for paper cup, (basis weight 320 g/m ² ).
Sealant layer material: Homopolymer PP used in Study 1 (sealant layer thickness 40 μm)
Heat-sealing layer material: A heat-sealing agent containing an acid-modified polypropylene resin aqueous dispersion (application amount: solid content 0.5 g/cm ² ). However, only the polypropylene melting point was changed in each experimental example as follows.
Experimental Example 4: 70°C
Experimental example 5: 90°C
Experimental example 6: 100° C.
Experimental Example 7: 120°C
Experimental example 8: 150° C.
A paper container of each experimental example was prepared in the same procedure as in Study 1, and 300 g of macaroni gratin was filled as the content. After that, the opening was covered with a lid formed by punching out the sheet-shaped material, and heat sealing layers facing each other in the flange portion were heat-sealed to bond the lid to the paper container. Then, the container and the contents were frozen, and the sealed container of each experimental example in which the contents were sealed in a frozen state was produced.
For the paper container immediately after the box making and the closed container immediately after the microwave oven heating, "peeling strength measurement between the flange portion and the auxiliary flange" and "visual observation of the peeled portion" were performed as in Study 1.
The conditions for heating the microwave oven were set to 500 W for 6 minutes. The temperature of the contents immediately after heating was measured and found to be 92°C to 95°C.
The results of Study 2 are shown in Table 2.

Immediately after box making, except for Experimental Example 4, the joint strength of the flange portion was sufficient. However, in Experimental Example 5, the joint strength of the flange portion decreased due to microwave heating, and interfacial peeling was observed between the flange portion and the auxiliary flange. It is considered that this is because the temperature of the filling material became equal to or higher than the melting point of PP contained in the heat seal layer by heating in the microwave oven, and the heat seal layer was softened.
In the paper containers of Experimental Examples 6 to 8 in which the melting point of PP contained in the heat-sealing layer was higher than the temperature of the filling after heating in the microwave oven, the flange portion and the auxiliary flange were firmly joined even after heating in the microwave oven. It was maintained.
From the above, it was shown that by setting the melting point of PP contained in the heat seal layer to 100° C. or higher, a strong joint between the flange portion and the auxiliary flange can be maintained not only immediately after box making but also after microwave heating. .. The paper container of the present embodiment is suitable for the purpose of containing food that is heated and eaten in a microwave oven.

As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and a configuration change, a combination, etc. within a range not departing from the gist of the present invention are also possible. included.
For example, the side surface portions that are bent along the joint portion are not limited to the side surface portions 11 and 13 described above, and can be set appropriately. In that case, the number of side surface portions along which the joint portion extends is not limited to two, and may be three or four. If the heat seal layer is formed at the position corresponding to the auxiliary flange in the flange portion on the side surface along which the joint portion extends, the above-described effect can be obtained.

1 blank 2 base material 2a first surface 2b second surface 4 sealant layer 5 heat seal layers 21a, 22a, 23a, 24a auxiliary flange 50 container body 60 lid member 101 hot air supply unit 102 cover

Claims (3)

A paper container having a container body formed by bending a blank made of a sheet-shaped material,
The container body is
Bottom part,
A plurality of side surface portions that rise from the bottom surface portion,
A joint formed between the side surfaces,
A flange portion extending from the side surface portion to the peripheral edge of the container body,
An auxiliary flange extending from a part of the joint portion to the peripheral edge of the container body,
The sheet material is
A paper base,
A sealant layer formed on the first surface side of the base material and containing polypropylene as a main component,
In the flange portion, formed on at least a part of the second surface opposite to the first surface, a heat-sealing layer containing an acid-modified polypropylene, and,
The melting point of polypropylene in the heat seal layer is 100° C. or higher,
Paper container. A base material made of paper and formed on a first surface side of the base material, which is formed of a sheet-like material having a sealant layer containing polypropylene as a main component, and further includes a lid member joined to the container body,
The paper container according to claim 1. A method for manufacturing a paper container for manufacturing the paper container according to claim 1, comprising:
Step A of placing the blank above the female mold,
A step B of arranging hot air supply units having jets at the four corners of the blank,
Step C of covering a part of the hot air supply unit with a cover to form a closed space around the ejection port,
A step D of supplying hot air into the closed space to melt a part of the sealant layer and softening the heat seal layer;
While pressing the blank toward the female mold and bending the blank, the sealant layers are partly opposed to each other and joined, and the auxiliary flange is brought into contact with the heat seal layer to be joined to the flange portion. Process E,
With
A method for manufacturing a paper container.

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