JPH11245928A - Food containers - Google Patents

Abstract

(57) [Problem] To provide a food container in which heat insulation performance and heat insulation performance suitable for performing good retort treatment are improved. SOLUTION: A material sheet in which a base material 32 made of a polypropylene-based resin foam sheet and a barrier layer 33 for suppressing oxygen permeation are laminated is molded by a mold. The cell structure inside the base sheet 32 was such that the number of cells having a maximum diameter of 500 μm or less was 50% or more of the total number of cells per unit area of the cross section of the base sheet 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a container for a retort food, for example, and more particularly to an improvement in a food container based on a foamed polypropylene resin sheet.

[0002]

2. Description of the Related Art Conventionally, there has been provided a food container formed by subjecting a material sheet based on, for example, a foamed polypropylene resin sheet to match molding. Such a food container is generally manufactured as shown in FIG.

FIG. 7 schematically shows a molding apparatus 1 for producing a food container 2 as a final product. The forming apparatus 1 includes an oven 4 for pre-heating a material sheet 3 (hereinafter, simply referred to as a “sheet 3”), a pair of press machines 5 and 6 for forming a pre-heated sheet 3, and
And a cutting machine 8 for cutting the formed material sheet 7 to finish the food container 2 as a product.

[0004] The sheet 3 is a long foamed polypropylene resin sheet, and is wound in a roll shape in advance. The sheet 3 is sequentially fed and supplied to the molding apparatus 1. The fed sheet 3 is preliminarily heated in an oven 4 and then formed by press machines 5 and 6. And it cuts by the cutting machine 8, and the food container 2 as a product is obtained.

By the way, in such a conventional molding method, by controlling the temperature of the sheet 3 in particular, the efficiency of the continuous molding operation is improved (for example, the molding cycle is improved) and the food container as a product is manufactured. 2, heat resistance,
The required performance such as heat insulation was realized. That is, by controlling the preheating temperature of the sheet 3 and forming the sheet 3 in a state close to the solid phase, the drawdown phenomenon of the sheet 3 (the sheet 3 softens due to the preheating and hangs down immediately before forming). Phenomenon) to eliminate the problem and to perform the molding operation efficiently, and secure the required heat resistance, heat insulation, etc. so that the retort treatment and reheating can be performed well by securing the bubble structure inside the food container 2. (Japanese Unexamined Patent Publication No.
218805).

However, in such a conventional molding method, the sheet 3 is molded in a state close to a solid state. From this, the food container 2 as a product usually has an air bubble structure formed inside. However, as a result of the sheet 3 being stretched in a state close to the solid phase at the time of molding, the air bubbles inside the food container 2 are also drawn. It will be in an extended state.

[0007] Such deformation of the bubbles themselves is caused by the food container 2
Although it does not have a significant adverse effect on the heat resistance, heat insulation performance, and cushioning performance of the foam, the improvement of the bubble structure leads to further improvement in performance.

Accordingly, an object of the present invention is to provide a food container having a good internal bubble structure and further excellent heat resistance, heat insulation and cushioning properties.

[0009]

In order to achieve the object of the present invention, a food container according to claim 1 comprises a material sheet in which a foamed polypropylene resin sheet and a barrier layer for suppressing oxygen transmission are laminated. In molded food containers,
The cell structure inside the polypropylene resin foam sheet is characterized in that the number of cells having a maximum diameter of 500 μm or less is 50% or more of the total number of cells per unit area of the cross section of the polypropylene resin foam sheet. It is.

According to this configuration, by setting the maximum diameter of the bubbles inside the foamed polypropylene resin sheet to 500 μm or less, it is possible to make the shape of the bubbles close to a sphere. In addition, by setting the number of cells having a nearly spherical shape to be 50% or more of the total number of cells in the unit area of the cross section of the polypropylene resin foam sheet, appropriate heat insulation of the food container is secured. And the heat resistance can be improved.

In order to achieve the object of the present invention, a food container according to claim 2 is the food container according to claim 1, wherein the barrier layer is made of a polypropylene resin, an ethylene vinyl alcohol resin, and a polypropylene resin. And a resin laminated in order.

According to this configuration, the same operation as that of the first aspect is obtained. In particular, in the claimed invention,
By using a layer in which a polypropylene resin, an ethylene vinyl alcohol resin, and a polypropylene resin are sequentially laminated as the barrier layer, it is possible to effectively suppress oxygen from passing through the food container.

Further, in order to achieve the object of the present invention, a food container according to claim 3 is the food container according to claim 1 or 2, wherein the barrier layer is disposed outside the food container. It is characterized by the following.

According to this configuration, since the barrier layer is disposed outside the food container, the barrier layer generally having poor water repellency may be damaged even when so-called soup is stored. Absent.

In addition, in order to achieve the object of the present invention, the food container according to claim 4 is the food container according to any one of claims 1 to 3, wherein the food container has a polyolefin resin layer on an inner surface thereof. Is further provided.

According to this configuration, the same operation as that of the invention according to any one of claims 1 to 3 is achieved. In addition, in the invention according to the present claim, since the polyolefin-based resin layer is provided on the inner surface of the food container, the inner surface of the food container can be finished to an extremely good smooth surface.

[0017]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing an appearance of a food container 30 according to an embodiment of the present invention, and FIG.
FIG. 1B is a front view, and FIG. 1C is a sectional view of a main part of a side wall 31 of the food container 30.

The food container 30 can be used, for example, for retort food, and is formed by molding a predetermined material sheet. The structure of the material sheet is the internal structure of the food container 30. The design shape and design dimensions of the food container 30 are as shown in FIGS. 1 (a) and 1 (b).
mm and a depth of 40 mm (the total height H is 42 mm).

Referring to FIG. 1 (c), the internal structure of the food container 30 has a four-layer structure, and a foamed polypropylene resin sheet (hereinafter referred to as "base sheet") 32 as a base material. A barrier layer 33 is laminated on the outside. The barrier layer 33 has a polypropylene resin layer 34, an ethylene vinyl alcohol resin layer 35, and a polypropylene resin layer 36, and is laminated on the base sheet 32 in this order.

In the present embodiment, the base sheet 32 has a thickness of 1.0 mm and a density of 0.2 g / cm ³ . Also,
The base sheet 32 has a Z-average molecular weight _MZ of at least 2.
At 0 × 10 ⁵ , the ratio M _Z / M _w with respect to the W average molecular weight is 3.0, and the molecular weight distribution curve by gel permeation chromatography shows a curve indicating that the polymer region contains a branched polymer. Uses a camel type with a certain shape.

On the other hand, with respect to each layer constituting the barrier layer 33, the polypropylene resin layer 34 has a thickness of 25 μm,
The thickness of the ethylene vinyl alcohol resin layer 35 is 30 μm.
m, the thickness of the polypropylene-based resin layer 36 is set to 30 μm.

The base sheet 32 and the barrier layer 33
Thickness is not limited to this value, setting the thickness of the base sheet 32 is 0.6Mm～3.0Mm, density in the range of 0.025g / cm ³ ~0.5g / cm ³ of The thickness of the polypropylene resin layer 34 is set to 10 μm to 50 μm, the thickness of the ethylene vinyl alcohol resin layer 35 is set to 20 μm to 50 μm, and the thickness of the polypropylene resin layer 36 is set to 20 μm to 100 μm. Is possible. Examples of the polypropylene resin include a polypropylene homopolymer, an ethylene-propylene block copolymer, and an ethylene-propylene random copolymer.

Next, the bubble structure inside the food container 30 will be described in detail. FIG. 2 shows the side wall 31 of the food container 30.
FIG. 4 is an enlarged view showing a structure of a cross section in a thickness direction of a unit area in detail. FIG. 2A is a diagram showing the distribution of bubbles 37, and FIG. 2B is a diagram for defining the shape of the bubbles.

Referring to FIG. 2B, bubbles 37 are contained inside the base sheet 32 and generally have an elliptical shape. In the present embodiment, the shape of the bubble 37 is specified by its major axis (maximum diameter dimension) L and its minor axis (minimum diameter dimension) S. When the major axis L is 500 μm or less, the bubble is spherical. Defined to be.

In this embodiment, as a result of observation with a microscope, the bubbles 37 are distributed as shown in FIG. 2A, and almost all the bubbles 37 are spherical. From this, the following operational effects are obtained.

By making the shape of the bubble 37 spherical, appropriate heat insulation can be ensured and heat resistance can be improved as compared with a conventional food container.
That is, by setting the heat insulating property of the food container 30 to an appropriate value, for example, when performing retort processing using the food container 30, sufficient heat is given to the inside of the container to perform good retort processing. In addition, by securing sufficient heat resistance, it is possible to prevent the food container 30 itself from being deformed and the food container 30 from becoming too hot even when reheating is performed in a microwave oven or the like.

In addition, the barrier layer 33 is provided on the food container 30.
Is provided, oxygen can be prevented from entering and exiting through the side wall 31 of the food container 30, and as a result, inconveniences such as oxidation of the contents, that is, a decrease in taste can be suppressed.

In particular, as the barrier layer, a polypropylene resin layer 34 and an ethylene vinyl alcohol resin layer 35
By adopting a layer in which the polypropylene-based resin layer 36 is sequentially laminated, the passage of oxygen through the food container 30 can be effectively suppressed, and the taste of the contents can be further prevented from lowering.

Further, although the barrier layer 33 generally lacks water repellency, in the present embodiment, since the barrier layer 33 is disposed outside the food container 30, a so-called soup is contained as a content. Also, the barrier layer 33 is not damaged, and as a result, it is possible to more effectively prevent the taste of the contents from being lowered.

In this embodiment, the material sheet is
Although the four-layer structure including the base sheet 32 and the barrier layer 33 is employed, a five-layer structure may be further provided by providing a polyolefin-based resin layer inside the base sheet 32.

By doing so, the surface of the base sheet 32, which is a foamed resin, is usually rough, but the inner surface of the food container 30 can be finished smoothly. As a result, when the food container 30 is provided with a required lid member and sealed, there is an advantage that the adhesion between the lid member and the food container 30 can be improved.

The polyolefin resin layer includes:
It is particularly preferable to employ CPP (a uniaxially stretched film of a polypropylene resin).

Next, a method of manufacturing the food container 30 according to the present embodiment will be described. FIG. 3 is a schematic diagram for explaining a method of manufacturing the food container 30. Referring to FIG. 3, this forming apparatus 11 is for manufacturing a food container 30 as a product, and includes an oven 14 for preheating a material sheet 12 as a raw material, and a preheated material. Presses 15 and 1 for forming sheet 12
6 and a cutting machine 18 for cutting the formed sheet 17 and finishing it into a food container 30 as a product.

The material sheet 12 is long and is wound in a roll in advance, and this is called an original sheet. Then, the material sheet 12 is sequentially unwound from the raw material, and the molding device 11
It is supplied to.

The press 15 has a so-called male mold 19.
The press 16 includes a female mold 20 that engages with the mold 19. Each of the presses 15 and 16 is provided with a cylinder 21 as a mold driving device.
The mold clamping / mold opening of 9, 20 is performed.

When the two dies 19 and 20 are clamped, a cavity is formed between the two dies 19 and 20, and the material sheet 12 is formed in a so-called match molding manner following the cavities. It has become. Further, a vacuum suction machine 23 is connected to the mold 20. As a result, good match molding can be performed by performing vacuum molding, and even if the finished thickness of the food container 30 as a product is thin, it can be extremely accurately finished to the designed dimensions. It has become.

On the other hand, the heater 13 is
Is provided, whereby the temperature in the oven 14 can be controlled. That is, by adjusting the calorific value of the heater 13, the preheating temperature of the material sheet 12 (the surface temperature of the material sheet 12 in the present embodiment).
Can be set to a desired temperature.

The material sheet 12 is formed by such a forming apparatus 11 in the following steps. That is, the material sheet 12 unwound from the raw material is first supplied into the oven 14 and preheated to a predetermined temperature. This is to soften the material sheet 12 in order to perform the molding with the presses 15 and 16 satisfactorily. Then, the preheated material sheet 12 is successively applied to the presses 15 and 16.
And are formed by the presses 15 and 16. Thereafter, the formed material sheet 17 is cut by the cutting machine 18 to obtain a food container 30 as a final product.

In the forming operation by the forming apparatus 11, in the preheating step, the surface temperature of the material sheet 12 is set to 160 ° C. to 200 ° C.
The molds 19 and 20 of 5 and 16 are set to 40 ° C. to 100 ° C. in advance.

The material sheet 12 includes the base sheet 32 (polypropylene resin foam sheet) as described above, and the base sheet 32 has bubbles inside. For this reason, a temperature difference occurs between the surface temperature and the internal temperature of the material sheet 12 at the time of preheating. However, experimentally, even if the surface temperature is increased to 200 ° C., there is no problem in molding. As means for heating the molds 19 and 20,
Although not shown in FIG. 3, a known heater or the like can be installed in the dies 19 and 20. Further, although not shown in FIG. 3, for example, by installing a non-contact radiation thermometer near the outlet of the oven 14,
2 can control the surface temperature.

FIG. 4 is a schematic diagram showing a state where the molds 19 and 20 are opened, and FIG. 5 is a schematic diagram showing a state where the molds are clamped. With reference to these figures, according to the molding apparatus 11, the material sheet 12 fed between the dies 19 and 20 (see FIG. 4) is molded by the dies 19 and 20 (see FIG. 4). At this time, the material sheet 12
Because the surface temperature is set to 160 ° C to 200 ° C,
The base sheet 32 can be formed in a state close to a molten state.

Accordingly, even if the material sheet 12 is pulled during the mold clamping and a temporary stress is generated, the base sheet 32
Is softened to a state close to a molten state, and then this stress is relaxed. That is, it is possible to minimize occurrence of residual stress in the formed base sheet 32. Further, even when the base sheet 32 is pulled at the time of mold clamping and the internal air bubbles are temporarily expanded, the air bubbles can thereafter return to a favorable state close to a spherical shape.

The molds 19 and 20 are kept at 40 ° C. to 100 ° C.
Is set at the time of molding, the material sheet 12 is
9, 20 can prevent rapid cooling. That is, the molds 19 and 20 are usually made of aluminum having a high thermal conductivity (a thermal conductivity of 3.18 kcal / mh).
° C), the material sheet 12 is deprived of heat by the dies 19 and 20 and rapidly cooled if the temperature of the dies 19 and 20 is low at the time of molding. Since the molds 19 and 20 are heated to 40 ° C. to 100 ° C., the material sheet 12 is not rapidly cooled. That is,
In the molding operation by the molding device 11, it is possible to prevent the base material sheet 32 from being cooled during the molding and from being in the solid state.

Therefore, as described above, even if the material sheet 12 is pulled during the mold clamping and a temporary stress is generated, the stress is sufficiently relaxed to prevent the residual stress from being generated in the formed base sheet 32. It is possible to further eliminate the bubbles, and it is possible to reliably return the temporarily expanded internal bubbles to a favorable state close to a spherical shape.

In addition, the surface temperature of the material sheet 12 is set to 16
Since the temperature is set in the range of 0 ° C. to 200 ° C., the base sheet 32 is not completely in a molten state, thereby making it possible to avoid the drawdown phenomenon of the material sheet 12 during molding.

Experimentally, the dies 19 and 20 were kept at 40 ° C.
If it is set to less than 1, the material sheet 12 is
If the temperature is set to be higher than 100 ° C., the material sheet 12 is not cooled after molding, and it is difficult to perform good mold release. Further, since the best molding operation can be performed when the surface temperature of the material sheet 12 is in the range of 170 ° C. to 190 ° C., it is preferable to set the surface temperature of the material sheet 12 to such a temperature range.

As described above, when the food container 30 is manufactured by the molding device 11, the internal bubble structure is made almost spherical without causing any residual stress inside the food container 30. An internal structure as shown in FIGS. 1 and 2 can be realized.

Further, the design of the molding apparatus 11 can be changed as follows. That is, in the molding apparatus 11, the molds 19 and 20 are all made of metal, but the convex portions 24 of the male mold 19 can be made of synthetic resin. As the synthetic resin, for example, a urethane-based synthetic resin containing a filler can be employed. This synthetic resin has excellent heat resistance and a thermal conductivity of 0.12.
It is kcal / mh ° C. and has a lower thermal conductivity than metal materials such as aluminum. By making such a design change, the thermal conductivity of the convex portion 24 of the mold 19 can be reduced, and the material sheet 12 is interposed between the mold 19 and a member having low thermal conductivity. Will be molded. Therefore, it is possible to more effectively prevent the preheated material sheet 12 from being rapidly cooled during molding, and as a result, even if the material sheet 12 is pulled at the time of molding, the base material sheet after molding is removed. The generation of residual stress in the base sheet 32 can be further eliminated, and the shape of the bubbles inside the base sheet 32 can be made closer to a sphere.

The synthetic resin used for the projections 24 is a filler-containing urethane-based synthetic resin having a thermal conductivity of 0.12 kcal / mh ° C. With the following, rapid cooling of the material sheet 12 can be avoided. In addition, as long as the thermal conductivity is 0.5 kcal / mh ° C. or less, it is preferable that the thermal conductivity is low. 08k
cal / mh ° C. As a material having such a thermal conductivity, for example, glass fiber or the like can be given.

In addition to using a synthetic resin on the male mold 19 side, a synthetic resin can be used on the female mold 20 side. In short, it is only necessary that a material having low thermal conductivity can be interposed when the material sheet 12 is formed.

Next, the results of performance comparison tests of the food container 30 according to the embodiment of the present invention and the conventional food container, such as heat insulation and heat resistance, will be described and discussed. The comparison data is shown in FIG. 6, the food container 30 according to the embodiment of the present invention is shown in Examples 1 to 3, and the conventional food container is shown as a comparative example.

(1) Test food container Example 1 The constituent materials were a base sheet (polypropylene resin foam sheet), a polypropylene resin layer laminated on the outside thereof,
It has an ethylene vinyl alcohol resin layer and a polypropylene resin layer, and has the four-layer structure described above. The thickness dimension of the side wall is 1.5 mm. The internal bubble structure is
The major axis is 0.2mm ~ 0.6mm, the minor axis is 0.2mm ~
0.3mm, average ratio of major axis to minor axis is 1.8, ratio of spherical bubbles is 5
0%. In addition, the spherical bubble ratio is a ratio of the number of spherical bubbles to the total number of bubbles per unit area of the side wall cross section, and the spherical bubble is a bubble having a longest diameter of 500 μm or less.

Example 2 The constituent materials are the same as in Example 1. The thickness dimension of the side wall is 0.9 mm. The inner bubble structure has a major axis of 0.
2mm ~ 0.6mm, minor axis 0.2mm ~ 0.4mm,
The average ratio of major axis to minor axis is 2.5, and the ratio of spherical bubbles is 80%.

Example 3 The constituent materials were the same as in Example 1, but a polypropylene resin layer was provided inside the food container. The thickness of the side wall is
0.9 mm. The inner bubble structure has a long diameter of 0.2m
m to 0.6 mm, minor axis is 0.2 mm to 0.4 mm, average major axis / minor axis ratio is 2.5, and spherical bubble ratio is 80%.

Comparative Example The constituent materials are the same as in Example 1. The thickness dimension of the side wall is 1.5 mm. The inner bubble structure has a major axis of 0.
9mm to 1.2mm, minor axis 0.1mm to 0.2mm,
The average ratio of major axis to minor axis is 5.0, and the ratio of spherical bubbles is 0%.

(2) Experimental conditions Retort treatment test Each test food container was heated at a temperature of 130 ° C. and a pressure of 0.25 MPa.
deformation of the food container was left for 30 minutes in an atmosphere of _a Check (surface roughness state).

Thermal Conductivity Test 200 cc of water is put into each test food container, and the temperature of the container side wall after boiling by heating in a microwave oven is examined.

(3) Test Results A test was conducted under the above conditions, and the results are shown in FIG.
As is clear from FIG. 6, in the comparative example in which the spherical bubble ratio is 0%, the surface roughness is large due to the retort treatment.

On the other hand, in each of the examples in which the ratio of the spherical bubbles is 50% or more, the surface roughness is small or no surface roughness can be confirmed.

In the thermal conductivity test, the temperature was 85 ° C. or less in each of the examples, and it was found that the samples had sufficient heat resistance and heat insulation.

[0061]

According to the first aspect of the present invention, the shape of the air bubbles inside the food container is made almost spherical, and the number of the air bubbles close to the spherical shape is determined by the total air bubbles in the unit area of the cross section of the base material sheet. When the number is 50% or more, appropriate heat insulating properties of the food container can be ensured, and heat resistance can be improved. That is, by setting the heat insulating property of the food container to an appropriate one, when performing retort treatment using the food container, for example, it is possible to perform sufficient retort treatment by applying sufficient heat to the inside,
By ensuring sufficient heat resistance, the food container itself does not become too hot even when reheating is performed in a microwave oven or the like. Furthermore, the fact that the bubble shape inside the food container is close to spherical means that no residual stress is generated inside, so that when reheating with a microwave oven or the like, the food container does not deform. .

According to the second aspect of the invention, the same effects as those of the first aspect of the invention can be obtained. In particular, in the invention according to the present claim, since the barrier layer can effectively suppress the passage of oxygen through the food container, even if the food container is used to constitute a retort food, the oxidation of the contents is prevented. Can be suppressed.

According to the third aspect of the invention, the same effects as those of the first or second aspect of the invention can be obtained. In addition, in the invention according to the present claim, it is possible to prevent the barrier layer from being damaged even when so-called soup is stored, and as a result, it is possible to more effectively suppress oxidation of the contents.

According to the fourth aspect of the invention, the same effects as those of the first to third aspects are obtained. In addition, in the invention according to the present claim, since the inner surface of the food container can be finished to a very good smooth surface, when the lid member is provided in the food container, the lid member and the food container can be closely adhered. This is advantageous in that the production of retort food becomes easy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a food container according to an embodiment of the present invention, wherein (a) is a plan view, (b) is a front view, and (c) is an enlarged cross-sectional view of a side wall. .

FIG. 2 is a view showing a bubble structure inside a food container;
(a) is an enlarged sectional view showing the state of the bubble, and (b) is a diagram for specifying the shape of the bubble.

FIG. 3 is a diagram schematically showing a molding apparatus for manufacturing a food container according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a state where a mold of a molding apparatus is opened.

FIG. 5 is a schematic view showing a state in which a mold of a molding apparatus is tightened with a shoulder.

FIG. 6 is a view showing a performance test result of a food container.

FIG. 7 is a schematic view showing a conventional food container manufacturing process.

[Explanation of symbols]

 Reference Signs List 30 Food container 31 Side wall 32 Base sheet 33 Barrier layer 34 Polypropylene resin layer 35 Ethylene vinyl alcohol resin layer 36 Polypropylene resin layer

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 29:00 105: 04 B29L 31:00

Claims (4)

[Claims] In a food container formed from a material sheet in which a foamed polypropylene resin sheet and a barrier layer for suppressing oxygen permeation are laminated, the cell structure inside the foamed polypropylene resin sheet has a maximum diameter. Wherein the number of cells having a particle size of not more than 500 μm is at least 50% of the total number of cells per unit area of the cross section of the foamed polypropylene resin sheet. 2. The food container according to claim 1, wherein the barrier layer is formed by sequentially laminating a polypropylene resin, an ethylene vinyl alcohol resin, and a polypropylene resin. 3. The food container according to claim 1, wherein the barrier layer is disposed outside the food container. 4. The food container according to claim 1, further comprising a polyolefin resin layer on an inner surface of the food container.