Method for producing a foamed sheet for thermoforming, method for producing a packaging container, foamed sheet for thermoforming, packaging container, and method for using the packaging container

Abstract

To provide a method for manufacturing a foamed sheet for thermoforming that can be expected to improve cost effectiveness by optimizing a laminating procedure of a laminated film as well as expressing an adhesive state between a foam base sheet and the laminated film suitable for an application and function of a container for packaging.SOLUTION: A method for manufacturing a foamed sheet 1 for thermoforming includes: a step of laminating a thin first film 12 on a foam base sheet 11 to obtain a foamed sheet with a film; and a second step of laminating a second film 13 including a barrier layer on the first film 12 side of the foamed sheet with the film to obtain the foamed sheet for thermoforming.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a foamed sheet for thermoforming obtained by laminating a film on a base sheet, a method for manufacturing a packaging container using the foamed sheet for thermoforming, the foamed sheet for thermoforming, the packaging container, and a method for using the packaging container.

Background Art

[0002] Conventionally, for example, packaging containers for food sold in supermarkets and convenience stores have been obtained by thermoforming a synthetic resin sheet. The sheet is obtained by adopting a known method such as a coextrusion method or a lamination method, and laminating a base sheet and, if necessary, a film. The properties such as the components and thickness of the base sheet and the film have been determined according to the use and function of the packaging container.

[0003] Patent Document 1 discloses a technique for obtaining a foamed sheet for deep drawing by heating and laminating a single-layer film with a thickness of 30 μm made of high-impact polystyrene as an impact-resistant auxiliary layer on a polystyrene foamed sheet as a base material using a hot roll, and then dry laminating a thermoplastic resin multilayer film made of a modified ethylene-vinyl alcohol copolymer as an oxygen barrier layer and polypropylene as a moisture-proof layer using a urethane-based adhesive.

[0004] Patent Document 2 discloses a technique related to a packaging container in which a laminated film laminated on a polystyrene foam sheet as a base material is dry laminated in the order of a coextrusion laminated film including a gas barrier layer, a dry laminating adhesive as a dry laminating adhesive layer, printing ink as a printing layer, and an unstretched polystyrene film as a polystyrene-based resin layer from the side farther from the base material, and the thicknesses of the printing layer and the polystyrene-based resin layer are 20 μm.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, Patent Document 1 does not disclose the peel (adhesion) strength of the laminated film with respect to the base material sheet. That is, as the thickness of the entire laminated film increases due to the addition of a barrier layer or the like, the laminated film is more likely to peel off from the base material sheet. Therefore, due to the properties of the film closest to the base material sheet, the lamination procedure including the above film, and the correlation with the method of sealing the food in the packaging container, there is a risk that the laminated film will peel off from the base material sheet when the food is opened.

[0007] In addition, in Patent Document 2, since the printed polystyrene resin layer and the coextruded laminated film are laminated by a dry lamination method using a dry laminating adhesive, the entire laminated film becomes thick. Therefore, in terms of the fact that the conditions such as the heating temperature when thermally laminating the laminated film to the base material sheet are narrowed, and it is difficult to exhibit the desired peel strength, there is a risk of reducing the production efficiency when processing the raw sheet or the packaging container.

[0008] From the viewpoint of extending the storage period of food, depending on the type of food, the use of a seal-type lid (hereinafter also referred to as "top seal") that is difficult for gases such as oxygen to permeate into the packaging container and a skin film that evacuates the inside of the packaging container is progressing. However, compared with the fitting-type lid that seals the conventional packaging container, the top seal and the skin film are likely to induce a phenomenon (hereinafter also referred to as "bagging phenomenon") in which the laminated film peels off from the base material without peeling off when opened because they are adhered to the laminated film.

[0009] Furthermore, the inventors assume air pockets between the base sheet and the laminated film as one of the problems other than the bagging phenomenon. Specifically, when the base sheet is a polystyrene foam sheet (hereinafter also referred to as "PSP"), butane gas is used as a foaming agent to secondarily foam the base sheet during the molding of the packaging container. Therefore, when the packaging container is filled with food and tightly packaged and then exposed to high temperatures, there is a concern that the butane gas will expand again, float up, and accumulate between the PSP and the laminated film to form an air pocket. From this, the inventors have come up with the idea that there is room for improvement in the properties of the layer closest to the PSP as the base sheet.

[0010] In addition, the inventors are considering maximizing the cost-effectiveness based on the balance between the cost incurred in each process and the number of processes. Specifically, assuming the extension of the food preservation period and the avoidance of the bagging phenomenon, there may be a difference in cost-effectiveness between operating a process with a high cost with a smaller number of man-hours and operating a process with a low cost with a larger number of man-hours. From this, the inventors have come up with the idea that there is room for improvement in the lamination procedure of the laminated film.

[0011] Therefore, an object of the present invention is to provide a method for manufacturing a foamed sheet for thermoforming that can expect an improvement in cost-effectiveness by optimizing the lamination procedure of the laminated film while realizing the adhesion state between the base sheet and the laminated film suitable for the use and function of the packaging container, a method for manufacturing a packaging container using the foamed sheet for thermoforming, the foamed sheet for thermoforming, the packaging container, and a method for using the packaging container.

Means for Solving the Problems

[0012] That is, the method for manufacturing a foamed sheet for thermoforming of a packaging container with a draw ratio of 0.1 to 0.45 in the present invention comprises a step of laminating a thin first film on a foamed base sheet By thermal compression bonding without an adhesive drying process to obtain a foamed sheet with a film, and A second film including a barrier layer is thermally compression bonded without an adhesive drying process to the first film side of the foamed sheet with the film a step of laminating to obtain a foamed sheet for thermoforming, and is characterized by including the above steps.

[0013] The manufacturing method of the foamed sheet for thermoforming preferably further includes a step of printing to obtain a thin first film with a pattern.

[0014] The thickness of the above-mentioned first film is preferably 10 μm or more and less than 30 μm. wherein the thickness of the second film is 20 μm or more and less than 60 μm It is desirable that.

[0015] In addition, the manufacturing method of the packaging container in the present invention is characterized by including a step of molding the foamed sheet for thermoforming manufactured by the manufacturing method of the foamed sheet for thermoforming.

[0016] In addition, in the present invention For a packaging container with a draw ratio of 0.1 to 0.45 The foamed sheet for thermoforming includes a foamed base sheet, a first film with a thickness of 10 μm or more and less than 30 μm thermally laminated to the foamed base sheet, and a barrier layer thermally laminated to the first film. Having a thickness of 20 μm or more and less than 60 μm A second film, and is characterized by comprising.

[0017] The above-mentioned first film is preferably a printed film with a pattern.

[0018] In addition, the packaging container in the present invention is characterized by being obtained by molding the above-mentioned foamed sheet for thermoforming.

[0019] In addition, the usage method of the packaging container in the present invention is characterized by gas replacement packaging or close packaging.

Effects of the Invention

[0020] According to the present invention, while realizing the adhesion state between the foamed base sheet and the laminated film suitable for the use and function of the packaging container, the lamination procedure of the laminated film can be optimized to expect an improvement in cost performance.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0022] Hereinafter, with reference to FIGS. 1 to 3, a method for manufacturing a foamed sheet for thermoforming, a method for manufacturing a packaging container made of the foamed sheet for thermoforming, the foamed sheet for thermoforming, the packaging container, and a method for using the packaging container according to an embodiment of the present invention will be described. In these figures, for convenience of explanation, a predetermined part and this lead line are shown by a broken line or an imaginary line (a two-dot chain line), and there is also a part where a cross-sectional part is shown by hatching.

[0023] <Outline of the manufacturing method of the foamed sheet for thermoforming> The manufacturing method of the foamed sheet 1 for thermoforming shown in FIG. 1 includes a step of laminating a thin first film 12 on a foamed base sheet 11 to obtain a foamed sheet with a film (hereinafter also referred to as the "first lamination step"), and a second step of laminating a second film 13 containing a barrier layer on the first film 12 side of the foamed sheet with a film to obtain a foamed sheet for thermoforming (hereinafter also referred to as the "second lamination step").

[0024] The foamed sheet 1 for thermoforming manufactured in these steps has a thin first film 12, and since the first film 12 is easily laminated because it is easily attached to the foamed base sheet, the peel strength between the first film 12 and the foamed base sheet 11 is improved, so that the foaming agent hardly floats from the foamed base sheet 11 during molding and hardly accumulates between the first film 12. Furthermore, since it does not include a dry lamination step, the peel strength between the film obtained by combining the first film 12 and the second film 13 (hereinafter referred to as the "laminated film 14") and the foamed base sheet 11 is also improved. Therefore, it is possible to expect an effect that the laminated film 14 is hardly peeled off from the foamed base sheet 11 and the bagging phenomenon is easily avoided.

[0025] In addition, each of these steps may all be set within the same production line for manufacturing the foamed sheet for thermoforming. However, since only one of them may be set within the above production line and the other may be set outside the above production line, it becomes easier to recombine the steps and change the equipment associated with the steps. Also, for example, in the case of the laminating method, the cost-effectiveness can be expected to improve because it is not necessary to adopt the dry lamination method, which is relatively costly, for the adhesive drying step.

[0026] The method for manufacturing a foamed sheet for thermoforming further includes a step of printing to obtain a thin first film 12 with a pattern (hereinafter also referred to as the "printing step").

[0027] Including this step, the foamed sheet for thermoforming manufactured can obtain a packaged container with a pattern while exhibiting a desired peel strength between the first film 12 and the foamed base sheet 11 and between the second film 13 and the first film 12. Therefore, it is possible to expect the effect of improving the commercial value according to the type of food to be packaged.

[0028] <Overview of Lamination> Lamination refers to laminating and adhering the first film 12 to the foamed base sheet 11, or laminating and adhering the second film 13 to the foamed sheet with a film to which the first film 12 is laminated and adhered. Here, the foamed base sheet 11 and the first film 12 may be laminated by thermocompression bonding while being thermocompression bonded with a heating roll, or may be laminated with an adhesive intervening between the foamed base sheet 11 and the first film. Also, in the lamination of the foamed sheet with a film to which the first film 12 is laminated and adhered and the second film 13, it may be laminated by thermocompression bonding, or an adhesive may intervene between the foamed sheet with a film and the second film 13. Such lamination means include, for example, the thermal lamination method and the extrusion lamination method, and preferably the thermal lamination method, which is relatively cost-effective.

[0029] The lamination adhesion temperature may be appropriately set according to the properties of the foam base sheet 11, the first film 12, and the second film 13, and it is only necessary that the desired peel strength can be exhibited between the foam base sheet 11 and the first film 12 and between the first film 12 and the second film 13.

[0030] When the material of the foam base sheet 11 is a polystyrene-based resin, for example, it may be 100°C to 300°C, preferably 130°C to 270°C, and more preferably 160°C to 240°C. When the material of the foam base sheet 11 is a polypropylene-based resin, for example, it may be 100°C to 300°C, preferably 130°C to 270°C, and more preferably 160°C to 240°C. When the material of the foam base sheet 11 is a polyethylene-based resin, for example, it may be 90°C to 280°C, preferably 100°C to 230°C, and more preferably 110°C to 190°C.

[0031] <Peel strength> Based on the peel adhesion strength test method of the adhesive specified in JIS K6854-2, the peel strength between the foam base sheet 11 and the first film 12 and / or the peel strength between the first film 12 and the second film 13 is 1.5 N / 15 mm or more, preferably 2.0 N / 15 mm or more, more preferably 4.0 N / 15 mm or more with impact resistance against vibrations and drops during logistics, still more preferably 5.0 N / 15 mm or more, and even more preferably 6.0 N / 15 mm or more. Also, it may be in a case where it is sufficiently adhered and difficult to peel.

[0032] <Thickness of the foamed sheet for thermoforming> The thickness of the foamed sheet 1 for thermoforming may be greater than the sum of the thickness of the foamed base material sheet 11, the thickness of the first film 12, and the thickness of the second film 13. When the material of the foamed base material sheet 11 is a polystyrene-based resin, it may be 3.0 mm to 4.5 mm, preferably 3.8 mm to 4.0 mm. When the material of the foamed base material sheet 11 is a polyolefin-based resin, it may be 0.5 mm to 2.5 mm, preferably 0.6 mm to 1.5 mm, and more preferably 0.8 mm to 1.2 mm.

[0033] <Thickness of the laminated film> The thickness of the laminated film 14 may be 40 μm to 100 μm. Preferably, it has impact resistance against vibrations and drops during logistics. Also, it is 50 μm to 70 μm to exhibit a desired peel strength within the range of the lamination adhesion temperature. If it is less than 40 μm, it is too thin to obtain the effects of the first film 12 and the second film 13. If it exceeds 100 μm, it is too thick and likely to peel from the foamed base material sheet 11. Also, in addition to the first film and the second film, for example, a third film may be laminated at an arbitrary location as needed.

[0034] The first film is not particularly limited. It may be colorless transparent, opaque, or translucent. As described later, it may have a printed surface or may be colored by kneaded pigments or the like. Such a printed surface may be formed by printing on the surface of the first film. For example, it may be formed on the surface on the side laminated with the foamed base material sheet.

[0035] <Outline of printing> The printed surface may be on both sides of the first film 12. Preferably, it is only on the surface that does not adhere to the second film 13 (the surface that adheres to the foamed base material sheet 11) so that the peel strength does not relatively decrease. The printing process may be set after the first lamination process. Preferably, it is set before the first lamination process to make the printed surface the surface that adheres to the foamed base material sheet 11.

[0036] <Combination of the first lamination process and the second lamination process> As patterns of combinations of the first laminating step and the second laminating step for the production line of the foamed sheet for thermoforming, when the first laminating step is set outside the above production line and the second laminating step is set inside the above production line (hereinafter also referred to as "process pattern 1"), when the first laminating step and the second laminating step are set inside the above production line (hereinafter also referred to as "process pattern 2"), when the first laminating step is set inside the above production line and the second laminating step is set outside the above production line (hereinafter also referred to as "process pattern 3"), and when the first laminating step and the second laminating step are set outside the production line of the foamed sheet for thermoforming (hereinafter also referred to as "process pattern 4"). Preferably, it is process pattern 1 or process pattern 2, and more preferably, it is process pattern 1. Outside the production line means, for example, in the same building and another production line, in the same building and a special production area, or in a different building.

[0037] <Combination of the printing step and the first laminating step> As a combination of the printing step and the first laminating step for the production line of the foamed sheet 1 for thermoforming, the printing step is preferably set together with the first laminating step. Specifically, in process pattern 1 or process pattern 4, it is set outside the above production line, and in process pattern 2 or process pattern 3, it is set inside the above production line.

[0038] <Details of the foamed base sheet> When the material of the foamed base sheet 11 is a polystyrene-based resin, the thickness of the foamed base sheet 11 may be 1.8 mm to 2.5 mm, and preferably 2.0 mm to 2.2 mm. When the material of the foamed base sheet 11 is a polyolefin-based resin, the thickness may be 0.5 mm to 2.5 mm, preferably 0.6 mm to 1.5 mm, and more preferably 0.8 mm to 1.2 mm. If it is less than the lower limit value, the strength and rigidity as a laminated sheet or a packaging container are too low and it is easy to break. If it exceeds the upper limit value, it is difficult to mold so that the wall thickness distribution is as set in the designed thickness as a packaging container, and the residual amount of the foaming agent added during production is too large, and floating or post-deformation is likely to occur.

[0039] The raw material of the foam base sheet 11 is, for example, a polyolefin resin such as a polypropylene-based resin or a polyethylene-based resin, or a thermoplastic resin such as a polystyrene-based resin. It may be one type or a mixture of two or more types in a predetermined ratio, or it may be a mixture of these with a filler (inorganic filler) kneaded in a predetermined weight ratio.

[0040] Examples of the inorganic filler include talc, calcium carbonate, silica, clay, wollastonite, potassium titanate, zonotrite, gypsum fiber, aluminum borate, fibrous magnesium compound (MOS), aramid fiber, carbon fiber, glass fiber, mica, glass flake, and polyoxybenzoyl whisker. It may be one type or a mixture of two or more types in a predetermined ratio, and preferably talc with a proven track record in the food packaging field.

[0041] As a method for manufacturing the foam base sheet 11, for example, a foaming agent may be added to a polystyrene-based resin as a raw material, and after melt-kneading with an extruder, it may be extruded and foamed to obtain a polystyrene foam sheet (PSP).

[0042] As the foaming agent, conventional compounds can be used, such as volatile foaming agents like propane, butane, pentane, and hexane, chemical foaming agents (decomposable foaming agents) like ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, and sodium citrate, and applicable foaming agents such as carbon dioxide, nitrogen gas, and water. These foaming agents may be used alone or in combination.

[0043] <Details of the First Film> The first film 12 is preferably easy to adhere to the foamed base material sheet 11 and contains 50% or more of the same raw material as that on the surface of the foamed base material sheet 11. For example, when the foamed base material sheet 11 is a polystyrene foam sheet, it is an unstretched polystyrene film (CPS film) or a biaxially stretched polystyrene film (OPS film); when the foamed base material sheet 11 is a polypropylene foam sheet, it is an unstretched polyolefin film (CPP film) or a biaxially stretched polyolefin film (OPP film); when the foamed base material sheet 11 is a polyethylene foam sheet, it is an inflation polyethylene film (IPE film) or an unstretched polyethylene film (CPE film).

[0044] The thickness of the first film 12 may be 10 μm or more and less than 30 μm, preferably 10 μm to 28 μm with impact resistance against vibrations and drops during logistics, and also exhibiting a desired peel strength within the range of the lamination adhesion temperature, more preferably 15 μm to 26 μm, still more preferably 18 μm to 25 μm. If it is thinner than 10 μm or thicker than 30 μm, the lamination adhesion temperature is likely to become narrow. Also, if it is thinner than 10 μm, the amount of components that function as a sealant will decrease, and there is concern that the desired effect of improving the peel strength cannot be expected. If it is thicker than 30 μm, there is concern that heat will not be evenly transmitted during the adhesion between the first film 12 and the foamed base material sheet, resulting in variations in the peel strength.

[0045] The first film 12 may be laminated on both sides of the foamed base material sheet, but in view of economy, it is preferably laminated and adhered only on the side where the second film is laminated.

[0046] <Details of the second film> As shown in FIG. 2, the second film 13 includes, in addition to the barrier layer, a resin layer made of a thermoplastic resin such as a polypropylene-based resin or a polyethylene-based resin as a raw material, and an adhesive layer that adheres the barrier layer and the resin layer, and these are co-extruded and laminated. The resin layers may have the same raw materials and lamination positions, or may include different first and second resin layers. The order of the layers included in the second film 13, from the side closer to the first film 12, is, for example, a first resin layer 131, an adhesive layer 132, a barrier layer 133, an adhesive layer 134, and a second resin layer 135.

[0047] The thickness of the second film 13 may be 20 μm to 60 μm, preferably 30 μm to 50 μm, which has impact resistance against vibrations and drops during logistics and exhibits a desired peel strength within the range of the lamination adhesion temperature. If it is less than 20 μm, it is too thin to obtain the effects of the barrier layer and the resin layer, and if it exceeds 60 μm, it is too thick and easily peels off from the first film 12.

[0048] The first resin layer 131 is preferably one that easily adheres to the first film 12. For example, it may be only polypropylene or only polyethylene, or a mixture of these in a predetermined ratio. The above ratio may be 90:10 to 10:90 for polypropylene:polyethylene, 80:20 to 20:80, or 70:30 to 30:70, or may be 1% by mass or less of polystyrene with respect to 100% by mass of polypropylene.

[0049] The adhesive layers 132 and 134 only need to be able to adhere the first resin layer 131 and the barrier layer 133 and the barrier layer 133 and the second resin layer 135. For example, they are polyolefin-based adhesive resins.

[0050] The barrier layer 133 is made of a resin through which gases that affect the quality of food, such as oxygen gas, water vapor gas, and carbon dioxide gas, hardly permeate. Preferably, the oxygen permeability according to JIS K7126 is 1000 ml / m at a thickness of 25 μm 2 ·24 hr·MPa (at 20 °C and 75% RH) or less and can be co-extruded, and is, for example, an ethylene-vinyl alcohol copolymer (EVOH) or a polyamide (PA).

[0051] Here, the thickness of the barrier layer is not particularly limited, but for example, it may be 1 μm to 15 μm, more preferably 4 μm to 10 μm, and even more preferably 5 μm to 8 μm. If the thickness of the barrier layer is less than 1 μm, there is a concern that the desired gas barrier property cannot be obtained. If it exceeds 15 μm, there is a concern about the cost increase due to the high material cost of the gas barrier resin such as the above-mentioned ethylene-vinyl alcohol copolymer (EVOH) or polyamide (PA).

[0052] The second resin layer 135 is preferably one that is easily thermally pressure-bonded to the top seal and the pressure-bonded top seal is easily removable (has easy peelability). For example, it may be only polypropylene or only polyethylene, or a mixture of these in a predetermined ratio. The above ratio may be 90:10 to 10:90 for polypropylene:polyethylene, 80:20 to 20:80, or 70:30 to 30:70, and may be 1% by mass or less of polystyrene with respect to 100% by mass of polypropylene.

[0053] In the present invention, it is preferable that a coating agent as an adhesive is interposed between the first film and the second film. According to such a coating agent, different materials can be reliably adhered to each other. Here, the components of the coating agent are not particularly limited, but a urethane-based resin adhesive is preferable. Such a coating agent may be applied in advance to the surface of the second film or the first film, or may be supplied between the first film and the second film when the first film and the second film are laminated.

[0054] Further, the adhesive start temperature of the coating agent functioning as an adhesive between the first film and the second film is preferably 150°C to 180°C, and more preferably 160°C to 170°C. According to such a configuration, less heat is required when, for example, the second film is thermally laminated to the first film. Here, the adhesive start temperature refers to the temperature required to exert the effect of the coating agent.

[0055] <Details of the printed surface> The printed surface may be, for example, a printed layer printed with a metal ink composed of metallic powder having glossiness. Examples of the metallic powder include aluminum powder, gold powder, silver powder, copper powder, bronze powder, and zinc powder. It may be one type or a mixture of two or more types. It may also be metallic powder having various conventionally known forms as metallic luster components such as powders of other metals or alloys or metal vapor deposition flakes. It may be metallic powder mixed with a colorant such as yellow or red to adjust the color tone, or it may be one in which a metal film is formed on the surface of an inorganic filler. The powder content is 5 mg / m 2 or more in order to sufficiently exhibit gloss, but preferably 5 mg / m 2 ~500 mg / m 2 is preferable, more preferably 10 mg / m 2 ~200 mg / m 2 and even more preferably 20 mg / m 2 ~100 mg / m 2 .

[0056] <Overview of the packaging container> The packaging container 2 shown in FIG. 3 is obtained by molding the foamed sheet 1 for thermoforming shown in FIG. 1 and is for packaging food in a lid or vacuum state. For example, it includes a bottom portion 21 on which food is placed, a side portion 22 continuously provided upward from the peripheral edge of the bottom portion 21, and a flange portion 23 continuously provided outward from the entire upper end edge of the side portion 22.

[0057] The manufacturing method of the packaging container 2 specifically includes a step of adding a foaming agent to the foamed sheet 1 for thermoforming in a state after manufacturing and before molding (hereinafter also referred to as the "first foamed sheet for thermoforming") to make it in a foamed state (hereinafter also referred to as the "second foamed sheet for thermoforming") (hereinafter also referred to as the "foaming step"), and a step of vacuum molding the second foamed sheet for thermoforming from one side (downward) or both sides (up and down) with a predetermined mold (hereinafter also referred to as the "molding step").

[0058] Here, regarding the molding process, there are no particular restrictions as long as a packaging container 2 of a desired shape can be molded from the foamed sheet 1 for thermoforming. Examples include the double-sided vacuum molding method and the single-sided vacuum molding method. It is preferable to select the single-sided vacuum molding method in which the mold does not contact the laminated film. In the case of the single-sided vacuum molding method, since the laminated film side is not pulled, the influence on the film side due to vacuum suction is small, reducing the adhesion variation in the packaging process for top sealing and skin packaging, and enabling stable adhesion.

[0059] When the lid is a top seal, the flange portion 23 for thermocompression bonding the top seal preferably has a substantially horizontal flat portion between the inner peripheral edge corresponding to the upper end edge of the side portion 22 and the outermost peripheral edge, or an arch-shaped curved portion in an end view that becomes the flat portion due to the pressure during thermocompression bonding, so as to facilitate adhesion to the top seal, in a state where the packaging container 2 is placed on a table.

[0060] Also, the flange portion 23 is preferably in a non-foamed state or a state where the fine irregularities on the surface are smoothed so as to facilitate adhesion to the top seal. The thickness of the flange portion 23 may be thinner than the thickness of the bottom portion 21 and the side portion 22. In the molding process, the thickness of the flange portion 23 may be made thinner than the thickness of the bottom portion 21 and the side portion 22 by performing double-sided vacuum molding with a mold in which the thickness of the space corresponding to the flange portion 23 is thinner than the thickness of the space corresponding to the bottom portion 21 and the side portion 22.

[0061] The thickness of the flange of the packaging container 2 may be 2.0 mm to 5.0 mm, preferably 2.5 mm to 4.0 mm, more preferably 2.7 mm to 3.5 mm when the material of the foamed base sheet 11 is a polystyrene-based resin. When the material of the foamed base sheet 11 is a polyolefin-based resin, it may be 0.5 mm to 2.5 mm, preferably 0.6 mm to 1.5 mm, and 0.8 mm to 1.2 mm.

[0062] Although there is no particular limitation on the draw ratio (S) of the packaging container of the present invention, the effects of the present invention are more effectively exhibited preferably when it is 0.1 to 0.45, more preferably 0.15 to 0.4, and still more preferably 0.2 to 0.35. Here, the draw ratio (S) refers to the value represented by the following formula (1). S = (depth of the container) / (diameter of the circle that inscribes the maximum diameter in the opening of the container) (1) That is, the draw ratio (S) is the value of the depth of the deepest part of the container divided by the diameter of the largest inscribed circle that contacts the shape of the recess (opening) formed in the plane of the sheet. For example, when the shape of the recess is a circle, its diameter; when it is an ellipse, its minor axis; and when it is a rectangle, the length of its short side becomes the diameter of the inscribed circle with the maximum diameter, respectively.

[0063] <Method of using the packaging container> Food may be gas barrier packaged or tightly packaged using the packaging container 2. Gas barrier packaging (MAP: Modified Atmosphere Packaging) is a gas barrier packaging in which the air inside the container is removed and filled with nitrogen, carbon dioxide, etc. or a mixture thereof, and the food is sealed with a top seal. Tight packaging is a vacuum packaging in which a heated skin film is attached to the inner surface of the container together with the food in a vacuum state to seal the food.

[0064] In the case of gas barrier packaging, the food is placed in the packaging container 2, the inside of the container is gas barrier replaced, and then a top seal is heat pressure bonded to the flange portion 23 from above with a top sealer to seal it. The order of each layer included in the top seal is, from the side farther from the flange portion 23, that is, the outer side that does not contact the food, for example, polyamide (PA), adhesive layer, barrier layer, adhesive layer, sealant layer (thermoplastic resin). The sealant layer preferably has easy opening properties. The adhesive layer is, for example, a polyolefin-based adhesive resin. The barrier layer is, for example, an ethylene-vinyl alcohol copolymer or polyamide.

[0065] In the case of close packaging, the food is placed in the packaging container 2. After moving the heated skin film above the packaging container 2, the inside of the container is put into a vacuum state by a skin pack packaging machine to degas the air inside the container, and then returned to the atmospheric state. Utilizing the differential pressure at that time, the skin film is attached to the inner surface of the packaging container 2 together with the food and sealed. The skin film includes, for example, an inner layer that adheres to the inner surface of the packaging container 2 and an outer layer laminated on the inner layer. The outer layer may have a shape retention property of being three-dimensionally stretched along the shape of the inner surface in a softened state when heated and retaining that shape when cooled. An intermediate layer having functionality such as a barrier layer or a reinforcing layer may be interposed between the inner layer and the outer layer.

Example

[0066] The evaluation tests of the foamed sheet for thermoforming manufactured by the manufacturing method of the foamed sheet for thermoforming in one embodiment of the present invention and the packaging container manufactured by the manufacturing method of the packaging container made of the above foamed sheet for thermoforming will be described below.

[0067] <Evaluation test method in the example> The manufacturing method of the foamed sheet for thermoforming includes at least a first lamination step and a second lamination step. The components of the foamed base material sheet (PSP or PP foam) are set as individual conditions, and the laminations in the first lamination step and the second lamination step adopt the thermal lamination method (roll speed = 8.5 m / min, pressure = 0.5 Mpa), and the combination of the first lamination step and the second lamination step or other lamination steps are set as individual conditions.

[0068] The first film is an unstretched polystyrene film (CPS film) or an unstretched polyolefin film (CPP film), and the presence or absence of printing on the foamed base material sheet side is set as an individual condition. The second film has a coating agent, a polypropylene-based resin layer (PP), a polyolefin-based adhesive resin layer (Adh), an ethylene-vinyl alcohol copolymer layer (EVOH), a polyolefin-based adhesive resin layer (Adh), and an easy peel layer (EP) laminated in this order from the side closer to the first film.

[0069] The manufacturing method of the packaging container as an example includes a foaming process and a molding process. The molding process employs a double-sided vacuum molding method. The manufactured packaging container includes a bottom, a side portion, and a flange portion. It is for gas replacement packaging, and a top seal is thermocompression bonded to the flange portion having a flat portion to seal it.

[0070] The peel strength test is carried out using a universal testing machine manufactured by Instron (distance between chucks = 25 mm, peel speed = 200 mm / min) based on the peel adhesion strength test method for adhesives specified in JIS K6854-2. The test pieces are a part of the cut first foamed sheet for thermoforming, a part of the cut second foamed sheet for thermoforming, and a part (15 mm width) of the flange portion in the packaging container, and a part of the laminated film of each of the above parts peeled off.

[0071] The flow of the peel strength test is to clamp the peeled laminated film on one chuck of the above testing machine, clamp the foamed substrate sheet to which the laminated film was attached on the other chuck, expand the distance between both chucks, and end when the laminated film peels off from the substrate sheet.

[0072] The individual conditions of Examples 1 to 4 and Comparative Examples 1 to 3 are as follows.

[0073] <Example 1> Foamed substrate sheet = PSP First film = Printed, CPS film (from the foamed substrate sheet side) Second film = Coating agent, PP, Adh, EVOH, Adh, EP (from the first film side) Thickness of the first film = 20 μm, thickness of the second film = 40 μm Combination of the first lamination process and the second lamination process = Process pattern 1 Lamination temperature during thermal lamination in the first lamination process and the second lamination process: 175°C

[0074] <Example 2> The conditions are the same as those of Example 1 except that the combination of the first lamination process and the second lamination process is process pattern 2.

[0075] <Example 3> The conditions are the same as those in Example 1, except that there is no printing on the first film.

[0076] <Example 4> Foamed base material sheet = PP foam First film = (from the side of the foamed base material sheet) coating agent, printing, CPP film Second film = same conditions as in Example 1 Thickness of the first film = 25 μm, thickness of the second film = 40 μm Lamination process = laminate the first film in the production line during the extrusion of the foamed base material sheet, and laminate the second film in the production line before molding. Lamination temperature during thermal lamination in the first lamination process: 170 °C Lamination temperature during thermal lamination in the second lamination process: 175 °C

[0077] <Comparative Example 1> The conditions are the same as those in Example 1, except that the dry lamination method is adopted in the second lamination process, the lamination temperature during thermal lamination is 205 °C, and the printing is on the second film side.

[0078] <Comparative Example 2> The conditions are the same as those in Example 1, except that there is no first film.

[0079] <Comparative Example 3> Foamed base material sheet = PP foam First film = (from the side of the foamed base material sheet) coating agent, CPP film, printing Second film = same conditions as in Comparative Example 1 Thickness of the first film = 25 μm, thickness of the second film = 40 μm Lamination process = dry laminate the first film and the second film outside the production line, and laminate the first film side inside the production line during the extrusion of the foamed base material sheet. Lamination temperature during thermal lamination: 170 °C

[0080] <Evaluation Results> The evaluation results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1, and the evaluation results of Example 4 and Comparative Example 3 are shown in Table 2. For convenience of reference, the above-mentioned individual conditions are also described in these tables.

[0081]

Table 1

[0082] <Examples 1 to 3> From Example 1, it was confirmed that the peel strength in the second thermoforming foam sheet was the highest. Also, when comparing the peel strengths of the first forming foam sheet, the second forming foam sheet, and all the molded products based on Example 1, it was confirmed that in Example 2, by setting the first lamination process and the second lamination process within the same production line, the above peel strength was improved, and in Example 3, if the process pattern was the same, the peel strength was equivalent even without printing. That is, from Example 3, it was found that the presence or absence of the printed surface was irrelevant to the peel strength between the foam base sheet and the first film.

[0083] <Comparative Examples 1 and 2> For Examples 1 to 3, in Comparative Example 1, the first film and the second film were laminated by a dry lamination method using a dry lamination adhesive, and since it was difficult to adhere at the desired heating temperature, it was confirmed that the peel strengths of the first forming foam sheet, the second forming foam sheet, and all the molded products decreased. Also, in Comparative Example 1, since the peel strength in the molded product was the lowest, when thermally laminating the laminated film with an increased thickness obtained by dry laminating the first film and the second film, it was speculated that the heat required for adhesion was not sufficiently transmitted, leading to a decrease in peel strength and becoming a factor in the quality degradation of the molded product. In Comparative Example 2, even if the overall thickness of the laminated film was thin, it was feared that it would be difficult to exhibit the desired peel strength without the first film.

[0084] That is, the difference between Example 3 and Comparative Example 2 is only the presence or absence of the first film, but this difference causes a significant difference in the peel strength. Rather than directly adhering a second film containing a barrier layer to the PSP as the foam base sheet using a coating agent, it is possible to achieve a stronger peel strength by adhering a second film containing a barrier layer to the foam sheet with a film obtained by heat-sealing a transparent plain CPS film as the first film to the PSP using a coating agent. This is presumably because the surface roughness of the PSP, which is a foam, is relatively high, so even when adhered using a coating agent, the adhesive surface area decreases, resulting in a decrease in the peel strength.

[0085]

Table 2

[0086] <Example 4 and Comparative Example 3> In Example 4, after obtaining a first thermoformable foam sheet by laminating a first film with a printed surface on the foam base sheet side to a foam base sheet made of PP foam using a coating agent, the second film was laminated to the first film using a coating agent without obtaining a second thermoformable foam sheet. On the other hand, in Comparative Example 3, after obtaining a laminated film by dry laminating the first film and the second film, a coating agent was applied to the foam base sheet side of the laminated film, and then the laminated film was thermally laminated to the foam base sheet to obtain a thermoformable foam sheet. That is, it is presumed that when the first film and the second film are dry laminated, the thickness of the film laminated to the foam base sheet at one time becomes thick, so that sufficient heat for adhesion is not provided, leading to a decrease in the peel strength.

Explanation of symbols

[0087] 1 Thermoformable foam sheet, 11 Foam base sheet, 12 First film, 13 Second film, 2 Packaging container, 21 Bottom, 22 Side, 23 Flange

Claims

1. A method for manufacturing a foamed sheet for thermoforming a packaging container for gas replacement packaging or close-fitting packaging with a draw ratio of 0.1 to 0.45, comprising: laminating a thin first film to a foamed base sheet by thermocompression bonding without including a drying process of an adhesive to obtain a foamed sheet with a film; laminating a second film including a barrier layer to the first film side of the foamed sheet with a film by thermocompression bonding without including a drying process of an adhesive to obtain a foamed sheet for thermoforming; the thickness of the first film is 10 μm or more and less than 30 μm; the thickness of the second film is 20 μm or more and less than 60 μm A method for manufacturing a foamed sheet for thermoforming, characterized by the above.

2. The first film contains 50% or more of the same raw material as the raw material on the surface of the foamed base sheet. A method for manufacturing a foamed sheet for thermoforming according to Claim 1, characterized by the above.

3. The foamed base sheet is a polystyrene foamed sheet, and the first film is an unstretched polystyrene film. A method for manufacturing a foamed sheet for thermoforming according to Claim 2, characterized by the above.

4. A first lamination step of laminating the first film to the foamed base sheet to obtain a foamed sheet with a film; A second lamination step of laminating the second film to the first film side of the foamed sheet with a film to obtain a foamed sheet for thermoforming; Both the first lamination step and the second lamination step are set in the manufacturing line of the foamed sheet for thermoforming. A method for manufacturing a foamed sheet for thermoforming according to any one of Claims 1 to 3, characterized by the above.

5. A first lamination step of laminating the first film to the foamed base sheet to obtain a foamed sheet with a film; A second lamination step of laminating the second film to the first film side of the foamed sheet with a film to obtain a foamed sheet for thermoforming; Only one of the first lamination step and the second lamination step is set in the manufacturing line of the foamed sheet for thermoforming. A method for manufacturing a foamed sheet for thermoforming according to any one of Claims 1 to 3, characterized by the above.

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