Method for manufacturing foam sheet for thermoforming, method for manufacturing packaging container, foam sheet for thermoforming, packaging container, and method for using packaging container

Abstract

To provide a foam sheet for thermoforming capable of exhibiting an adhesion state between a foam base material sheet and a laminated film suitable for use and function of a packaging container, and capable of expecting improvement of cost effectiveness by optimizing a lamination procedure of the laminated film.SOLUTION: The foam sheet for thermoforming is a foam sheet for thermoforming of a packaging container for gas replacement packaging or close contact packaging having a draw ratio of 0.1 to 0.45, and includes a foam base material sheet 11, a first film 12 having a thickness of 10 μm or more and less than 30 μm and laminated on the foam base material sheet 11 without including an adhesive for dry lamination, and a second film 13 having a thickness of 20 μm or more and less than 60 μm and including a barrier layer and laminated on the first film 12 without including an adhesive for dry lamination.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thermoformable foam sheet obtained by laminating a film to a base sheet, a method for producing a packaging container made from the thermoformable foam sheet, the thermoformable foam sheet, the packaging container, and a method for using the packaging container. [Background technology]

[0002] Conventionally, food packaging containers sold, for example, at supermarkets and convenience stores, have been obtained by thermoforming synthetic resin sheets. The sheets are formed by laminating a base sheet and, if necessary, a film using a known method such as coextrusion or lamination, and the properties of the base sheet and film, such as their composition and thickness, have been determined depending on the application and function of the packaging container.

[0003] Patent Document 1 discloses a technology for obtaining a foamed sheet for deep drawing, in which a 30 μm-thick monolayer film made of high-impact polystyrene as an impact-resistant auxiliary layer is heat-laminated onto a polystyrene foamed sheet as a substrate using a heat roll, and then 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 is dry-laminated using a urethane adhesive.

[0004] Patent Document 2 discloses a technology relating to a packaging container in which a laminated film is laminated on a polystyrene foam sheet as a substrate by a dry lamination method, in which, from the side furthest from the substrate, a co-extruded laminated film including a gas barrier layer, a dry lamination adhesive as a dry lamination adhesive layer, printing ink as a printing layer, and an unstretched polystyrene film as a polystyrene-based resin layer are laminated in this order, and the thickness of the printing layer and the polystyrene-based resin layer are 20 μm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-51264 [Patent Document 2] Patent No. 6572191 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 does not disclose the peel (adhesion) strength of the laminate film to the base sheet. That is, the addition of a barrier layer, etc. increases the overall thickness of the laminate film, making it more likely to peel from the base sheet. Therefore, depending on the correlation between the properties of the film closest to the base sheet, the lamination procedure including the film, and the method of sealing the food in the packaging container, there is a risk that the laminate film will peel from the base sheet when the food is opened.

[0007] Furthermore, in Patent Document 2, the printed polystyrene resin layer and the co-extruded laminate film are laminated by a dry lamination method using a dry lamination adhesive, which results in a thick laminate film as a whole. This narrows the range of conditions, such as the heating temperature, that can be used when thermally laminating the laminate film onto the base sheet, making it difficult to achieve the desired peel strength. This may result in a decrease in production efficiency when processing raw sheets and packaging containers.

[0008] From the perspective of extending the shelf life of foods, the use of seal-type lids (hereinafter also referred to as "top seals") that make it difficult for gases such as oxygen to pass into the packaging container and skin films that create a vacuum inside the packaging container is becoming more common depending on the type of food. However, compared to conventional snap-on lids that seal packaging containers, top seals and skin films are tightly attached to the laminated film, and are therefore more likely to induce a phenomenon in which the laminated film peels off from the base material without peeling off when the container is opened (hereinafter also referred to as "bagging phenomenon").

[0009] Furthermore, the inventors have hypothesized that another problem besides the bag-forming phenomenon is air pockets between the base sheet and the laminated film. 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 cause secondary expansion of the base sheet during molding of the packaging container. Therefore, there is a concern that after food ingredients are placed in the packaging container and exposed to high temperatures during tight packaging, the butane gas will expand again, float up, and accumulate between the PSP and the laminated film, forming air pockets. This led the inventors to realize that there is room for improvement in the properties of the layer closest to the PSP used as the base sheet.

[0010] The inventors are also considering maximizing cost-effectiveness by balancing the cost incurred in each process with the number of processes. Specifically, assuming that the shelf life of food is extended and bagging phenomenon is avoided, there may be a difference in cost-effectiveness between operating more expensive processes with fewer steps and operating less expensive processes with more steps. This led the inventors to 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 producing a thermoformable foam sheet that can achieve an adhesive state between a base sheet and a laminate film that is suitable for the application and function of the packaging container, and that can be expected to improve cost-effectiveness by optimizing the lamination procedure of the laminate film, a method for producing a packaging container made from the thermoformable foam sheet, the thermoformable foam sheet, the packaging container, and methods for using the packaging container. [Means for solving the problem]

[0012] That is, the method for producing a thermoformable foam sheet for a packaging container having a drawing ratio of 0.1 to 0.45 in the present invention is characterized by comprising: a step of laminating a thin first film onto a foam base sheet by thermocompression bonding without a drying step of an adhesive to obtain a film-coated foam sheet; and a step of laminating a second film including a barrier layer onto the first film side of the film-coated foam sheet by thermocompression bonding without a drying step of an adhesive to obtain a thermoformable foam sheet.

[0013] The method for producing a foam sheet for thermoforming preferably further comprises the step of obtaining a thin first film with a pattern by printing.

[0014] It is desirable that the thickness of the first film be 10 μm or more and less than 30 μm, and that the thickness of the second film be 20 μm or more and less than 60 μm.

[0015] The method for producing a packaging container according to the present invention is characterized by comprising the step of molding the foamed sheet for thermoforming produced by the method for producing a foamed sheet for thermoforming described above.

[0016] The present invention also provides a thermoformable foam sheet for a packaging container for gas replacement packaging or close-contact packaging, having a draw ratio of 0.1 to 0.45, comprising: a foam base sheet; a first film having a thickness of 10 μm or more and less than 30 μm and laminated to the foam base sheet without containing a dry lamination adhesive; and a second film having a thickness of 20 μm or more and less than 60 μm and including a barrier layer, laminated to the first film without containing a dry lamination adhesive.

[0017] The first film is preferably a printed patterned film.

[0018] The packaging container of the present invention is characterized by being obtained by molding the above-mentioned foam sheet for thermoforming.

[0019] The method of using the packaging container of the present invention is characterized by carrying out gas replacement packaging or tightly sealed packaging. [Effects of the Invention]

[0020] According to the present invention, it is possible to achieve an adhesive state between the foam substrate sheet and the laminate film that is suitable for the application and function of the packaging container, and it is also possible to optimize the lamination procedure for the laminate film, thereby improving cost-effectiveness. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a partially enlarged cross-sectional view of a foam sheet for thermoforming according to one embodiment of the present invention. [Figure 2] FIG. 2 is another partially enlarged cross-sectional view of the foam sheet for thermoforming. [Figure 3] 1 is an example of a packaging container made of a thermoformable foam sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a method for producing a thermoformable foam sheet according to one embodiment of the present invention, a method for producing a packaging container made from the thermoformable foam sheet, a thermoformable foam sheet, a packaging container, and a method for using the packaging container will be described with reference to Figures 1 to 3. In these figures, for the sake of convenience, certain parts and their leading lines are shown by dashed lines or imaginary lines (two-dot chain lines), and cross sections are also shown by hatching.

[0023] <Outline of manufacturing method for thermoformable foam sheets> The method for producing the thermoformable foam sheet 1 shown in FIG. 1 includes a step of laminating a thin first film 12 onto a foam substrate sheet 11 to obtain a film-attached foam sheet (hereinafter also referred to as the "first laminating step"), and a second step of laminating a second film 13 including a barrier layer onto the first film 12 side of the film-attached foam sheet to obtain a thermoformable foam sheet (hereinafter also referred to as the "second laminating step").

[0024] In the thermoformable foam sheet 1 produced by these steps, the first film 12 is thin and can be securely thermocompressed to the foam base sheet, so that the first film 12 easily adheres to the foam base sheet 11, facilitating lamination. Because lamination is easier, the peel strength between the first film 12 and the foam base sheet 11 is improved, so that the foaming agent is less likely to rise from the foam base sheet 11 and accumulate between the first film 12 and the foam base sheet 11 during molding. Furthermore, because the process does not include a dry lamination step, the peel strength between the film (hereinafter referred to as "laminate film 14") formed by combining the first film 12 and the second film 13 and the foam base sheet 11 is also improved, so that the laminate film 14 is less likely to peel from the foam base sheet 11, and the phenomenon of forming a bag can be easily avoided.

[0025] Furthermore, each of these steps may be set up within the same production line for thermoforming foam sheets, or one may be set up within the production line and the other outside the production line. This makes it easier to rearrange the steps and change equipment associated with the steps, and is expected to improve cost-effectiveness by eliminating the need to employ, for example, a dry lamination method, which is expensive among lamination methods due to the adhesive drying step.

[0026] The method for producing a foam sheet for thermoforming further includes a step of obtaining a thin first film 12 with a pattern by printing (hereinafter also referred to as a "printing step").

[0027] The thermoformable foam sheet produced including this process can produce a patterned packaging container while exhibiting the desired peel strength between the first film 12 and the foam base sheet 11 and between the second film 13 and the first film 12, and is therefore expected to have the effect of improving the commercial value depending on the type of food being packaged.

[0028] <Overview of Lamination> Lamination refers to laminating a first film 12 onto a foam substrate sheet 11, or laminating a second film 13 onto a film-attached foam sheet to which the first film 12 has been laminated. Here, the foam substrate sheet 11 and the first film 12 may be laminated by thermocompression bonding using a heated roll, or may be laminated with an adhesive interposed between the foam substrate sheet 11 and the first film. Furthermore, laminating a film-attached foam sheet to which the first film 12 has been laminated and the second film 13 may also be performed by thermocompression bonding, or may be performed with an adhesive interposed between the film-attached foam sheet and the second film 13. Examples of such lamination methods include thermal lamination and extrusion lamination, with the thermal lamination being preferred because it is relatively cost-effective.

[0029] The lamination bonding temperature may be set appropriately depending on the properties of the foam base sheet 11, the first film 12, and the second film 13, and may be within a range that can achieve the desired peel strength 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 foam substrate sheet 11 is a polystyrene resin, the temperature may be, for example, 100°C to 300°C, preferably 130°C to 270°C, and more preferably 160°C to 240°C. When the material of foam substrate sheet 11 is a polypropylene resin, the temperature may be, for example, 100°C to 300°C, preferably 130°C to 270°C, and more preferably 160°C to 240°C. When the material of foam substrate sheet 11 is a polyethylene resin, the temperature may be, for example, 90°C to 280°C, preferably 100°C to 230°C, and more preferably 110°C to 190°C.

[0031] <Peel strength> According to the peel strength test method for adhesives specified in JIS K6854-2, the peel strength between the foam substrate 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 that provides impact resistance against vibrations, drops, etc. during distribution, even more preferably 5.0 N / 15 mm or more, and even more preferably 6.0 N / 15 mm or more. It is also acceptable if the films are sufficiently bonded and peeling is difficult.

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

[0033] <Thickness of laminated film> The thickness of laminated film 14 may be 40 μm to 100 μm, and is preferably 50 μm to 70 μm, which provides impact resistance against vibrations and drops during distribution and also provides the desired peel strength within the range of lamination bonding temperatures, and if it is less than 40 μm, it is too thin and it is difficult to obtain the effects of first film 12 and second film 13, while if it is more than 100 μm, it is too thick and is easily peeled from foam substrate sheet 11. In addition to the first film and second film, for example, a third film may be laminated at any location as needed.

[0034] The first film is not particularly limited, and may be colorless and transparent, opaque, or translucent, and may have a printed surface as described below, or may be colored with a kneaded pigment, etc. Such a printed surface may be formed by printing on the surface of the first film, for example, on the surface that will be laminated with the foam substrate sheet.

[0035] <Printing Overview> The printing surface may be on both sides of the first film 12, but preferably only on the surface that does not adhere to the second film 13 (the surface that adheres to the foam substrate sheet 11) so that the peel strength does not become relatively low.The printing process may be set after the first lamination process, but is preferably set before the first lamination process so that the printing surface becomes the surface that adheres to the foam substrate sheet 11.

[0036] <Combination of the first lamination process and the second lamination process> Combination patterns of the first lamination step and the second lamination step for a production line for a thermoformable foam sheet include a case where the first lamination step is set outside the production line and the second lamination step is set inside the production line (hereinafter also referred to as "process pattern 1"), a case where the first lamination step and the second lamination step are set inside the production line (hereinafter also referred to as "process pattern 2"), a case where the first lamination step is set inside the production line and the second lamination step is set outside the production line (hereinafter also referred to as "process pattern 3"), and a case where the first lamination step and the second lamination step are set outside the production line for a thermoformable foam sheet (hereinafter also referred to as "process pattern 4"). Process pattern 1 or process pattern 2 is preferred, and process pattern 1 is more preferred. "Outside the production line" refers to, for example, a different production line in the same building, a special production area in the same building, or a different building.

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

[0038] <Details of foam base sheet> When foam substrate sheet 11 is made of a polystyrene resin, the thickness of foam substrate sheet 11 may be 1.8 mm to 2.5 mm, and preferably 2.0 mm to 2.2 mm. When foam substrate sheet 11 is made of a polyolefin resin, the thickness may be 0.5 mm to 2.5 mm, and preferably 0.6 mm to 1.5 mm, and more preferably 0.8 mm to 1.2 mm. If the thickness is below the lower limit, the strength and rigidity of the laminate sheet or packaging container will be too low and the sheet will be prone to breakage. If the thickness is above the upper limit, the sheet will be difficult to mold into a desired thickness distribution as designed for the packaging container, and the remaining amount of foaming agent added during production will be too high, leading to lifting and subsequent deformation.

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

[0040] Examples of inorganic fillers include talc, calcium carbonate, silica, clay, wollastonite, potassium titanate, xonotlite, gypsum fiber, aluminum borate, fibrous magnesium compound (MOS), aramid fiber, carbon fiber, glass fiber, mica, glass flakes, and polyoxybenzoyl whiskers. These fillers may be of one type or a mixture of two or more types in a predetermined ratio, with talc, which has a proven track record in the field of food packaging, being preferred.

[0041] The foam substrate sheet 11 may be produced, for example, by adding a foaming agent to a polystyrene resin as a raw material, melt-kneading the mixture in an extruder, and then extruding and foaming the mixture to obtain a polystyrene foam sheet (PSP).

[0042] The blowing agent may be any of conventional compounds, such as volatile blowing agents such as propane, butane, pentane, and hexane, chemical blowing agents (decomposition type blowing agents) such as ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, and sodium citrate, carbon dioxide, nitrogen gas, water, etc. These blowing agents may be used alone or in combination.

[0043] <Details of the first film> The first film 12 is preferably easily adhered to the foam base sheet 11 and contains 50% or more of the same material as the material of the surface of the foam base sheet 11. For example, if the foam base sheet 11 is a polystyrene foam sheet, the first film 12 is an unstretched polystyrene film (CPS film) or a biaxially oriented polystyrene film (OPS film); if the foam base sheet 11 is a polypropylene foam sheet, the first film 12 is an unstretched polyolefin film (CPP film) or a biaxially oriented polyolefin film (OPP film); and if the foam base sheet 11 is a polyethylene foam sheet, the first film 12 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, and is preferably 10 μm to 28 μm, which provides impact resistance against vibrations and drops during transportation and also provides the desired peel strength within the range of lamination bonding temperatures, more preferably 15 μm to 26 μm, and even more preferably 18 μm to 25 μm. If the thickness is less than 10 μm or more than 30 μm, the lamination bonding temperature range is likely to be narrow. If the thickness is less than 10 μm, the amount of components that function as a sealant will be reduced, and there is a concern that the desired effect of improving peel strength will not be achieved. If the thickness is more than 30 μm, there is a concern that heat will not be transferred uniformly when bonding the first film 12 and the foam base sheet, resulting in variations in peel strength.

[0045] The first film 12 may be laminated on both sides of the foam substrate sheet, but from an economical standpoint, it is preferably laminated and bonded only to the side on which the second film is to be laminated.

[0046] <Details of the second film> 2, the second film 13 includes a barrier layer, a resin layer made of a thermoplastic resin such as a polypropylene resin or a polyethylene resin, and an adhesive layer that bonds the barrier layer and the resin layer, and these are co-extruded and laminated together. The resin layers may be made of the same material and may be laminated in the same position, or the second film 13 may include a first resin layer and a second resin layer that are different from each other. The order of the layers included in the second film 13, from closest to the first film 12, is, for example, first resin layer 131, adhesive layer 132, barrier layer 133, adhesive layer 134, and second resin layer 135.

[0047] The thickness of the second film 13 may be 20 μm to 60 μm, and is preferably 30 μm to 50 μm, which provides impact resistance against vibrations and drops during transportation and also provides the desired peel strength within the range of lamination bonding temperatures.If the thickness is less than 20 μm, it is too thin and it is difficult to obtain the effects of the barrier layer and resin layer, and if the thickness is more than 60 μm, it is too thick and is easily peeled off from the first film 12.

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

[0049] The adhesive layers 132 and 134 may be made of, for example, a polyolefin adhesive resin, as long as they can bond the first resin layer 131 to the barrier layer 133 and the barrier layer 133 to the second resin layer 135.

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

[0051] There are no particular limitations on the thickness of the barrier layer, but it may be, for example, 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 properties may not be obtained, and if it exceeds 15 μm, there is a concern that the cost will increase due to the high material cost of the gas barrier resin, such as the ethylene-vinyl alcohol copolymer (EVOH) or polyamide (PA).

[0052] The second resin layer 135 is preferably one that can be easily thermocompressed to the top seal and that allows the compressed top seal to be easily removed (has easy-to-open properties), and may be, for example, made of only polypropylene or only polyethylene, or a mixture of these in a predetermined ratio, where the ratio of polypropylene:polyethylene may be 90:10 to 10:90, 80:20 to 20:80, or 70:30 to 30:70, or the ratio may be 100% by mass of polypropylene to 1% by mass or less of polystyrene.

[0053] In the present invention, it is preferable that a coating agent be interposed between the first film and the second film as an adhesive. Such a coating agent can reliably bond dissimilar materials together. While there are no particular limitations on the components of the coating agent, a urethane resin adhesive is preferred. Such a coating agent may be applied to the surface of the second film or the first film in advance, or may be supplied between the first and second films when laminating them.

[0054] Furthermore, the adhesion initiation temperature of the coating agent that functions 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. This configuration reduces the amount of heat required when, for example, thermally laminating the second film onto the first film. Here, the adhesion initiation temperature refers to the temperature required for the coating agent to exert its effects.

[0055] <Printing details> The printed surface may be, for example, a printing layer printed with a metallic ink made of glossy metal powder. Examples of the metal powder include aluminum powder, gold powder, silver powder, copper powder, bronze powder, and zinc powder. These may be one type or a mixture of two or more types. They may also be metal powders of various forms conventionally known as metallic gloss components, such as powders of other metals or alloys or metal-deposited flakes. They may also be metal powders whose color tone has been adjusted by mixing with a colorant such as yellow or red, or inorganic fillers with a metal film formed on their surfaces. The powder content should be 5 mg / m² to fully develop gloss. 2However, it is preferable to use a printing layer of 5 mg / m to avoid deterioration of formability due to the printing layer being too thick. 2 ~500mg / m 2 is preferred, and more preferably 10 mg / m 2 ~200mg / m 2 , and even more preferably 20 mg / m 2 ~100mg / m 2 is.

[0056] <Overview of packaging containers> The packaging container 2 shown in Figure 3 is obtained by molding the thermoformable foam sheet 1 shown in Figure 1, and is used to package food with a lid or in a vacuum state.It has, for example, a bottom 21 on which the food is placed, side portions 22 extending upward from the peripheral edge of the bottom 21, and flange portions 23 extending outward from the entire upper edge of the side portions 22.

[0057] Specifically, the manufacturing method of the packaging container 2 includes a step (hereinafter also referred to as the "foaming step") of adding a foaming agent to the thermoforming foam sheet 1 after production but before molding (hereinafter also referred to as the "first thermoforming foam sheet") to create a foamed state (hereinafter also referred to as the "second thermoforming foam sheet"), and a step (hereinafter also referred to as the "molding step") of vacuum molding the second thermoforming foam sheet from one side (downward) or both sides (upward and downward) using a predetermined mold.

[0058] There are no particular limitations on the molding process as long as the desired shape of packaging container 2 can be molded from thermoformable foam sheet 1, but examples include double-sided vacuum molding and single-sided vacuum molding, and it is preferable to select single-sided vacuum molding, in which the mold does not come into contact with the laminated film. With single-sided vacuum molding, the laminated film side is not pulled, so the impact of vacuuming on the film side is minimal, reducing adhesion variations during the packaging process using top sealing or skin packing, and ensuring stable adhesion.

[0059] When the lid is a top seal, the flange portion 23 to which the top seal is heat-pressed preferably has, between the inner peripheral edge corresponding to the upper edge of the side portion 22 and the outermost peripheral edge, a flat portion that is approximately horizontal when the packaging container 2 is placed on a desk, or a curved portion that is arch-shaped in end view and becomes the above-mentioned flat portion when pressurized during heat-pressing, so as to make it easier to adhere to the top seal.

[0060] Furthermore, preferably, to facilitate adhesion to the top seal, the thickness of flange portion 23 may be thinner than the thickness of bottom portion 21 and the thickness of side portion 22 when it is not foamed or when any fine irregularities on the surface have been smoothed. In the molding process, the thickness of flange portion 23 may be made thinner than the thickness of bottom portion 21 and the thickness of side portion 22 by vacuum molding from both sides using a mold in which the thickness of the space corresponding to flange portion 23 is thinner than the thickness of the spaces corresponding to bottom portion 21 and 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, and more preferably 2.7 mm to 3.5 mm, when the material of the foam base sheet 11 is a polystyrene-based resin; and 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, when the material of the foam base sheet 11 is a polyolefin-based resin.

[0062] The drawing ratio (S) of the packaging container of the present invention is not particularly limited, but the effects of the present invention are more effectively exhibited when it is preferably 0.1 to 0.45, more preferably 0.15 to 0.4, and even more preferably 0.2 to 0.35. Here, the drawing ratio (S) refers to the value shown by the following formula (1). S = (depth of container) / (diameter of the largest circle inscribed in the opening of the container) (1) That is, the drawing ratio (S) is the depth of the deepest part of the container divided by the diameter of the largest inscribed circle that touches the shape of the recess (opening) formed on the plane of the sheet. For example, if the shape of the recess is a circle, the diameter is the diameter of the largest inscribed circle; if it is an ellipse, the minor axis is the diameter; if it is a rectangle, the length of the minor side is the diameter of the largest inscribed circle.

[0063] <How to use the packaging container> The packaging container 2 may be used to package food products using modified atmosphere packaging or sealed packaging. Modified atmosphere packaging (MAP) is a type of gas packaging in which the air inside the container is removed, and the container is filled with nitrogen, carbon dioxide, or a mixture of these, and the food is sealed with a top seal. Sealed packaging is a type of vacuum packaging in which a heated skin film is attached to the inside surface of the container together with the food product, under vacuum conditions, to seal the food product.

[0064] In the case of gas-flushing packaging, food is placed in the packaging container 2, and after the gas inside the container has been flustered, a top seal is heat-pressed from above onto the flange 23 using a top sealing machine to seal the container. The order of the layers included in the top seal, from the side furthest from the flange 23 (i.e., from the outside that does not come into contact with the food), is, for example, polyamide (PA), adhesive layer, barrier layer, adhesive layer, and sealant layer (thermoplastic resin). The sealant layer is preferably easy to open. 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 tight-contact packaging, the food is placed in the packaging container 2, a heated skin film is moved above the packaging container 2, and then a skin pack packaging machine is used to create a vacuum inside the container, evacuate the air inside the container, and return it to atmospheric pressure. The differential pressure created during this process is used to attach the skin film to the inner surface of the packaging container 2 and seal it together with the food. The skin film may, for example, comprise 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 shape-retaining properties that allow it to stretch three-dimensionally to conform to the shape of the inner surface when heated and softened, and retain that shape when cooled. A functional intermediate layer, such as a barrier layer or a reinforcing layer, may be interposed between the inner and outer layers. [Example]

[0066] Hereinafter, evaluation tests of a thermoformable foam sheet produced by the method for producing a thermoformable foam sheet according to one embodiment of the present invention and a packaging container produced by the method for producing a packaging container from the thermoformable foam sheet will be described.

[0067] <Evaluation test methods in examples> The method for producing a foam sheet for thermoforming includes at least a first lamination step and a second lamination step, in which the components of the foam substrate sheet (PSP or PP foam) are individual conditions, and the lamination in the first lamination step and the second lamination step is performed by a thermal lamination method (roll speed = 8.5 m / min, pressure = 0.5 MPa), and a combination of the first lamination step and the second lamination step or another lamination step is individual conditions.

[0068] The first film is a non-oriented polystyrene film (CPS film) or a non-oriented polyolefin film (CPP film), and the presence or absence of printing on the foam base sheet side is an individual condition. The second film is laminated with, from the side closest to the first film, a coating agent, a polypropylene resin layer (PP), a polyolefin adhesive resin layer (Adh), an ethylene-vinyl alcohol copolymer layer (EVOH), a polyolefin adhesive resin layer (Adh), and an easy-peel layer (EP).

[0069] The manufacturing method for a packaging container in the embodiment includes a foaming process and a molding process, and the molding process uses a double-sided vacuum molding method.The manufactured packaging container has a bottom, sides, and a flange, is intended for gas replacement packaging, and is sealed by heat-pressing a top seal onto the flange, which has a flat portion.

[0070] The peel strength test is conducted using an Instron universal testing machine (chuck distance = 25 mm, peel rate = 200 mm / min) in accordance with the peel strength test method for adhesives specified in JIS K6854-2. The test specimens are a portion of a cut first foam sheet for thermoforming, a portion of a cut second foam sheet for thermoforming, and a portion (15 mm wide) of the flange of a packaging container, with a portion of the laminate film peeled off from each of the above portions.

[0071] The peel strength test procedure involves clamping the peeled laminate film in one chuck of the testing machine, clamping the foam base sheet to which the laminate film was attached in the other chuck, and widening the gap between the two chucks until the laminate film peels off from the base sheet.

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

[0073] Example 1 Foam base sheet = PSP First film = (from the foam base sheet side) printing, CPS film Second film = (from the first film side) Coating agent, PP, Adh, EVOH, Adh, EP First film thickness = 20 μm, second film thickness = 40 μm Combination of the first lamination process and the second lamination process = Process pattern 1 Lamination temperature during thermal lamination in the first and second lamination processes: 175°C

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

[0075] Example 3 The conditions were the same as in Example 1, except that the first film had no printing.

[0076] Example 4 Foam base sheet = PP foam First film = (from the foam base sheet side) 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: A first film is laminated in the production line when the foam base sheet is extruded, and a second film is laminated in the production line before molding. Lamination temperature during the first lamination process: 170°C Lamination temperature during the second lamination process: 175°C

[0077] <Comparative Example 1> The conditions were the same as in Example 1, except that the dry lamination method was used in the second lamination step, the lamination temperature during thermal lamination was 205°C, and printing was on the second film side.

[0078] <Comparative Example 2> The conditions were the same as in Example 1, except that the first film was not used.

[0079] <Comparative Example 3> Foam base sheet = PP foam First film = (from the foam base sheet side) coating agent, CPP film, printing Second film: same conditions as Comparative Example 1 Thickness of the first film = 25 μm, thickness of the second film = 40 μm Laminating step: The first film and the second film are dry-laminated outside the production line, and the first film side is laminated inside the production line when the foam substrate sheet is extruded. Lamination temperature during thermal lamination: 170℃

[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 ease of reference, these tables also list the individual conditions mentioned above.

[0081] [Table 1]

[0082] <Examples 1 to 3> Example 1 confirmed that the second foam sheet for thermoforming had the highest peel strength. Furthermore, when comparing the peel strengths of all the foam sheets for first molding, second molding, and molded products based on Example 1, Example 2 confirmed that the peel strength was improved by performing the first lamination step and the second lamination step on the same production line, and Example 3 confirmed that the peel strength was equivalent even without printing as long as the process pattern was the same. In other words, Example 3 demonstrated that the presence or absence of a printed surface is irrelevant to the peel strength between the foam substrate sheet and the first film.

[0083] <Comparative Examples 1 and 2> In contrast to Examples 1 to 3, in Comparative Example 1, the first and second films were laminated by dry lamination using a dry lamination adhesive, which made it difficult to bond them at the desired heating temperature, resulting in reduced peel strength for the first molding foam sheet, second molding foam sheet, and molded product. Furthermore, since the peel strength of the molded product in Comparative Example 1 was the lowest, it is presumed that the heat required for adhesion was not sufficiently transferred when dry laminating the first and second films and thermally laminating the thicker laminated film, resulting in reduced peel strength and causing a deterioration in the quality of the molded product. In Comparative Example 2, even if the overall thickness of the laminated film was thin, there was concern that the desired peel strength would be difficult to achieve without the first film.

[0084] That is, the only difference between Example 3 and Comparative Example 2 is the presence or absence of the first film, but this difference results in a large difference in peel strength. A stronger peel strength is achieved by using a coating agent to bond a second film including a barrier layer to a film-attached foam sheet in which a transparent, plain CPS film as the first film is heat-sealed to the PSP, rather than by using a coating agent to bond a second film including a barrier layer directly to the PSP as a foam base sheet. This is presumably because the surface roughness of the PSP foam is relatively high, so even if a coating agent is used to bond the film, the adhesive surface area is reduced, resulting in a decrease in peel strength.

[0085] [Table 2]

[0086] <Example 4 and Comparative Example 3> In Example 4, a first film having a printed surface facing the foam substrate sheet was laminated with a coating agent onto a PP foam substrate sheet to obtain a first foam sheet for thermoforming, and then a second film was laminated with the coating agent onto the first film without obtaining a second foam sheet for thermoforming. On the other hand, in Comparative Example 3, the first and second films were dry-laminated to obtain a laminate film, a coating agent was applied to the foam substrate sheet side of the laminate film, and then the laminate film was thermally laminated onto the foam substrate sheet to obtain a foam sheet for molding. In other words, when the first and second films are dry-laminated, the thickness of the film laminated to the foam substrate sheet at one time increases, which presumably prevents sufficient heat from being applied for adhesion, resulting in a decrease in peel strength. [Explanation of symbols]

[0087] 1 thermoforming foam sheet, 11 foam base sheet, 12 first film, 13 second film, 2 packaging container, 21 bottom, 22 side, 23 flange

Claims

1. A foam sheet for thermoforming of a packaging container for gas replacement packaging or close-contact packaging, having a drawing ratio of 0.1 to 0.45, A foam substrate sheet; a first film having a thickness of 10 μm or more and less than 30 μm that is laminated to the foam substrate sheet without using a dry lamination adhesive; and a second film having a thickness of 20 μm or more and less than 60 μm, the second film including a barrier layer laminated to the first film without containing a dry lamination adhesive. A foam sheet for thermoforming, characterized by:

2. The first film is a printed patterned film. The foam sheet for thermoforming according to claim 1 .

3. The foam substrate sheet is a polystyrene foam sheet, and the first film is a non-stretched polystyrene sheet. It is a styrene film 3. The thermoformed foam sheet according to claim 2.

4. A gas-purging foam obtained by molding the foam sheet for thermoforming according to any one of claims 1 to 3. Packaging containers for packaging or close packaging.

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