Molded container and method for manufacturing the same

Abstract

To provide a molded container which is excellent in glossiness and hardly generates peeling, and to provide a manufacturing method in which break or peeling hardly occurs in molding the container.SOLUTION: A molded container has a polystyrene-based resin foam sheet layer (I) and a polypropylene-based resin film layer (II) as the essential layer constitution. The molded container in which the polypropylene-based resin film layer (II) is positioned in the inner surface of the container is such that: a surface roughness (Ra) on an inner surface side surface of the bottom surface part of the molded container is 0.3 (μm) or less; when the polypropylene-based resin film layer (II) is peeled from a flat part in the bottom surface part of the molded container, a melting peak temperature of the peeled film in DSC measurement is 160°C or more; and a tensile breaking induced strain of the peeled film in a direction where a strain stress in a tensile testing in accordance with JISK7127:1999 becomes maximum is 250% or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a formed container made of a polystyrene resin foamed sheet laminated with a polypropylene resin film.

Background Art

[0002] Formed containers formed from polystyrene resin foamed sheets by vacuum thermoforming, pressure air thermoforming, etc. are widely used in supermarkets, convenience stores, etc. as food containers for selling bento boxes and prepared foods.

[0003] Such formed containers, especially when used as food containers for microwave heating, are laminated with a polypropylene resin film on the polystyrene resin foamed sheet in order to protect the polystyrene resin foamed sheet from the oil of the heated ingredients at high temperature. The laminated sheet is formed into a container shape so that the polypropylene resin film layer is on the inner surface of the container, that is, the food contact surface, and is used.

[0004] As the polypropylene resin film constituting the polypropylene resin film layer in the above laminated sheet, there are an unstretched polypropylene resin film (hereinafter referred to as "CPP film") manufactured by extruding molten polypropylene resin with a T-die and rapidly cooling and solidifying it with a cooling roll, and a biaxially stretched polypropylene resin film (hereinafter referred to as "OPP film") manufactured by extruding molten polypropylene resin with a T-die, cooling and solidifying it with a cooling roll, and then stretching it biaxially in the longitudinal direction (MD direction) and the transverse direction (TD direction). These are generally used.

[0005] Of these, molded containers using OPP film have the characteristic of having a high gloss on the OPP film layer side, which gives a favorable impression to the aesthetics of the container. Therefore, from the standpoint of gloss, OPP film can be said to be superior. However, OPP film does not stretch easily when heated and softened, and has high thermal shrinkage stress, so depending on the shape of the container, "tearing" or "peeling" may occur in the OPP film layer of the molded container. Here, "tearing" refers to the phenomenon in which the film tears due to instantaneous stretching during thermoforming. "Peeling" refers to the state in which the film peels off from the polystyrene resin foam sheet because the film could not fully unfold into the mold shape due to vacuum pressure or compressed air pressure during thermoforming.

[0006] Therefore, conventionally, in molded containers made by vacuum forming a polystyrene foam sheet laminated with a polypropylene resin film, a technique has been known to improve the adhesion between the polystyrene foam sheet layer, which is the base material, and the polypropylene resin film layer of the molded container without impairing the gloss of the polypropylene resin film layer on the molded container side, by using a uniaxially oriented polypropylene film that is stretched 3 to 5 times in only one axis as the polypropylene resin film (see Patent Document 1).

[0007] However, molded containers using uniaxially oriented polypropylene film manufactured by the method described in Patent Document 1, while having good gloss, still experience strong thermal shrinkage stress in the so-called MD direction. As a result, tearing of the film itself during molding is unavoidable, and sufficient improvement in peeling from the substrate is not achieved. In particular, when deep-drawn containers with a large sheet expansion ratio are created, tearing and peeling during molding are more likely to occur. In addition, even after molding, especially in deep-drawn molded containers, the tensile stress of the polypropylene layer is high, and shrinkage of the polypropylene layer is easily caused by external forces or heat history during microwave cooking. This can cause the molded product to deform, resulting in spillage of contents and failure to function as a container.

[0008] On the other hand, laminated sheets using CPP film have the property of being easily stretched when heated and softened, so even if deep-drawn containers are made, the aforementioned tearing and peeling are less likely to occur. However, thermoformed containers with laminated CPP film have a low gloss on the CPP film side and do not result in aesthetically pleasing containers.

[0009] For example, Patent Document 2 discloses a technique for improving the gloss of a molded container laminated with CPP film, in which the heat roll temperature when laminating the CPP film with a polystyrene foam sheet is adjusted to a lower temperature than usual, 160-175°C, and the resulting laminated sheet is thermoformed.

[0010] However, in the technology described in Patent Document 2, the lamination temperature during the production of the laminated sheet is low, so the CPP film is not sufficiently melted before being laminated with the polystyrene foam sheet. As a result, sufficient adhesive strength with the polystyrene foam sheet cannot be obtained, and peeling is likely to occur when deep drawing is performed. In addition, the gloss improvement effect has not reached a sufficient level. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2007-023091 [Patent Document 2] Japanese Patent Publication No. 2019-43076 [Overview of the project] [Problems that the invention aims to solve]

[0012] Therefore, the problem that the present invention aims to solve is to provide a manufacturing method for a molded container made of a polystyrene foam sheet with laminated polypropylene resin films, which has excellent gloss on the polypropylene resin film layer side and adhesive strength of the film, and is less prone to cracking or peeling during molding. [Means for solving the problem]

[0013] The present inventors, after diligently studying to solve the above problems, have found that by adjusting the surface roughness (Ra) of the inner surface of the bottom of the molded container that stores the contents such as food to a predetermined range, and by adjusting the values ​​of the strain stress and tensile fracture nominal strain in the tensile test of the polypropylene resin film cut from the flat part of the bottom to a predetermined range, it is possible to effectively prevent the gloss of the molded container, the adhesive strength (peel strength) of the film, and furthermore, cracking and peeling of the polypropylene resin film layer on the surface of the molded container during formation, thus completing the present invention.

[0014] That is, the present invention relates to a molded container having a polystyrene-based resin foam sheet layer (I) and a polypropylene-based resin film layer (II) as essential layer components, wherein the polypropylene-based resin film layer (II) is located on the inner surface of the container. The surface roughness (Ra) of the inner surface of the bottom portion of the molded container is 0.3 (μm) or less. When the polypropylene resin film (ii) constituting the polypropylene resin film layer is peeled off from the flat portion at the bottom of the molded container, the melting point peak temperature of the peeled film in differential scanning calorimetry is 160°C or higher. The release film, in a tensile test in accordance with JIS K7127:1999, has a 100% strain stress (130°C, strain rate 200% / sec) of 15.0 MPa or more and 29.5 MPa or less in the direction in which the strain stress is maximum (hereinafter referred to as the "X direction"). This invention relates to a molded container characterized by having a tensile fracture strain of 250% or more in the X direction.

[0015] Furthermore, the present invention relates to a differential scanning calorimetry method in which the melting point peak temperature is 160°C or higher. The polypropylene-based resin film is characterized in that the 100% strain stress (at 130°C, strain rate 200% / sec) in the direction in which the strain stress is maximum in the tensile test conforming to JIS K7127:1999 (hereinafter, this direction is referred to as the "X direction") is 15.0 MPa or more and 29.5 MPa or less, and the tensile fracture elongation in the X direction is 250% or more.

[0016] The present invention further provides a method for obtaining a highly crystallized polypropylene-based resin film by treating an unstretched polypropylene-based resin film at 125 to 150°C (step 1), applying a dry lamination adhesive, if necessary, on the micro-stretched polypropylene-based resin film (step 2), further laminating a polystyrene-based resin film, if necessary, on the coating layer of the dry lamination adhesive (step 3), obtaining a single-layer or multi-layer film of the obtained unstretched polypropylene-based resin film laminating with a polystyrene-based resin foam sheet so that the micro-stretched polypropylene-based resin film becomes the surface layer to obtain a composite sheet (step 4), and then thermoforming the composite sheet (step 5). The present invention relates to a method for manufacturing a formed container characterized by this.

Advantages of the Invention

[0017] According to the present invention, in a formed container composed of a polystyrene-based resin foam sheet laminated with a polypropylene-based resin film, it is possible to provide a manufacturing method that is excellent in the gloss on the polypropylene-based resin film layer side and the adhesive strength (peel strength) of the film, and is less likely to crack or peel during molding.

Brief Description of the Drawings

[0018] [Figure 1] Figure 1 is a schematic diagram showing the manufacturing process of the polypropylene-based resin film constituting the polypropylene-based resin film layer of the formed container of the present invention. [Figure 2]Figure 2 is a schematic end view showing a cross-section of the molded container of the present invention. [Modes for carrying out the invention]

[0019] As described above, the molded container of the present invention has a surface roughness (Ra) of 0.3 (μm) or less on the inner surface of the bottom portion of the molded container. When the polypropylene resin film (ii) constituting the polypropylene resin film layer is peeled off from the flat portion at the bottom of the molded container, the melting point peak temperature of the peeled film in differential scanning calorimetry is 160°C or higher. The release film is characterized in that, in a tensile test in accordance with JIS K7127:1999, the 100% strain stress (130°C, strain rate 200% / sec) in the direction where the strain stress is maximum (hereinafter referred to as the "X direction") is between 15.0 MPa and 29.5 MPa, and the nominal tensile fracture strain is 250% or more.

[0020] Here, the inner surface of the bottom of the molded container refers to the inner surface (container side) of the bottom of a tray-shaped or cup-shaped molded container having an opening at the top. If legs or ribs are provided on the bottom, it is preferable that the bottom surface is a flat surface that does not include them. In this invention, a molded container with excellent gloss can be obtained by having a surface roughness (Ra) of 0.3 (μm) or less on the inner surface of this flat surface. Surface roughness (Ra) refers to the arithmetic mean roughness at a reference length. For example, the inner surface of the bottom of the molded container can be measured at a magnification of 1000x using a Keyence laser microscope (VK-X200 series) in accordance with JIS B0601-2013, and the Ra can be calculated using an evaluation length of 1250 μm, a cutoff λs of 2.5 μm, and a cutoff λc of 0.25 mm.

[0021] Next, when the polypropylene resin film (ii) constituting the polypropylene resin film layer is peeled off from the flat portion of the bottom surface of the molded container, the resulting release film can be obtained by, for example, cutting a piece with sides of 10 to 100 mm from the flat portion of the bottom surface of the molded container and peeling off the polypropylene resin film (ii), or by cutting out a piece of the same size together with the polystyrene resin foam sheet layer (I), and then peeling off the polypropylene resin film (ii) from the cut-out test piece to obtain the test film. In this case, if the polypropylene resin film (ii) is used as a multilayer film (M) as described later, the adhesive layer and polystyrene resin film can be dissolved and removed from the peeled or cut-out test piece with a solvent such as limonene to obtain the release film. In this case, even if the dry laminate adhesive layer (II-b) remains on the release film, it will not affect the various evaluation values ​​of the polypropylene resin film (ii), so it can be used as is for each test. Furthermore, the adhesive layer (II-b) may be completely removed with a suitable solvent before being used for each test.

[0022] The release film obtained in this way can be used to evaluate various properties. The present invention is characterized in that the melting point peak temperature of such release film in differential scanning calorimetry (hereinafter referred to as "DSC") is 160°C or higher. Because the melting point peak temperature is 160°C or higher, changes in properties due to the thermal history during molding can be suppressed, and a good gloss can be produced in the molded container. Furthermore, the polypropylene resin film layer (II) of the molded container of the present invention plays a role in protecting the polystyrene resin foam sheet layer from oil and other substances from food that has been heated to a high temperature by microwave heating. If the melting point peak temperature of the polypropylene resin film (ii) constituting the polypropylene resin film layer (II) is 160°C or higher, the polystyrene resin foam sheet layer (21) can be adequately protected from oil and other substances from food that has been heated to a high temperature.

[0023] Here, the thickness of the polypropylene resin film layer (II) constituting the release film is not particularly limited, but is preferably in the range of 15 to 100 μm. That is, by setting it to 15 μm or more, a container with excellent oil resistance can be made. On the other hand, by setting it to 100 μm or less, good adhesion between the multilayer film and the polystyrene resin foam sheet layer (A) can be achieved. In terms of an excellent balance of these performances, a range of 20 to 50 μm is particularly preferred.

[0024] Furthermore, the release film is characterized in that, in a tensile test conforming to JIS K7127:1999, the 100% strain stress (130°C, strain rate 200% / sec) in the direction where the strain stress is maximum (hereinafter referred to as the "X direction") is 15.0 MPa or more and 29.5 MPa or less, and the nominal tensile fracture strain in the X direction is 250% or more. Here, the direction in which the strain stress is maximum in a tensile test conforming to JIS K7127:1999 varies depending on the film manufacturing and molding conditions, but is usually preferably the so-called MD direction.

[0025] Furthermore, the 100% strain stress, measured at a test atmosphere of 130°C and a test rate of 200% / second, correlates with the glossiness of the polypropylene resin film layer (II) of the molded container of the present invention. The higher the tensile stress of the polypropylene resin film layer (II) when stretched by thermoforming, the smoother the surface of the polypropylene resin film layer (II) of the molded container becomes, resulting in a higher glossiness. Here, "100% strain stress" refers to the strain stress when stretched to 100% strain in the longitudinal or transverse direction. For example, it corresponds to the strain stress when a rectangular sheet with dimensions of 10 cm in length and width is unfolded into a food container with a rectangular base of 8 cm in length and width and a depth of 5 cm (the laminated sheet is stretched twice in the longitudinal or transverse direction). In the present invention, excellent gloss can be obtained when such "100% strain stress" is 15.0 MPa or higher, and it is particularly preferable that it be 17.0 MPa or higher.

[0026] The test atmosphere temperature of 130°C is intended to simulate the heating and softening temperature when the laminated sheet is thermoformed into a container shape. The test strain rate of 200% / second is intended to simulate the elongation rate when the polypropylene resin film layer (II) stretches instantaneously as the laminated sheet is unfolded into a container shape by vacuum thermoforming. On the other hand, if the 100% strain stress is too high, cracking and peeling are more likely to occur during molding, so it is preferable that it be 29.5 MPa or less, and particularly 25.0 MPa or less. Hereinafter, when the 100% strain stress in the X direction (130°C, strain rate 200% / second) is between 15.0 MPa and 29.5 MPa, it also has the characteristic that it is less likely to cause a decrease in gloss even when laminated under high temperature conditions of 185-190°C.

[0027] Furthermore, in this invention, since the tensile fracture nominal strain in the X direction of the release film in the tensile test is 250% or more, cracking and peeling during molding can be suppressed, and peeling when subjected to thermal history in the molded container can be effectively prevented. In this invention, it is particularly preferable that the tensile fracture strain be 350% or more from this viewpoint.

[0028] The release film described above may be a so-called unstretched film, but it is preferable that it be a slightly stretched film that is slightly stretched in the uniaxial direction, as this makes it easier to adjust the 100% strain stress in the X direction (130°C, strain rate 200% / sec) to a range of 15.0 MPa to 29.5 MPa.

[0029] Furthermore, in the present invention, it is preferable that the release film has a 100% strain stress (130°C, strain rate 200% / sec) of 5.0 MPa or more and a tensile fracture nominal strain of 500% or more in the Y direction, when the test direction perpendicular to the X direction and the plane direction is defined as the Y direction, and that the tensile fracture nominal strain in the Y direction is 500% or more, as this provides an excellent balance between gloss and peelability in molded containers.

[0030] (1) Layer configuration of laminated sheets constituting the molded container

[0031] The layer structure of the molded container of the present invention will be explained with reference to Figure 1. The molded container (1) of the present invention has a polystyrene resin foam sheet layer (I) and a polypropylene resin film layer (II) as essential layer structures. In the present invention, the polypropylene resin film layer (II) may be directly laminated on the polystyrene resin foam sheet layer (I), but it is preferable that the polystyrene resin foam sheet layer (I) is laminated on the polystyrene resin foam sheet layer (I) as a multilayer film layer (M) in which a polystyrene resin film layer (II-a), a dry laminate adhesive layer (II-b), and the polypropylene resin film layer (II) are laminated in this order, as this provides good adhesion between the polystyrene resin foam sheet layer (A), which is the base material, and the multilayer film layer (M).

[0032] Here, the polystyrene resin foam sheet (i) constituting the polystyrene resin foam sheet layer (I) may be one which is formed into a sheet by foaming and extruding polystyrene resin using a known method. Examples of polystyrene resins that constitute the polystyrene resin foam sheet (i) include styrene homopolymer (GPPS), high-impact polystyrene (HIPS), polybranched polystyrene, styrene-acrylic copolymer, or a mixture of styrene homopolymer (GPPS) and polyphenylene ether, or a mixture thereof. However, if it is to be used as a food container for microwave heating, it is preferable to use a mixture of styrene homopolymer (GPPS) and polyphenylene ether from the viewpoint of heat resistance.

[0033] The foaming ratio of the polystyrene resin foam sheet layer (I) is preferably in the range of 5 to 40 times, in which case the foaming ratio of the polystyrene resin foam sheet (i) is in the range of 3 to 20 times. In particular, for high-foaming sheets where high heat resistance is required, the foaming ratio of the polystyrene resin foam sheet layer (I) is preferably in the range of 10 to 40 times, and the foaming ratio of the polystyrene resin foam sheet (i) is preferably in the range of 5 to 20 times. In the case of such high-foaming sheets, fine irregularities on the surface of the foam sheet become more pronounced, and the polypropylene film (ii) laminated thereon is affected by the shape of these irregularities, making it easier for the gloss to be impaired. However, a notable feature of the present invention is that the influence of the shape of the irregularities on the surface of the foam sheet, which is the base material, can be effectively suppressed, and excellent gloss can be achieved.

[0034] Furthermore, the basis weight of the polystyrene-based resin foam sheet (i) is preferably 90 to 400 g / m². 2 More preferably 100-350 g / m² 2 That is the case.

[0035] The thickness of the polystyrene-based resin foam sheet (i) is preferably 0.5 to 4 mm, and more preferably in the range of 1 to 3 mm.

[0036] Next, the multilayer film layer (M) is composed of a multilayer film (m) laminated in the order of polystyrene resin film (ii-a) / dry laminating adhesive (ii-b) / polypropylene resin film (ii). Here, the polystyrene resin film layer (II-a), composed of polystyrene resin film (ii-a), serves as a heat-sealing surface when the multilayer film (m) is bonded to the polystyrene resin foam sheet (i) by heat lamination. The dry laminating adhesive layer (II-b) serves as an adhesive layer for bonding the polypropylene resin film (ii), which constitutes the polypropylene resin film (II) layer, to the polystyrene resin film (ii-a). As explained in the background art, the polypropylene resin film layer (II) serves to protect the polystyrene resin foam sheet from oil and other substances in food that have been heated to high temperatures by microwave heating.

[0037] The polystyrene resin film (ii-a) constituting the polystyrene resin film layer (II-a) may be one which has been formed into a film by a known method such as the T-die method or the inflation method.

[0038] Examples of polystyrene resins constituting the polystyrene resin film (ii-a) include styrene homopolymer (GPPS), high-impact polystyrene (HIPS), branched polystyrene, syndiotactic polystyrene (SPS), styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-maleic anhydride copolymer, styrene-α-methylstyrene copolymer, or a mixture of styrene homopolymer (GPPS) and polyphenylene ether, or a mixture thereof. Preferably, styrene homopolymer (GPPS), branched polystyrene, high-impact polystyrene (HIPS), or a mixture thereof is used. Furthermore, the polystyrene resin film (ii-a) may also contain a polypropylene resin along with the polystyrene resin, to the extent that it does not impede adhesion to the polystyrene resin foam sheet (i). The thickness of the polystyrene resin film layer (II-a) is not particularly limited, but if it is too thick, the roll temperature during heat lamination with the polystyrene resin foam sheet (i) may not be easily transmitted to the bonding surface, potentially resulting in low bonding strength. On the other hand, if the thickness is too thin, it may be susceptible to the effects of surface irregularities on the polystyrene resin foam sheet (i), potentially affecting the gloss improvement effect. From this viewpoint, the thickness of the polystyrene resin film layer (II-a) is preferably in the range of 10 to 40 μm. In particular, since the present invention can produce excellent gloss even with a thin polystyrene resin film layer (II-a), the thickness is especially preferably in the range of 10 to 17 μm.

[0039] Examples of dry laminating adhesives that form the dry laminating adhesive layer (II-b) include urethane-based, acrylic-based, or epoxy-based dry laminating adhesives, but urethane-based adhesives are preferred from the viewpoint of adhesive strength, etc. The thickness or application amount of the dry laminating adhesive layer (II-b) is not particularly limited, but the thickness is in the range of 1 to 8 μm, and the application amount is 0.5 to 5 g / m². 2 In particular, 1-3 g / m 2 It is preferable that it be within the range of [specify range].

[0040] The multilayer film layer (M) may have a printed layer formed between the polystyrene resin film layer (II-a) and the dry laminate adhesive layer (II-b), or between the dry laminate adhesive layer (II-b) and the polypropylene resin film layer (II).

[0041] The polypropylene resin film (ii) constituting the polypropylene resin film layer (II) is preferably one in which the melting point peak temperature in differential scanning calorimetry is 160°C or higher, the 100% strain stress (130°C, strain rate 200% / sec) in the X direction is 10 MPa or more and 25 MPa or less, and the tensile fracture nominal strain in the X direction is 300% or more.

[0042] Examples of polypropylene resins having a peak melting point temperature of 160°C or higher include propylene homopolymers, propylene-ethylene random copolymers with an ethylene polymerization amount of 5% by mass or less, or mixtures of propylene homopolymers and propylene-ethylene random copolymers with an ethylene polymerization amount of 5% by mass or less. Among these, propylene homopolymers are preferred.

[0043] (2) Method for manufacturing molded containers As described above, the molding method of the present invention involves treating an unstretched polypropylene resin film at 125 to 150°C to obtain a highly crystallized polypropylene resin film (ii) (step 1), If necessary, a dry laminating adhesive is applied to the polypropylene resin film (ii) (step 2), Furthermore, if necessary, a polystyrene resin film (ii-a) is laminated on top of the dry laminate adhesive coating layer (step 3). The obtained single layer (II) or multilayer film (M) of the unstretched polypropylene resin film is laminated with a polystyrene resin foam sheet (i) such that the slightly stretched polypropylene resin film becomes the surface layer to obtain a composite sheet (step 4), and then, The present invention is characterized by thermoforming the composite sheet (step 5).

[0044] [Process 1] Step 1 is a process of heat-treating an unoriented polypropylene resin film (CPP film) at 125 to 150°C. In this invention, by heat-treating a CPP film without stretching it, a molded container can be obtained that has excellent adhesion to the substrate and excellent gloss while preventing cracks and tears. In this invention, as step 1, it is preferable to uniaxially stretch the film by 1.1 to 1.9 times in the MD direction while performing the heat treatment, as this results in an even better gloss for the molded container.

[0045] Here, the CPP film used as the material is preferably one whose melting point peak temperature, as measured by differential scanning calorimetry (hereinafter referred to as "DSC"), is 160°C or higher. Specifically, examples include propylene homopolymers, propylene-ethylene random copolymers with an ethylene polymerization amount of 5% by mass or less, or mixtures of propylene homopolymers and propylene-ethylene random copolymers with an ethylene polymerization amount of 5% by mass or less. Among these, propylene homopolymers are preferred. Furthermore, the polypropylene resin may contain, as needed, nucleating agents, antioxidants, lubricants, antistatic agents, antifogging agents, antiblocking agents, etc.

[0046] The uniaxial stretching process in step 1 will be explained based on Figure 1. Figure 1 is a schematic diagram showing the manufacturing process from heat treatment of an unoriented polypropylene resin film to obtaining a highly crystallized polypropylene resin film (ii). As mentioned above, it is preferable to perform slight stretching of the unoriented polypropylene resin film in step 1 along with the heat treatment, and the manufacturing process including the slight stretching step will be described in detail below.

[0047] The unoriented polypropylene resin film used as a material is preheated by preheating rolls (H1, H2, H3, H4), and then slightly stretched while being heated by two heating and stretching rolls (S1, S2). The rotation speed of the outlet stretching roll (S2) is set faster than that of the inlet stretching roll (S1). This difference in speed between the two heating and stretching rolls slightly stretches the film. After heating and stretching, the film passes through annealing rolls (A1, A2) and cooling rolls (C1, C2) to produce the polypropylene resin film (ii) that constitutes the polypropylene resin layer of the molded container of the present invention. Here, the set temperature of the heat stretching rolls (S1, S2) is preferably 130 to 145°C, and more preferably 135 to 140°C. The set temperature of the heat stretching rolls can be considered as the temperature of the film itself during heat stretching. In the present invention, this set temperature of the heat stretching rolls is an important processing condition.

[0048] The set temperatures for the preheating rolls (H1, H2, H3, H4) are set based on the set temperatures for the heat stretching rolls (S1, S2). That is, it is preferable that the temperature of the film itself reaches the set temperature of the heat stretching roll (S1) when the film enters the heat stretching roll (S1). Therefore, it is preferable to set the set temperatures for the preheating rolls (H1, H2, H3, H4) starting at a temperature 30°C lower than the set temperature of the heat stretching rolls (S1, S2) and gradually approaching the set temperature of the heat stretching rolls.

[0049] The set temperature for the annealing rolls (A1, A2) should be set lower than the set temperature for the heated stretching rolls (S1, S2), within a range of 20°C lower than the set temperature for the heated stretching rolls. The set temperature for the cooling rolls (C1, C2) should be set so that the set temperature for cooling roll (C2) is 40-50°C. The set temperature for cooling roll (C1) should be set between the set temperature for the annealing roll (S2) and the set temperature for cooling roll (C1).

[0050] The stretching ratio in the MD direction applied to the film by the heated stretching rolls (S1, S2) is preferably less than 2 times, and more preferably in the range of 1.2 to 1.5 times. This range of stretching ratio, like the set temperature of the heated stretching rolls, is an important processing condition in the present invention, and in this way a micro-stretched film can be obtained.

[0051] The polypropylene resin film (ii) obtained in this manner preferably has a tensile fracture nominal strain of 365% or more in the MD direction and 700% or more in the TD direction when measured in accordance with JIS K7127:1999 at a test atmosphere of 130°C and a test speed of 100% strain / second.

[0052] Here, the tensile fracture nominal strain measured at a test atmosphere of 130°C and a test rate of 200% / second correlates with the elongation of the polypropylene resin film layer (II) during molding, i.e., whether or not the polypropylene resin film layer (II) tears or peels off in the molded container. By setting the tensile fracture nominal strain of the polypropylene resin film (II) to 350% or more in the MD direction and 700% or more in the TD direction, a molded container can be obtained in which no tears occur in the polypropylene resin film layer (II).

[0053] When measured under the conditions detailed above (in accordance with JIS K7127:1999, test atmosphere 130°C, test rate of strain rate 100% / second), the 100% strain tensile stress of the polypropylene resin film (ii) is preferably 15.0 MPa to 29.5 MPa in the MD direction, particularly 15.0 MPa to 25 MPa in the MD direction, and more preferably 6.1 MPa to 8.9 MPa in the TD direction.

[0054] The polypropylene resin film (ii) obtained in this manner has a melting point peak temperature of 160°C or higher in differential scanning calorimetry, and the release film has a 100% strain stress (130°C, strain rate 200% / sec) of 15.0 MPa or more and 29.5 MPa or less in the direction (X direction) where the strain stress is maximum in a tensile test in accordance with JIS K7127:1999, and a tensile fracture nominal strain of 250% or more in the X direction, which constitutes the polypropylene resin film of the present invention. The polypropylene resin film of the present invention is subjected to the next step, step 2, but can also be used as a packaging bag for flexible packaging due to its excellent balance of strength and elongation.

[0055] Furthermore, the polypropylene resin film (ii) obtained through step 1 has the unique property of being highly crystallized despite being substantially unstretched or slightly stretched. Specifically, the degree of crystallinity of the polypropylene resin film (ii) is preferably 40% or higher. Here, the degree of crystallinity of the release film is a value measured by differential scanning calorimetry (DSC). Specifically, the heat of fusion (ΔHm, unit: J / g) and heat of cold crystallization (ΔHc, unit: J / g) of the release film were measured using a differential scanning calorimetry device at a heating rate of 10°C / min, and the degree of crystallinity was determined by the following formula. Crystallinity (%)=(ΔHm-ΔHc) / ΔHPP×100 (Here, ΔHPP is the value of 209 J / g reported in "J. Brandrup and EM Innergut: Polymer Handbook. Interscience New York (1965)" as the heat of fusion for polypropylene resin with 100% crystallinity.)

[0056] [Process 2] Next, step 2 is the step of applying a dry laminating adhesive onto the obtained micro-stretched polypropylene resin film (ii), and this is an optional step that may be omitted. Examples of dry laminating adhesives used here include urethane-based, acrylic-based, or epoxy-based dry laminating adhesives. Among these, urethane-based adhesives are preferred due to their excellent adhesive strength. The thickness or amount of the dry laminating adhesive layer (II-b) is not particularly limited, but is preferably 0.5 to 5 g / m². 2 More preferably 1-3 g / m 2 That is the case.

[0057] [Step 3] If Step 2 has been completed, then in Step 3, a polystyrene resin film (ii-a) can be laminated on top of the adhesive layer (II-b) of the dry laminating adhesive. Specifically, a multilayer film (M) can be obtained by dry laminating a polystyrene resin film (ii-a) to the adhesive-coated surface of a film coated with the dry laminating adhesive obtained through step 2 using a dry lamination method.

[0058] [Step 4] Next, step 4 is a step in which a single-layer or multi-layer film (M) of the obtained unstretched polypropylene resin film (ii) is laminated with a polystyrene resin foam sheet (i) such that the slightly stretched polypropylene resin film (ii) becomes the surface layer to form a composite sheet. This can be done by thermal lamination, dry lamination, or extrusion lamination, which involves foaming and extruding polystyrene resin to form a sheet while laminating it.

[0059] [Step 5] Step 5 is the process of shaping the composite sheet obtained in Step 4 into the desired container shape by thermoforming. The molding method can be a standard method, for example, by vacuum forming. In this invention, since an unstretched to slightly stretched polypropylene resin film is used, it does not crack or peel even when subjected to so-called deep drawing molding, and it has excellent adhesive strength, and in addition, it can produce a glossy product. For the thermoforming temperature conditions in step 5, it is preferable that the heater temperature is in the range of 200 to 300°C. Furthermore, while the present invention can be applied to various food trays, cups, etc., it can be used as a highly foamed, deep-drawn container with excellent durability. For example, it can be suitably used in containers where the total surface area of ​​the container is 2 to 4 times the opening width of the container opening. For example, in the container end view of Figure 2, it is preferable that the depth is 0.5 to 1.5 times the planar length and the unfolded length is 1.5 to 4 times.

[0060] As described above, the molded container obtained in this manner exhibits excellent gloss. The gloss of the molded container can be measured on the polypropylene resin film layer (II) side of the molded container of the present invention in accordance with JIS Z 8741-1997, and in the present invention, it is preferable that the 60-degree specular gloss is 60% or higher. If it is 60% or higher, the gloss can be perceived by human vision. [Examples]

[0061] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0062] [Examples 1-7] (1) Manufacturing of polypropylene resin films According to the heat stretching roll temperature and stretching ratio listed in Table 1, a CPP film (manufactured by Santox Co., Ltd., product name "KL-12", thickness 25 μm) was subjected to uniaxial stretching in the MD direction to produce a polypropylene resin film that constitutes the polypropylene resin film layer of a molded container. Uniaxial stretching was performed using a uniaxial stretching machine with the same roll configuration as shown in Figure 1. Specifically, the heated stretching rolls (S1, S2) were set to the temperatures listed in Table 1, and the rotation speed of the outlet-side heated stretching roll (S2) was set faster than the rotation speed of the inlet-side heated stretching roll (S1), thereby performing uniaxial stretching in the MD direction on the CPP film. For the unstretched polypropylene resin film of Example 6, stretching was not performed using the uniaxial stretching machine shown in Figure 1. Instead, a 300 x 300 mm piece of CPP film was cut, clipped around its edges, and treated at 140°C for 30 seconds to obtain the polypropylene resin film.

[0063] (2) Method for manufacturing laminated sheets To the polypropylene resin film that has been uniaxially stretched using the method described above, apply 2g / m² of urethane-based dry laminating adhesive (TOMOFLEX, manufactured by Toyo Morton). 2 The material was coated, and a polystyrene resin film (manufactured by FPCO ALUITE Co., Ltd., GPPS: 85% by mass + HIPS: 15% by mass, thickness 15 μm) was laminated to it by dry lamination to obtain a multilayer film.

[0064] Next, the multilayer film was laminated to a heat-resistant polystyrene foam sheet (manufactured by Sekisui Chemical Co., Ltd., product name "Esren Sheet", basis weight 110 g / m², thickness 1.7 mm) made of a mixture of GPPS, HIPS, and polyphenylene ether, by passing it between opposing heat laminating rolls set to a temperature of 185°C, with the polystyrene foam film side of the multilayer film facing the heat-resistant polystyrene foam sheet.

[0065] (3) Manufacturing of molded containers The laminated sheets described above were molded into a container shape using a vacuum pressure thermoforming machine. For the tray containers of Examples 1-3 and 5-6, the laminated sheet was heated and softened in a furnace set to 200°C with the polypropylene resin film layer facing the inner surface of the container. Then, a mold was formed using a mold with a rectangular opening measuring 200 mm vertically and 150 mm horizontally, a rectangular bottom measuring 150 mm vertically and 100 mm horizontally, a depth of 70 mm, and an unfolded length of 220 mm vertically and 170 mm horizontally, as schematically shown in the end view of Figure 2, to obtain a tray-shaped molded container. 100 molded containers were produced.

[0066] For the cup container of Example 4, the laminated sheet was heated and softened in a heating furnace set to 200°C with the polypropylene resin film layer facing the inner surface of the container. Then, it was molded using a mold with a container shape schematically shown in the end view of Figure 2, which has a circular opening with a diameter of 100 mm, a circular bottom with a diameter of 70 mm, a depth of 70 mm, and an unfolded length of 230 mm, to obtain a cup-shaped molded container. 100 molded containers were produced.

[0067] [Comparative Examples 1-3] A molded container was obtained in the same manner as in Examples 1 to 4, except that a CPP film (manufactured by Santox Co., Ltd., product name "KL-12", thickness 25 μm) was used as the polypropylene resin film constituting the polypropylene resin film layer of the molded container.

[0068] [Comparative Example 4] A molded container was obtained in the same manner as in Example 1, except that the heat treatment temperature of the CPP film was set to 120°C.

[0069] [Comparative Example 5] A molded container was obtained in the same manner as in Comparative Examples 1 to 3, except that a commercially available uniaxially oriented polypropylene film (manufactured by Futamura Chemical Co., Ltd., product name "MCMD-AS", stretching ratio 2 × 1.5 times, thickness 25 μm, characteristic: straight cut type) was used as the polypropylene resin film constituting the polypropylene resin film layer of the molded container.

[0070] [Comparative Examples 6-7] A molded container was obtained in the same manner as in Comparative Example 1, except that the heat lamination temperature was set to 160°C (Comparative Example 6) and 175°C (Comparative Example 7).

[0071] (4) Evaluation method

[0072] <Film peel strength> From the bottom surface of the molded containers obtained from each example and comparative example, test pieces measuring 25 mm in width and 70 mm in length were cut in the MD and TD directions of the molded product, and measurements were performed using Shimadzu Corporation's "Autograph AG-X plus" in accordance with JIS K6854-1:1999. Specifically, a 20mm strip of film was peeled from one end of the test specimen, the specimen was held in a roller-type peeling device, and the peeled film was secured with an Autograph gripper. The peeling was then performed over a 50mm length at a test speed of 500mm / min while maintaining a peeling angle of 90 degrees.

[0073] <Preparation of release film for evaluation> From the flat area at the bottom of the molded containers obtained in each example and comparative example, strip-shaped test pieces (test piece type 2 as defined in JIS K7127:1999) measuring 10 mm in width and 100 mm in length were cut in the MD and TD directions of the film, and the multilayer film was peeled off. Next, the polystyrene resin film layer and the dry laminate adhesive layer were removed from the obtained peeled multilayer film with limonene to obtain an evaluation release film.

[0074] <Method for measuring melting point peak temperature using differential scanning calorimetry> The melting point peak temperature of the evaluation release film obtained from the molded containers in each example and comparative example was measured using a scanning calorimeter (Shimadzu Corporation "DSC-60"). A 3 mg sample was taken from the film and its melting point peak temperature was measured when it was heated from 40°C to 200°C at a heating rate of 10°C / min.

[0075] <Method for measuring tensile fracture nominal strain and 100% strain tensile stress> The tensile fracture nominal strain and 100% strain stress of the evaluation release film obtained from the molded containers obtained in each example and comparative example were measured using a tensile testing machine ("Autograph AG-X plus" manufactured by Shimadzu Corporation) and a constant temperature chamber ("TCH-220-T" manufactured by Shimadzu Corporation) in accordance with JIS K7127:1999, at a test atmosphere of 130°C and a test rate of 200% / second.

[0076] Specifically, the evaluation release film was fixed with a gripping distance of 12.5 mm and held in a constant temperature chamber set to 130°C for 90 seconds. Then, measurements were taken at a test speed of 25 mm / second (strain rate of 200% / second) until the gripping distance reached a maximum of 88 mm (700% strain), and the tensile fracture nominal strain and 100% strain stress were measured.

[0077] <Presence or absence of cracks and peeling of the polypropylene resin film layer in molded containers> The 100 molded containers produced as described above were visually inspected for any cracks or peeling in the polypropylene resin film layer, and evaluated according to the following criteria. ◎: No containers have tears or peeling of the film. "Tears": One or more containers have tears in the film. "Peeling": The film on all molded containers can be easily peeled off by pinching it with your fingers.

[0078] <Surface roughness of molded container (Ra)> The surface roughness (Ra) of the inner surface of the bottom of the molded container was measured at a magnification of 1000x using a Keyence laser microscope (VK-X200 series) in accordance with JIS B0601-2013, and calculated using an evaluation length of 1250 μm, a cutoff λs of 2.5 μm, and a cutoff λc of 0.25 mm.

[0079] <Glossiness of molded containers> From the 100 molded containers prepared as described above, 10 were randomly selected from those without tears or peeling of the polypropylene resin film layer. A 2 cm square test piece was cut from the flat bottom of each container, and the glossiness of the polypropylene resin film layer was measured using a gloss meter (GlossMeterVG7000, manufactured by Nippon Denshoku Industries, Ltd.) to obtain a 60-degree specular gloss in accordance with JIS Z 8741.

[0080] (5) Evaluation Results The evaluation results are shown in Tables 1 and 2.

[0081] [Table 1]

[0082] In all of the molded containers in Examples 1 to 4 (heating roll temperature 135 to 140°C, stretching ratio 1.2 to 1.5 times), no tearing or peeling occurred in the polypropylene resin film layer, and the 60-degree mirror gloss on the polypropylene resin film layer side was 60% or higher.

[0083] [Table 2]

[0084] In Comparative Examples 1-3 (where CPP film was used as is as the polypropylene resin film layer), no tearing or peeling of the polypropylene resin film layer occurred in the molded containers, but the 60-degree mirror-like gloss on the polypropylene resin film layer side was lower than in each of the examples. In Comparative Example 4 (heat-stretched roll 120°C, MD-direction stretching ratio 1.2 times), no tearing or peeling occurred on the polypropylene resin film layer side of the molded container, but the 60-degree mirror gloss on the polypropylene resin film layer side was insufficient at 48%.

[0085] In Comparative Example 5 (OPP film, stretching ratio 2.5 × 3 times), the molded containers and cups exhibited tearing and / or peeling on the polypropylene resin film layer side. Considering this in comparison with the examples, it was found that increasing the stretching ratio to 3 × 3 times makes it impossible to eliminate tearing and / or peeling of the polypropylene resin film layer of the molded container to the level targeted by the present invention.

[0086] In Comparative Examples 6 and 7 (CPP film, traced from Patent Document 2), the molded containers had low thermal lamination temperatures of 160°C or 175°C, resulting in insufficient adhesive strength between the polypropylene resin film and the polystyrene resin foam sheet, leading to tearing and / or peeling. [Explanation of Symbols]

[0087] I. Polystyrene foam sheet layer II. Polypropylene resin film layer H1... Preheating Roll H2... Preheating Roll H3... Preheating Roll H4... Preheating Roll S1...Heated stretching roll S2...Heated stretching roll A1... Annealed Roll A2... Annealed Roll C1... Cooling Roll C2... Cooling Roll

Claims

1. A molded container having a polystyrene foam sheet layer (I) and a polypropylene resin film layer (II) as essential layer components, wherein the polypropylene resin film layer (II) is located on the inner surface of the container, The surface roughness (Ra) of the inner surface of the bottom portion of the molded container is 0.3 (μm) or less. When the polypropylene resin film (ii) constituting the polypropylene resin film layer is peeled off from the flat portion at the bottom of the molded container, the melting point peak temperature of the peeled film in differential scanning calorimetry is 160°C or higher. The release film has a 100% strain stress (130°C, strain rate 200% / sec) of 15.0 MPa or more and 29.5 MPa or less in the direction in which the strain stress is maximum in a tensile test in accordance with JIS K7127:1999 (hereinafter referred to as the "X direction"), and A molded container characterized by having a tensile fracture nominal strain of 250% or more in the X direction.

2. The molded container according to claim 1, wherein, when the test direction perpendicular to the X direction and the surface direction is defined as the Y direction, the 100% strain stress in the Y direction (130°C, strain rate 200% / sec) is 5.0 MPa or more and 10.0 MPa or less, and the tensile fracture nominal strain in the Y direction is 500% or more.

3. The molded container according to claim 1 or 2, wherein the layer structure of the molded container is formed by laminating a polystyrene resin foam sheet layer (I), a polystyrene resin film layer (II-a), a dry laminate adhesive layer (II-b), and a polypropylene resin film layer (II) in this order.

4. The molded container according to claim 3, wherein the polystyrene resin foam sheet layer (I) has a foaming ratio in the range of 5 to 40 times.

5. A polypropylene resin film with high crystallinity is obtained by treating an unoriented polypropylene resin film at 125 to 150°C (Step 1). If necessary, a dry laminating adhesive is applied to the polypropylene resin film (step 2). Furthermore, if necessary, a polystyrene resin film is laminated on top of the dry laminate adhesive coating layer (step 3). The single layer of the highly crystallized polypropylene resin film obtained, or the multilayer film obtained in step 3 The polypropylene resin film is laminated with a polystyrene resin foam sheet so that it forms the surface layer to obtain a composite sheet (step 4), and then, A method for manufacturing a molded container, characterized by thermoforming the composite sheet (step 5).

6. The method for manufacturing a molded container according to claim 5, wherein step 1 is a step of uniaxially stretching an unstretched polypropylene resin film by 1.1 to 1.9 times in the MD direction while treating it at 125 to 150°C.

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