Paper container and base paper for molding

Abstract

To provide a paper container capable of improving moldability, heat resistance and oil resistance.SOLUTION: The paper containers C and C' are laminated with film layers 1F and 1' F on the inside surfaces, and the film layers 1F and 1' F are composed of (i) a first polypropylene layer 1B laminated on a paper base material 1pp and a first polyethylene layer 1pp laminated on the first polypropylene layer 1pe. (ii) a second polyethylene layer 1B laminated on the paper base material 2pe, a second polypropylene layer 2pe laminated on the second polyethylene layer 2pp, and a third polyethylene layer 2pp laminated on the second polypropylene layer 3pe.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a paper container laminated with a resin film layer. [Background technology]

[0002] Conventionally, paper containers have been constructed by extrusion laminating (hereinafter also referred to as "extrusion lamination" or "EL") PE (polyethylene) onto a paper base material to impart water resistance and strength, but when heat resistance and oil resistance are required, PP (polypropylene) is used to EL the paper base material (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-553917 Summary of the Invention [Problem to be solved by the invention]

[0004] However, molding a highly heat-resistant resin using a paper container molding machine requires conditions suited to PP, which increases the difficulty and may result in a decrease in productivity and yield. This point is not fully considered in Patent Document 1, and there is still room for improvement in the structure of paper containers laminated with resin film layers (hereinafter simply referred to as "film layers").

[0005] An object of the present invention is to provide a paper container that can have improved formability, heat resistance, and oil resistance. [Means for solving the problem]

[0006] A first form of the paper container according to the present invention is a paper container having a film layer laminated on the inner surface, characterized in that the film layer is composed of (i) a first polypropylene layer laminated on a paper base material and a first polyethylene layer laminated on the first polypropylene layer, or (ii) a second polyethylene layer laminated on the paper base material, a second polypropylene layer laminated on the second polyethylene layer, and a third polyethylene layer laminated on the second polypropylene layer.

[0007] A second embodiment of the paper container of the present invention is the first embodiment, characterized in that the thickness of the first polypropylene layer, the first polyethylene layer, the second polyethylene layer, the second polypropylene layer, and / or the third polyethylene layer is 4 to 50 μm.

[0008] A third aspect of the paper container according to the present invention is the paper container described as the first aspect, characterized in that the basis weight of the film layer relative to the basis weight of the paper base material is 20:1 to 3:1.

[0009] A fourth embodiment of the paper container according to the present invention is the first embodiment, characterized in that the surface of the inner side on which the film layer is laminated has a surface roughness (Ra) of 1.4 to 5.0 μm or a smoothness of 2 sec to 450 sec.

[0010] A fifth aspect of the paper container according to the present invention is the one described as the first aspect, characterized in that the smoothness of the surface of the paper base material on which the film layer is laminated is 1 to 1000 sec.

[0011] A sixth embodiment of the paper container according to the present invention is the first embodiment described above, characterized in that in structure (i), the difference between laminating the first polypropylene layer onto the paper base material and laminating the first polyethylene layer onto the first polypropylene layer is 0 to 3 seconds, and in structure (ii), the difference between laminating the second polypropylene layer onto the second polyethylene layer and laminating the third polyethylene layer onto the second polypropylene layer is 0 to 3 seconds.

[0012] A seventh aspect of the paper container according to the present invention is a base paper for forming into the paper container according to any one of the first to sixth aspects. [Effects of the Invention]

[0013] According to the paper container of the present invention, it is possible to improve formability, heat resistance, and oil resistance. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a paper container according to one embodiment of the present invention. [Figure 2] 1A and 1B are schematic diagrams showing a paper container according to one embodiment of the present invention, in which (a) is a front view and (b) is a cross-sectional view taken along the line IIb-IIb in FIG. [Figure 3] 3A and 3B are cross-sectional views of a paper container according to one embodiment of the present invention and a modified example thereof, where (a) shows part IIIa in FIG. 2, and (b) is a cross-sectional view of a paper container according to a modified example, showing part IIIa in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to Figures 1 to 3. However, the present invention is not limited to this embodiment.

[0016] <Structure of paper container> FIG. 1 is a perspective view of a paper container C according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the paper container C according to this embodiment, with FIG. 2(a) being a front view and FIG. 2(b) being a cross-sectional view taken along the line IIb-IIb in FIG. 1. FIG. 3 is a cross-sectional view of paper containers C and C' according to this embodiment and its modified example, with FIG. 3(a) showing part IIIa in FIG. 2 and FIG. 3(b) showing part IIIa in FIG. 2 as a cross-sectional view of paper container C' according to the modified example. In FIGS. 3(a) and 3(b), the upper layer in the figure represents the inner layer of the paper container C and C', and the lower layer in the figure represents the outer layer of the paper container C and C'. The corners of the upper and lower ends of the paper container C according to this embodiment are rounded as shown in FIG. 1, but are depicted as angular in FIG. 2 for ease of illustration.

[0017] As shown in FIGS. 1 to 3 , the paper container C according to this embodiment comprises a bottom 10D that is circular when viewed from above and a body 10S that is shaped like an inverted truncated cone. The bottom edge of the body 10S is joined to the bottom 10D. In this embodiment, a resin film layer 1F is laminated on the inner surface of the paper container C. The body 10S is formed into an inverted truncated cone shape by rolling a laminated paper sheet that is approximately fan-shaped, overlapping both ends, and heat-welding the film layer 1F at the overlapping portion. The upper end of the body 10S has a curled portion that is outwardly curled, and the lower end has a folded portion that is bent inward. Paper containers shaped like this embodiment, such as those in a paper cup, are generally referred to as paper cups. The paper container C according to this embodiment can be used for a variety of purposes, including as a drinking container such as a cup, a lunch box, or a rice bowl. The shape of the paper container is not limited to the above, and various shapes can be adopted as long as the effects of the present invention are achieved.

[0018] As shown in Figures 1 to 3, the paper container C of this embodiment is a paper container C having a film layer 1F laminated on the inner surface, and the film layer 1F is composed of a first polypropylene layer 1pp laminated on a paper base material 1B and a first polyethylene layer 1pe laminated on the first polypropylene layer 1pp.

[0019] The base paper for molding with resin laminated in this configuration can improve moldability, heat resistance, and oil resistance. In addition, the heat-sealed portion of the paper container C (between the bottom 10D and the body 10S) has good adhesion, and oil resistance can be improved compared to a configuration in which a single layer of PP is simply laminated on a paper base material.

[0020] The paper container C according to this embodiment is formed by a forming machine (including a box-making machine). The film layer 1F (or the film layer 1'F described below) can be formed by a conventionally known method, such as extrusion lamination, in which a resin is extruded from an extruder onto one surface of a substrate.

[0021] Furthermore, in the paper container C according to this embodiment, the thickness of the first polypropylene layer 1pp, the first polyethylene layer 1pe, the second polyethylene layer 2pe, the second polypropylene layer 2pp, and / or the third polyethylene layer 3pe, which will be described later, is 4 to 50 μm. If each layer is thinner than 4 μm, film-forming properties are poor, and if it is thicker than 50 μm, the processing speed is slow. To achieve the effects of the present invention, the thickness of each layer is preferably 5 to 30 μm.

[0022] Furthermore, in the paper container C according to this embodiment, the ratio of the basis weight of the film layer 1F to the basis weight of the paper base material 1B is 20:1 to 3:1.

[0023] In the paper container C according to this embodiment, the surface of the inner side on which the film layer 1F is laminated has a surface roughness (Ra) of 1.4 to 5.0 μm or a smoothness of 2 sec to 450 sec.

[0024] In the paper container C according to this embodiment, the surface smoothness of the paper base material 1B on which the film layer 1F is laminated is 1 to 1000 sec. Here, the smoothness of the surface of the paper container C refers to the smoothness of the interface between the film layer 1F and the paper base material 1B. To achieve the effects of the present invention, the smoothness is preferably 2 to 500 sec.

[0025] In the paper container C according to this embodiment, the difference between laminating the first polypropylene layer 1pp onto the paper base material 1B and laminating the first polyethylene layer 1pe onto the first polypropylene layer 1pp is set to 0 to 3 seconds.

[0026] A paper container C' according to a modified example of this embodiment is a paper container C' having a film layer 1'F laminated on the inner surface, as shown in Figure 3(b), and the film layer 1'F is composed of a second polyethylene layer 2pe laminated on the paper base material 1B, a second polypropylene layer 2pp laminated on the second polyethylene layer 2pe, and a third polyethylene layer 3pe laminated on the second polypropylene layer 2pp.

[0027] The base paper for forming process laminated with resin in this configuration can improve formability, heat resistance, and oil resistance, as in one embodiment of the present invention.

[0028] In the paper container C' according to the modified example, the difference between laminating the second polypropylene layer 2pp onto the second polyethylene layer 2pe and laminating the third polyethylene layer 3pp onto the second polypropylene layer 2pp is set to 0 to 3 seconds.

[0029] According to this embodiment, it is possible to obtain a well-balanced improvement in heat resistance and oil resistance, improvement in heat sealing suitability, provision of environmentally friendly paper containers by reducing plastic use, suppression of curling, prevention of pinholes, and improvement of adhesion by preventing interfacial breakdown.

[0030] <Manufacturing method> The paper containers described above can be manufactured using the forming base paper configured as described above. That is, a body blank and a bottom blank are punched into appropriate shapes (generally, a roughly fan-shaped and a disk-shaped) from a sheet-like forming base paper in which a resin layer is laminated on a paper base material, and the outer periphery of the bottom blank is further bent downward by squeezing to form a sandwiched portion, thereby producing the bottom.

[0031] The body blank is wrapped around the body by heating both side edges with the resin layer facing inward, and the side edges are bonded together with the molten resin material of the resin layer to form side seals, producing a tubular body. Next, the sandwiched portion of the bottom piece and the lower portion of the body related to the body are heated, and the molten resin material of the resin layer bonds the sandwiched portion of the bottom piece to the inner wall of the lower portion of the body. The lower end of the body is then folded back and upward to form a hem, which is then bonded to the inner peripheral wall of the sandwiched portion to form a bottom. Pressurization of the formed bottom crimps the bonded portion to form a bottom seal.

[0032] The crimping method is a roll-out (rotary crimping) method, in which a pressure tool placed inside the thread base is used to pressurize the sandwiched part of the bottom piece and the lower part of the body piece, including the main body and skirt. Furthermore, a so-called curling process is performed to roll the side edge of the upper opening of the body outward to form a curled part, thereby producing a paper container.

[0033] The heating temperature for bonding the side seal portion and bottom seal portion is set to a temperature equal to or higher than the melting point of the resin that forms the resin layer during bonding, so the molding machine temperature is set to about 300 to 450°C, for example.

[0034] <Evaluation> The present invention will be explained in more detail below based on the evaluations of Examples 1 and 2 and Comparative Examples 1 to 4.

[0035] Example 1 290 g / m as paper base material 2 The white food paperboard was used as the paper base material, and 20 μm of polypropylene and 20 μm of polyethylene were extrusion laminated onto the paper base material (paper / PP / PE) in that order to form a base paper for molding. Using the method described above, a paper container (a paper cup container with a mouth inner diameter of 142 mm, height of 66 mm, and internal height of 58 mm) was obtained. The sealing temperature during paper container production was 350°C.

[0036] <Example 2> A paper container was obtained in the same manner as in Example 1, except that polyethylene 20 μm, polypropylene 20 μm, and polyethylene 20 μm were laminated in this order on the paper substrate (paper / PE / PP / PE).

[0037] <Comparative Example 1> A paper container was obtained in the same manner as in Example 1, except that only 40 μm of polyethylene was laminated onto the paper substrate (paper / PE).

[0038] <Comparative Example 2> A paper container was obtained in the same manner as in Example 1, except that only 40 μm of polypropylene was laminated onto the paper substrate (paper / PP).

[0039] <Comparative Example 3> A paper product was obtained in the same manner as in Comparative Example 2, except that the sealing temperature during production was 420°C.

[0040] <Comparative Example 4> A paper container was obtained in the same manner as in Comparative Example 3, except that only 60 μm of polypropylene was laminated onto the paper substrate (paper / PP).

[0041] The evaluation results of Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0042] [Table 1]

[0043] [Sealing performance evaluation criteria] ○: The base papers are strongly bonded together, and when you try to peel them apart, the base papers tear. △: The adhesion between the base papers is weak and there are some parts that peel off easily. ×: The base papers are not adhered to each other, or they peel off easily when trying to peel them off. (〇 means pass, △·× means fail)

[0044] [Evaluation method and criteria for oil resistance 1 (immersion at room temperature)] The paper container was filled with olive oil to a depth of 5 mm from the bottom, and after leaving it at room temperature for 4 days, the degree to which the olive oil had penetrated was checked.

[0045] As a result, containers with no leakage or seepage of olive oil on the outer surface were rated as ◯, and those with leakage or seepage were rated × (◯ was a pass, △ and × were fail).

[0046] [Evaluation method and criteria for oil resistance 2 (when cooking with microwave)] 350g of commercially available Neapolitan spaghetti was packed into a paper container, cooked in a microwave oven at 1600W for 1 minute 10 seconds, and then left to stand at room temperature for 3 hours, after which the degree of oil penetration was observed.

[0047] As a result, containers with no oil penetration on the outer surface were marked with an ◯, and containers with oil penetration on the outer surface were marked with an × (◯ is pass, △ and × are fail).

[0048] From the evaluation results of the Examples and Comparative Examples, it was found that the product of the present invention has excellent oil resistance and also has excellent suitability for container molding (good sealing properties and cost advantage since there is no need to increase the sealing temperature compared to base paper with a single layer of polyethylene).

[0049] <Other> The present invention is not limited to the above-described embodiments or the modifications described throughout, and appropriate changes and modifications can be made without departing from the technical concept of the present invention. [Explanation of symbols]

[0050] C, C' paper container 10S, 10S' body 1B Paper base material 1F, 1'F film layer 1pe 1st polyethylene layer 1pp 1st polypropylene layer 2pe Second polyethylene layer 2pp Second polypropylene layer 3pe 3rd polyethylene layer 10D bottom

Claims

1. A paper container having a film layer laminated on the inner surface, The film layer comprises: (i) a first polypropylene layer laminated on a paper substrate and a first polyethylene layer laminated on the first polypropylene layer; or (ii) A second polyethylene layer laminated on a paper substrate, a second polypropylene layer laminated on the second polyethylene layer, and a third polyethylene layer laminated on the second polypropylene layer. A paper container characterized by:

2. The paper container according to claim 1, characterized in that the thickness of the first polypropylene layer, the first polyethylene layer, the second polyethylene layer, the second polypropylene layer, and / or the third polyethylene layer is 4 to 50 μm.

3. 2. The paper container according to claim 1, wherein the basis weight of the film layer relative to the basis weight of the paper substrate is 20:1 to 3:

1.

4. The paper container according to claim 1, characterized in that the surface of the inner side on which the film layer is laminated has a surface roughness (Ra) of 1.4 to 5.0 μm or a smoothness of 2 sec to 450 sec.

5. 2. The paper container according to claim 1, wherein the surface of the paper substrate on which the film layer is laminated has a smoothness of 1 to 1000 seconds.

6. In the structure (i), the difference between the time when the first polypropylene layer is laminated onto the paper base material and the time when the first polyethylene layer is laminated onto the first polypropylene layer is 0 to 3 seconds; In the configuration (ii), the difference between the time when the second polypropylene layer is laminated onto the second polyethylene layer and the time when the third polyethylene layer is laminated onto the second polypropylene layer is 0 to 3 seconds. The paper container according to claim 1 .

7. A base paper for molding processing for molding the paper container according to any one of claims 1 to 6.

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