Paper containers and manufacturing methods

Abstract

The present invention provides a method for manufacturing paper containers that ensures the desired barrier properties while press-molding barrier paper. [Solution] The method for manufacturing a paper container comprises step A, preparing barrier paper on which a barrier layer mainly composed of polyvinylidene chloride is formed on a paper substrate, and heating the barrier layer to obtain an IR peak (1041 cm²) originating from the polyvinylidene chloride crystal portion, measured by FT-IR. -1 The absorption intensity I1 of ) and the IR peak (1067 cm) originating from the amorphous region of polyvinylidene chloride. -1 The method comprises step B, which sets the ratio I1 / I2 of the absorption strength to less than 1.4, and step C, which press-moldes the barrier paper while I1 / I2 is less than 1.4.

Description

[Technical Field]

[0001] This invention relates to paper containers, and more particularly to paper containers made by molding barrier paper. The invention also describes a method for manufacturing these paper containers. [Background technology]

[0002] It is widely known that barrier containers can be manufactured using barrier paper, which has an oxygen barrier layer formed on a paper substrate. Patent Document 1 exemplifies polyvinylidene chloride as a material for the oxygen barrier layer in such barrier paper. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-5031 [Overview of the project] [Problems that the invention aims to solve]

[0004] Patent Document 1 describes a paper cup as an example of a container with barrier properties, but it is also known that barrier paper can be press-molded into the shape of a container.

[0005] As will be explained in more detail later, the inventor encountered a situation where a container made by press molding of barrier paper having a barrier layer made of polyvinylidene chloride did not exhibit the expected barrier properties, unlike paper cups and the like that made without press molding. Through various investigations, the inventor completed the present invention.

[0006] The present invention aims to provide a method for manufacturing a paper container that can ensure the desired barrier properties while press-molding barrier paper having a barrier layer made of polyvinylidene chloride. [Means for solving the problem]

[0007] A first aspect of the present invention is a method for manufacturing a paper container. This method involves step A, preparing barrier paper in which a barrier layer mainly composed of polyvinylidene chloride is formed on a paper substrate, and heating the barrier layer to obtain an IR peak (1041 cm²) originating from the polyvinylidene chloride crystal portion, measured by FT-IR. -1 The absorption intensity I1 of ) and the IR peak (1067 cm) originating from the amorphous region of polyvinylidene chloride. -1 The method comprises step B, which sets the ratio I1 / I2 of the absorption strength to less than 1.4, and step C, which press-moldes the barrier paper while I1 / I2 is less than 1.4.

[0008] A second aspect of the present invention is a paper container formed by press-molding barrier paper, on which a barrier layer mainly composed of polyvinylidene chloride is formed on a paper substrate. This paper container has a gas barrier performance per unit area, with an oxygen permeability of 20 cc / m². 2 • Less than 1 / day·atm, and water vapor transmission rate of 20 g / m² 2 • day·atm (Satisfying at least one of these conditions) [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for manufacturing a paper container that can ensure the desired barrier properties while press-molding barrier paper. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the layer structure of barrier paper according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing a paper container according to one embodiment of the present invention. [Figure 3] This graph shows the crystallization index of the barrier layer in the manufacturing process of paper containers. [Figure 4] This graph shows the change in the crystallization index of the barrier layer over time. [Modes for carrying out the invention]

[0011] One embodiment of the present invention will be described with reference to Figures 1 to 4. Figure 1 shows the layer structure of the barrier paper 1 according to this embodiment. As shown in Figure 1, the barrier paper 1 comprises a paper substrate 10, a barrier layer 20 formed on the first surface 10a of the paper substrate 10, and a sealant layer 30 formed on the second surface 10b of the paper substrate 10 and on the barrier layer 20.

[0012] Various types of paper can be used as the material for the paper substrate 10, and a printing layer for various displays may be provided on one or both sides. Furthermore, a sealing layer to flatten surface irregularities may be provided on one or both sides. The barrier layer 20 is primarily composed of polyvinylidene chloride (PVDC), meaning it has the highest mass ratio of PVDC. PVDC is a crystalline polymer with excellent oxygen and water vapor barrier properties. The sealant layer 30 is a layer used for heat sealing when attaching a lid to a container made of barrier paper. The material of the sealant layer 30 can be selected according to the configuration of the lid to be joined, and examples include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and very low-density polyethylene (VLDPE). The sealant layer 30 may be provided on only one of the second surface 10b and the barrier layer 20.

[0013] A paper container made of barrier paper 1 can be manufactured by press molding barrier paper 1. Figure 2 shows a schematic diagram of a paper container 50 according to this embodiment. The paper container 50 is formed by deforming a single sheet of barrier paper 1 by press molding, and as shown in Figure 2, it has a bottom surface 51, side surfaces 52 rising from the periphery of the bottom surface, and a flange 53 provided on the upper part of the side surfaces 52, and has an opening Op at the top. The paper container 50 is usually manufactured so that the barrier layer 20 is on the inner side, but this is not essential, and it may also be manufactured so that the barrier layer 20 is on the outer side.

[0014] In the paper container 50, there is no particular limitation on the planar shape (substantially the same as the normal direction of the bottom surface 51) as viewed from the opening Op side, and various shapes such as a quadrangle, other polygons, a circle, an ellipse, etc. can be appropriately selected. Within the range where the barrier paper 1 does not tear or the like during press molding, the number and height of the side surfaces 52, the rising angle from the bottom surface 51, and the angle formed by the side surface 52 and the flange 53 can also be appropriately set. The upper limit of the elongation amount of the barrier paper 1 that can be press-molded without causing tearing or the like is approximately 10%.

[0015] After filling the paper container with contents such as food, a lid film (not shown) having barrier properties is heat-sealed to the sealant layer 30 of the flange 53 to seal the opening Op, so that the contents can be stored in a space having oxygen and water vapor barrier properties until the lid film is peeled off and opened. Thereby, the expiration date or the freshness-keeping period of the contents can be extended, and when the contents are food, it can contribute to reduction of food loss.

[0016] The inventor had made a large number of trial products of paper containers using the barrier paper 1 with PVDC used as the barrier layer, and encountered many cases where the produced paper containers did not exhibit the expected barrier properties based on the barrier layer. When the inventor analyzed the trial products with insufficient barrier properties, a large number of pinholes were found in the barrier layer, and it was found that this was the main cause of reducing the barrier properties.

[0017] When the inventor further investigated, it was found that the pinholes were caused by cracks generated in the barrier layer when the barrier paper stretched during molding (hereinafter referred to as "mechanism 1"), and those generated by the rupture of bubbles generated during the coating of the coating liquid for forming the barrier layer (hereinafter referred to as "mechanism 2"). Furthermore, · The ratio of mechanism 1 is overwhelmingly higher than that of mechanism 2 · Mechanism 2 can be controlled by adjusting the coating conditions, but it is difficult to completely eliminate mechanism 1 even by increasing the thickness of the barrier layer has also been found.

[0018] The inventor focused on the fact that PVDC, the main component of the barrier layer 20, is a crystalline polymer, and considered changing the crystallinity of the barrier layer 20 in order to modify this crystallinity. The degree of crystallinity of a PVDC film can be determined by measuring the infrared absorption intensity of the film surface using FT-IR measurement. Specifically, the IR peak (1041 cm²) originating from the crystalline portion of the target PVDC film can be identified. -1 The absorption intensity I1 of the amorphous region and the IR peak (1067 cm) originating from the amorphous region. -1 By determining the crystallinity index I1 / I2, which is the ratio of the absorption intensity I2 to the crystallinity index I1, the degree of crystallinity of the PVCD layer at the time of measurement can be determined.

[0019] The inventors measured the crystallization indices I1 / I2 of the barrier layer at multiple points in the manufacturing process of paper containers. Figure 3 shows some of the results. After coating the barrier paper with PVDC emulsion and drying it to form a barrier layer, the crystallization index of all three barrier paper samples immediately after aging in a 40°C constant temperature bath for 48 hours was above 1.4. Three samples of barrier paper, prepared by placing a polyethylene film on a barrier layer, passing the paper between rolls heated to 110°C to fuse the polyethylene film to the barrier layer, and then applying a sealant layer and allowing 24 hours to pass, all showed a crystallization index of less than 1.4. A similar decrease in crystallization index was observed in barrier paper samples prepared by passing the paper between rolls without a polyethylene film. These results suggest that the crystallinity of the PVDC barrier layer can be reduced by heating it at a temperature higher than that used during aging.

[0020] Next, Figure 4 shows data obtained by observing the time course of this decrease in the crystallization index using samples after roll heating. As shown in Figure 4, the crystallization index I1 / I2 decreases significantly immediately after roll heating, then returns to a value close to 1.4 after 24 hours, but it was shown that it remains below 1.4 for at least 96 hours after roll heating.

[0021] In parallel, paper containers were produced by press molding of samples 24 hours and 100 hours after roll heating, and no pinholes were observed in the barrier layer. From these results, it was considered that press molding can almost completely prevent the occurrence of pinholes in mechanism 1 by performing press molding when the crystallinity index I1 / I2 of the barrier layer is less than 1.4. Furthermore, it was found that even if the crystallinity index returns to 1.4 or higher after temporarily lowering the crystallinity index of the barrier layer to accommodate the elongation during press molding, there is no effect on the barrier properties.

[0022] There are no particular restrictions on the heating method used to temporarily lower the crystallization index of the barrier layer, but the roll heating method described above is one of the preferred methods. In the inventor's studies, when aged samples were heated in an oven, even at a set temperature of 95°C to 115°C, there were cases where the crystallization index did not decrease sufficiently, or where the crystallization index returned to 1.4 or higher soon after heating. When using roll heating, conditions such as the roll temperature (°C) and passage speed (m / min) can be appropriately determined according to the composition and area of ​​the barrier paper, but for example, they can be set to around 95°C to 115°C and 0.5 to 2.0 m / min.

[0023] The method for manufacturing a paper container according to this embodiment, based on the above findings, comprises the following steps. Step A: Prepare barrier paper by providing a barrier layer made of PVDC on a paper substrate 10. Step B: Heat the barrier paper obtained in Step A to reduce the crystallinity index I1 / I2 of the barrier layer to less than 1.4. Step C: The barrier paper that has gone through Step B is press-molded while the crystallization index I1 / I2 of the barrier layer is less than 1.4.

[0024] As described above, step B may be performed by roll heating, which involves passing barrier paper between heated rolls, and a sealant layer may be provided on the barrier layer at this time. The paper container manufactured by this manufacturing method has a barrier layer made of PVDC and retains sufficient barrier properties while being formed by press molding. Sufficient barrier properties mean, for example, an oxygen transmission rate (OTR) of less than 20 cc / m 2 ·day·atm, or a water vapor transmission rate (WVTR) of less than 20 g / m 2 ·day·atm, based on the inner surface area of the paper container.

[0025] The paper container and its manufacturing method according to this embodiment will be further described using examples. The technical scope of the present invention is not limited based only on the specific content of the examples.

[0026] (Example 1) As the paper base material, clay-coated paper (FibreForm Silky manufactured by BILLERUD, basis weight 165 g / m 2 ) having a sealing layer on the surface was used. A PVDC emulsion (B206 manufactured by Solvay) was coated and dried on the sealing layer to form a barrier layer with a dry film thickness of 43 μm, and aging was performed in a constant temperature bath at 40°C for 48 hours to obtain the barrier paper according to Example 1. (Examples 2 to 5) Barrier papers according to Examples 2 to 5 were obtained in the same procedure as in Example 1, except that the dry film thickness of the barrier layer was 35 μm, 21 μm, 10 μm, and 7 μm, respectively. (Comparative Examples 1 to 5) Barrier papers according to Comparative Examples 1 to 5 were obtained in the same procedure as in Example 1, except that the dry film thickness of the barrier layer was 43 μm, 20 μm, 13 μm, 10 μm, and 7 μm, respectively. That is, the barrier papers according to Comparative Examples 1, 4, and 5 are substantially the same as the barrier papers according to Examples 1, 4, and 5. The barrier paper according to the example was heated by roll heating by passing it at a speed of 1.1 m / min between rolls heated to 110°C. On the other hand, the barrier paper according to the comparative example was not subjected to roll heating.

[0027] (Measurement of crystallization index) The barrier paper in the example was subjected to FT-IR measurement using a JASCO FT / IR-6300 at a timing of 24 hours to less than 96 hours after roll heating, and the barrier paper in the comparative example was subjected to FT-IR measurement at a timing of 24 hours to less than 96 hours after the end of aging. The IR peak originating from the crystalline portion (10⁴ cm⁻¹) was measured. -1 The absorption intensity I1 of the amorphous region and the IR peak (1067 cm) originating from the amorphous region. -1 The absorption intensity I2 of the sample was obtained, and the crystallization index I1 / I2 was calculated.

[0028] (Creating paper containers) After FT-IR measurement, barrier paper for each case was molded using a cold-press method, and multiple paper containers for each case were produced. The maximum elongation of the barrier paper during molding was approximately 10%. As shown in Figure 2, the completed paper containers have a flange 53 around the opening Op, and the barrier layer is located on the inner surface side of the container.

[0029] (Pinhole test) One paper container was selected from each example, and a penetrating solution (Red Mark R-1A(NT) manufactured by Eishin Chemical Co., Ltd.) was applied to the barrier layer and left to stand. After 5 minutes, the penetrating solution was wiped off, and the areas where the penetrating solution had seeped into the paper substrate were counted as pinhole locations in the barrier layer. The evaluation was based on the following two levels. ○(Good): No pinholes were observed. × (Bad): Allows at least one pinhole.

[0030] (Gas barrier performance measurement) Two paper containers were selected from each example, and their openings Op were placed opposite each other, with the flanges in contact. In this state, the flanges were heated and heat-sealed using PVDC to create a sealed container made solely of paper containers. For each example of a sealed container, OTR (20°C, 65%RH (relative humidity)) and WVTR (40°C, 90%RH) were measured using the Mocon method. The results are shown in Table 1.

[0031] [Table 1]

[0032] As shown in Table 1, in comparative examples with a crystallization index exceeding 1.4, numerous pinholes were observed in the barrier layer after press molding, regardless of the barrier layer thickness. As a result, the gas barrier properties could not be measured due to being over-range. On the other hand, in the example, despite having the same structure as the comparative example, the crystallization index was less than 1.4 during press molding, resulting in no pinholes occurring in the barrier layer. As a result, good barrier properties were maintained, and sufficient gas barrier performance was observed. Based on the above, the usefulness of the method for manufacturing paper containers according to this embodiment has been confirmed.

[0033] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration that do not depart from the spirit of the present invention are also included. [Explanation of symbols]

[0034] 1. Barrier paper 10 Paper base material 20 Barrier layer 30 sealant layer

Claims

1. Step A involves preparing barrier paper in which a barrier layer mainly composed of polyvinylidene chloride is formed on a paper substrate, The barrier layer is heated, and the IR peak (1041 cm) originating from the polyvinylidene chloride crystal portion is measured from FT-IR. －１ The absorption intensity I1 of ) and the IR peak (1067 cm) originating from the amorphous region of polyvinylidene chloride. －１ Step B involves making the ratio I1 / I2 of the absorption intensity to less than 1.4, Step C involves press-molding the barrier paper while the ratio I1 / I2 is less than 1.4, Equipped with, A method for manufacturing paper containers.

2. Step B is performed by roll heating, which involves passing the barrier paper between heated rolls. A method for manufacturing a paper container according to claim 1.

3. In step B, a sealant layer mainly composed of polyethylene is formed on the barrier layer. A method for manufacturing a paper container according to claim 2.

4. A paper container formed by press-molding barrier paper, on which a barrier layer mainly composed of polyvinylidene chloride is formed on a paper base material, The gas barrier performance per unit area is an oxygen permeability of 20 cc / m³. ２ - Less than 1 / day atm, and water vapor transmission rate of 20 g / m² ２ - Satisfying at least one of the following conditions: Paper container.

Images