JP7658765B2 - Paper containers - Google Patents

Description

The present invention relates to paper containers that require oil resistance.

Paper containers that store food ingredients that contain a large amount of oil are required to be oil-resistant (Patent Document 1 and Patent Document 2).

In particular, food ingredients are now often heated in microwave ovens, making oil resistance even more important.

JP 2006-056127 A JP 2009-030192 A

An example of a paper container is a paper cup. A paper cup has a circular bottom and a body that stands upright from the bottom in an inverted truncated cone or cylinder shape. If appropriate, the cup may have a flange or a lid on the upper edge of the body.

The body of the paper cup is made by rolling a sector-shaped blank, placing one end underneath and the other end on top of it, and then overlapping and joining the two ends (for example, by heat welding).

When molding the container, pinholes may occur when the blank is deformed. Pinholes may also occur when the joints are thermally welded.

When heated in a microwave oven, the temperature inside the container can exceed 100°C, which can cause pinholes to form due to moisture foaming or softening of the coating layer.

These pinholes can cause oil seepage, and generally speaking, joints are particularly prone to problems.

Generally, various designs are printed on the outside of commercially available paper containers used for packaging food. Oil stains greatly impair the aesthetic appearance.

The present invention aims to solve the above problems and provide a technology that prevents the contents from bleeding into paper containers such as paper cups.

The paper container of the present invention, which achieves the above object, comprises a body portion formed by rolling a blank and joining the ends of the blank together, and a bottom portion joined to the lower end of the body portion. The paper container is formed from a base paper that has been treated on the inside to make it oil-resistant, and a high-melting point polyethylene layer that covers the inside of the base paper. The melting point of the high-melting point polyethylene layer is 115°C or higher.

The use of a high melting point polyethylene layer helps prevent pinholes from occurring when heated in the microwave. In addition, even if pinholes do occur, the oil-resistant treatment helps prevent bleeding through the pinholes.

Preferably, the high melting point polyethylene layer is formed from a low melting point polyethylene layer coated on the inside thereof, and the melting point of the low melting point polyethylene layer is lower than the melting point of the high melting point polyethylene layer.

Preferably, the melting point of the low melting point polyethylene layer is at least 10°C lower than the melting point of the high melting point polyethylene layer.

This ensures good adhesion, which in turn improves leakage from the joint.

Preferably, at one end of the blank, the low melting point polyethylene layer is folded over to cover the end surface.

This reduces the risk of the contents seeping through the blank edge. In addition, the low-melting-point polyethylene layers are heat-welded together, further improving bonding.

Preferably, it contains contents that include oil.

The paper container of the present invention can prevent the contents, including oil, from bleeding.

The present invention can prevent the contents from bleeding.

General method for forming paper containers Cross-section of joint (comparison with general example) Summary of verification results

～Basic configuration～
1 is a diagram showing an outline of a method for forming a paper cup. The paper container of this embodiment includes a paper cup. The body of the paper cup is formed from a sector-shaped blank.

The blank is rolled, one end is placed on the bottom and the other end is placed on top so that the joining surfaces face each other, and both ends are overlapped and joined at a specified joining width. This forms the body of the paper cup.

The bottom of the paper cup is circular. The paper cup is formed by joining the paper cup body and the paper cup bottom.

~Characteristic composition~
This embodiment suitably has the following characteristic configurations (see FIG. 2).

The inside of the base paper 1 (the side that comes into contact with the contents) is treated to be oil-resistant, and an oil-resistant layer 2 is formed. In detail, the base paper 1 is made from multiple pulp layers (e.g., five layers), and only the innermost pulp layer is treated to be oil-resistant. It is preferable that the outside is not treated to be oil-resistant, as it will be used for design printing. If printing is not required on the bottom, both sides may be treated to be oil-resistant.

In addition, the inside of the base paper 1 is coated with a high melting point polyethylene layer 3.

The inside of the high melting point polyethylene layer 3 is covered with a low melting point polyethylene layer 4.

At one end of the blank, the low melting point polyethylene layer 4 is folded back to cover the end surface 5 (edge protection (EP) treatment). As a result, the low melting point polyethylene layer at one end and the low melting point polyethylene layer at the other end are joined.

For comparison, a cross-sectional view of a typical paper cup joint is added to Figure 2.

～Verification test～
A number of sample examples created for the verification test of the above characteristic configuration will be described (see FIG. 3).

General example: Neither the body nor the base are treated for oil resistance. There is no high melting point polyethylene layer. The low melting point polyethylene layer is 15 μm thick. No EP treatment has been applied (see Figure 2).

Sample A: Only the bottom part is treated for oil resistance. The high melting point polyethylene layer is 20 μm thick. The low melting point polyethylene layer is 20 μm thick. EP treated.

Sample B: Only the bottom part is treated for oil resistance. The high melting point polyethylene layer is 20 μm thick. There is no low melting point polyethylene layer. It is EP treated.

Sample C: Only the bottom part is treated for oil resistance. The high melting point polyethylene layer is 40 μm thick. There is no low melting point polyethylene layer. It is EP treated.

Sample D: The body and bottom are oil-resistant. The high-melting point polyethylene layer is 20 μm thick. There is no low-melting point polyethylene layer. Not EP treated.

Sample E: The body and bottom are oil-resistant. The high-melting-point polyethylene layer is 20 μm thick. The low-melting-point polyethylene layer is 20 μm thick. It has been EP-treated (see Figure 2).

Note that the above samples are merely examples, and the present invention is not limited to the above samples.

Two verification tests were conducted on the above sample example.

Mabo tofu microwave heating: Mabo tofu was placed in a paper cup and microwaved at 1520W for 20 seconds, and the oil seepage was observed.

Shrimp chili left for 10 hours: Shrimp chili was placed in a paper cup and left for 10 hours, after which oil seepage was observed.

The above tests are examples of problems that may arise when a paper container is used to store food ingredients that contain a large amount of oil, and the present invention is not limited to these problems.

The base paper for the above samples had a basis weight of 250 to 260 g/m ² for the body and 200 to 220 g/m ² for the bottom.

Below, we explain each point by comparing the results of the verification tests.

～Point 1～
When oily contents are heated in a microwave oven, the contents can exceed 100°C, causing pinholes due to moisture foaming and softening of the polyethylene layer, which can lead to oil seepage. To address this issue, a high melting point polyethylene layer is used.

Compare the verification results of the general example with those of samples A and B. None of the barrels have been treated to be oil resistant. The general example has a low melting point polyethylene layer, while samples A and B have a high melting point polyethylene layer on the inside.

When comparing the results of the microwave heating test for mapo tofu, in the general example, bleeding occurred around the entire outer surface of the container, whereas in sample A and sample B, no bleeding was observed.

By replacing the low-melting-point polyethylene layer with a high-melting-point polyethylene layer, the occurrence of pinholes during microwave heating can be suppressed, regardless of whether or not the product is oil-resistant. In addition, the results for sample B show that the occurrence of pinholes during microwave heating can be suppressed even without a low-melting-point polyethylene layer.

For the low melting point polyethylene, low density polyethylene (LDPE) is used. The melting point of low density polyethylene is around 100-115°C. The melting point of the low melting point polyethylene in the above sample was 108°C.

High-melting-point polyethylene includes high-density polyethylene (HDPE) and low-density polyethylene with a higher melting point by incorporating high-density polyethylene or ethylene-propylene copolymers. The melting point of high-density polyethylene is around 120-140°C. The melting point of the high-melting-point polyethylene in the above sample was 128°C. The melting point of high-melting-point polyethylene is increased by incorporating ethylene-propylene copolymers into low-melting-point polyethylene.

In this application, polyethylene with a melting point of less than 115°C is defined as low-melting-point polyethylene, and polyethylene with a melting point of 115°C or higher is defined as high-melting-point polyethylene.

The melting point of the low melting point polyethylene layer is preferably at least 10°C lower than the melting point of the high melting point polyethylene layer. In the above sample, the difference is 20°C.

Point 2
By covering the inside of the base paper with a high melting point polyethylene layer, there is a risk that the heat welding of the joints during container molding will be insufficient. As a result, there is a risk that the contents will leak from the unsealed parts of the bottom. By increasing the heating temperature, the heat welding can be achieved reliably, but there is a risk that the base paper will be damaged, such as by burning. To address this issue, a low melting point polyethylene layer is used.

Compare the verification results of Sample A and Sample C. Neither of them have been treated to make the body oil-resistant. Sample C has the same structure as Sample B, but the polyethylene layer thickness is the same as Sample A (layer thickness 40 μm). Sample A is coated with a low-melting point polyethylene layer, whereas Sample C is not.

When comparing the test results of leaving shrimp chili for 10 hours, sample C had a leak at the bottom in one out of ten tests, whereas sample A had no leaks at the bottom in any of the ten tests.

The low melting point polyethylene layer is reliably heat welded to ensure adhesion. As a result, leakage from unwelded areas can be improved.

For reference, the verification results of the general example and sample D are compared. The general example has not been treated to be oil resistant, whereas sample D has been treated to be oil resistant. The general example does not have a high melting point polyethylene layer, whereas sample D has a high melting point polyethylene layer.

The results of a test in which shrimp chili was left for 10 hours showed that leakage was observed from the bottom, although the degree of leakage varied.

This suggests that a high melting point polyethylene layer coating and oil resistance treatment alone are insufficient to address the issue of bottom leakage.

Point 3
When forming a container, the body of the paper cup is made by rolling up a sector-shaped blank. There is a risk of pinholes occurring due to blank deformation. In addition, since the joints are heat-welded during container formation, there is a risk of pinholes occurring at the joints. To address this issue, oil-resistant treatment is applied.

Compare the verification results of Sample A and Sample E. Sample A does not have an oil-resistant treatment on the body, whereas Sample E has an oil-resistant treatment on the body. The rest of the structure is the same.

When comparing the test results after leaving shrimp chili for 10 hours, slight bleeding was observed at the joint edge of sample A, whereas no bleeding was observed at all with sample E.

Even if pinholes do occur, oil-resistant treatment can prevent bleeding through the pinholes.

Oil resistance (= oil repellency) is exhibited when the surface tension of a solid surface (base paper surface) is lower than that of the liquid (oil). If fluorine compounds, etc. are present on the base paper surface, the intermolecular forces that the oil receives from the base paper at the interface between the base paper and the oil are weak, destabilizing the oil at the interface and making it easier for the surface tension of the oil to act, resulting in oil repellency. In other words, even if there are pinholes, bleeding through the pinholes can be suppressed.

Examples of oil-resistant agents include fluorine-based compounds, acrylic compounds, and silicon-based compounds. Oil-resistant agents can be added during papermaking (internal addition method) or impregnated or coated on the surface after papermaking (external addition method). Generally, fluorine-based compounds are used for papermaking using the internal addition method.

An AC agent (anchor coating agent) may be used to improve adhesion between the oil-resistant treated base paper and the polyethylene layer.

Point 4
Furthermore, there is a risk of the contents seeping through the blank edge. To address this issue, edge protection (EP) processing is used.

Compare the verification results of sample D and sample E. Sample D has not been EP processed, whereas sample E has been EP processed.

When comparing the results of the test where shrimp chili was left for 10 hours, sample D showed bleeding to the same extent as the general example, whereas sample E showed no bleeding at all.

In particular, in sample E, the EP treatment heat-welds the low-melting-point polyethylene layer at one end to the low-melting-point polyethylene layer at the other end, further improving the bondability (see point 2).

In EP processing, part of the edge of the base paper is shaved off and folded back together with the low melting point polyethylene layer and the high melting point polyethylene layer. The thickness of the EP-treated part is made the same as the laminate thickness. This allows the edge to be protected by the coating layer.

1 Base paper 2 Oil-resistant layer 3 High melting point polyethylene layer 4 Low melting point polyethylene layer 5 End surface

Claims (2)

A paper container that is microwaveable and can accommodate contents containing oil, and that includes a body portion formed by rolling a blank and joining the blank end portions together, and a bottom portion joined to the lower end of the body portion,
A base paper having an innermost pulp layer which is an oil-resistant layer;
A high melting point polyethylene layer coated on the inside of the base paper;
a low melting point polyethylene layer coated on the inside of the high melting point polyethylene layer;
is formed from
The melting point of the high melting point polyethylene layer is 115° C. or higher,
The melting point of the low melting point polyethylene layer is lower than the melting point of the high melting point polyethylene layer,
At one end of the blank, the low melting point polyethylene layer is folded back to cover the end surface.
A paper container characterized by: The paper container according to claim 1 , wherein the melting point of the low melting point polyethylene layer is lower by 10° C. or more than the melting point of the high melting point polyethylene layer.