JP7577602B2 - Manufacturing method for flanged paper cup - Google Patents

Description

The present invention relates to a method for manufacturing a flanged paper cup with excellent strength.

In order to achieve the Sustainable Development Goals (SDGs), there is a desire to move away from fossil fuels, and the use of biomass materials has been proposed as one way to achieve this. Biomass resin is a representative example of a biomass material that is being put to practical use.

Polylactic acid (PLA) is known as a biomass resin, but its properties differ significantly from general-purpose resins such as polyethylene and PET, and so it has not yet come into widespread use. For this reason, efforts are underway to produce ethylene from renewable plant raw materials and use it to synthesize biomass-derived polyethylene resin (hereinafter referred to as "biomass polyethylene resin") (Patent Document 1).

However, because polyethylene resin has a wide range of uses, the optimal manner of using biomass polyethylene resin for each application has not been clarified. In particular, no consideration has been given to flange strength, an important characteristic for the application of paper cups, which is the subject of this invention (Patent Documents 2 to 4).

Special Publication No. 2011-506628 JP 2014-133338 A JP 2015-214365 A JP 2017-196777 A

The present invention was made in consideration of the above circumstances, and aims to provide a flanged paper cup that has a small environmental impact and excellent flange strength.

The inventors discovered that by blending low-density biomass polyethylene resin into the outer polyethylene resin layer, the flange strength is significantly improved, leading to the completion of the present invention.

That is, one embodiment of the present invention relates to a method for manufacturing a flanged paper cup comprising a body portion having a flange formed therein and a bottom portion, wherein the body portion is composed of a laminate comprising an outer polyethylene resin layer, a paper base material, and an inner polyethylene resin layer laminated in this order, the resin density of the outer polyethylene resin layer being 0.91 g/cm3 ^or more and less than 0.93 g/ ^cm3 , and the outer polyethylene resin layer containing a low-density biomass polyethylene resin having a density of 0.91 g/ ^cm3 or more and less than 0.93 g/ ^cm3 , and the method for manufacturing a flanged paper cup comprises a molding process for molding the upper end of the body portion into a flange shape, and a heating process for applying heat after the flange is molded.

One embodiment relates to a method for manufacturing the above flanged paper cup, characterized in that the heating step is heating by convection and/or thermal radiation.

One embodiment relates to a method for producing the flanged paper cup described above, characterized in that the polyethylene resin layer contains at least 0.5% by mass of low-density biomass polyethylene resin.

With the completion of this invention, it has become possible to manufacture flanged paper cups that have a small environmental impact and excellent flange strength.

FIG. 2 is a schematic cross-sectional view showing an enlarged view of a flange of a paper cup according to one embodiment.

The present invention relates to a method for manufacturing a flanged paper cup, which consists of a body portion with a flange formed thereon and a bottom portion. The details are explained below.

Flanged Paper Cup
Body The body is made of a laminate of an outer polyethylene resin layer, a paper base material, and an inner polyethylene resin layer, in that order. By using a laminate with a polyethylene resin layer, it is possible to join the bottom and form a flange without using adhesives, etc.

Body: Paper base material <br/> There are no particular limitations on the paper base material that constitutes the laminate, but uncoated paper, coated paper, etc. can be used. In addition, from the viewpoint of realizing the strength as a container, the basis weight of the paper base material is preferably 150 to 400 g/ ^m2 , and more preferably 250 to 350 g/ ^m2 .

Uncoated paper can be produced by adding fillers such as clay, talc, titanium dioxide, calcium carbonate, and aluminum hydroxide powder to the raw pulp, and adding sizing agents, paper strength agents, and fixing agents as necessary. In addition, to improve the paper surface strength, chemicals such as styrene resin, styrene-maleic acid resin, starch, carboxymethyl cellulose, polyvinyl alcohol, and polyacrylamide may be coated on the surface.

Coated paper can be obtained by preparing a coating liquid containing pigments such as calcium carbonate, titanium dioxide, and aluminum hydroxide, and adhesives such as polyvinyl alcohol, styrene-butadiene latex, and methyl methacrylate-butadiene latex, and applying the liquid to the surface.

Body: polyethylene resin layer <br/> Polyethylene resin layers are laminated on both sides of the paper base material. As mentioned above, by laminating polyethylene resin layers (outer polyethylene resin layer and inner polyethylene resin layer) on both sides of the paper base material, it is possible to join the body and bottom and form a flange without using adhesives, etc.

In the present invention, the outer polyethylene resin layer needs to have a resin density of 0.91 g/cm3 ^or more and less ^than 0.93 g/ ^cm3 , and contain a low-density biomass polyethylene resin having a density of 0.91 g/cm3 or more and less than 0.93 g/ ^cm3 . By making the resin density of the outer polyethylene resin layer 0.91 g/ ^cm3 or more and less than 0.93 g/ ^cm3 , and by containing a low-density biomass polyethylene resin having a density of 0.91 g/cm3 ^or more and less than 0.93 g/ ^cm3 , the strength of the flange can be improved.

Here, biomass polyethylene resin refers to polyethylene resin synthesized from plant-derived ethylene. Plant-derived ethylene can be produced by well-known methods using raw materials such as ethanol obtained by fermenting plants (corn, sugar cane, tapioca, etc.). In the present invention, polyethylene resin derived from fossil fuels is referred to as petrochemical polyethylene resin and is handled to be distinguished from biomass polyethylene resin.

The "biomass degree" (concentration of biomass-derived carbon in polyethylene resin) is a value obtained by measuring the amount of biomass-derived carbon by radiocarbon (C14) measurement, and more specifically, refers to the amount of biomass-derived carbon (mass%) in total carbon calculated by measurement according to the biobased concentration test standard "ASTM-D6866-20". Carbon dioxide in the atmosphere contains a certain amount of C14, and the C14 content of plants that grow by absorbing carbon dioxide from the atmosphere is also about the same. On the other hand, fossil fuels contain almost no C14. Therefore, by measuring the proportion of C14 contained in polyethylene resin, the biomass-derived carbon concentration in the polyethylene resin, the "biomass degree", can be calculated.

Furthermore, even if the resin is biomass polyethylene, in the case of high-density biomass polyethylene resin (density 0.93 ^cm3 or higher), the adhesiveness of the resin is poor and the strength of the flange cannot be improved.

Furthermore, it is preferable that the low-density biomass polyethylene resin blended into the inner polyethylene resin layer is 70% by mass or less, and more preferably 50% by mass or less. As shown in Figure 1, the inner polyethylene resin layer is the exterior of the flange and is the part that comes into direct contact with the flange molding machine. Therefore, if too much low-density biomass polyethylene resin with excellent adhesive properties is blended, fine resin pieces (dust) tend to adhere and accumulate on the flange molding machine during the primary heating process, which can lead to reduced productivity and quality.

It is also preferable to make the resin density of the inner polyethylene resin layer higher than that of the outer polyethylene resin layer. As shown in Figure 1, the inner polyethylene resin layer is the exterior of the flange and is the part that comes into direct contact with the flange molding machine during the molding process. Therefore, by making the density of the inner polyethylene resin layer higher than that of the outer polyethylene resin layer and making it less likely to soften or melt, it is possible to prevent resin pieces from adhering to and accumulating on the flange molding machine.

Body: Flange There is no particular restriction on the shape of the flange, and a round flange or a bent flange as shown in Figure 1 can be used. The method of molding the flange will be described later.

Bottom The bottom is made of at least a paper base material. In the present invention, since a polyethylene resin layer is formed on the inner surface of the body, the body and bottom can be joined even if a polyethylene resin layer is not formed on the bottom. However, from the viewpoint of waterproofing, it is preferable to laminate a polyethylene resin layer on the inner surface of the bottom. In the present invention, the inner polyethylene resin layer of the body is referred to as the "inner polyethylene resin layer", and the polyethylene resin layer formed on the inner surface of the bottom is referred to as the "bottom/inner polyethylene resin layer".

Manufacturing method of flanged paper cups Next, a manufacturing method of flanged paper cups will be described.

Method for Producing the Body Section <br/> First, an example of a method for producing the body section will be described. First, a laminate having an inner polyethylene resin layer, a paper base material, and an outer polyethylene resin layer in this order is punched out into a fan shape. Next, the laminate is rolled up so that the inner polyethylene resin layer is on the inside, and the ends are heat sealed to produce a cylindrical body section.

Manufacturing method of the body part: Lamination conditions Here, an example of a method for laminating a polyethylene resin layer onto a paper base material is extrusion lamination.
The extrusion lamination method can be appropriately selected from the single lamination method, the tandem lamination method, the sandwich lamination method, the coextrusion lamination method, and the like.

The temperature of the polyethylene resin (directly below the T-die) during lamination is preferably 260 to 350°C, more preferably 280 to 330°C. Within this range, the laminate strength between the polyethylene resin layer and the paper substrate can be made suitable. In addition, it is preferable to control the surface temperature of the cooling roll within the range of 10 to 50°C.

There are no particular limitations on the thickness of the polyethylene resin layer after lamination, but 30 to 150 μm is preferable, and 40 to 100 μm is more preferable. Within this range, sufficient cup strength can be achieved after the cup is molded.

In addition, if the take-up speed is too slow, productivity is poor, so the take-up speed is preferably 40 m/min or more, and more preferably 60 m/min. On the other hand, if the take-up speed is too fast, the polyethylene resin is likely to neck in, which reduces productivity. Therefore, the pulling speed is preferably 130 m/min or less, and more preferably 110 m/min or less.

Next, we will explain the air gap. Here, the air gap refers to the distance from the extrusion opening of the T-die to the nip roll.

If the air gap during lamination is too wide, the polyethylene resin will neck in and productivity will decrease, so an air gap of 250 mm or less is preferable, and 200 mm or less is even more preferable.

In the present invention, it is preferable to perform surface treatment with ozone gas and/or oxygen gas while the polyethylene resin is passing through the air gap. By performing surface treatment with ozone gas and/or oxygen gas, it is possible to promote the formation of an oxide film and improve the adhesive strength with the substrate layer. There is no particular restriction on the amount of ozone gas and/or oxygen gas to be treated, but from the viewpoint of promoting the oxidation of the polyethylene resin, it is preferable that the amount is 0.5 mg/m2 or ^more .

Method for making the bottom part <br/> An example of a method for making the bottom part will be described. First, a laminate consisting of a bottom part/inner polyethylene resin layer and a paper base material (not necessarily including a bottom part/inner polyethylene resin layer) is punched into a circle. Next, the peripheral edge of the punched laminate is folded by a press to make the bottom part.

Joining the body and bottom parts <br/>The bottom part with its folded periphery is fitted into the body part. At this time, the lower end of the body part is folded so that the periphery of the bottom part is sandwiched in the gap. Next, the body member and the bottom plate member are joined by heat welding or the like.

Flange forming process In the present invention, the flange forming process includes a molding process in which at least the upper end of the body is heated while being molded into a flange, and a heating process in which heat is applied after the flange is molded. This will be described in detail below.

Molding process <br/>The molding process is a process in which the upper end of the body is curled outward little by little to obtain a flange. When obtaining a flange with a bent corner (a bent corner flange) as shown in Figure 1, the flange formed by curling (a round flange) can be fitted into a mold and pressed from above to form a bent corner shape.

In addition, it is preferable to heat the upper end of the body during molding. Heating softens the paper base material, making it easier to mold, and improving productivity and yield. It is not necessary to heat the paper base material all the time during molding, and the timing and intervals of heating can be changed as appropriate depending on the thickness and hardness of the paper base material, molding speed, etc. For example, if the paper base material is soft and the molding speed is fast, heating can be applied at the beginning of the molding process or during molding. On the other hand, if the paper base material is thick and the molding speed is slow, it is preferable to heat the paper base material all the time.

Heating process <br/>The heating process is a process in which heat is applied to the flange after the flange has been molded. Here, the heating process in the present invention is distinguished from the heating during the molding process, since the purpose of the process is different. Specifically, the heating during molding is primarily intended to soften the paper base material, whereas the heating in the heating process is intended to soften and melt the polyethylene resin layer to increase the adhesive strength and more firmly fix the flange.

In addition, in the heating process, the polyethylene resin layer needs to be heated to a degree that softens and melts, and if it is heated by heat transfer, resin pieces will adhere to and accumulate on the equipment, which can lead to reduced productivity and quality. Therefore, heating by convection and/or thermal radiation, which can reduce contact with the equipment, is preferred. An example of a heating device that uses convection is an oven. An example of a heating device that uses thermal radiation is an infrared heater.

The area to be heated can be changed as appropriate depending on the application of the paper cup. Specifically, when the outer polyethylene resin layer is foamed to use it as a foamed paper cup, the entire paper cup can be heated, not just the flange. On the other hand, when it is used as a non-foamed paper cup, it is necessary to heat only a portion of the flange so that the outer polyethylene resin layer does not foam.

Even if the outer polyethylene resin layer does not contain low-density biomass polyethylene resin and is made only of low-density polyethylene resin derived from fossil fuels, the flange strength is improved by undergoing a heating process. However, low-density polyethylene resin derived from fossil fuels has lower adhesiveness than low-density biomass polyethylene resin, making it difficult to improve the flange strength.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Note that "parts" and "%" described below represent "parts by mass" and "% by mass" unless otherwise noted.

Polyethylene resins In this example, biomass-derived low-density biomass polyethylene resin (B-LPDE), high-density biomass polyethylene resin (B-HDPE), and fossil fuel-derived low-density polyethylene resin (F-LDPE) were used. The product names, manufacturers, and resin densities are as shown in Table 1.

Laminate 1
(Step 1) A mixed resin of B-LDPE and B-HDPE (B-LDPE:B-HDPE = 40:60, density 0.943 g/ ^cm3 ) was extrusion laminated onto one side of the paper substrate to form a 40 μm thick inner polyethylene resin layer. (Step 2) Next, F-LDPE was extrusion laminated onto the side opposite the inner polyethylene resin layer, sandwiching the paper substrate between them, to form a 70 μm thick outer polyethylene resin layer (Laminate 1).

The paper substrate and lamination conditions are as follows.
(Step 1)
Paper base material: moisture content 23g/m ² , basis weight 320g/m ²
Extrusion temperature (T die exit temperature): 320℃
Take-off speed (lamination speed): 60m/min Air gap: 80mm

(Step 2)
Extrusion temperature (T die exit temperature): 310℃
Take-off speed (lamination speed): 60m/min Air gap: 80mm

Laminates 2 to 10
Laminates 2 to 10 were produced by changing the resin raw material used for the outer polyethylene resin layer as shown in Table 2. The conditions other than the resin raw material (extrusion temperature, take-up speed, etc.) were the same as those for Laminate 1.

Prototype 1
The laminate 1 was punched out into a sector shape, rolled up so that the inner polyethylene resin layer was on the inside, and the end was heat sealed to produce a cylindrical body. Separately from the body, the laminate 1 was punched out into a circle, and the peripheral portion of the punched out laminate was folded by a press to produce a bottom. The bottom portion with the folded peripheral portion was then fitted into the body and heat welded at 400°C (0.5 seconds x 2 times) to produce a paper cup (without flange).

The flange was then heated at 420°C for 0.3 seconds, and immediately thereafter the top end of the body was curled outward to create a flange (round). It was then fitted into a mold and pressed from above to form the flange into a square fold, yielding a paper cup with a flange (before the heating process). Finally, the paper cup with flange was heated in an oven at 120°C for 360 seconds to obtain a paper cup with a flange (prototype 1). The paper cup had a mouth diameter of 96φ and a height of 107mm.

Prototype examples 2 to 10
As shown in Table 3, Prototype Examples 2 to 10 were produced by changing the laminate 1 to laminates 2 to 10. The conditions other than the laminate (molding conditions, heating conditions, aperture, etc.) were the same as those of Prototype Example 1.

(evaluation)
The flange strength and productivity before and after the heating step were evaluated according to the following criteria.

Flange strength The compression strength of the flange (hereinafter referred to as "flange strength") was measured using a compression tester. The measurement conditions were as follows:
Compression tester: Tensilon RTC-131OA (A&D Co.), 100N load cell Measurement method: The flange was fixed at a position 90 degrees clockwise from the body/heat seal part (when viewed from above the paper cup), and pressure was applied from a position 90 degrees counterclockwise from the body/heat seal part (180 degrees from the fixed position). The strength (N) at which the flange broke was recorded as the flange strength.

Productivity <br/> For each prototype, 40,000 paper cups were flanged and evaluated based on the amount and shape of the resin pieces that adhered to the flange molding machine after molding.
○: No resin pieces attached △: Resin pieces attached to areas that are likely to come into contact with the flange (heater, mold) ×: Resin pieces attached to various parts inside the flange molding machine

From Table 3, it can be seen that the flange strength is improved by going through the heating process. This is thought to be due to the fact that the low-density polyethylene resin melts during the heating process, resulting in strong adhesion. Furthermore, a comparison of prototype 1 with prototypes 2 to 10 shows that the inclusion of low-density biomass polyethylene resin further improves the flange strength after the heating process. Furthermore, since there is no difference in the flange strength before the heating process, the effectiveness of low-density biomass polyethylene resin in the heating process is clear.

1: Outer polyethylene resin layer 2: Inner polyethylene resin layer 3: Paper base material

Claims (3)

A method for manufacturing a flanged paper cup having a body portion with a flange and a bottom portion, comprising the steps of:
The body portion is made of a laminate having an outer polyethylene resin layer, a paper base material, and an inner polyethylene resin layer laminated in this order,
The resin density of the outer polyethylene resin layer is 0.91 g/ ^cm3 or more and less than 0.93 g/ ^cm3 ;
The outer polyethylene resin layer contains 0.5% by mass or more and 30% by mass or less of a low-density biomass polyethylene resin having a density of 0.91 g/ ^cm3 or more and less than 0.93 g/ ^cm3 ,
The resin density of the inner polyethylene resin layer is higher than the resin density of the outer polyethylene resin layer,
The method further includes a molding process for molding the upper end of the body into a flange shape, and a heating process for applying heat after the flange is molded.
A method for manufacturing a flanged paper cup, comprising the steps of: The method for manufacturing a flanged paper cup according to claim 1, characterized in that the heating step is heating by convection and/or thermal radiation. 3. The method for producing a flanged paper cup according to claim 1, wherein the inner polyethylene resin layer contains 70% or less of low-density biomass polyethylene resin.

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