Laminate for paper cups, and paper cups

Abstract

To provide a laminate for paper cup molding that has low environmental load and less troubles such as interfacial peeling during molding and liquid leakage, and to provide a paper cup.SOLUTION: The present inventors have found that the problem can be solved by a laminate for paper cup molding that includes at least a paper substrate layer and an inner surface layer made of a biomass polyethylene resin, and in which, characterized, the density of the biomass polyethylene resin is 0.92 g / cm3 or more and 0.95 g / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminate for molding paper cups, comprising a polyethylene resin layer derived from biomass, and to a paper cup. [Background technology]

[0002] 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 means to achieve this.

[0003] Polylactic acid (PLA) is a known biomass resin, but its properties differ significantly from general-purpose resins such as polyolefins and PET, and therefore it has not become widely adopted. For this reason, efforts are underway to produce ethylene from renewable plant materials and use it to synthesize biomass-derived polyethylene resin (hereinafter referred to as "biomass polyethylene resin") (Patent Document 1).

[0004] However, because polyethylene resin has a wide range of applications, the optimal use of biomass polyethylene resin for each application has not been clarified. In particular, in the case of paper cups, which is the target of this invention, interfacial delamination that occurs between polyethylene resins during molding and liquid leakage, which are important physical properties for cups, have not been considered at all (Patent Documents 2-4). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2011-506628 [Patent Document 2] Japanese Patent Publication No. 2014-133338 [Patent Document 3] Japanese Patent Publication No. 2015-214365 [Patent Document 4] Japanese Patent Publication No. 2017-196777 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above circumstances, and aims to provide a laminate for paper cups and paper cups that have a low environmental impact and are less prone to interfacial delamination during molding and leakage when liquid is poured in. [Means for solving the problem]

[0007] The present inventors have provided a laminate for molding paper cups comprising at least a paper base layer and an inner layer made of biomass polyethylene resin, wherein the density of the biomass polyethylene resin is 0.92 g / cm³. 3 More than 0.95g / cm 3 We have found that the above problem can be solved by a laminate for molding paper cups, characterized as follows. [Effects of the Invention]

[0008] With the completion of this invention, it has become possible to manufacture laminates and paper cups for paper cups that have a low environmental impact and excellent physical properties. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram illustrates the configuration of Example 1 in cross-sectional view. [Figure 2] This is a cross-sectional view of the leg. [Figure 3] This diagram shows the route of the liquid leak. [Modes for carrying out the invention]

[0010] The present invention relates to a laminate for molding paper cups, comprising at least a paper substrate layer and an inner layer made of biomass polyethylene resin. Further details will be described below.

[0011] paper base material The paper base material constituting the laminate of the present invention is not particularly limited, and uncoated paper, coated paper, etc. can be used. Further, from the viewpoint of realizing toughness as a container, the basis weight of the paper base material is preferably 150 to 400 g / m 2 and more preferably 250 to 350 g / m 2 is more preferred.

[0012] The uncoated paper can be manufactured by adding fillers such as clay, talc, titanium dioxide, calcium carbonate, aluminum hydroxide powder, etc. to the raw material pulp, and adding a sizing agent, paper strength enhancer, fixing agent, etc. as necessary. Further, in order to improve the paper surface strength, chemicals such as styrene resin, styrene-maleic acid resin, starch, carboxymethylated cellulose, polyvinyl alcohol, polyacrylamide, etc. may be coated on the surface.

[0013] The coated paper can be obtained by preparing a coating liquid containing pigments such as calcium carbonate, titanium dioxide, aluminum hydroxide, etc. and adhesives such as polyvinyl alcohol, styrene-butadiene latex, methyl methacrylate-butadiene latex, etc. and coating it on the surface.

[0014] Inner layer In the present invention, it is necessary to provide an inner layer made of biomass polyethylene resin. Although the detailed mechanism is not clear, it has been clarified that by using the biomass polyethylene resin for the inner layer, the cup strength and the laminate strength are improved. The cup strength refers to the adhesive force between the body and the bottom, and by increasing the cup strength, liquid leakage when pouring water or the like can be prevented. The laminate strength refers to the laminate strength between the paper base material and the inner layer, and by increasing the laminate strength, troubles during molding such as interfacial peeling can be prevented.

[0015] Here, biomass polyethylene resin refers to polyethylene resin synthesized from ethylene derived from plants. Plant-derived ethylene can be produced by well-known methods using ethanol obtained by fermenting plants (corn, sugarcane, tapioca, etc.) as a raw material. In this invention, polyethylene resin derived from fossil fuels is referred to as petrochemical polyethylene resin and treated separately from biomass polyethylene resin.

[0016] Furthermore, "biomass content" (the concentration of biomass-derived carbon in polyolefin resin) is a value measured by radiocarbon (C14) measurement to determine the amount of biomass-derived carbon. More specifically, it refers to the amount of biomass-derived carbon in the total carbon, calculated according to the bio-based concentration test standard "ASTM-D6866-20" (mass %). Atmospheric carbon dioxide contains a certain amount of C14, and the C14 content of plants that grow by taking in atmospheric carbon dioxide is about the same. On the other hand, fossil fuels contain almost no C14. Therefore, by measuring the proportion of C14 contained in polyolefin resin, the biomass-derived carbon concentration in the polyolefin resin, or "biomass content," can be calculated.

[0017] In this invention, it is not necessary for the material to be 100% biomass; polyethylene resin with a biomass content of 5% or more is referred to as biomass polyethylene resin. This is because replacing a portion of the polyethylene resin with biomass-derived materials can achieve the objective of reducing the use of fossil fuels.

[0018] Furthermore, in this invention, the biomass polyethylene resin has a density of 0.93 g / cm³. 3 More than 0.97g / cm 3 Preferably, it contains the following high-density biomass polyethylene resin, 0.945 g / cm³ 3 More than 0.960g / cm 3 It is more preferable to include the following high-density biomass polyethylene resin. Including high-density biomass polyethylene resin improves the cup's strength and prevents leakage when liquid is poured in.

[0019] Furthermore, as the biomass polyethylene resin, it is preferable to contain a low-density biomass polyethylene resin having a density of 0.90 g / cm 3 or more and less than 0.93 g / cm 3 . More preferably, it contains a low-density biomass polyethylene resin having a density of 0.910 g / cm 3 or more and 0.925 g / cm 3 or less. By including the low-density biomass polyethylene resin, the laminate strength can be improved and interfacial delamination can be prevented.

[0020] Furthermore, not only the high-density biomass polyethylene resin and the low-density biomass polyethylene resin are included, but the average density of the biomass polyethylene resin (a mixture of the high-density biomass polyethylene resin and the low-density biomass polyethylene resin) constituting the inner layer is 0.92 g / cm 3 or more and 0.95 g / cm 3 or less, and it is more preferably 0.935 g / cm 3 or more and 0.945 g / cm 3 or less. By adjusting the average density of the biomass polyethylene resin constituting the inner layer within this range, liquid leakage and interfacial delamination can be prevented.

[0021] Furthermore, it is preferable not to provide an intermediate layer between the paper base material layer and the inner layer. This is because providing an intermediate layer increases the materials used and the environmental load. When an intermediate layer has to be provided, a polylactic acid film, a PET film, a CPP film, an OPP film, a nylon film, etc., and a barrier film obtained by vapor-depositing aluminum oxide or the like on these films can be appropriately selected and used. Note that these films can be used regardless of whether they are derived from biomass raw materials or fossil fuel raw materials.

[0022] outer layer In the present invention, an outer layer may be provided on the surface opposite to the inner layer with the paper base material sandwiched therebetween. By providing the outer layer, the waterproof property and the heat insulation property can be enhanced.

[0023] In this invention, a foamed layer may be provided as the outer layer. In this case, the foamed layer has a density of 0.91 g / cm³. 3 More than 0.93g / cm 3 It is preferable to use a low-density polyolefin resin with a melting point of less than 1. By using a low-density polyolefin resin with a low melting point in the foamed layer, it is possible to foam only the outer layer during the foaming process without foaming the inner layer.

[0024] When the outer layer is used as a waterproofing layer, there are no particular limitations on the material of the outer layer; polyethylene resin, polypropylene resin, polyester resin, etc., can be used as appropriate.

[0025] Manufacturing method There are no particular limitations on the method for forming the inner and outer layers, but extrusion lamination or the like can be used.

[0026] Extrusion lamination conditions As for the extrusion lamination method, single lamination, tandem lamination, sandwich lamination, co-extrusion lamination, etc., can be selected as appropriate.

[0027] The temperature of the polyethylene resin (directly beneath the T-die) during lamination is preferably 260 to 350°C, and more preferably 280 to 330°C. Within this range, the lamination strength between the polyethylene resin layer and the paper substrate can be optimized. Furthermore, the surface temperature of the cooling roll is preferably controlled within the range of 10 to 50°C.

[0028] There are no particular limitations on the thickness of the polyethylene resin layer after lamination, but 30 to 150 μm is preferred, and 40 to 100 μm is more preferred. Within this range, sufficient cup strength can be achieved after cup molding.

[0029] Furthermore, if the pickup speed is too slow, productivity will be poor, so a pickup speed of 40 m / min or more is preferable, and 60 m / min is more preferable. On the other hand, if the pull-up speed is too fast, the polyethylene resin is more likely to get stuck in the neck, which can reduce productivity. Therefore, a tensile speed of 130 m / min or less is preferable, and 110 m / min or less is more preferable.

[0030] Next, let's discuss the air gap. Here, the air gap refers to the distance from the T-die's extrusion port to the nip roll.

[0031] If the air gap during lamination is too wide, the polyethylene resin will neck in, reducing productivity. Therefore, an air gap of 250 mm or less is preferable, and 200 mm or less is more preferable.

[0032] In this invention, it is preferable to surface-treat the polyethylene resin with ozone gas and / or oxygen gas while it is passing through the air gap. Surface treatment with ozone gas and / or oxygen gas promotes the formation of an oxide film and improves the lamination strength between the substrate layer and the polyethylene resin. There are no particular limitations on the amount of ozone gas and / or oxygen gas used, but 0.5 mg / m² is preferable from the viewpoint of promoting the oxidation of the polyethylene resin. 2 The above is preferable. [Examples]

[0033] Prototype Example 1 (Step 1) Polyethylene resin (SBC818:SHC7260LS-L=90:10) was laminated onto one side of a paper substrate by extrusion lamination to create an inner layer with a thickness of 40 μm, thereby producing a laminate (Prototype Example 1). The processing conditions were as follows.

[0034] (Lamination conditions) Paper base material: moisture content 23g / m 2 , basis weight 320g / m 2 Extrusion temperature (T die exit temperature): 320℃ Pickup speed (lamination speed): 60m / min Air gap: 80mm

[0035] Prototype Examples 2-24 Laminates (Prototype Examples 2-24) were manufactured under the same lamination conditions as Prototype Example 1, with the polyethylene resin used for the inner layer changed as shown in Tables 1-1 and 1-2. The polyethylene resins used in this example are shown in Table 2. In Tables 1-3, "LDPE" refers to low-density polyethylene resin, and "HDPE" refers to high-density polyethylene resin. Biomass polyethylene resin is abbreviated as "bio," and petrochemical polyethylene resin as "petrochemical."

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3]

[0039] The body and bottom components were cut from prototype example 1, and a paper cup (Example 1) was manufactured using a known paper cup molding machine. Similarly, paper cups (Examples 2-16, Comparative Examples 1-8) were manufactured from prototype examples 2-24 using the same method as in Example 1. The shape of the paper cup is as follows: Height: 107mm (Leg height: 9mm) Aperture: 95mm (with rim) Bottom diameter: 64mm Taper angle: 6.5°

[0040] Rating: Density The density of plastics was measured according to the standard test method for density gradient (ASTM D1505-10). Prior to measurement, the test specimens (prepared from pellet samples) were left to stand at 23°C for 40 hours to stabilize their temperature.

[0041] Rating: Lamination strength A cross-shaped cut (size: approximately 30 mm per side, depth: approximately 50 μm (the cut reaches the paper substrate but does not penetrate the substrate)) was made on the inner layer (resin layer side) of the prototype using a cutter, and adhesive tape (cloth tape 50 mm, 25 mm roll 121-50, manufactured by Nichiban Co., Ltd.) was applied to cover the area, and the adhesive tape was peeled off quickly. The following evaluation was made based on the peel interface at this time. Furthermore, compared to cases where the paper is peeling, interfacial delamination results in lower lamination strength, making defects more likely during molding. ○ (Good): The paper is peeling off completely. *Paper peeling...a condition where the paper substrate is damaged. ○△: There is a mixture of paper peeling and interfacial delamination between the paper substrate and resin, with a large area of ​​paper peeling. △: There is a mixture of paper peeling and interfacial delamination between the paper substrate and the resin, and the area of ​​interfacial delamination is large. × (Defective): Delamination has occurred at the interface between the paper substrate and the resin throughout the entire surface.

[0042] Rating: Leakage Fifty paper cups were prepared for each of the Examples 1-16 and Comparative Examples 1-8. 300 mL of score roll solution was filled into each cup, and after standing for 30 minutes, the number of paper cups that leaked was counted. Scoreroll solution: 1000 mL water, 1 mL scoreroll concentrate (Scoreroll 700, Kitahiro Chemical), 0.5 g eriochrome black T

[0043] This embodiment shows that biomass polyethylene resin tends to be less prone to leakage. Furthermore, during the development of this invention, it was discovered that the decrease in cup strength and leakage occur for the following reasons. First, when forming the legs, heat and pressure are applied, causing the polyethylene resin to flow to some extent. A slight thinning of the polyethylene resin thickness does not affect leakage, but if the fluidity is high, areas where the polyethylene resin is almost absent and the paper substrates come into contact with each other (pinholes) will occur. When liquid is poured into a paper cup with pinholes and left to stand for a while, the liquid penetrates the paper substrate through the pinholes, causing leakage. Furthermore, the cup strength tends to decrease as the number of pinholes increases, so a correlation can be observed between cup strength and leakage.

[0044] [Table 4]

[0045] [Table 5] [Explanation of Symbols]

[0046] 1...Paper base material 2. Inner layer 11. Paper base material for the body 12. Inner layer of the torso 21...Bottom paper base material 22...bottom inner layer 31...Route of liquid leakage

Claims

1. A laminate for molding paper cups, comprising an outer layer consisting of a foamed layer containing low-density polyolefin, a paper substrate layer, and an inner layer containing biomass polyethylene resin, The aforementioned inner layer is Density 0.945g / cm 3 More than 0.960g / cm 3 The following high-density polyethylene resins, Density 0.910g / cm 3 More than 0.925g / cm 3 It consists of a mixture with the following low-density polyethylene resins: The mixing ratio of the high-density polyethylene resin and the low-density polyethylene resin is High-density biomass polyethylene resin: Low-density biomass polyethylene resin = 10:90 to 61:39 High-density petrochemical polyethylene resin: Low-density biomass polyethylene resin = 45:55 to 61:39 Alternatively, it is characterized by being one of the following: high-density biomass polyethylene resin: low-density petrochemical polyethylene resin = 45:55 to 61:

39. Laminate for molding paper cups.

2. A paper cup made of the laminate for paper cup molding according to claim 1.

Images