Foamed paper laminate and method for producing the same, and foamed paper container

Abstract

A foamed paper laminate comprising foamed paper and a printed layer, wherein the foamed paper comprises a thermoplastic resin layer (A), a paper substrate, and a foamed thermoplastic resin layer (B) in this order, the printed layer being formed on the surface of the foamed thermoplastic resin layer (B) of the foamed paper, and the number of foamed cells per unit area of ​​the foamed thermoplastic resin layer (B) being 1000 cells / 1 cm 2 As described above, the printed layer includes a binder resin including a polyurethane resin, and the residual rate of the printed layer after being immersed in ethanol at 25° C. for 30 minutes is 50% by mass or more.

Description

Technical Field

[0001] An embodiment of the present invention relates to a foamed paper laminate and a method for producing the same. In addition, another embodiment of the present invention relates to a foamed paper container including the foamed paper laminate. Background Art

[0002] Due to their excellent thermal insulation properties, foam containers are widely used for foods containing high- or low-temperature liquids. They are particularly essential for instant noodles, such as ramen, udon, and soba, which can be consumed minutes later by simply adding a suitable amount of boiling water to a container. Known foam containers for cup noodles include expanded polystyrene and foam paper. However, foam paper containers have recently gained attention due to concerns about environmental impact and safety.

[0003] Foamed paper containers are manufactured using a foamed paper material having a paper base material and a thermoplastic resin layer that is foamed by heating during container manufacturing to form an insulating layer. Typically, a printed layer containing a decorative pattern, company name, barcode, or other printed pattern is formed on the surface of the foamed paper container (foamed paper material). Therefore, when the thermoplastic resin layer of the foamed paper material is foamed by heating to form an insulating layer, it is desirable that the printed layer has excellent foaming followability without hindering foaming. In addition, it is desirable that the surface (printed surface) of the printed layer after the thermoplastic resin layer is foamed is smooth, free of cracks and bubbles, and has an excellent appearance. Furthermore, it is desirable that the printed surface has excellent various resistances, such as friction resistance and heat resistance, required for container manufacturing.

[0004] Traditionally, oil-based inks, such as oil-based gravure inks and oil-based flexographic inks, have been used to form the printed layer of foam paper containers. Due to the solubility and drying properties of the binder resin, oil-based inks typically contain organic solvents such as toluene. However, in recent years, regulations regarding the use of organic solvents have become increasingly stringent due to environmental impact and workplace safety and hygiene concerns, leading to increasing demand for water-based inks. Consequently, in the field of food containers such as cup noodles, the development of foam paper laminates with printed layers formed using water-based inks that are suitable for use as materials for foam paper containers is underway.

[0005] For example, Patent Document 1 discloses a water-based flexographic ink for a foam cup, which contains a binder resin, a pigment, and water as ink for a printing layer forming a foam paper laminate, wherein the binder resin contains a polyurethane resin. In addition, Patent Document 2 discloses that the foaming of the foam layer is suppressed within a predetermined range by a coating portion (printing layer) of the water-based ink. The water-based ink disclosed in Patent Document 2 contains a colorant and a binder resin, and the resin solid content of the binder resin contains more than 30% by mass of a urethane resin having a glass transition point of not less than -20°C and not more than 30°C. Furthermore, Patent Document 3 discloses a water-based ink containing an acrylic resin, an acrylic-urethane copolymer resin, a styrene-maleic acid copolymer resin, or a polyurethane resin as a binder resin.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-058955

[0009] Patent Document 2: International Publication No. 2018 / 066031

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2011-068381 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] The thermal insulation properties of foamed paper containers primarily depend on the foamability of the thermoplastic resin layer that constitutes the foamed layer (insulating layer) in the foamed paper laminate. However, as the foamability of the thermoplastic resin layer increases during heating, the printed layer formed on the thermoplastic resin layer is more susceptible to surface cracking, blistering, and other cosmetic defects. Therefore, to ensure that the printed layer does not hinder the foaming of the thermoplastic resin layer while preventing cosmetic defects such as cracking and blistering, it is desirable that the printed layer uniformly suppresses foaming.

[0013] However, compared to conventional oil-based inks used to form the printed layer of foamed paper laminates, using water-based inks makes it difficult to achieve the desired foaming properties, friction resistance, and heat resistance in the printed layer, leading to a decrease in the quality of the foamed paper laminate. Furthermore, it is difficult to uniformly suppress foaming in the thermoplastic resin layer using the printed layer. Consequently, cracks and blistering are likely to occur, resulting in a poor appearance of the printed surface of the foamed thermoplastic resin layer (hereinafter referred to as the foamed appearance). Furthermore, in the food industry, solvents such as ethanol are often used for disinfection, and therefore chemical resistance, such as ethanol resistance, is also required in the printed layer.

[0014] However, printed layers typically formed using aqueous inks have high hydrophilicity, making it difficult to achieve excellent ethanol resistance. Even when printed layers are formed using aqueous inks, such as those disclosed in Patent Documents 1 to 3, it has been difficult to provide a foam paper laminate that fully meets the various properties required in the food container industry, and further improvements are desired.

[0015] Therefore, in view of the above circumstances, an embodiment of the present invention provides a foam paper laminate and a method for manufacturing the same, wherein the foam paper laminate is a foam paper laminate having a printed layer formed using a water-based ink, wherein the printed layer has excellent foaming followability without hindering the foaming of the thermoplastic resin layer during heating processing, and the printed layer surface has excellent foaming appearance, friction resistance, heat resistance, and ethanol resistance.

[0016] Methods for solving problems

[0017] To address the above-mentioned issues, the present inventors conducted extensive research on the relationship between the foaming properties of a thermoplastic resin layer during heat processing and the ability of the printed layer to suppress foaming. As a result, they discovered that using an aqueous ink composition containing a specific binder resin to form a printed layer can achieve excellent foaming properties of the thermoplastic resin layer, as well as excellent printed surface properties such as foam appearance, friction resistance, heat resistance, and ethanol resistance. This led to the completion of the present invention. The present invention relates to the following embodiments, but is not limited thereto and encompasses various embodiments.

[0018] One embodiment relates to a foamed paper laminate comprising foamed paper and a printed layer, wherein the foamed paper comprises a thermoplastic resin layer (A), a paper base material, and a foamed thermoplastic resin layer (B) in this order, and the printed layer is formed on a surface of the foamed thermoplastic resin layer (B) of the foamed paper.

[0019] The number of foamed cells per unit area of ​​the foamed thermoplastic resin layer (B) is 1000 cells / 1 cm 2 above,

[0020] The printed layer includes a binder resin including a polyurethane resin, and a residual rate of the printed layer after immersion in ethanol at 25° C. for 30 minutes is 50% by mass or more.

[0021] In the foam paper laminate, the stress of the binder resin at an elongation of 50 to 4,000% is preferably 0.1 to 50 mPa. The binder resin preferably has a glass transition temperature of -100 to 0°C.

[0022] In the foam paper laminate, the printed layer preferably has a thickness of 0.5 to 5.0 μm.

[0023] In the foam paper laminate, the printed layer preferably includes a cured product formed from a binder resin including a polyurethane resin having an acid value of 1 to 100 mgKOH / g and at least one of a carbodiimide curing agent and an isocyanate curing agent.

[0024] In the foam paper laminate, it is preferred that the printed layer has a plurality of layers, with the outermost layer being a transparent layer.

[0025] In the foamed paper laminate, the foamed thermoplastic resin layer (B) preferably has a thickness of 500 to 950 μm.

[0026] One embodiment relates to a foamed paper container including the foamed paper laminate according to the above embodiment.

[0027] One embodiment relates to a method for producing a foamed paper laminate, the foamed paper laminate comprising foamed paper and a printed layer, the foamed paper comprising, in order, a thermoplastic resin layer (A), a paper base material, and a foamed thermoplastic resin layer (B), the printed layer being formed on a surface of the foamed thermoplastic resin layer (B) of the foamed paper, the foamed thermoplastic resin layer (B) having a foamed cell count per unit area of ​​1,000 cells / cm 2 The above, wherein the residual rate of the printed layer after immersion in ethanol at 25° C. for 30 minutes is 50% by mass or more, and the method for producing the foamed paper laminate comprises:

[0028] A foamed paper material is prepared, which comprises, in order, a thermoplastic resin layer (A), a paper base material, and a foamed thermoplastic resin layer forming layer (B0) having a lower melting point than the thermoplastic resin layer (A) and foamed by heating;

[0029] preparing an aqueous ink composition comprising a binder resin including a polyurethane resin and water;

[0030] Applying the aqueous ink composition on the surface of the foamed thermoplastic resin layer forming layer (B0) of the foamed paper material to form a printing layer;

[0031] The foamed paper material having the printed layer is heated to foam the foamed thermoplastic resin layer forming layer ( B0 ) of the foamed paper material to form a foamed thermoplastic resin layer (B).

[0032] In the above-mentioned production method, as the above-mentioned aqueous ink composition, it is preferred to prepare an aqueous ink composition containing a binder resin, water, and at least one of a carbodiimide-based curing agent and an isocyanate-based curing agent, wherein the binder resin contains a polyurethane resin having an acid value of 1 to 100 mgKOH / g.

[0033] In the above-mentioned production method, it is preferred that the printed layer has multiple layers, with the outermost layer being a transparent layer.

[0034] In the above-mentioned production method, the film thickness of the foamed thermoplastic resin layer forming layer (B0) is preferably 40 to 150 μm.

[0035] The disclosed content of this application is related to the subject matter described in Japanese Patent Application No. 2020-006574 filed on January 20, 2020, and the entire disclosed content is incorporated herein by reference.

[0036] Effects of the Invention

[0037] The present invention provides a foamed paper laminate having a printed layer, which exhibits excellent foaming followability, excellent foam appearance, friction resistance, heat resistance, and ethanol resistance, without hindering foaming of the thermoplastic resin layer during heat processing, and a method for producing the same. Furthermore, the present invention provides a foamed paper container comprising the foamed paper laminate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] [ Figure 1 ] Figure 1 This is a perspective view showing a structural example of a foam paper container including a foam paper laminate according to one embodiment.

[0039] [ Figure 2 ] Figure 2 It means Figure 1 This is a schematic cross-sectional view showing an enlarged portion of the foamed paper container (see portion I). DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described below, and includes various embodiments.

[0041] <1> Foam paper laminate

[0042] One embodiment relates to a foamed paper laminate. The foamed paper laminate is characterized by comprising foamed paper and a printed layer, wherein the foamed paper comprises, in order, a thermoplastic resin layer (A), a paper substrate, and a foamed thermoplastic resin layer (B), the printed layer being formed on the surface of the foamed thermoplastic resin layer (B) of the foamed paper, and the number of foamed cells per unit surface area of ​​the foamed thermoplastic resin layer (B) being 1000 cells / 1 cm 2 As described above, the printed layer contains a binder resin including a polyurethane resin, and the residual rate of the printed layer after immersion in ethanol at 25° C. for 30 minutes is 50% by mass or more.

[0043] A larger number of foamed cells per unit surface area of ​​the foamed thermoplastic resin layer (B) (hereinafter also referred to as the foamed layer (B)) means that the bubbles in the foamed layer (B) are smaller, while a smaller number of cells means that the bubbles in the foamed layer (B) are larger. If the bubbles in the foamed layer (B) become larger, it is likely to cause appearance defects such as cracks and bubbles on the printed surface.

[0044] In one embodiment, the number of foamed cells per unit surface area of ​​the foamed layer (B) is preferably 1000 cells / 1 cm 2 More than 1250 pieces / 1cm 2 When the number of foamed cells is within the above range, an excellent foamed appearance without cracks and bubbles can be easily obtained in the printed layer formed on the foaming layer (B). On the other hand, the upper limit of the number of foamed cells is not particularly limited. In one embodiment, from the perspective of manufacturing conditions, the number of foamed cells can be 1600 / 1cm 2 the following.

[0045] Here, the "number of foamed cells per unit area" refers to the number of independent cells (bubbles) present in the surface of the foamed layer (B) within a range divided by a certain length in the vertical and horizontal (XY) directions, and is calculated as the number of cells per 1 cm 2 The closed cell number is determined by removing the printed layer of the foamed paper laminate with a solvent to expose the surface of the foamed layer (B), and then observing the surface of the foamed layer (B) using an optical microscope.

[0046] From the viewpoint of thermal insulation, the thickness of the foaming layer (B) is preferably 500 μm or more, more preferably 630 μm or more. If the thickness of the foaming layer (B) is 500 μm or more, it is easy to continue to hold the container with bare hands even when the foam paper laminate is formed into a cup-shaped container and hot water of about 100°C is injected into the container. On the other hand, from the viewpoint of resource conservation, the amount of resin used is preferably as small as possible. In addition, from the viewpoint of thermal insulation, the thickness of the insulating layer does not need to be too thick so that the quality is too high. Therefore, the thickness of the foaming layer (B) is preferably 950 μm or less, more preferably 900 μm or less, and extremely preferably 800 μm.

[0047] From this perspective, in one embodiment, the thickness of the foam layer (B) is preferably 500 to 950 μm, more preferably 500 to 900 μm, and even more preferably 500 to 800 μm. The thickness of the foam layer (B) is determined by observing a cross-section of the foamed paper laminate using an optical microscope and measuring the height from the upper surface of the paper substrate to the lower surface of the printed layer.

[0048] In the foam paper laminate of the above embodiment, the foam layer (B) of the foam paper refers to the state after the thermoplastic resin layer is foamed by heating. That is, the foam layer (B) is formed by heating the unfoamed thermoplastic resin layer (foamed thermoplastic resin layer forming layer (B0)) as a precursor to foam it. In one embodiment, in order to constitute the above-mentioned foam paper laminate, a foam paper material (foamed paper before heating) can be used which sequentially has a thermoplastic resin layer (A), a paper substrate, and a foamed thermoplastic resin layer forming layer (B0) having a lower melting point than the above-mentioned thermoplastic resin layer (A) and foamed by heat treatment. The foam paper material can be composed of materials well known in the art. Below, the constituent materials of the foam paper laminate are specifically described.

[0049] (Paper base material)

[0050] The paper substrate constituting the foamed paper laminate is not particularly limited. For example, kraft paper or high-grade paper can be used. From the perspective of achieving sufficient toughness when used as a container, the weight per square meter of the paper substrate is preferably 150 to 450 g / m2. 2 , more preferably 250 to 400 g / m 2 Furthermore, from the viewpoint of obtaining appropriate foaming properties of a thermoplastic resin such as polyethylene, the water content in the paper base material is preferably 4 to 10% by mass, more preferably 5 to 8% by mass.

[0051] (Thermoplastic resin layer, foaming layer forming layer)

[0052] In one embodiment, the thermoplastic resin layer (A) and the foamed thermoplastic resin layer-forming layer (B0) (hereinafter also referred to as the foamed layer-forming layer (B0)) can each be a film made of a resin material conventionally known as a container material. For example, a film (thermoplastic resin film) made of at least one thermoplastic resin selected from the group consisting of stretched and unstretched polyolefins such as polyethylene and polypropylene, polyester, nylon, cellophane, and vinylon can be used. In one embodiment, a polyethylene film can be suitably used due to its excellent lamination suitability and foaming properties.

[0053] The foam paper material can be formed by laminating thermoplastic resin films with different melting points on a paper substrate. Here, the material is selected in such a way that the melting point (Mp) of the thermoplastic resin film provided on one side of the paper substrate as the foaming layer forming layer (B0) is lower than that of the thermoplastic resin film provided on the other side of the paper substrate as the thermoplastic resin layer (A). In the foam paper material, the moisture in the paper substrate evaporates during heat treatment, and the evaporated moisture is squeezed out to the side of the foaming layer forming layer (B0) (low Mp resin film) that has become softened. Then, accompanied by such extrusion, the low Mp resin film expands (foams) toward the outside to form a foam layer (B). The foam layer (B) thus formed acts as an insulating layer in the container. On the other hand, for the thermoplastic resin layer (A) (high Mp resin film), a material that does not melt or soften when the low Mp resin film is foamed by heat treatment is selected.

[0054] From the perspective of using a foamed paper laminate to manufacture a foamed paper container, the foamed paper material can have, for example, a structure in which a high-Mp polyethylene film (thermoplastic resin layer (A)) having a melting point of approximately 125°C to 140°C is laminated on one side of a paper substrate (the inner side of the container), and a low-Mp polyethylene film (foaming layer-forming layer (B0)) having a melting point of approximately 105°C to 120°C is laminated on the other side of the paper substrate (the outer side of the container). The low-Mp polyethylene film is foamed by heating, for example, during the manufacture of the foamed paper container, to form a foamed layer. Meanwhile, the high-Mp polyethylene film preferably functions as a coating layer. That is, the coating layer can suppress the evaporation of moisture from the paper substrate to the outside during the foaming of the low-Mp polyethylene film, thereby contributing to the efficient foaming of the moisture in the paper substrate.

[0055] In one embodiment, the material of the foaming layer forming layer (B0) preferably comprises a low-density polyethylene resin (density 910 to 925 kg / m 3 , melting point 105-120°C). The density of the low-density polyethylene resin is more preferably 910-922 kg / m 3 , more preferably 910~918kg / m 3 As the material of the foaming layer forming layer (B0), a medium-density polyethylene resin (density 925-940 kg / m 3 , melting point 115 ~ 130 ℃), and high-density polyethylene resin (density 940 ~ 970kg / m 3 In the case of a polyethylene resin having a high melting point (melting point of 125-140°C), the melting point is high and sufficient foaming properties tend to be difficult to obtain. In addition, from the perspective of obtaining a uniformly foamed layer, the melt flow rate (hereinafter referred to as "MFR") of the polyethylene resin is preferably 8-28 g / 10 min, more preferably 10-20 g / 10 min.

[0056] Although not particularly limited, in one embodiment, the film thickness of the foam-forming layer (B0) is preferably 40 μm or more, more preferably 60 μm or more. By adjusting the film thickness to 40 μm or more, sufficient thermal insulation can be obtained after heat treatment.

[0057] On the other hand, from the perspective of resource conservation, the amount of resin used is preferably as small as possible. Furthermore, from the perspective of thermal insulation, it is not necessary to have such a thickness that the quality is too high. Therefore, the film thickness of the foaming layer-forming layer (B0) is preferably 150 μm or less, more preferably 100 μm or less, and most preferably 80 μm or less.

[0058] (Printing layer)

[0059] In the foam paper laminate of the above embodiment, the printed layer is a coating film formed by applying an aqueous ink composition to the surface of the foam layer-forming layer (B0) of the foam paper material. The coating film constituting the printed layer is primarily composed of a binder resin in the aqueous ink composition, and the binder resin preferably contains at least a polyurethane resin.

[0060] By containing at least a polyurethane resin as a binder resin, the printed layer can easily achieve excellent foaming followability without hindering foaming when the foaming layer-forming layer (B0) is heated and foamed to form the foamed layer (B). Furthermore, the foaming properties of the foaming layer-forming layer (B0) can be appropriately suppressed, making it easy to adjust the number of foamed cells per unit surface area of ​​the foamed layer (B). Thus, the use of a polyurethane resin can achieve an excellent foamed appearance, and further, can easily achieve excellent friction resistance and heat resistance in the printed layer.

[0061] In one embodiment, from the viewpoint of the foaming suppression ability and friction resistance of the printed layer, the thickness of the printed layer (coated film after drying) is preferably 0.5 to 5.0 μm, more preferably 0.5 to 4.0 μm, and even more preferably 0.5 to 3.5 μm.

[0062] Regarding the printed layer, from the perspective of ethanol resistance, the residual rate of the printed layer after immersion in ethanol at 25°C for 30 minutes is preferably 50% by mass or greater. A residual rate of 50% by mass or greater prevents problems such as blurred printing, even when ethanol is used for disinfection or cleaning during the food container manufacturing process, and the printed layer can be well maintained. Considering the food container's intended use, the residual rate of the printed layer after immersion in ethanol at 25°C for 30 minutes is more preferably 60% by mass or greater, and even more preferably 70% by mass or greater.

[0063] The residual rate of the printed layer described in this specification does not require strict control of the ethanol immersion conditions. That is, conditions such as temperature and immersion time can be slightly modified. For example, "immersion for 30 minutes" means that the printed layer only needs to be immersed in ethanol for approximately 30 minutes. Therefore, the immersion time can be extended by 5 to 10 minutes, depending on pre- and post-immersion operations and post-processing. For example, stirring can be included as a pre- and post-immersion operation. Stirring conditions are preferably 50 to 150 rpm.

[0064] Generally speaking, when constructing a water-based ink composition, it is preferable to increase the hydrophilicity of the binder resin from the perspective of printability. However, increasing the hydrophilicity of the binder resin tends to reduce the ethanol resistance of the printed layer. Conversely, by adjusting the structure and physical properties of the polyurethane resin used as the binder resin, in addition to the desired properties such as foaming conformability, foaming suppression, friction resistance, and heat resistance described above, the desired ethanol resistance can also be achieved. The following describes specific embodiments of a water-based ink composition containing a polyurethane resin as the binder resin.

[0065] <2> Water-based ink composition

[0066] One embodiment relates to an aqueous ink composition suitable for forming a print layer of the foam paper laminate of the above-described embodiment. The aqueous ink composition comprises a binder resin and water, and may further comprise a colorant such as a pigment. In addition to the aforementioned components, the aqueous ink composition may further comprise various additives as needed. The composition of the aqueous ink composition is described below.

[0067] (Binder resin)

[0068] During the heat treatment to form the foaming layer (B), the printed layer preferably does not hinder the foaming of the foaming layer-forming layer (B0), thereby exhibiting excellent foaming followability. On the other hand, to prevent poor foaming appearance, such as cracking and blistering on the printed surface, it is preferable that the printed layer appropriately control the foaming of the foaming layer-forming layer (B0). In contrast, since the binder resin is the main component of the printed layer (coating film), the foaming followability and foaming suppression of the printed layer can be well adjusted by selecting an appropriate binder resin.

[0069] In one embodiment, from the perspective of foam followability, the binder resin in the aqueous ink composition forming the print layer preferably has an elongation of 50-4,000%. On the other hand, even if the binder resin has an elongation of 50-4,000%, if the stress is too low, the print layer will follow the foaming, but the foaming cannot be properly controlled, resulting in cracks and foaming, which can easily degrade the foam appearance. Therefore, from the perspective of achieving a balance between foam followability and the foam appearance of the printed surface, the binder resin preferably has an elongation of 50-4,000% and a stress of 0.1 mPa or greater.

[0070] The term "elongation" used herein refers to a value measured on a sample having a thickness of 0.3 mm and a width of 15 mm using a small tensile tester manufactured by Instron at a tensile speed of 100 mm / min and a room temperature of 25°C.

[0071] In one embodiment, the stress of the binder resin at an elongation of 50-4,000% is preferably 0.1 mPa or greater, more preferably 1 mPa or greater, and even more preferably 5 mPa or greater. On the other hand, the stress at an elongation of 50-4,000% is preferably 50 mPa or less, more preferably 40 mPa or less, and even more preferably 30 mPa or less. The stress of the binder resin at an elongation of 50-4,000% may be 0.1 mPa to 50 mPa.

[0072] When the binder resin has an elongation and stress within the above ranges, not only good foaming followability but also good foaming appearance is likely to be achieved. Furthermore, a binder resin having an elongation and stress within the above ranges is also preferred from the perspective of improving ethanol resistance because it is easy to achieve a desired residual rate of the printed layer.

[0073] In one embodiment, the binder resin preferably has a glass transition temperature (Tg) of -100°C to 0°C. The Tg of the binder resin may more preferably be below -10°C, and may further preferably be below -25°C. When the Tg of the binder resin is within the above range, excellent foaming followability can be obtained during the heat treatment of the foam paper material and the reduction in thermal insulation can be suppressed. In addition, poor foaming appearance such as cracks and blistering on the printed surface can be suppressed. Tg only needs to be above -100°C, preferably above -90°C, and more preferably above -80°C. The binder resin having a Tg within the above range is also preferred from the perspective of ethanol resistance because it is easy to obtain the desired residual rate of the printed layer.

[0074] As described above, from the perspective of the foaming followability of the printed layer during foaming, the binder resin preferably contains at least a polyurethane resin. Using a polyurethane resin makes it easy to construct an aqueous ink composition capable of forming a printed layer that exhibits excellent resistance to various factors, such as light resistance, heat resistance, friction resistance, and blocking resistance, and further exhibits excellent adhesion to the low-Mp resin film (foaming layer-forming layer (B0)) serving as a substrate during printing. Furthermore, using a polyurethane resin as the binder resin allows for excellent results in various properties of the printed layer, such as friction resistance, blocking resistance, and adhesion to the low-Mp resin film serving as a substrate, even when the aqueous ink composition is stored for long periods of time under the influence of heat or light.

[0075] As the binder resin, other than polyurethane resin, well-known resins can also be used. By using various resins with elongation and stress in the above range and Tg, excellent printing characteristics can be easily obtained. The control of the elongation and stress of the binder resin can be achieved by the combination of various resins, molecular weight control during resin synthesis, Tg change of monomers, and adjustment of crosslinking density. From such a viewpoint, as an example of a resin that can be used as a binder resin other than polyurethane resin, acrylic resin, styrene-acrylic acid copolymer resin, and styrene-maleic acid copolymer resin can be listed.

[0076] In one embodiment, the content of the polyurethane resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 85% by mass or more, based on the total mass of the resin components in the binder resin. In one embodiment, the binder resin may also be composed solely of the polyurethane resin.

[0077] The term "polyurethane resin" as used in this specification refers to a broad range of polyurethane resins, including general polyurethane resins and modified polyurethane resins such as polyurethane urea resins, which have been used in this technical field. Furthermore, the polyurethane resins used in this specification are not particularly limited by their production methods and may be various polyurethane resins obtained using methods known or generally accepted for use in polyurethane resins. The following describes polyurethane resins suitable for use as binder resins in more detail.

[0078] (Polyurethane resin)

[0079] Although not particularly limited, a preferred embodiment of the polyurethane resin includes a polyurethane resin obtained by reacting at least a polyol with a polyisocyanate. Another embodiment includes a polyurethane urea resin obtained by chain-extending a polyurethane resin prepolymer with an amine compound.

[0080] In one embodiment, from the viewpoint of preparing the aqueous ink composition, the polyurethane resin used as the binder resin is preferably an aqueous polyurethane resin (also referred to as a water-based polyurethane resin). The "aqueous polyurethane resin" recorded in this specification refers to a polyurethane resin that can be dissolved in or easily dispersed in water or a water-soluble solvent. That is, in one embodiment, the polyurethane resin preferably has an acid value (acidic functional group) and can obtain any form of "water-soluble" and "emulsion" by neutralizing or modifying the acidic functional group. The acidic functional group can be a carboxyl group and a sulfonic acid group, but is preferably a carboxyl group. Although not particularly limited, the polyurethane resin used as the binder resin is preferably water-soluble.

[0081] On the other hand, when aqueous polyurethane resins are typically used to form aqueous ink compositions, achieving sufficient ethanol resistance in the printed layer is often difficult when considering use in food containers. Therefore, to impart the desired ethanol resistance to the printed layer, the polyurethane resin used as a binder resin preferably has a structure or physical properties that are difficult to dissolve in ethanol. While not particularly limited, the following method can easily improve the ethanol resistance of the printed surface.

[0082] For example, there is a method of selecting a polyol having a structure that is poorly soluble in ethanol as the main component of the polyurethane resin. In this method, at least one of polycarbonate diol and polyester polyol is preferably used as the polyol.

[0083] Another method for increasing the weight-average molecular weight of the polyurethane resin is to increase the molecular weight. In one embodiment, when the weight-average molecular weight of the polyurethane resin is greater than 20,000, ethanol resistance can be easily improved. However, the weight-average molecular weight of the polyurethane resin is not particularly limited. Even when the weight-average molecular weight of the polyurethane resin is less than 20,000, excellent ethanol resistance can be easily achieved, for example, by using a curing agent in combination.

[0084] In addition, methods for increasing the glass transition temperature (Tg) of the polyurethane resin can be mentioned. The preferred range of the Tg of the polyurethane resin can be -100°C to 0°C, as described above as a characteristic of the binder resin. In one embodiment, from the perspective of ethanol resistance, the Tg of the polyurethane resin is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -60°C or higher. On the other hand, the Tg of the polyurethane resin is preferably -10°C or lower, more preferably -20°C or lower.

[0085] In addition, methods for adjusting the rigidity (elongation and stress) of the polyurethane resin can be cited. Along with this, methods for adjusting the concentration of urethane bonds or urea bonds in the polyurethane resin can also be considered. It should be noted that the preferred ranges of the elongation and stress of the polyurethane resin can be as described above as the characteristics of the binder resin, where the stress at an elongation of 50 to 4,000% is 0.1 mPa or more. In one embodiment, from the perspective of ethanol resistance, the elongation of the polyurethane resin is preferably 100 to 2,500%, more preferably 300 to 1,500%, and further preferably 300 to 1,200%. The stress is preferably 1 to 40 mPa, more preferably 3 to 30 mPa, and further preferably 5 to 25 mPa.

[0086] By using a polyurethane resin formed by applying any one of the above methods or a combination of methods as a binder resin, a printed layer having a residual rate of 50% by mass or more after immersion in ethanol at 25° C. for 30 minutes can be easily formed.

[0087] Hereinafter, the raw materials and production method of the polyurethane resin will be described.

[0088] (Polyol)

[0089] To produce polyurethane resin, various polyols can be used. For example, the following polyols can be suitably used. The following polyols can be used alone or in combination of two or more.

[0090] (1) Polyether polyols such as polymers or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, etc.;

[0091] (2) Polyester polyols obtained by dehydrating and condensing saturated and unsaturated low molecular weight glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, octanediol, nonanediol, methylnonanediol, diethylene glycol, triethylene glycol, and dipropylene glycol; alkyl glycidyl ethers such as n-butyl glycidyl ether and 2-ethylhexyl glycidyl ether; monocarboxylic acid glycidyl esters such as versatate glycidyl ether; and dibasic acids such as adipic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, glutaric acid, pimelic acid, azelaic acid, sebacic acid, and dimer acid, or their anhydrides;

[0092] (3) Other polycarbonate diols, polybutadiene diols, and diols obtained by addition of bisphenol A to ethylene oxide or propylene oxide;

[0093] (4) Dimer alcohols.

[0094] In one embodiment, the polyurethane resin is preferably made from at least one polyol selected from polyether polyols, polyester polyols, and polycarbonate diols, and preferably has structural units derived from these raw materials. More preferably, polyether polyols and / or polyester polyols are used as the polyol. That is, in one embodiment, the polyurethane resin may be a polyether-based polyurethane resin, a polyester-based polyurethane resin, or a polyether / polyester polyurethane resin.

[0095] The polyether polyol preferably contains at least one selected from polyethylene glycol, polypropylene glycol, and polybutylene glycol, and more preferably contains polyethylene glycol.

[0096] The polyester polyol preferably includes a polyester polyol that is a condensate of a low molecular weight diol and a dibasic acid. The low molecular weight diol is preferably a branched diol. "Branched diol" refers to a diol in which at least one hydrogen atom in the alkylene group of an alkylene glycol is substituted with a group other than hydrogen. The substituent is preferably an alkyl group having 1 to 10 carbon atoms.

[0097] In one embodiment, when the polyester polyol exemplified in (2) above is used to form a polyester-based polyurethane resin, up to 5 mol% of the polyol may be replaced with other various polyols. Examples of other various polyols include glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, and pentaerythritol.

[0098] The structure and number average molecular weight of the polyol are appropriately determined in consideration of the ethanol resistance, drying properties, elongation, and stress characteristics of the polyurethane resin obtained as the reaction product. While not particularly limited, the number average molecular weight of the polyol is generally preferably in the range of 500 to 10,000, more preferably 500 to 6,000.

[0099] (Polyisocyanate)

[0100] The polyisocyanate that can be used in the manufacture of polyurethane resin is preferably a diisocyanate compound. As specific examples, aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, etc. can be mentioned. The polyisocyanate can be a compound having an isocyanurate ring structure formed by trimerizing various diisocyanates.

[0101] Examples of the aromatic diisocyanate include 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylenedicyanate, 1,4-phenylenedicyanate, and toluene diisocyanate.

[0102] Examples of the aliphatic diisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0103] Examples of the alicyclic diisocyanate include cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, norbornane diisocyanate, m-tetramethylxylylene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, and dimer diisocyanates obtained by converting carboxyl groups of dimer acid into isocyanate groups.

[0104] Among the polyisocyanates, at least one selected from the group consisting of tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, bis(isocyanatomethyl)cyclohexane, hexamethylene diisocyanate, and a trimer of hexamethylene diisocyanate is preferred. The polyisocyanates may be used alone or in combination of two or more.

[0105] (Dihydroxy acid)

[0106] When a dihydroxy acid is used in addition to a polyol and polyisocyanate in the production of a polyurethane resin, an acidic functional group (carboxyl group) derived from the dihydroxy acid is introduced, resulting in a polyurethane resin with an acid value. Polyurethane resins with an acid value are easily water-based and therefore are suitable for use as aqueous polyurethane resins in aqueous ink compositions.

[0107] The dihydroxy acid may be any compound having two hydroxyl groups and an acidic group in the molecule. Known diol compounds containing a carboxyl group can be suitably used. For example, dimethylolalkanoic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and 2,2-dimethylolpentanoic acid can be mentioned, and these can be used as appropriate. These can be used alone or in combination of two or more.

[0108] In one embodiment, when a polyurethane urea resin is produced as a polyurethane resin, the molar equivalent ratio of isocyanate group / hydroxyl group is preferably set to a range of 1.2 / 1 to 3 / 1. In other embodiments, when a polyurethane resin without a urea bond is produced, the molar equivalent ratio of isocyanate group / hydroxyl group is preferably set to a range of 0.5 / 1 to 0.98 / 1. When the raw materials are formulated within the above-mentioned molar equivalent ratio range, it is easy to control the elongation and stress of the polyurethane resin, as well as the ethanol resistance. The polyurethaneization reaction in the production of the polyurethane resin is generally carried out at a reaction temperature in the range of 80°C to 200°C, preferably in the range of 90°C to 150°C.

[0109] The polyurethane reaction can be carried out in a solvent or in a solvent-free atmosphere. When a solvent is used, the solvent exemplified below can be appropriately selected from the viewpoints of controlling the reaction temperature, viscosity, and side reactions. In addition, when the polyurethane reaction is carried out in a solvent-free atmosphere, in order to obtain a uniform polyurethane resin, it is preferred to increase the temperature (heat) to a degree that allows sufficient stirring to reduce the viscosity. The reaction time of the polyurethane reaction is preferably set to 10 minutes to 5 hours. The end point of the reaction can be determined by methods such as viscosity measurement, confirmation of the NCO peak based on IR measurement, and NCO% measurement based on titration.

[0110] In one embodiment, a polyurethane urea resin that can be suitably used is a resin obtained by reacting the polyols exemplified above with an organic diisocyanate to synthesize a polyurethane resin prepolymer having terminal isocyanate groups, and then introducing urea bonds into the polyurethane resin prepolymer using an amine compound as a chain extender and reaction terminator. Among polyurethane resins, the use of such a polyurethane urea resin can further enhance various properties of a coating film (printed surface) formed using an aqueous ink composition.

[0111] (Chain Extender)

[0112] Examples of the chain extender that can be used to introduce a urea bond include various known polyamines. Polyamines are compounds having multiple amino groups in the molecule.

[0113] Specific examples of polyamines include ethylenediamine, propylenediamine, hexamethylenediamine, triethylenetetramine, diethylenetriamine, isophoronediamine, and dicyclohexylmethane-4,4'-diamine. Other specific examples include diamines having hydroxyl groups in the molecule, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, and di-2-hydroxypropylethylenediamine, and dimer diamines obtained by converting the carboxyl groups of dimer acids into amino groups.

[0114] (Reaction terminator)

[0115] A reaction terminator may also be used in combination with the polyamine. Examples of the reaction terminator include dialkylamines such as di-n-butylamine, monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, tris(hydroxymethyl)aminomethane, 2-amino-2-ethyl-1,3-propanediol, N-di-2-hydroxyethylethylenediamine, N-di-2-hydroxyethylpropylenediamine, and N-di-2-hydroxypropylethylenediamine, and monoamine-type amino acids such as glycine, alanine, glutamic acid, taurine, aspartic acid, aminobutyric acid, valine, aminocaproic acid, aminobenzoic acid, aminoisophthalic acid, and aminosulfonic acid.

[0116] When introducing urea bonds into a polyurethane resin prepolymer, the production method is not particularly limited. For example, assuming that the number of free isocyanate groups present at both ends of the prepolymer is 1, the total number of amino groups in the chain extender and reaction terminator used is preferably within a range of 0.5 to 1.3.

[0117] The solvents used in the production of polyurethane resins and polyurethaneurea resins can generally be known compounds that can be used as solvents for inks used to form print layers. Examples include alcohol solvents such as methanol, ethanol, isopropanol, n-propanol, and n-butanol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate, propyl acetate, and butyl acetate; and non-aromatic hydrocarbon solvents such as methylcyclohexane and ethylcyclohexane. These solvents can be used alone or in combination of two or more.

[0118] When a ketone-based solvent is used during production, a ketimine group is generated between the ketone and the amine used as a chain extender, hindering the smooth progress of the reaction. Therefore, to suppress the generation of ketimine groups and promote smooth reaction, it is preferable to use a small amount of water. When an organic solvent is used in the synthesis reaction, it is preferable to include a step of removing the organic solvent by reduced pressure distillation and replacing it with water in order to prepare an aqueous solution of the polyurethane resin.

[0119] In one embodiment, the polyurethane resin is preferably a polyurethane resin having an acid value, from the perspective of being easily water-based by neutralization. In one embodiment, the polyurethane resin preferably has an acid value of 1 to 100 mgKOH / g. The acid value is more preferably 10 to 70 mgKOH / g, and even more preferably 20 to 60 mgKOH / g. Although not particularly limited, the hydroxyl value of the polyurethane resin is preferably 1 to 20 mgKOH / g. Here, the values ​​of the acid value and hydroxyl value are measured based on the method described in JIS K0070 (1992).

[0120] (Neutralizer)

[0121] In order to make the polyurethane resin having an acid value water-based by neutralization, various neutralizing agents can be used. For example, in order to neutralize the carboxyl groups in the polyurethane resin, a basic compound can be used.

[0122] Specific examples of alkaline compounds that can be used as neutralizing agents include sodium hydroxide, potassium hydroxide, ammonia, methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, ethanolamine, propanolamine, diethanolamine, N-methyldiethanolamine, dimethylamine, diethylamine, triethylamine, N,N-dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, and morpholine. Any one of these may be used alone, or two or more may be used in combination. Ammonia is preferred from the perspectives of water resistance and residual odor of printed materials.

[0123] The manufacture of waterborne polyurethane resin can be implemented by using the method known or known all the time, without particular limitation. For example, reference can be made to the manufacture method of waterborne polyurethane resin described in Japanese Patent Application Publication No. 2013-234214, Japanese Patent Application Publication No. 2013-249401, Japanese Patent Application Publication No. 2015-67818 and Japanese Patent Application Publication No. 2018-184512.

[0124] In one embodiment, when a water-based polyurethane resin is used as the binder resin, its weight-average molecular weight may be in the range of 5,000 to 100,000, more preferably 10,000 to 90,000, and even more preferably 20,000 to 80,000. When the weight-average molecular weight of the polyurethane resin is within the above range, desired properties such as elongation and stress are easily obtained. Furthermore, in one embodiment, from the perspective of improving ethanol resistance, the weight-average molecular weight of the polyurethane resin is preferably 21,000 to 80,000, more preferably 25,000 to 75,000, and particularly preferably 30,000 to 70,000.

[0125] Although not particularly limited, in a preferred embodiment, the polyurethane resin used as the binder resin may be a polyurethane resin aqueous solution obtained as follows.

[0126] (1) First, poly(3-methyl-1,5-pentane adipate) diol, polyethylene glycol, and dimethylolbutyric acid are mixed and stirred, and isophorone diisocyanate is further added to react to form a terminal isocyanate prepolymer. Next, an organic solvent such as 2-aminoethylethanolamine and isopropyl alcohol is added to the terminal isocyanate prepolymer (I) to form a solvent-based polyurethane resin solution.

[0127] (2) Next, aqueous ammonia and ion-exchanged water are slowly added to the solvent-based polyurethane resin solution to neutralize it, thereby forming an aqueous polyurethane resin solution. Furthermore, the organic solvent in the aqueous polyurethane resin solution is removed by vacuum distillation, and then water is added to adjust the solid content to obtain an aqueous solution of the aqueous polyurethane resin (aqueous polyurethane resin solution).

[0128] In one embodiment, the polyurethane resins (A) to (G) described later in the Examples can be suitably used as the binder resin constituting the aqueous ink composition. Each of the polyurethane resins (A) to (G) can be used alone, but a combination of two or more is more preferred for ease of adjusting various properties. For example, the combined use of the polyurethane resin (A) and the polyurethane resin (B) tends to yield more suitable properties.

[0129] In one embodiment, the total content of the binder resin is preferably 30% by mass or less, more preferably 5 to 25% by mass, based on the total mass of the aqueous ink composition (solids content). When the amount of the binder resin is adjusted within this range, a moderate ink viscosity can be easily achieved, thereby improving the efficiency of ink production and printing.

[0130] (Curing Agent)

[0131] In one embodiment, the aqueous ink composition preferably further comprises a curing agent for the resin serving as the binder resin. When the aqueous ink composition comprises a curing agent, the printed layer is formed as a cured coating film, but the reaction method is not particularly limited. Specifically, the printed layer may be a cured coating film formed from the resin in the binder resin and the curing agent. Alternatively, the printed layer may be a cured coating film formed from the curing agent itself.

[0132] In one embodiment, when a polyurethane resin having an acid value is used as the binder resin, the aqueous ink composition preferably further includes a curing agent. In one embodiment, the polyurethane resin preferably has an acid value of 1 to 100 mgKOH / g. The acid value is more preferably 10 to 70 mgKOH / g, and even more preferably 20 to 60 mgKOH / g.

[0133] In one embodiment, the combined use of a polyurethane resin having an acid value of 1 to 100 mgKOH / g and a curing agent facilitates the formation of a printed layer exhibiting a residual rate of 50% or greater after immersion in ethanol at 25°C for 30 minutes. Consequently, the printed layer can readily achieve excellent ethanol resistance. Furthermore, embodiments in which the aqueous ink composition includes a polyurethane resin having an acid value of 1 to 100 mgKOH / g and a curing agent achieve excellent results in various properties, in addition to ethanol resistance, such as the printed surface's abrasion resistance and foaming appearance.

[0134] As a curing agent for a polyurethane resin having an acid value, compounds well known in the art can be used. Among these, as a curing agent, it is preferred to use at least one selected from the group consisting of epoxy curing agents, carbodiimide curing agents, and isocyanate curing agents. In one embodiment, it is more preferred to use at least one of a carbodiimide curing agent and an isocyanate curing agent. It is further preferred to use at least a carbodiimide curing agent.

[0135] In one embodiment, the aqueous ink composition used to form the print layer preferably includes an aqueous polyurethane resin having an acid value of 1 to 100 mgKOH / g and at least one of a carbodiimide-based curing agent and an isocyanate-based curing agent. The print layer formed using such an aqueous ink composition includes a cured product (cured coating film) formed from the aqueous polyurethane resin having an acid value of 1 to 100 mgKOH / g and at least one of a carbodiimide-based curing agent and an isocyanate-based curing agent.

[0136] As long as the carbodiimide curing agent is a compound having a carbodiimide group in the molecule. Preferably, it is a compound having two or more carbodiimide groups in the molecule. As a specific example of the carbodiimide curing agent, p-phenylene-bis (2,6-xylylcarbodiimide), tetramethylene-bis (tert-butylcarbodiimide) and cyclohexane-1,4-bis (methylene-tert-butylcarbodiimide) can be mentioned. The carbodiimide curing agent can be a polycarbodiimide compound as a polymer having a carbodiimide group. They can be used alone or in combination of two or more.

[0137] In one embodiment, the chemical formula weight (NCN equivalent) per 1 mol of carbodiimide groups in the compound used as the carbodiimide curing agent is preferably 250 to 700, more preferably 300 to 600. As the carbodiimide curing agent, commercially available products can also be used. For example, the CARBODILITE series V-02, V-02-L2, SV-02, V-04, V-10, SW-12G, E-02, E-03A, E-05 manufactured by Nisshinbo Co., Ltd. can be mentioned. One of these can be used alone, or two or more can be used in combination.

[0138] The isocyanate curing agent may be any compound having an isocyanate group in the molecule. Preferably, the compound has two or more isocyanate groups in the molecule. The compound used as the isocyanate curing agent is preferably water-based, i.e., dispersed in water, or diluted with water. Such aqueous isocyanate curing agents are also commercially available, for example, AQUANATE 100, AQUANATE 110, AQUANATE 200, and AQUANATE 210 (all trade names, manufactured by Nippon Polyurethane Industries, Ltd.); Bayhydur TPLS-2032, SUB-Isocyanate L801, Bayhydur VPLS-2319, Bayhydur 3100, VPLS-2336, and VPLS-2150 / 1 (all trade names, manufactured by Bayer Urethane Co., Ltd.); TAKENATE WD-720, TAKENATE WD-725, and TAKENATE WD-220 (all trade names, manufactured by Mitsui Takeda Chemicals, Inc.); RESAMINE D-56 (trade name, manufactured by Dainichi Seika Industries, Ltd.). These may be used alone or in combination of two or more.

[0139] In one embodiment, the curing agent content in the aqueous ink composition for forming the print layer is preferably 100:1 to 100:100, more preferably 100:2 to 100:60, and even more preferably 100:3 to 100:30, in terms of the mass ratio of binder resin to curing agent.

[0140] The amount of curing agent added is preferably adjusted according to the structure of the printed layer. More specifically, in one embodiment, when the printed layer is formed as a single layer, the amount of curing agent added is preferably 100:2 to 100:100, more preferably 100:2 to 100:60, and even more preferably 100:5 to 100:30, based on the mass ratio of binder resin to curing agent.

[0141] In one embodiment, when the printed layer is formed in multiple layers, the curing agent content is preferably 100:1.5 to 100:100, more preferably 100:2 to 100:60, and even more preferably 100:3 to 100:30, in terms of the mass ratio of binder resin to curing agent in each layer.

[0142] By adjusting the curing agent content within the above range, it is possible to easily form a printed layer with a residual rate of 50% or more after immersion in ethanol at 25°C for 30 minutes. As a result, excellent foam followability, as well as excellent foam appearance, abrasion resistance, heat resistance, and ethanol resistance on the printed surface, can be easily achieved.

[0143] (colorant)

[0144] Colorants used in aqueous ink compositions can include various inorganic pigments and organic pigments commonly used in printing inks and coatings. Examples of inorganic pigments include white pigments such as titanium oxide, colored pigments such as red iron oxide, dark blue pigments, ultramarine, carbon black, and graphite, and extender pigments such as calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc. Furthermore, examples of organic pigments include colored pigments such as soluble azo pigments, insoluble azo pigments, azo chelate pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments. The content of these pigments can be appropriately selected based on the desired ink hue, but is generally preferably within a range of 0.5 to 50% by mass based on the total mass of the aqueous ink composition.

[0145] In one embodiment, when preparing a white aqueous ink composition, the amount of white pigment incorporated is preferably set in the range of 20 to 50% by mass based on the total mass of the aqueous ink composition. Titanium dioxide is preferably used as the white pigment from the perspectives of concealability, pigment concentration, and light resistance. On the other hand, when preparing a colored aqueous ink composition, colored organic pigments and colored inorganic pigments such as iron oxide red, dark blue pigment, ultramarine, carbon black, and graphite can be appropriately selected for use. From the perspectives of color development and light resistance, organic pigments are preferred. The amount of colored pigment incorporated is preferably in the range of 10 to 30% by mass based on the total mass of the aqueous ink composition.

[0146] The aqueous ink composition can also use an organic solvent as a solvent except water within the scope of not hindering its effect. When using an organic solvent, it is preferably an alcoholic organic solvent. As a specific example of an organic solvent, for example, ethanol, 1-propyl alcohol, 2-propyl alcohol, 1-butanol, 2-methyl-1-propyl alcohol, 2-butanol, tert-butyl alcohol, and 2-methyl-2-propyl alcohol can be enumerated. When using these organic solvents, it is preferred to control the wettability of the aqueous ink composition and substrate. In one embodiment, the substrate can be a foam paper material. The aqueous ink composition is applied to the upper surface of the foaming layer of the foam paper material to form a printed layer (B0).

[0147] When the aqueous ink composition contains an organic solvent, the amount thereof is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the aqueous ink composition. In one embodiment, the organic solvent content in the aqueous ink composition is most preferably 5% by mass or less. The aqueous ink composition may also contain no organic solvent.

[0148] (Other additives)

[0149] The aqueous ink composition may contain various additives as needed. Suitable examples of additives include anti-blocking agents, various waxes, thickeners, rheology modifiers, defoamers, leveling agents, preservatives, surface tension modifiers, adhesion promoters, and pH adjusters.

[0150] (Adhesion aid)

[0151] From the viewpoint of improving the adhesion between the printed layer and the substrate, the aqueous ink composition may further contain an adhesion aid. As the adhesion aid, at least one of a hydrazine compound and an epoxy compound is preferably used.

[0152] As the hydrazine compound, adipic acid dihydrazide, sebacic acid dihydrazide, isophthalic acid dihydrazide and other dihydrazide compounds are preferred.

[0153] The epoxy compound refers to a compound having an epoxy group, and examples thereof include alicyclic epoxies such as ADEKA Resin EP-4000, EP-4005, and 7001 manufactured by ADEKA Corporation.

[0154] These adhesion aids are preferably used in an amount of 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, based on the total mass of the aqueous ink composition.

[0155] In one embodiment, when the white ink composition is formed as an aqueous ink composition, the preferred composition, based on the total mass of the white ink, is 10-50% by mass of white inorganic pigment, 5-35% by mass of polyurethane resin (solids), and 5-30% by mass of water. A more preferred composition of the white ink composition is 20-50% by mass of white inorganic pigment, 5-30% by mass of polyurethane resin (solids), and 5-25% by mass of water. In another embodiment, in addition to the above-mentioned composition, the white ink composition may further include 0.5-15% by mass of a curing agent. The curing agent preferably includes at least one of a carbodiimide curing agent and an isocyanate curing agent.

[0156] In one embodiment, when a color ink composition such as magenta, yellow, and cyan is formed as an aqueous ink composition, the preferred composition, based on the total mass of the color ink, is 10-25% by mass of organic pigment, 5-35% by mass of polyurethane resin (solid content), and 5-30% by mass of water. A more preferred composition of the color ink is 10-20% by mass of organic pigment, 5-30% by mass of polyurethane resin (solid content), and 5-25% by mass of water. In another embodiment, in addition to the above color ink composition, the composition may further include 0.5-15% by mass of a curing agent. The curing agent preferably includes at least one of a carbodiimide curing agent and an isocyanate curing agent.

[0157] The aqueous ink composition forming the print layer can be produced by mixing the various components described above using known techniques. More specifically, the following method can be used: first, a binder resin, water, and, if necessary, a pigment, a pigment dispersant, a surfactant, etc. are stirred and mixed, followed by grinding using various grinders such as a bead mill, a ball mill, a sand mill, an attritor, a roll mill, and a pearl mill, and then the remaining materials are added and mixed.

[0158] <3> Method for producing foam paper laminate

[0159] One embodiment relates to a method for producing a foamed laminate. Specifically, one embodiment relates to a method for producing a foamed paper laminate comprising foamed paper and a printed layer, wherein the foamed paper comprises, in order, a thermoplastic resin layer (A), a paper base material, and a foamed layer (B), the printed layer being formed on the surface of the foamed layer (B) of the foamed paper, wherein the number of foamed cells per unit surface area of ​​the foamed layer (B) is 1000 cells / cm 2 The above-mentioned, after immersing in ethanol at 25° C. for 30 minutes, the residual rate of the printed layer is 50% by mass or more. The manufacturing method comprises the following steps (i) to (iv), namely:

[0160] (i) preparing a foam paper material comprising, in order, a thermoplastic resin layer (A), a paper base material, and a foam layer-forming layer (B0) having a lower melting point than the thermoplastic resin layer (A) and foaming by heating,

[0161] (ii) preparing an aqueous ink composition comprising a binder resin including a polyurethane resin and water,

[0162] (iii) applying the aqueous ink composition on the surface of the foam layer forming layer (B0) of the foam paper material to form a printing layer,

[0163] (iv) The foam paper material having the printed layer is heated to foam the foam layer forming layer (B0) of the foam paper material to form a foam layer (B).

[0164] In the above-described production method, each step involving (i) preparing the foam paper material, (ii) preparing the aqueous ink composition, (iii) forming the printed layer, and (iv) forming the foam layer (B) by heating can be carried out according to methods well known in the art. Each step is described below.

[0165] (Step (i): Preparation of foam paper material)

[0166] (i) The preparation of the foam paper material can be implemented according to, for example, an extrusion lamination method. The constituent materials of the paper substrate, thermoplastic resin layer (A), and foaming layer forming layer (B0) constituting the foam paper material are as described above. As the extrusion lamination method, well-known methods such as a single-layer lamination method, a tandem lamination method, a sandwich lamination method, and a co-extrusion lamination method can be appropriately selected. In one embodiment, as the constituent materials of the thermoplastic resin layer (A) and the foaming layer forming layer (B0), polyethylene resins with different melting points can be appropriately used respectively.

[0167] The foaming layer forming layer (B0) is formed using a polyethylene resin having a melting point (Mp) lower than that of the polyethylene resin constituting the thermoplastic resin layer (A) (low-Mp polyethylene resin). The foamed paper material can be produced by extruding a low-Mp polyethylene resin into a film on one side of a paper substrate using a T-die extruder, and extruding a high-Mp polyethylene resin into a film on the other side of the paper substrate.

[0168] The temperature of the polyethylene resin during lamination (the temperature just below the T-die) is preferably 300°C to 350°C, more preferably 320°C to 340°C. Within this temperature range, sufficient lamination strength can be achieved between each polyethylene resin layer (A, B0) and the paper substrate. The surface temperature of the cooling roll passed after lamination is preferably controlled within the range of 10°C to 50°C.

[0169] In one embodiment, the lamination speed is preferably 50 to 130 m / min, more preferably 60 to 110 m / min. If the lamination speed is too slow, the productivity is low. On the other hand, if the lamination speed is too fast, there is a tendency for the yield rate to decrease due to necking. Necking refers to the phenomenon that when a polyethylene resin is extruded and film-formed by a T-die extruder, the width of the extruded polyethylene resin film is less than the effective width of the T-die. At this time, the two ends of the film are thicker than the central portion. When the thickness of the two end portions deviates from the standard, the two ends are usually cut off and removed, but in the case of severe necking, the area deviating from the standard increases, so the yield rate decreases.

[0170] In one embodiment, the air gap is preferably less than 300 mm, more preferably less than 200 mm. If the air gap is too large, the polyethylene resin will neck and there is a tendency for the yield to decrease. The air gap refers to the distance from the extrusion port of the T-die to the nip roller. In the process of the polyethylene resin passing through the air gap, it is preferred to use ozone gas and / or oxygen to carry out surface treatment of the polyethylene resin. By using ozone gas and / or oxygen for surface treatment, the formation of an oxide film can be promoted and the adhesion to the substrate layer can be improved. The treatment amount of ozone gas and / or oxygen is not particularly limited, but is preferably 0.5 mg / m 2 above.

[0171] (Step (ii): Preparation of Aqueous Ink Composition)

[0172] In the production method of the above embodiment, the specific structure and preparation method of the above-mentioned (ii) aqueous ink composition are as described in the above embodiment of the aqueous ink composition.

[0173] In one embodiment, a water-based ink composition (ii-1) is preferably prepared containing a binder resin comprising a water-based polyurethane resin and water. The binder resin is preferably a water-based polyurethane resin having an acid value, and more preferably, the binder resin is made water-based by neutralization. Furthermore, the stress at an elongation of 50 to 4,000% is preferably 0.1 to 50 mPa.

[0174] In another embodiment, it is preferred to prepare an aqueous ink composition (ii-2) containing the following binder resin, water, and at least one of a carbodiimide-based curing agent and a polyisocyanate-based curing agent, in place of the aqueous ink composition (ii-1). The binder resin comprises an aqueous polyurethane resin having an acid value of 1 to 100 mgKOH / g; water; and at least one of a carbodiimide-based curing agent and a polyisocyanate-based curing agent. The polyurethane resin having an acid value of 1 to 100 mgKOH / g is preferably rendered aqueous by neutralization.

[0175] (Step (iii): Formation of Printing Layer)

[0176] The formation of the printed layer (iii) is not particularly limited, and known techniques may be applied. For example, when a white aqueous ink composition is printed on the entire surface of the foaming layer forming layer (B0) (low Mp resin film) as a base layer, a coating machine such as a bar coater, a roller coater, or a reverse roller coater may be used. Various printing methods may also be applied.

[0177] Among various printing methods, preferably, a printing method using flexographic printing or gravure printing is used. When forming a printed layer using these printing methods, the aqueous ink compositions (ii-1) and (ii-2) of the embodiments described above can be appropriately used. In particular, when a printing method using flexographic printing is used, a printed layer can be formed with good productivity and a high yield rate. Representative methods of flexographic printing methods are described below.

[0178] (Flexographic printing method)

[0179] (1) Anilox roller

[0180] In the flexographic printing method, an anilox roll may be used, for example, a ceramic anilox roll with cell engraving or a chrome-plated anilox roll.

[0181] In order to obtain a printed layer (printed material) with excellent dot reproducibility, an anilox roller with a line count of 5 times or more, preferably 6 times or more, the line count of the plate used for printing is used. For example, when the line count of the plate used is 75 lpi, an anilox roller with a line count of 375 lpi or more is required. On the other hand, when the line count of the plate is 150 lpi, an anilox roller with a line count of 750 lpi or more is required. From the perspective of the drying and adhesion properties of the aqueous ink composition used, the capacity of the anilox roller can be 1 to 8 cc / m 2 , preferably 2 to 6 cc / m 2 .

[0182] (2)flexo

[0183] In flexographic printing, a photosensitive resin plate cured with ultraviolet light from a UV light source can be used. Alternatively, a plate made of an elastomer material using direct laser engraving can be used. Regardless of the method used to form the image portion of the flexographic plate, a plate with a screen resolution of 75 lpi or higher can be used. Any sleeve or cushion tape can be used to attach the plate.

[0184] (3) Printing press

[0185] As a specific example of a flexographic printing press, a CI type multi-color flexographic printing press and a UNIT type multi-color flexographic printing press etc. can be enumerated. As a specific example of an ink supply method, a cavity method and a twin-roller method can be enumerated. A printing press that can be applied to a flexographic printing method can be appropriately selected for use.

[0186] In one embodiment, the printed layer preferably comprises multiple layers. The printed layer may include a base layer covering the entire surface of the foaming layer-forming layer (B0) and a printed pattern provided on at least a portion of the surface of the base layer. For example, the base layer may be formed from a white aqueous ink composition, and the printed pattern may be formed from an aqueous color ink composition.

[0187] In one embodiment, from the perspectives of foam suppression and friction resistance caused by the printed layer, the thickness of the printed layer is preferably adjusted so that the thickness of the dry coating film is 0.5 to 5.0 μm. The thickness of the printed layer (dried coating film) may more preferably be 0.5 to 4.0 μm, and even more preferably 0.5 to 3.5 μm. When the printed layer is composed of multiple layers, the thickness of the printed layer is preferably adjusted so that the thickness of the entire printed layer is within the above range.

[0188] In other embodiments, the printed layer may comprise multiple layers, preferably having a clear layer as its outermost layer. The clear layer may be formed using a pigment-free clear ink composition. In one embodiment, the clear ink composition may be similar to the aqueous ink compositions (ii-1) and (ii-2) described above, except that it lacks a pigment.

[0189] The presence of a transparent layer can easily improve the printed surface's resistance to friction, ethanol, and water abrasion. In one embodiment, the thickness of the transparent layer (dry film thickness) is preferably 0.1 to 3.0 μm, more preferably 0.1 to 2.5 μm, and even more preferably 0.1 to 2.0 μm. When the printed layer includes a transparent layer, the overall thickness of the printed layer, including the thickness of the transparent layer, is preferably adjusted to be within the range of 0.5 to 5.0 μm.

[0190] When the printed layer comprises multiple layers, the aqueous ink constituting at least one of the multiple layers preferably comprises a binder resin containing a polyurethane resin and a curing agent. In one embodiment, the aqueous ink composition constituting at least the base layer and / or the outermost layer preferably comprises a binder resin containing a polyurethane resin and a curing agent. More preferably, the aqueous ink composition is used to form the base layer (white) ink layer and the outermost layer (ink layer or clear layer), and most preferably, to form all of the multiple layers.

[0191] (Step (iv): Formation of Foamed Layer (B))

[0192] In the above-mentioned step (iv) of forming the foaming layer (B) by heating, the appropriate heating temperature and heating time vary depending on the properties of the paper substrate and the thermoplastic resin film used. Those skilled in the art can determine the optimal combination of heating temperature and heating time based on the materials used, such as the thermoplastic resin film. Although not particularly limited, the heat treatment is generally performed during the container forming process. If the heating temperature during the heat treatment is too low, sufficient foaming properties cannot be achieved. If the heating temperature is too high, the foaming cells will coalesce, easily causing blistering.

[0193] Although not particularly limited, when the foaming layer forming layer is composed of a low-density polyethylene film, the heating temperature may preferably be 100 to 125°C, and may more preferably be 110 to 120°C. The heating time can be appropriately adjusted according to the heating temperature, but is preferably 3 to 10 minutes, and more preferably 5 to 7 minutes. In one embodiment, when the foaming layer forming layer is composed of a low-density polyethylene film and a printing layer is formed thereon using the aqueous ink composition (ii-1) or (ii-2) described above, the heating temperature is preferably adjusted to 110 to 123°C, and the heating time is preferably adjusted to 5 to 7 minutes. It is more preferred to adjust the heating temperature to 115 to 121°C, and the heating time is adjusted to 5 to 7 minutes. When heating is performed under the above conditions, it is easy to appropriately control the foaming of the foaming layer forming layer during heating processing through the printing layer.

[0194] As the heating means, any means such as hot air, electric heat, electron beam, etc. can be used. If heating is performed by hot air or electric heat in a channel equipped with a conveying means using a conveyor belt, a large amount of heat treatment can be carried out inexpensively.

[0195] <4> Foam paper container

[0196] One embodiment relates to a foamed paper container comprising the foamed paper laminate of the above embodiment. The foamed paper container is characterized in that it comprises a container body member and a bottom plate member, wherein the container body member is formed of the foamed paper laminate of the above embodiment. Figure 1 1 is a perspective view showing the structure of a foamed paper container 10A obtained by heat treatment after the container is assembled and formed. Figure 1 As shown, a foamed paper container 10A comprises a container body member 10, which is formed from a foamed paper laminate, and a bottom plate member 12. In the container body member (foamed paper laminate) 10, a high-MP resin film forms the container's inner wall surface 10a, while a printed layer on the low-MP resin film (foamed layer) forms the container's outer wall surface 10b.

[0197] Figure 2 It will Figure 1 The schematic cross-sectional view of the container body member of the foam paper container shown in FIG. The container body member (foam paper laminate) 10 is enlarged and shown in FIG. Figure 1 ) has a high Mp resin film 20, a paper base material 30, a foamed low Mp resin film (foamed layer) 40, and a printed layer 50 in sequence, and the printed layer 50 has a base layer 50a and a printed pattern 50b.

[0198] The forming process of foam paper containers can be implemented by applying well-known techniques. For example, first, a foam paper laminate formed with a printed layer (foam paper laminate before heating) is punched into a predetermined shape along a mold to obtain a container main body component. Similarly, the bottom plate material is punched into a predetermined shape to obtain a bottom plate component. Then, using a commonly used container manufacturing device, the container main body component and the bottom plate component are assembled and formed into the shape of the container. The assembly and forming of the container performed by the container manufacturing device is implemented in a manner such that the above-mentioned high Mp resin film of the container main body component forms the inner wall surface, the above-mentioned low Mp resin film forms the outer wall surface, and the laminated surface of the bottom plate component becomes the inner side. After the container is assembled and formed by the container manufacturing device in this way, the low Mp resin film is foamed by heat treatment to form a foaming layer (insulating layer), thereby obtaining a foam paper container with thermal insulation properties.

[0199] In one embodiment, when the inner wall surface and outer wall surface of the main body of a foamed paper container are each composed of polyethylene film, it is preferred that one side of the paper substrate (the inner wall surface of the container) be laminated with a medium-density or high-density polyethylene film, and the other side (the outer wall surface of the container) be laminated with a low-density polyethylene film. The thickness of each film laminated on the paper substrate is not particularly limited. However, the thickness of the low-MPp resin film constituting the outer wall surface of the container main body is preferably appropriately set to a sufficient thickness for the foamed film to function as a thermal insulation layer when the film is foamed.

[0200] For example, when the outer wall surface of the container body is composed of a low-density polyethylene film, the thickness of the film laminated on the paper substrate can be 40 to 150 μm. On the other hand, when the inner wall surface of the container body is composed of a medium-density or high-density polyethylene film, the thickness of the film laminated on the paper substrate is not particularly limited. However, in order to ensure the permeability resistance of the contents when used as an insulating foam paper container, it is preferred to appropriately set the thickness of the film. Since the thickness of the film laminated on the paper substrate varies depending on the resin material of the film used, it is preferred that those skilled in the art consider the characteristics of the resin material and appropriately set it.

[0201] Example

[0202] The present invention will be described in further detail below with reference to Examples, but the present invention is not limited to these Examples. It should be noted that, unless otherwise specified, "parts" and "%" described below represent "parts by mass" and "mass %".

[0203] <1>Methods for measuring various properties

[0204] Various properties of the binder resin and aqueous ink composition described below represent values ​​obtained by the following measurement methods.

[0205] (Glass transition temperature)

[0206] Each polyurethane resin aqueous solution obtained in the synthesis examples described below was applied to a polyethylene substrate and then dried at 40°C for 3 days to obtain a dry coating film with a thickness of 0.5 mm. Each dry coating film was measured using a dynamic viscoelasticity automatic measuring instrument (DDV-GP series (LeoVibron) manufactured by A&D Co., Ltd.), with the peak temperature of the loss tangent tanδ being designated as Tg (°C). The measurement was conducted in the temperature range of -120°C to 40°C at a heating rate of 10°C / minute.

[0207] (Elongation and stress of adhesive resin)

[0208] Each polyurethane resin aqueous solution obtained in the synthesis examples described below was dried to prepare a coating test sample (thickness 0.30 mm, width 5.0 mm, length 20.0 mm). The elongation and stress of each sample were measured using a small tensile testing machine manufactured by Instron. The measurements were carried out at a tensile speed of 100 mm / min and a room temperature of 25°C.

[0209] It should be noted that for embodiments in which the aqueous ink composition includes a curing agent, a coating film test sample (thickness 0.30 mm, width 5.0 mm, length 20.0 mm) was prepared using a binder resin and a curing agent in the same proportions as in the aqueous ink composition. Using this sample, the elongation and stress of the binder resin (cured product) were measured using the same methods as described above.

[0210] (Residual rate of printed layer)

[0211] The residual rate of the printed layer is a test for evaluating the ethanol resistance of the printed layer formed on the foam paper (the surface of the foam paper laminate), and is carried out as follows.

[0212] First, cut the foam paper laminate into test pieces (samples) measuring 100 mm long by 100 mm wide. Measure the mass of the cut test piece and record it as the sample mass before ethanol immersion. Then, for ease of immersion, crush the test piece to approximately 20 mm long by 20 mm wide.

[0213] Next, ethanol (25°C) and the crushed test piece were placed in a container at a mass ratio of ethanol to test piece of 100:4.5, and the test piece was immersed in the ethanol. The test piece was allowed to stand in the 25°C ethanol for 2 minutes while stirring at 100 rpm, then for 30 minutes, and then for 1 minute while stirring at 100 rpm. The test piece was removed and its mass after drying was measured. This was recorded as the sample mass after immersion.

[0214] Furthermore, the residual rate of the printed layer was calculated according to the following formula from the sample mass before immersion and the sample mass after immersion measured as described above.

[0215] Residual rate of printed layer = (mass of sample after immersion / mass of sample before immersion) × 100

[0216] (Thickness of printed layer)

[0217] The thickness of the printed layer was determined from a scanning electron microscope (SEM) photograph (magnification 5000) of a cross section of the foam paper laminate. The printed layer was measured at five random locations, and the average value was recorded as the thickness of the printed layer.

[0218] (Number of bubble holes)

[0219] The printed layer of the foam paper laminate was removed with methyl ethyl ketone (MEK) to expose the surface of the foamed thermoplastic resin layer (foamed layer). The surface of the foamed layer was then observed using an optical microscope (Nikon AZ100M) (magnification 25x) to determine the number of closed cells within a range defined by a certain length in the vertical and horizontal (XY) directions. The number of cells per 1 cm was then calculated. 2 Observe 5 random locations and record their average value as the number of foamed cells.

[0220] (Thickness of foaming layer)

[0221] The thickness of the foamed layer was determined by observing a cross-section of the foamed paper laminate using an optical microscope photograph and measuring the height from the upper surface of the paper substrate to the lower surface of the printed layer. The thickness before foaming corresponds to the thickness of the foamed layer-forming layer. Therefore, the thickness of the low-density polyethylene resin used to form the foamed layer was used as the value.

[0222] (Binder resin)

[0223] (Synthesis Example 1) Polyurethane resin (A)

[0224] To a reactor equipped with a reflux condenser, a dropping funnel, a gas inlet tube, a stirrer, and a thermometer, 328.16 parts of poly(3-methyl-1,5-pentane adipate) diol (PMPA2000, number average molecular weight 2,000), 10.0 parts of polyethylene glycol (PEG2000, number average molecular weight 2,000), 57.81 parts of dimethylolbutanoic acid (DMBA), and 350 parts of methyl ethyl ketone (MEK) were added while nitrogen was introduced. While mixing and stirring, 200.76 parts of isophorone diisocyanate (IPDI) was further added dropwise over one hour. The mixture was then allowed to react at reflux for six hours to form a terminal isocyanate prepolymer. The reaction solution was then cooled to 30°C, and 100 parts of isopropyl alcohol was added to obtain a solvent solution of the terminal isocyanate prepolymer.

[0225] A mixed solution of 28.21 parts of 2-aminoethylethanolamine (AEA) and 150 parts of isopropyl alcohol (IPA) was slowly added to the obtained terminal isocyanate prepolymer at room temperature (25° C.), and reacted at 40° C. for 3 hours to obtain a solvent-based polyurethane resin solution.

[0226] Next, 23.69 parts of 28% aqueous ammonia and 1800 parts of ion-exchanged water were slowly added to the solvent-based polyurethane resin solution for neutralization, thereby obtaining an aqueous polyurethane resin solution. Furthermore, MEK and IPA were removed from the aqueous polyurethane resin solution by vacuum distillation, and then water was added to adjust the solids content to 25%.

[0227] As described above, an aqueous solution (25% solids content) of a polyurethane resin (A) having an acid value of 35 mgKOH / g and a weight-average molecular weight of 35,000 was obtained. The elongation, stress, and other properties of the polyurethane resin (A) were measured according to the methods described above. The results are shown in Table 1.

[0228] (Synthesis Examples 2 to 8)

[0229] According to the synthesis method described in Japanese Patent Application Laid-Open No. 2018-184512, the same procedures as in Synthesis Example 1 were followed, except that the raw materials and amounts described in Synthesis Example 1 were modified to reflect the properties described in Table 1. Aqueous solutions of polyurethane resins (B) to (H) having a solids content of 25% (hereinafter sometimes referred to as polyurethane resins (B) to (H)) were obtained. The elongation, stress, and other properties of the polyurethane resins (B) to (H) were measured according to the methods described above, and the results are shown in Table 1.

[0230] [Table 1]

[0231]

[0232] <2> Example of producing a water-based ink composition

[0233] (Manufacturing Example 1) Manufacture of white ink (W1)

[0234] According to the formulation described in Table 2, 10 parts of an aqueous solution of a polyurethane resin (A), 20 parts of an aqueous solution of a polyurethane resin (B), 40 parts of a white pigment (titanium oxide, TITANIX JR808 (manufactured by TAYCA Co., Ltd.), 0.1 parts of a defoaming agent, 0.2 parts of adipic acid dihydrazide (ADH), 1 part of n-propanol, and 5 parts of water were stirred and mixed, and then dispersed using a sand mill. Subsequently, 4 parts of an aqueous solution of a polyurethane resin (A), 14 parts of an aqueous solution of a polyurethane resin (B), and 6 parts of water were further added to the mixture obtained by the dispersion treatment, and the mixture was stirred and mixed to obtain a white ink (W1).

[0235] (Manufacturing Examples 2 to 9) Manufacture of White Inks (W2) to (W9)

[0236] White inks (W2) to (W9) were obtained by the same production method as in Production Example 1 except that the two polyurethane resin aqueous solutions used in Production Example 1 were changed in the formulation described in Table 2.

[0237] In addition, the binder resins described in Table 2 are as follows.

[0238] Polyurethane resins A to H: aqueous solutions of the polyurethane resins (A) to (H) prepared in Synthesis Examples 1 to 8 (solid content: 25%).

[0239] Polyurethane resin I: product name "UREARNO W321" manufactured by Arakawa Chemical Industries, Ltd. (an aqueous solution of a polyurethane resin having a resin elongation of 600% and a stress of 7.0 mPa).

[0240] Acrylic resin: BASF Corporation product name "Joncryl 7100" (an acrylic resin emulsion having a weight average molecular weight of 200,000, a glass transition temperature of -10°C, an acid value of 51 mgKOH / g, a resin elongation of 180%, and a stress of 6.5 mPa).

[0241] Vinyl chloride resin: product name "VINYBLAN 700" manufactured by Nissin Chemical Industry Co., Ltd. (an emulsion of a vinyl chloride resin having a glass transition temperature of 70° C. and an acid value of 57 mgKOH / g).

[0242] (Manufacturing Example 10) Manufacture of Blue Ink (B1)

[0243] According to the formulation described in Table 2, 20 parts of an aqueous solution of a polyurethane resin (B), 20 parts of an aqueous solution of a polyurethane resin (C), 20 parts of a blue pigment (LIONOL BLUE FG-7358-G (manufactured by TOYO-COLOR CO., LTD.), 0.10 parts of a defoamer, 0.20 parts of ADH, 2.5 parts of n-propanol, and 10 parts of water were stirred and mixed, and then dispersed using a sand mill. Subsequently, 4 parts of an aqueous solution of a polyurethane resin (B), 16 parts of an aqueous solution of a polyurethane resin (C), and 8 parts of water were added to the dispersed mixture, and the mixture was stirred and mixed to obtain a blue ink (B1).

[0244] (Manufacturing Examples 11 to 18) Manufacture of Blue Inks (B2) to (B9)

[0245] Blue inks (B2) to (B9) were obtained in the same manner as in Production Example 10 except that the two polyurethane resin aqueous solutions described in Production Example 10 were changed to the formulations described in Table 2.

[0246] (Manufacturing Example 19) Manufacture of Clear Ink (C1)

[0247] According to the formulation described in Table 2, 82 parts of the polyurethane resin (C) aqueous solution, 0.1 parts of a defoaming agent, 0.2 parts of ADH, 1 part of n-propanol, and 17 parts of water were stirred and mixed to obtain a clear ink (C1) for overprinting.

[0248] (Manufacturing Examples 20 to 27) Manufacture of Clear Inks (C2) to (C9)

[0249] Clear inks (C2) to (C9) were obtained in the same manner as in Production Example 19 except that the polyurethane resin aqueous solution described in Production Example 19 was changed to the formulation described in Table 2.

[0250] [Table 2]

[0251]

[0252] <3> Example of producing a foam paper laminate

[0253] (1) Example of manufacturing foam paper material

[0254] The foamed paper material is produced by (step 1) extrusion laminating a medium-density polyethylene resin (M) on one side of a paper substrate to form a water vapor barrier layer, and then (step 2) extrusion laminating a low-density polyethylene resin (L) on the other side (non-laminated side) of the paper substrate.

[0255] Various conditions in step 1 and step 2 are as follows.

[0256] (Process 1)

[0257] Paper substrate: moisture content 23kg / m 3 , weight per square meter 320kg / m 3

[0258] Medium-density polyethylene resin (M): Petrosen LW04-1 manufactured by Tosoh Corporation, MFR 4.3 g / 10 min, density 940 kg / m 3

[0259] Extrusion temperature (T die outlet temperature): 320℃

[0260] Taking-up speed (laminating speed): 50m / min

[0261] Air gap: 130mm

[0262] Thickness: 40 μm (thickness of the center portion of the polyethylene resin layer)

[0263] (Process 2)

[0264] Low-density polyethylene resin (L); described later

[0265] Extrusion temperature (T die outlet temperature): 310°C

[0266] Taking-up speed (laminating speed): 60m / min

[0267] Air gap: 130mm

[0268] It should be noted that the low-density polyethylene resin (L) used in step 2 above serves as the foam layer-forming layer (B0). In Example 18, a low-density polyethylene resin (L2) was used as the low-density polyethylene resin (L). In all other examples, a low-density polyethylene resin (L1) was used to produce a foam paper material. Details of the low-density polyethylene resins (L1) and (L2) are as follows.

[0269] Low-density polyethylene resin (L1): Petrosen 07C03C manufactured by Tosoh Corporation, density 918 kg / m 3 , melting point 106℃, MFR 15g / 10min

[0270] Low-density polyethylene resin (L2): NOVATEC LDLC720 manufactured by Japan Polyethylene Co., Ltd., density 922 kg / m 3 , melting point 110℃, MFR 9g / 10min

[0271] (2) Production Example of Forming a Printed Layer on a Foamed Paper Material (Foamed Paper Laminate Before Foaming)

[0272] Using the white inks (W1 to W9), blue inks (B1 to B9), and clear inks (C1 to C9) prepared above, a printed layer was formed on the foam paper material as described below.

[0273] (Example 1)

[0274] As shown in Table 3, 3 parts by mass of CARBODILITE SV-02 (manufactured by Nisshinbo Co., Ltd.), a carbodiimide-based curing agent, was added to 100 parts by mass of each of white ink (W1), blue ink (B1), and clear ink (C1) to obtain printing inks. The curing agent had a chemical formula weight of 430 per mol of carbodiimide groups and a solids content of 40% by mass.

[0275] A central impression (CI) flexographic printing press was used to form a printed layer on a low-density polyethylene resin (L) foam paper material. Printing ink (W1), printing ink (B1), and printing ink (C1) were overprinted in this order using an anilox roller and a resin plate. The printing speed was 150 m / min.

[0276] (Examples 2 to 19, and Comparative Examples 1 to 4)

[0277] As shown in Table 3, in the embodiment in which a curing agent is added to the white ink, blue ink, and clear ink, a curing agent was further added to obtain each printing ink. The amount of CARBODILITE SV-02 (manufactured by Nisshinbo Co., Ltd.) added was 5.0 parts by mass in Example 3, 1.0 parts by mass in Example 12, and 5.0 parts by mass in Example 13. The amount of CARBODILITE SV-02 added was 3 parts by mass in the same manner as in Example 1 for the other examples. In Example 11, TAKENATE WD-725 (manufactured by Mitsui Chemicals, Inc., a water-based isocyanate curing agent with a solids content of 50% by mass) was used as a curing agent in an amount of 3 parts by mass. Overprinting was performed in the same manner as in Example 1, except that the respective printing inks were combined as described in Table 3, to form a printed layer.

[0278] (3) Example of manufacturing a foam paper laminate

[0279] The foamed paper material having the printed layer produced as described above (pre-foamed paper laminate) was heat-treated under the following conditions to foam the low-density polyethylene resin layer (L) to form a foamed layer, thereby producing a foamed paper laminate (post-foamed laminate). It should be noted that in the Examples and Comparative Examples other than Examples 14 and 15 and Comparative Example 4, the heat treatment was performed under standard conditions.

[0280] Standard conditions: heating in an oven at 120°C for 6 minutes

[0281] Example 14: Heating in an oven at 120°C for 9 minutes

[0282] Example 15: Heating in an oven at 122°C for 6 minutes

[0283] Comparative Example 4: Heating in an oven at 124°C for 6 minutes

[0284] <4> Evaluation of foam paper laminates

[0285] The foam paper laminates of Examples 1 to 19 and Comparative Examples 1 to 4 produced as described above were evaluated for various properties according to the methods described below.

[0286] <Foaming followability>

[0287] For each surface of the foam paper laminates of Examples 1-19 and Comparative Examples 1-4, the height difference between the white ink-printed area and the blue ink-printed area after heat treatment (after foaming the low MP film) was measured with a finger. The degree of depression of the blue ink-printed area was evaluated according to the following criteria. A higher numerical value indicates better foam followability and a flatter printed surface.

[0288] (Evaluation Criteria)

[0289] 5: There is almost no difference in height from the white ink printed part.

[0290] 4: A slight difference in height from the white ink printed portion is felt.

[0291] 3: A clear difference in height from the white ink printed portion is felt.

[0292] 2: The height difference from the white ink printed portion is quite noticeable.

[0293] 1: The height difference from the white ink printed portion is very noticeable.

[0294] <Foaming appearance: foaming>

[0295] The printed surfaces of the foam paper laminates of Examples 1 to 19 and Comparative Examples 1 to 4 were visually observed. The evaluation criteria are as follows. The results shown in Table 3 represent the most frequent values ​​among the observations and evaluations of 10 randomly prepared foam paper laminate samples. In the event of multiple modes, the value with the lower mode was used.

[0296] (Evaluation Criteria)

[0297] 5: No foaming at all (no foaming was observed).

[0298] 4: Blisters with a long diameter less than 5mm are present in every 100cm 2 1 exists.

[0299] 3: The bubbles with a long diameter less than 5mm are within 100cm 2 There are 2.

[0300] 2: The bubbles with a long diameter less than 5mm are within 100cm 2 There are 3 to 5 bubbles or bubbles with a long diameter of 5 to 20 mm per 100 cm 2 1 exists.

[0301] 1: The bubbles with a long diameter less than 5mm are within 100cm 2 There are 6 or 5 to 20 mm long diameter bubbles per 100 cm 2 There are more than 2 bubbles or bubbles with a long diameter of more than 20 mm per 100 cm 2 There are more than 1.

[0302] It should be noted that when multiple bubbles with different major diameters are mixed, a lower evaluation is adopted. Specifically, 2 When there were two bubbles with a major diameter of less than 5 mm and one bubble with a major diameter of 5 to 20 mm, the evaluation was "2".

[0303] <Foaming appearance: cracks>

[0304] The printed surfaces of the foamed paper laminates of Examples 1-19 and Comparative Examples 1-4 were visually observed in the same manner as for the evaluation of foaming. The evaluation criteria are as follows. The results shown in Table 3 represent the most frequent values ​​among the observations and evaluations of 10 randomly prepared foamed paper laminate samples. In the event of multiple most frequent values, the value with the lower most frequent value was used.

[0305] (Evaluation Criteria)

[0306] 5: No cracks at all (no cracks were confirmed).

[0307] 4: Cracks less than 2mm in length are detected every 100cm 2 1 exists.

[0308] 3: Cracks less than 2mm in length are detected every 100cm 2 There are 2 to 4 items.

[0309] 2: Cracks less than 2mm in length are detected every 100cm 2 There are 5 to 10 cracks or cracks with a length of 2 to 5 mm per 100 cm. 2 1 exists.

[0310] 1: Cracks less than 2mm in length are detected every 100cm 2 There are more than 11 cracks or cracks with a length of 2 to 5 mm per 100 cm. 2 There are more than 2 cracks or cracks longer than 5mm per 100cm 2 There are more than 1.

[0311] It should be noted that, when multiple cracks of different lengths are mixed, a lower evaluation is adopted. Specifically, 2 When there was one crack of 1 mm in length and one crack of 4 mm in length, the evaluation was "2".

[0312] <Ethanol resistance>

[0313] For the foam paper laminates of Examples 1 to 19 and Comparative Examples 1 to 4, a muslin cloth (JIS L0803) containing 70% ethanol (ethanol:water = 70:30) was moved back and forth once on the surface of the printed layer (coating film) on the low-melting-point film that had been foamed by heat treatment, while applying a load with a friction piece. A load of 200 g was applied using a Gakushin testing machine (manufactured by TESTER Sangyo Co., Ltd.) while the muslin cloth was moved back and forth. The coating film was then visually observed, and the ethanol resistance was evaluated by calculating the area ratio after the coating film (ink) peeled off, using the total area of ​​the coating film before the test as a reference. The evaluation criteria are as follows.

[0314] (Evaluation Criteria)

[0315] 5: Ink peeling is less than 30%.

[0316] 4: The ink peeling is 30% or more and less than 40%.

[0317] 3: The ink peeling is 40% or more and less than 60%.

[0318] 2: The ink peeling rate is 60% or more and less than 70%.

[0319] 1: The ink peeling is 70% or more.

[0320] <Friction resistance>

[0321] For the foam paper laminates of Examples 1-19 and Comparative Examples 1-4, the white ink-printed surface, or the white and transparent ink-printed surface (coating surface) of each laminate was used as the friction material. A Gakushin testing machine (manufactured by TESTER Sangyo Co., Ltd.) was used to reciprocate the coating surface once with a load of 200 g. The abrasion resistance was evaluated based on the degree of blue ink color shift on the white ink-printed surface.

[0322] (Evaluation Criteria)

[0323] 5: No ink color shift.

[0324] 4: There is slight color shift of the ink (less than 1%).

[0325] 3: There is color shift of ink (1% or more and less than 10%).

[0326] 2: There is obvious color shift of the ink (10% or more and less than 30%).

[0327] 1: There is very noticeable color shift of the ink (30% or more).

[0328] Thermal insulation

[0329] Heat resistance was evaluated by placing the foamed paper laminate on a hot plate heated to 90°C with the foamed surface facing upward. The temperature of the foamed surface (non-contact surface) was measured after 4 minutes. More specifically, the temperatures of 10 foamed paper laminate samples after heating were measured as described above, and the average temperature was calculated. Heat resistance was evaluated based on the obtained average temperature according to the following evaluation criteria.

[0330] (Evaluation Criteria)

[0331] 5: The temperature of the foaming noodles is less than 80℃.

[0332] 4: The temperature of the foamed noodles is 80°C or higher and lower than 82°C.

[0333] 3: The temperature of the foamed noodles is 82°C or higher and lower than 84°C.

[0334] 2: The temperature of the foamed noodles is 84°C or higher and lower than 88°C.

[0335] 1: The temperature of the foaming noodles should be above 88℃.

[0336] [Table 3-1]

[0337]

[0338] [Table 3-2]

[0339]

[0340] From the results of the above examples and comparative examples, it can be seen that the residual rate of the printed layer after immersion in ethanol at 25°C is 50% by mass or more, and the number of foamed cells in the foamed layer is 1,000 cells / 1cm 2The above foam paper laminates (Examples 1 to 19) can achieve excellent foam appearance, friction resistance, heat resistance, and ethanol resistance. In addition, as is clear from the comparison of Examples 1 to 19 with Comparative Example 1, in order to form the aqueous ink composition used to form the above-mentioned printing layer, it is preferable to include at least a polyurethane resin as a binder resin. As can be seen from Comparative Example 1, when only an acrylic resin is used as the binder resin (without a polyurethane resin), the elongation and stress of the resin are lower than when a polyurethane resin is used, and the foam followability and foam appearance are significantly reduced. Furthermore, as is clear from the comparison of Examples 1 to 19 with Comparative Examples 2 and 3, by adjusting the weight-average molecular weight and other components of the polyurethane resin, excellent foam followability and foam appearance can be achieved, and the ethanol resistance and friction resistance of the printing layer can be improved.

[0341] It is obvious from the above description that various embodiments can be widely constructed without departing from the spirit and scope of the present invention, and the present invention is not limited to the specific embodiments except as defined in the claims.

[0342] Explanation of symbols

[0343] 10 Foam paper laminate (container main body member)

[0344] 10A Foam paper container

[0345] 10a Outer wall of container

[0346] 10b Inner wall of container

[0347] 12 Bottom plate component 12

[0348] 20 High MP resin film (thermoplastic resin layer (A))

[0349] 30 Paper substrate

[0350] 40 Foamed low-Mp resin film (foamed thermoplastic resin layer (B), foamed layer (B))

[0351] 50 printing layers

[0352] 50a basal layer

[0353] 50b Printed pattern.

Claims

1. A foamed paper laminate comprising foamed paper and a printed layer, wherein the foamed paper comprises a thermoplastic resin layer (A), a paper substrate, and a foamed thermoplastic resin layer (B) in this order, and the printed layer is formed on a surface of the foamed thermoplastic resin layer (B) of the foamed paper. The number of foamed cells per unit area of ​​the foamed thermoplastic resin layer (B) is 1250 cells / 1 cm 2 More than 1600 pieces / 1cm 2 Hereinafter, the number of foamed cells per unit area is calculated by counting the number of independent cells existing in a range divided by a certain length along the vertical and horizontal directions, that is, the XY directions on the surface of the foamed thermoplastic resin layer, and expressing the number of cells per 1 cm 2 The value calculated from the number of closed cells, the number of closed cells being determined by removing the printed layer of the foamed paper laminate with a solvent to expose the surface of the foamed thermoplastic resin layer, and then observing the surface of the foamed thermoplastic resin layer with an optical microscope, The printed layer comprises a cured product formed by a binder resin and at least one of a carbodiimide curing agent and an isocyanate curing agent, and the residual rate of the printed layer after immersion in ethanol at 25° C. for 30 minutes is 50% by mass or more, and the binder resin comprises a polyurethane resin having an acid value of 1 to 100 mgKOH / g. 2 . The foamed paper laminate according to claim 1 , wherein the stress of the binder resin at an elongation of 50 to 4,000% is 0.1 MPa to 50 MPa. 3 . The foamed paper laminate according to claim 1 , wherein the binder resin has a glass transition temperature of −100 to 0° C. 4 . The foam paper laminate according to claim 1 , wherein the printed layer has a thickness of 0.5 to 5.0 μm. 5 . The foam paper laminate according to claim 1 , wherein the printed layer has multiple layers, and the outermost layer is a transparent layer. 6 . The foamed paper laminate according to claim 1 , wherein the foamed thermoplastic resin layer (B) has a thickness of 500 to 950 μm. 7 . A foamed paper container comprising the foamed paper laminate according to claim 1 .

8. A method for producing a foamed paper laminate, the foamed paper laminate comprising foamed paper and a printed layer, the foamed paper comprising a thermoplastic resin layer (A), a paper substrate, and a foamed thermoplastic resin layer (B) in this order, the printed layer being formed on the surface of the foamed thermoplastic resin layer (B) of the foamed paper, the number of foamed cells per unit area of ​​the foamed thermoplastic resin layer (B) being 1250 cells / 1 cm 2 More than 1600 pieces / 1cm 2 Hereinafter, the number of foamed cells per unit area is calculated by counting the number of independent cells existing in a range divided by a certain length along the vertical and horizontal directions, that is, the XY directions on the surface of the foamed thermoplastic resin layer, and expressing the number of cells per 1 cm 2 The value calculated from the number of independent cells of the foamed paper laminate is determined by removing the printed layer of the foamed paper laminate with a solvent to expose the surface of the foamed thermoplastic resin layer, and then observing the surface of the foamed thermoplastic resin layer with an optical microscope, wherein the residual rate of the printed layer after immersion in ethanol at 25° C. for 30 minutes is 50% by mass or more, and the method for producing the foamed paper laminate comprises: A foamed paper material is prepared, which comprises, in order, a thermoplastic resin layer (A), a paper base material, and a foamed thermoplastic resin layer forming layer (B0) having a lower melting point than the thermoplastic resin layer (A) and foaming by heating; preparing an aqueous ink composition comprising a binder resin containing a polyurethane resin having an acid value of 1 to 100 mgKOH / g, water, and at least one of a carbodiimide curing agent and an isocyanate curing agent; Applying the aqueous ink composition on the surface of the foamed thermoplastic resin layer forming layer (B0) of the foamed paper material to form a printing layer; The foamed thermoplastic resin layer (B) is formed by heating the foamed paper material having the printed layer so as to foam the foamed thermoplastic resin layer forming layer (B0) of the foamed paper material. 9 . The method for producing a foam paper laminate according to claim 8 , wherein the printed layer has multiple layers, and the outermost layer is a transparent layer. 10 . The method for producing a foamed paper laminate according to claim 8 , wherein the foamed thermoplastic resin layer forming layer ( B0 ) has a film thickness of 40 to 150 μm.

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