Backing paper for skin pack and skin pack packaging

Abstract

The present invention provides a backing paper for a skin pack, the backing paper having a thermoplastic resin layer, a paper base material, and a coating layer, in that order, wherein the degree of fibrillation of the pulp in the paper base material is 1.0% or less, the coating layer contains a resin, the surface roughness of the surface of the coating layer on the opposite side from the paper base material is 1.50 μｍ to 4.20 μm, and the geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the backing paper for a skin pack is 37.0 N·m / g or more.

Description

Skin pack mount and skin pack packaging

[0001] The present disclosure relates to a skin pack liner and a skin pack packaging body.

[0002] In the field of food packaging, skin pack packaging, in which a tray and the food placed on it are vacuum-packed with a barrier film, is increasingly being used to maintain the freshness and extend the shelf life of food. Skin pack packaging, particularly when used to package meat and other products, has the advantage of being able to extend the shelf life and reduce food waste because it can suppress dripping (the moisture that escapes from food during storage).

[0003] In light of this, taking into consideration design aspects due to printability and reduced environmental impact, skin pack packaging has been developed in which food is placed on a paper-based backing sheet instead of resin trays such as polystyrene and polypropylene, and then packed in a film. In the production of such skin pack packaging, paper dust is generated when punching the backing sheet or when friction is applied to the back surface of the backing sheet during transport, etc., resulting in problems such as foreign matter contamination and missing prints.

[0004] Therefore, skin pack liner sheets that generate less paper dust have been developed. For example, Patent Document 1 describes that the generation of paper dust can be suppressed by setting the Taber stiffness of the skin pack liner to 150 mN·m or less in the longitudinal direction and 80 mN·m or less in the lateral direction.

[0005] Japanese Patent Application Laid-Open No. 2021-191690

[0006] By fixing the contents in the center of the backing, skin pack packaging allows many products to be hung or stored or displayed on an inclined surface. As such, the use modes of skin pack packaging are diversifying, and skin pack backings are required to have properties suitable for those modes of use. For example, when storing or displaying skin pack packaging on an inclined surface, the backing must be non-slip when placed on the inclined surface. On the other hand, skin pack backings must naturally have the properties required for use in skin pack packaging, such as not curling due to film shrinkage during skin pack packaging, and these properties cannot be sacrificed in order to impart other additional properties.

[0007] For these reasons, depending on the manner in which the skin pack packaging is used, it is necessary to develop a new technology for suppressing the generation of paper dust, separate from the technology described in Patent Document 1, in order to impart properties to the skin pack backing paper that are suitable for that manner of use.

[0008] The object of the present disclosure is to provide a skin pack backing that generates little paper dust, is less likely to slip when placed on an inclined surface, and suppresses warping during skin pack packaging.

[0009] As a result of extensive research, the inventors of the present disclosure have found that the above-mentioned problems can be solved by setting the tensile strength index of the skin pack liner and the degree of fibrillation of the pulp in the paper base material within predetermined ranges, and by providing a coating layer with a predetermined surface roughness on one side of the paper base material.

[0010] [1] A skin pack liner having, in this order, a thermoplastic resin layer, a paper base material, and a coating layer, wherein the degree of fibrillation of pulp in the paper base material is 1.0% or less, the coating layer contains a resin, the surface roughness of the coating layer opposite to the paper base material is 1.50 to 4.20 μm, and the geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the skin pack liner is 37.0 N m / g or more. [2] The mass per unit area of ​​the resin in the coating layer is 0.10 to 1.90 g / m ２[3] The liner for skin packs according to [1], wherein the resin contained in the coating layer comprises at least one selected from the group consisting of water-soluble resins and water-dispersible resins (preferably starch). [4] The liner for skin packs according to [3], wherein the water-soluble resin comprises at least one selected from the group consisting of oxidized starch, cationized starch, polyvinyl alcohol, and polyacrylamide (preferably at least one selected from the group consisting of oxidized starch and cationized starch). [5] The liner for skin packs according to any of [1] to [4], wherein the geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the liner for skin packs is 53.0 N·m / g or less. [6] The liner for skin packs according to any of [1] to [5], wherein the paper base material comprises at least 0.10% by mass of a paper strength agent relative to the total amount of the paper base material. [7] The liner for a skin pack according to any one of [1] to [6], wherein the paper base material is a laminated paper or a single paper having, in this order, a paper layer A, an adhesive layer, and a paper layer B. [8] A skin pack packaging body comprising the liner for a skin pack according to any one of [1] to [7], a contained item, and a resin film, wherein the contained item is contained between the thermoplastic resin layer of the liner for a skin pack and the resin film.

[0011] According to the present disclosure, it is possible to provide a skin pack backing that generates less paper dust, is less likely to slip when placed on an inclined surface, and suppresses warping during skin pack packaging.

[0012] Fig. 1 is a schematic diagram showing an example of a skin pack mount according to the present embodiment. Fig. 2 is a schematic diagram of pulp for explaining the degree of fibrillation.

[0013] In the present disclosure, unless otherwise specified, the expressions "X or more and Y or less" and "X to Y" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints. When the lower limit and upper limit of a numerical range are stated separately, the numerical range can be a combination of any lower limit and any upper limit.

[0014] In the present disclosure, a description such as "one or more selected from the group consisting of X, Y, and Z" means any of X, Y, Z, a combination of X and Y, a combination of X and Z, a combination of Y and Z, or a combination of X, Y, and Z. Furthermore, in the present disclosure, a description such as "X such as X1, X2, and X3" lists X1, X2, and X3 as examples of X, and does not mean that X is limited to X1, X2, and X3.

[0015] In this disclosure, the "longitudinal direction" of the skin pack liner and paper substrate refers to the machine direction (MD) of the paper substrate, which is the direction in which the fibers are oriented, and the "transverse direction" refers to the direction perpendicular to the machine direction (CD).

[0016] 1. Skin Pack Liner A first embodiment of the present disclosure is a skin pack liner (hereinafter sometimes simply referred to as "liner") having, in this order, a thermoplastic resin layer, a paper substrate, and a coating layer, in which the pulp fibrillation degree in the paper substrate is 1.0% or less, the coating layer contains resin, the surface roughness of the coating layer on the side opposite the paper substrate is 1.50 to 4.20 μm, and the geometric mean of the longitudinal specific tensile strength and the transverse specific tensile strength of the skin pack liner is 37.0 N·m / g or more. The skin pack liner according to this embodiment generates little paper dust, is less likely to slip when placed on an inclined surface, and is less likely to warp during skin pack packaging. Therefore, skin pack packages using this skin pack liner are suitable for storage, display, etc., when placed on an inclined surface.

[0017] One embodiment of a skin pack liner according to this embodiment is shown in Figure 1. In Figure 1, the skin pack liner 10 includes, in this order, a thermoplastic resin layer 11, a paper substrate 13, and a coating layer 15. The skin pack liner 10 may also include layers other than these, such as other layers (not shown) described below.

[0018] In this embodiment, the reason why it is possible to prevent the backing paper from slipping off when placed on an inclined surface and from curling up when packaging in a skin pack while also suppressing the generation of paper dust from the backing paper is thought to be as follows.

[0019] First, when a coating layer is provided on one side of the paper substrate, the surface of the paper substrate is covered and the exposed pulp is reduced, which is thought to make it less likely for paper dust to be generated.

[0020] Furthermore, in this embodiment, a paper base material made of pulp with a low fibrillation degree is used. The fibrillation degree is also called the external fibrillation degree. Referring to FIG. 2, the fibrillation degree is an index showing the extent to which fluffy external fibrils (fine fibers) 23 exist on the surface of fibrils 21 in fibers 20. The external fibrils fall off from the fibrils due to punching and friction of the backing paper, and become paper dust. Therefore, it is believed that the generation of paper dust can be suppressed by using a paper base material made of pulp with a low fibrillation degree.

[0021] The degree of fibrillation is calculated using formula (1) based on the description in H.R. Motamedian et al., “Mechanisms of strength and stiffness improvement of paper after PFI refining with a focus on the effect of fines”, Cellulose (2019) 26:4099-4124.

[0022] A Ｆ : Area of ​​fibril A Ｅｘｆ : total area of ​​external fibrils A Ｆ and A Ｅｘｆ is the area measured by projecting the fiber from above.

[0023] When skin pack packaging is performed, the contents are placed on the thermoplastic resin layer of the skin pack backing. The surface of the paper substrate opposite the surface that contacts the thermoplastic resin layer remains exposed and not covered by a packaging film even after skin pack packaging. Therefore, providing a coating layer on the surface of the paper substrate opposite the surface that contacts the thermoplastic resin layer can suppress the generation of paper dust, as described above. However, the coating layer covers the fine irregularities on the paper substrate surface, reducing surface roughness, which can lead to the problem of the backing slipping and tipping over when the skin pack package is stored, displayed, or otherwise handled on an inclined surface. On the other hand, if the pulp has a low degree of fibrillation, the gaps between the pulp fibers are large, which makes the surface of the paper substrate more likely to become irregular, increasing the surface roughness of the paper substrate itself. Therefore, even with the coating layer, the surface irregularities of the paper substrate can ensure a certain degree of surface roughness, which is thought to make it possible to prevent the backing from slipping even when the skin pack package is stored, displayed, or otherwise handled on an inclined surface.

[0024] Thus, using pulp with a low degree of fibrillation suppresses the generation of paper dust from the backing paper and makes the backing paper less slippery. On the other hand, external fibrils increase the surface area of ​​the fibers, increasing the bonding area between fibers and strengthening the bonds between the fibers, thereby increasing the tensile strength index. Therefore, a low degree of fibrillation of pulp reduces the tensile strength index of the skin pack backing paper. If the tensile strength index of the skin pack backing paper is excessively low, the edges of the backing paper will curl up due to thermal shrinkage of the packaging film during skin pack packaging, resulting in a poor appearance of the skin pack package. Therefore, in this embodiment, while maintaining the fibrillation index of the pulp at a predetermined value or less, the tensile strength index of the paper base material is improved, for example, by adding a paper strength enhancer to the paper base material, thereby imparting to the skin pack backing paper a tensile strength index sufficient to withstand the shrinkage force of the packaging film, thereby suppressing curling of the backing paper during skin pack packaging. In addition, improving the tensile strength index of the paper substrate means, in other words, increasing the number of bonding points between fibers and strengthening the bonding strength between fibers. Therefore, by making the tensile strength index of the skin pack liner equal to or greater than a predetermined value, it is thought that it will also be possible to prevent the outer fibrils from falling off the paper substrate.

[0025] (The geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the skin pack mount) The geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the skin pack mount ((specific tensile strength in the longitudinal direction × specific tensile strength in the transverse direction) １／２ (hereinafter, sometimes referred to as the "geometric mean of specific tensile strength") is usually 37.0 N·m / g or more, preferably 38.0 N·m / g or more, more preferably 40.0 N·m / g or more, even more preferably 41.0 N·m / g or more, even more preferably 42.0 N·m / g or more, and particularly preferably 45.0 N·m / g or more. By setting the geometric mean of the specific tensile strength of the skin pack liner to be equal to or greater than the above lower limit, it is possible to suppress the generation of paper dust from the liner and the curling of the liner during skin pack packaging. Note that the "longitudinal specific tensile strength" is the value obtained by dividing the longitudinal tensile strength by the basis weight, and the "transverse specific tensile strength" is the value obtained by dividing the transverse tensile strength by the basis weight.

[0026] Furthermore, the geometric mean of the specific tensile strength of the skin pack mount is typically 56.0 N·m / g or less, preferably 53.0 N·m / g or less, more preferably 52.0 N·m / g or less, even more preferably 51.0 N·m / g or less, even more preferably 50.0 N·m / g or less, and particularly preferably 48.0 N·m / g or less. By setting the geometric mean of the specific tensile strength of the skin pack mount to the above upper limit or less, the cushioning properties of the skin pack mount are improved, making it easier to absorb impact, thereby effectively suppressing the occurrence of breakage due to drop impact. When the skin pack package is stored, displayed, etc., in a state where it is placed on an inclined surface or hung, there is an increased risk that the skin pack package will fall during operation, and if the skin pack package falls, the skin pack mount may break due to the drop impact. Therefore, in order to store, display, etc., in a state where it is placed on an inclined surface or hung, the skin pack package is required to have a property that is less likely to break due to drop impact. Therefore, it is even more preferable to set the geometric mean of the specific tensile strength of the skin pack backing paper to be equal to or less than the above upper limit, so that the skin pack packaging can be suitable not only for storage, display, etc. when placed on an inclined surface, but also when hung.

[0027] From the above, the ranges of the specific tensile strength of the skin pack mount include 37.0 to 56.0 N·m / g, 38.0 to 53.0 N·m / g, 40.0 to 52.0 N·m / g, 41.0 to 51.0 N·m / g, 42.0 to 50.0 N·m / g, and 45.0 to 48.0 N·m / g.

[0028] In this disclosure, "crease" of a skin pack mount means that a visually noticeable crease is formed in the skin pack mount due to the impact of the drop. Therefore, whether or not a crease is formed in the mount is determined by visual observation, as shown in the examples described below.

[0029] The method for adjusting the tensile strength index of the skin pack liner is not particularly limited, but a preferred example is a method in which a predetermined amount of a paper strength enhancer is added to the paper base material. The paper strength enhancer increases the number of bonding points between fibers, thereby increasing the tensile strength index of the paper base material. Alternatively, the tensile strength index of the paper base material can be adjusted by adding a predetermined amount of softwood kraft pulp (NKP) to the pulp that makes up the paper base material. Softwood kraft pulp (NKP) has long fibers and has the effect of increasing the tensile strength index of the paper base material. By adjusting the tensile strength index of the paper base material using these methods, the tensile strength index of the skin pack liner can be adjusted.

[0030] The longitudinal and transverse tensile strength indexes of the skin pack liner are measured using a horizontal tensile tester ("CODE SE-06" manufactured by L&W) in accordance with JIS P 8113:2006 ("Paper and paperboard -- Test methods for tensile properties -- Part 2: Constant rate of extension method", published December 20, 2006). The geometric mean of the tensile strength index of the skin pack liner is calculated from the measured longitudinal and transverse tensile strength indexes according to the above formula.

[0031] (Thickness of Skin Pack Mounting Sheet) The thickness of the skin pack mounting sheet is not particularly limited, but is preferably 450 μm or more, more preferably 500 μm or more, even more preferably 550 μm or more, still more preferably 600 μm or more, and is preferably 800 μm or less, more preferably 750 μm or less, even more preferably 720 μm or less, and still more preferably 700 μm or less. That is, the thickness of the skin pack can range from 450 to 800 μm, 500 to 750 μm, 550 to 720 μm, and 600 to 700 μm.

[0032] By making the thickness of the skin pack mount at or above the lower limit, cushioning properties are improved and it becomes easier to absorb the impact of a fall, so that the occurrence of breakage due to the impact of a fall can be more effectively suppressed. On the other hand, by making the thickness of the skin pack mount at or below the upper limit, the occurrence of breakage due to the impact of a fall can be suppressed.

[0033] The thickness of the skin pack liner is measured in accordance with JIS P 8118:2014 ("Paper and paperboard -- Test methods for thickness, density and specific volume," published November 20, 2014). The arithmetic mean value of the thicknesses of 10 samples is used as the thickness of the skin pack liner. If the skin pack liner has layers other than paper, such as an adhesive layer and a thermoplastic resin layer, as described below, the thickness of each layer is measured from an observation image of the cross section of the skin pack liner using an electron microscope (SEM), and the thickness of the skin pack liner is calculated from the measurement results. In other words, if the skin pack liner has layers other than paper, such as an adhesive layer and a thermoplastic resin layer, as described below, the thickness of the skin pack liner is the thickness including those layers.

[0034] (Basis Weight of Skin Pack Mounting Sheet) The basis weight of the skin pack mounting sheet is not particularly limited, but is preferably 450 g / m ２ More preferably, 480 g / m ２ More preferably, 500 g / m ２ or more, and even more preferably 550 g / m ２ and preferably 650 g / m ２ or less, more preferably 620 g / m ２ More preferably 600 g / m or less ２ or less, and even more preferably 600 g / m ２ That is, the basis weight range of the skin pack mount is 450 to 650 g / m ２ , 480-620g / m ２ , 500-600g / m ２ , and 550 to 600 g / m ２ By setting the basis weight of the skin pack mount within the above range, it is possible to prevent the skin pack mount from being broken due to the impact of being dropped.

[0035] The basis weight of the skin pack liner is measured in accordance with JIS P 8124:2011 ("Paper and paperboard -- Method for measuring basis weight," published March 22, 2011).

[0036] (Density of Skin Pack Mounting Sheet) The density of the skin pack mounting sheet is not particularly limited, but is preferably 0.650 g / cm ３More preferably, 0.700 g / cm ３ More preferably, 0.800 / cm ３ or more, and preferably 1.000 g / cm ３ or less, more preferably 0.950 g / cm ３ More preferably, 0.920 g / cm ３ That is, the density range of the skin pack mount is 0.650 to 1.000 g / cm ３ , 0.700~0.950g / cm ３ , and 0.800 to 0.920 g / cm ３ By setting the density of the skin pack mount within the above range, it is possible to effectively prevent breakage due to the impact of dropping.

[0037] The density of the skin pack mount is calculated by dividing the basis weight measured by the above method by the thickness.

[0038] 1-1. Paper Base Material (Pulp) The pulp constituting the paper base material is not particularly limited as long as its fibrillation degree is within a specific range. The fibrillation degree of the pulp in the paper base material is usually 1.0% or less, and from the viewpoint of further suppressing paper dust generation and increasing the surface roughness of the surface in contact with the coating layer, it is preferably 0.7% or less, more preferably 0.5% or less, even more preferably 0.4% or less, even more preferably 0.3% or less, and particularly preferably 0.2% or less. The lower limit of the fibrillation degree of the pulp in the paper base material is not particularly limited, but is preferably 0.2% or more. That is, the range of the fibrillation degree of the pulp in the paper base material can be 0.2 to 1.0%, 0.2 to 0.7%, 0.2 to 0.5%, 0.2 to 0.4%, or 0.2 to 0.3%.

[0039] The fibrillation degree of the pulp can be adjusted within the above range by adjusting the degree of beating. By reducing the beating, fibrillation can be suppressed, resulting in a pulp with a low fibrillation degree. More specifically, to achieve the above fibrillation degree, the pulp slurry used to prepare the paper base is beaten so that the Canadian Standard Freeness (CSF) is preferably 400 mL or more, more preferably 450 mL or more, even more preferably 500 mL or more, even more preferably 550 mL or more, and particularly preferably 600 mL or more. The upper limit of the CSF of the pulp slurry used to prepare the paper layer is not particularly limited, but is preferably 700 mL or less, more preferably 650 mL. That is, the CSF range of the pulp slurry to achieve the above fibrillation degree can be 400 to 700 mL, 450 to 700 mL, 500 to 650 mL, 550 to 650 mL, or 600 to 650 mL.

[0040] The type of pulp constituting the paper base material is not particularly limited as long as it is a commonly used type, but plant-derived pulp is preferred, and wood pulp is more preferred.

[0041] Specific examples of the paper substrate or the paper layer described below include kraft paper, fine paper, (white) paperboard, paper container base paper, milk carton base paper, cup base paper, liner paper, coated paper, one-side glazed paper, glassine paper, and graphene paper. Among these, paper layer A and paper layer B are preferably selected from the group consisting of kraft paper, fine paper, (white) paperboard, paper container base paper, cup base paper, and one-side glazed paper, and from the standpoint of rigidity and strength, among (white) paperboard, it is more preferable that they be selected from the group consisting of high-quality paperboard, special paperboard, cup base paper, and kraft paper. Examples of kraft paper include bleached kraft paper, unbleached kraft paper, and one-side glazed bleached kraft paper. Of these, the kraft paper is preferably selected from the group consisting of bleached kraft paper and one-side glazed bleached kraft paper from the standpoint of printability and hygiene.

[0042] As mentioned above, the pulp constituting the paper base material is preferably wood pulp, and more preferably kraft pulp. Kraft pulp is classified into hardwood kraft pulp (LKP) and softwood kraft pulp (NKP) based on the difference in raw materials. Hardwood kraft pulp (LKP) is preferably bleached hardwood kraft pulp (LBKP), and softwood kraft pulp (NKP) is preferably bleached softwood kraft pulp (NBKP). Furthermore, based on the difference in processing state, bleached kraft pulp (BKP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP) are listed, and bleached kraft pulp (BKP) is preferred from the viewpoint of printability.

[0043] Among these, the pulp is preferably one or more selected from the group consisting of hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), more preferably a mixture of hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), and even more preferably a mixture of hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP). In this mixture, the mass ratio of hardwood kraft pulp (LKP) to softwood kraft pulp (NKP) (LKP / NKP) is not particularly limited as long as it is a ratio used in general paper, and is preferably 1 / 99 to 99 / 1, more preferably 30 / 70 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0044] When the pulp is made of hardwood kraft pulp (LKP) and / or softwood kraft pulp (NKP), the content of hardwood kraft pulp (LKP) relative to the total amount of pulp is usually 0% by mass or more, preferably 1% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is usually 100% by mass or less, preferably 99% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. That is, the content of softwood kraft pulp (NKP) relative to the total amount of pulp can range from 0 to 100% by mass, 1 to 99% by mass, 30 to 70% by mass, and 40 to 60% by mass.

[0045] Furthermore, when the pulp is made of hardwood kraft pulp (LKP) and / or softwood kraft pulp (NKP), the content of softwood kraft pulp (NKP) relative to the total amount of pulp is usually 0 to 100% by mass or more, and from the viewpoint of keeping the specific tensile strength of the paper base within a predetermined range, it is preferably 1% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and is preferably 99% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. That is, the range of the content of hardwood kraft pulp (LKP) relative to the total amount of pulp can be 0 to 100% by mass, 1 to 99% by mass, 30 to 70% by mass, or 40 to 60% by mass.

[0046] (Paper Strength Reinforcing Agent) The paper strength reinforcing agent in the paper base material is a component that increases the number of bonding points between fibers and improves the tensile strength index. Therefore, the tensile strength index of the skin pack liner can be adjusted by adjusting the content of the paper strength reinforcing agent in the paper base material. The paper strength reinforcing agent may be contained in one of the paper layers that make up the paper base material, or in two or more paper layers. Furthermore, as described below, the paper strength reinforcing agent may be applied between each layer during multi-layer papermaking and then combined to be contained between each layer of paper.

[0047] Examples of the paper strength agent in the paper base material include starch, cationized starch, polyacrylamide, and polyamidoaminoepichlorohydrin, and preferably one or more selected from the group consisting of starch, cationized starch, and polyacrylamide.

[0048] The content of the paper strength agent in the paper base material varies depending on the type of paper strength agent and the desired specific tensile strength, but is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.40% by mass or more, even more preferably 0.80% by mass or more, and particularly preferably 1.00% by mass or more, relative to the total amount of the paper base material, and is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, even more preferably 3.00% by mass or less, even more preferably 2.00% by mass or less, and particularly preferably 1.80% by mass or less. In other words, the content range of the paper strength agent in the paper base material can be 0.05 to 5.00% by mass, 0.10 to 4.00% by mass, 0.40 to 3.00% by mass, 0.80 to 2.00% by mass, or 1.00 to 1.80% by mass.

[0049] The content of the paper strength enhancer in the paper substrate of the skin pack liner is measured by mass spectrometry using a pyrolysis GC / MS decomposition device (e.g., a device manufactured by Agilent Technologies, Inc.) for a sample punched out from the entire paper substrate layer (100 μg). When measuring the content of the paper strength enhancer in the paper substrate from the skin pack liner, the thermoplastic resin layer is removed prior to mass spectrometry using the following procedure. First, the skin pack liner is placed in a beaker containing xylene heated to 100°C and left to stand in the xylene for 30 minutes to dissolve the thermoplastic resin. Next, any thermoplastic resin remaining on the surface of the paper substrate is wiped off with a rag. If any thermoplastic resin remains, the paper substrate is again immersed in xylene and the process is repeated until the thermoplastic resin is completely removed.

[0050] (Layer structure) The layer structure of the paper base material is not particularly limited as long as the geometric mean of the longitudinal specific tensile strength and the transverse specific tensile strength of the mount can be within the above range. The paper base material may be a slip sheet containing two or more paper layers, or a monolithic paper consisting of one paper layer, but in terms of ease of controlling the specific tensile strength of the skin pack mount, a slip sheet having a multilayer structure, a monolithic paper consisting of paper layers having a multilayer structure obtained by multilayer papermaking, or a slip sheet containing paper layers having a multilayer structure obtained by multilayer papermaking.

[0051] When the paper base material is a slip sheet, there are no particular limitations on the number of paper layers included in the slip sheet, the lamination method of each paper layer, the physical properties of each paper layer, etc. The paper base material preferably has a paper layer A, an adhesive layer, and a paper layer B in this order. A slip sheet having a paper layer A, an adhesive layer, and a paper layer B in this order may be a slip sheet consisting of only the paper layer A, the adhesive layer, and the paper layer B, or may be a slip sheet in which another paper layer is laminated via an adhesive layer. In this case, the same paper layer as the paper layer A may be used as the paper layer B. Furthermore, the same paper layer as the paper layer A or the paper layer B may be used as the other paper layer.

[0052] When the paper base material is an interleaf paper, the paper base material is preferably a laminate having, in order from the surface in contact with the thermoplastic resin layer, a paper layer A, an adhesive layer, and a paper layer B. The paper base material may further have other paper layers as long as the effects of the present disclosure are not impaired. The constituent materials and layer configurations of the paper layer A and the paper layer B (hereinafter sometimes simply referred to as "paper layers") are not particularly limited.

[0053] The paper layer may be a single-layer paper layer made by single-layer papermaking, or a multi-layer paper layer made by multi-layer papermaking. From the viewpoint of easily controlling the tensile strength index and from the viewpoint of freely adjusting the raw material composition, basis weight, and papermaking conditions of each layer, the paper layer preferably has a multi-layer structure. When the paper layer has a multi-layer structure, the number of layers constituting the paper layer is usually 2 to 10, preferably 3 to 9, more preferably 4 to 8, and even more preferably 4 to 6.

[0054] The Oken smoothness (JIS P 8155:2010) of the paper layer is preferably 5 seconds or more, more preferably 10 to 1,000 seconds. From the viewpoint of printability, the 75° gloss of the paper layer is preferably 5% or more, more preferably 10 to 70%.

[0055] The basis weight, thickness, and density of the paper layer are preferably within the ranges that allow the basis weight, thickness, and density of the skin pack mount to be adjusted within the above-mentioned ranges, and the specific values ​​are as follows:

[0056] The basis weight of the paper layer A is preferably 300 to 1,000 g / m ２ , more preferably 350 to 800 g / m ２ , more preferably 400 to 600 g / m２ The thickness of the paper layer A is preferably 300 to 1,000 μm, more preferably 400 to 800 μm, and even more preferably 450 to 600 μm. The density of the paper layer A is preferably 0.50 to 1.20 g / cm ３ , more preferably 0.70 to 1.00 g / cm ３ is.

[0057] The basis weight of the paper layer B is preferably 40 to 400 g / m ２ , more preferably 50 to 300 g / m ２ , more preferably 60 to 150 g / m ２ The thickness of the paper layer B is preferably 50 to 500 μm, more preferably 70 to 300 μm, and even more preferably 90 to 200 μm. The density of the paper layer B is preferably 0.50 to 1.20 g / cm ３ , more preferably 0.60 to 1.00 g / cm ３ is.

[0058] The basis weight, density, and thickness of the paper layer are measured by the same methods as those for the basis weight, density, and thickness of the skin pack liner, respectively.

[0059] Furthermore, it is preferable that the basis weight of paper layer A and the basis weight of paper layer B satisfy the relationship of basis weight of paper layer A ≥ basis weight of paper layer B. Because paper layer A is in contact with the thermoplastic resin layer, it is less likely to absorb and release moisture than paper layer B. Therefore, by making the basis weight of paper layer A equal to or greater than the basis weight of paper layer B, the paper base material is less susceptible to the effects of moisture, which can suppress curling.

[0060] When the paper layer is a single sheet, the above-mentioned paper layer A is preferably used as the single sheet.

[0061] (Adhesive Layer) The adhesive layer that bonds the paper layer A and the paper layer B may be a layer made of a material that has adhesive properties, but preferably contains a thermoplastic resin. By using a thermoplastic resin, an interleaf paper can be easily obtained by coating at least one paper layer with a heat-melted adhesive layer and then laminating the other paper layer.

[0062] The thermoplastic resin preferably contains one or more selected from the group consisting of polyolefin-based resins, polyester-based resins, polylactic acid, styrene-based resins, and acrylic-based resins, and more preferably contains a polyolefin-based resin.

[0063] Examples of polyolefin resins include polyethylene (such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE)), polypropylene (PP), and polymethylpentene. Among these, from the viewpoints of extrusion lamination properties and ease of application to a paper layer, one or more selected from the group consisting of LDPE and MDPE are more preferred, and MDPE is even more preferred.

[0064] Examples of polyester resins include polyethylene terephthalate and polybutylene terephthalate.

[0065] Examples of styrene-based resins include polystyrene, acrylonitrile styrene, and acrylonitrile butadiene styrene.

[0066] Examples of the acrylic resin include acrylic acid ester polymers.

[0067] The following adhesives may be used for the adhesive layer. The adhesive is not particularly limited, and may be a water-based adhesive, a solvent-based adhesive, a UV-based adhesive, or the like. Among these, the adhesive used for the adhesive layer is preferably a water-based adhesive. The water-based adhesive is preferably one or more selected from the group consisting of an acrylic adhesive, a polyurethane adhesive, and an isocyanate adhesive, and an acrylic adhesive is more preferred in terms of ease of control of adhesive strength and excellent heat resistance.

[0068] The mass per unit area of ​​the adhesive layer (in terms of solid content) is not particularly limited, but is preferably 1.0 to 50.0 g / m ２ , more preferably 1.0 to 20.0 g / m ２ When forming the adhesive layer, it is preferable to coat the adhesive on the paper layer A and / or the paper layer B so that the solid content is in this amount.

[0069] The adhesive layer may be formed as a single layer of a single resin, a single layer of a mixture of multiple resins, or multiple layers of the same or different resins. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 5 to 50 μm.

[0070] 1-2. Coating layer The skin pack liner has a resin-containing coating layer. The coating layer is adjacent to the surface of the paper base opposite to the surface that comes into contact with the thermoplastic resin layer, and has the effect of suppressing the generation of paper dust from the liner.

[0071] In the present disclosure, the term "coating layer" refers to a layer formed by applying a coating liquid. The term "coating" as used herein includes printing methods such as gravure printing, offset printing, flexographic printing, and inkjet printing.

[0072] The surface roughness of the coating layer on the side opposite the paper substrate is typically 1.50 μm or more, preferably 2.00 μm or more, more preferably 2.50 μm or more, even more preferably 3.00 μm or more, and even more preferably 3.50 μm or more to ensure the non-slip properties of the skin pack liner. The surface roughness of the coating layer on the side opposite the paper substrate is typically 4.20 μm or less, preferably 4.00 μm or less, and more preferably 3.80 μm or less to more effectively suppress the generation of paper dust from the liner. Examples of surface roughness ranges for the coating layer on the side opposite the paper substrate include 1.50 to 4.20 μm, 2.00 to 4.00 μm, 2.50 to 4.00 μm, 3.00 to 3.80 μm, and 3.50 to 3.80 μm.

[0073] To measure the surface roughness of the coating layer on the side opposite the paper substrate, first, a 3D shape measuring machine (Keyence Corporation "VR3200") is used to photograph the backside of the skin pack mount at a magnification of 12x. Next, the entire captured image is used as the reference surface, and analysis software (for example, Keyence Corporation "VR3000") is used to remove waviness with wavelengths of 5 mm or more. The arithmetic mean height Sa is measured in accordance with ISO 25178-2:2021 ("Geometric Product Specifications (GPS) - Surface Texture - Part 2: Terms, Definitions and Surface Texture Parameters", published April 2012), and this is used as the surface roughness of the coating layer on the side opposite the paper substrate.

[0074] The resin contained in the coating layer is not particularly limited as long as the surface roughness of the surface of the coating layer opposite the paper substrate falls within the above-mentioned range, but preferably contains one or more resins selected from the group consisting of water-soluble resins and water-suspendable resins. Examples of water-soluble resins include oxidized starch, cationized starch, polyvinyl alcohol, and polyacrylamide. Of these, the water-soluble resin preferably contains one or more resins selected from the group consisting of oxidized starch and cationized starch, and more preferably contains oxidized starch, in order to more effectively suppress the generation of paper dust from the backing paper. Examples of water-suspendable resins include starch, polyvinylidene chloride resin, and polyurethane. Of these, the water-suspendable resin preferably contains starch in order to more effectively suppress the generation of paper dust from the backing paper.

[0075] The surface roughness of the coating layer on the side opposite the paper substrate can be adjusted by the surface roughness of the paper substrate's surface in contact with the coating layer and the mass per unit area of ​​the resin in the coating layer (solid content equivalent; hereinafter, sometimes referred to as "resin coating amount"). As mentioned above, the surface roughness of the paper substrate's surface in contact with the coating layer can be adjusted by the degree of fibrillation of the pulp that constitutes the paper layer having that surface. Furthermore, the surface roughness of the coating layer on the side opposite the paper substrate decreases as the resin coating amount increases. The resin coating amount is not particularly limited as long as the surface roughness of the coating layer on the side opposite the paper substrate is kept within the above range, but is preferably 0.10 g / m in order to more effectively suppress the generation of paper dust from the backing paper. ２ More preferably, 0.30 g / m ２More preferably, 0.40 g / m ２ or more, and even more preferably 0.50 g / m ２ More preferably, 1.00 g / m ２ The amount of resin coating is preferably 1.90 g / m to ensure a surface roughness that makes the mount slippery. ２ or less, more preferably 1.80 g / m ２ More preferably, 1.60 g / m or less ２ or less, and even more preferably 1.50 g / m ２ That is, the range of the resin coating amount is 0.10 to 1.90 g / m ２ ,0.30~1.80g / m ２ ,0.40~1.60g / m ２ ,0.50~1.50g / m ２ , and 1.00 to 1.50 g / m ２ The above ranges can be mentioned.

[0076] The resin coating weight is measured by the following method. First, the type of resin is identified by surface analysis of the skin pack liner. The method for identifying the type of resin is not particularly limited, but for example, if the resin is starch, a method utilizing the iodine / starch reaction can be used. Next, the thermoplastic resin layer and paper substrate are removed using a grinding device (e.g., a device manufactured by Sagawa Corporation; grinding wheel dimensions: φ50.8 × 12.7 mm) so that a portion of the skin pack liner from the coating layer surface to a depth of 20 μm remains. The resin content is then measured using the piece of paper with the coating layer remaining after grinding. The method for measuring the resin content is not particularly limited, and any known method can be used. For example, if the resin is starch, the resin content can be measured using a biosensor method. More specifically, the amount of starch can be calculated by treating the coated paper pieces with an amylase solution containing glucoamylase, filtering the treated solution through a filter (e.g., "Ekicrodisc 13" manufactured by Nippon Pall Corporation), and then measuring the starch concentration in the resulting filtrate with a biosensor (e.g., "BF-2" manufactured by Oji Scientific Instruments Co., Ltd.).

[0077] In addition, when the paper strength agent and the resin in the coating layer are the same type of resin, for example, when both the paper strength agent and the resin in the coating layer are starch-based resins, the resin coating amount is measured by the following method. First, if the paper substrate is an interleaf paper, the skin pack liner is ground using a grinding device so that the coating layer and the paper layer adjacent to the coating layer remain. If the paper substrate is a monolithic paper, the skin pack liner is ground using a grinding device so that the coating layer and the monolithic paper remain. Then, the amount of starch-based resin contained in the paper piece with the coating layer remaining after grinding is measured. Next, the skin pack liner is ground using a grinding device so that a portion from the surface of the coating layer of the skin pack liner to a depth of 40 μm to 70 μm remains. Then, the amount of starch-based resin contained in the paper piece remaining after grinding is measured. At this time, a substantially constant concentration of starch-based resin per pulp is detected near the center of the paper piece. This starch-based resin is a starch-based resin that has been added to a paper layer or a single sheet as a paper strength enhancer, and it can be said that this concentration of starch-based resin is uniformly distributed throughout the entire paper layer or single sheet. Utilizing this, the amount of starch-based resin that has been added to a paper layer or a single sheet as a paper strength enhancer in a coated piece of paper is calculated. The resin coating amount is calculated by subtracting the "amount of starch-based resin that has been added to a paper layer or a single sheet as a paper strength enhancer in a coated piece of paper" from the "amount of starch-based resin contained in the coated piece of paper."

[0078] The coating layer may contain components other than resin, such as titanium oxide, kaolin, and calcium carbonate, as long as the effects of the present disclosure are not impaired.

[0079] When the coating layer contains titanium oxide, the coating layer also serves as the laser printing layer described below. When the coating layer contains titanium oxide, the content of titanium oxide in the coating layer is the same as the content of titanium oxide in the laser printing layer described below, and the preferred embodiments thereof are also the same.

[0080] 1-3. Thermoplastic Resin Layer The skin pack liner has a thermoplastic resin layer on one side of the paper base material. The thermoplastic resin layer protects the surface of the skin pack liner from the contents, such as food, and protects the contents from external stimuli, such as oxygen. Furthermore, for example, when the contents are sandwiched between the skin pack liner and a resin film, the thermoplastic resin layer serves to adhere to the resin film.

[0081] The thermoplastic resin layer may be a single layer of a thermoplastic resin or a laminate containing a thermoplastic resin, but is preferably a laminate containing a barrier layer, and particularly preferably a laminate having a barrier layer between thermoplastic resin layers, such as "thermoplastic resin layer / barrier layer / thermoplastic resin layer." The thermoplastic resin layer may also be a laminate layer.

[0082] When the thermoplastic resin layer is a laminate having a barrier layer, the barrier layer is not particularly limited as long as it is a layer that can barrier oxygen and / or water vapor, and may be a layer with a single layer structure or a layer with a multilayer structure of two or more layers.

[0083] Specifically, the resin forming the barrier layer is preferably one or more selected from the group consisting of polyamide resins, polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymers (EVOH), and polyvinylidene chloride resins, more preferably one or more selected from the group consisting of polyamide resins, polyvinyl alcohol, and ethylene-vinyl alcohol copolymers, and even more preferably an ethylene-vinyl alcohol copolymer. The polyamide resin is preferably an aromatic polyamide, more preferably polyamide MXD6. The barrier layer may further contain one or more other resins, such as biomass resins and biodegradable resins. Alternatively, the barrier layer may be a metal layer.

[0084] The thickness of the barrier layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 3 to 50 μm, and even more preferably 5 to 30 μm.

[0085] The thermoplastic resin used in the thermoplastic resin layer is preferably one that can be laminated to the paper layer. Any known thermoplastic resin may be used as the thermoplastic resin.

[0086] Known thermoplastic resins include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; polyolefin-based resins such as polyvinyl chloride, polyvinylidene chloride, polybutene, polybutadiene, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, and polymethylpentene; polycarbonate; polyurethane; polyamides such as nylon 6; polyacrylonitrile; and poly(meth)acrylate.

[0087] Among these thermoplastic resins, the thermoplastic resin is preferably a polyolefin resin, more preferably one or more selected from the group consisting of polyethylene (PE) and polypropylene (PP), because of its excellent extrusion lamination properties. Furthermore, the PE is preferably one or more selected from the group consisting of low-density polyethylene (LDPE) and medium-density polyethylene (MDPE), because of its excellent extrusion lamination properties.

[0088] The thickness of the entire thermoplastic resin layer is not particularly limited, but is preferably 1 to 200 μm, more preferably 1 to 100 μm, even more preferably 10 to 80 μm, and still more preferably 20 to 50 μm.

[0089] Commercially available resin laminates (laminate films) suitable for use in the thermoplastic resin layer include a PE (polyethylene) / EVOH (ethylene-vinyl alcohol copolymer) / PP (polypropylene) three-layer film (trade name: Diamiron YF1966, film thickness 40 μm) manufactured by Mitsubishi Chemical Corporation, a PP / PVOH (polyvinyl alcohol) / PP three-layer film (trade name: ECO-B, film thickness 20 μm) manufactured by Futamura Chemical Industry Co., Ltd., a NY6 (nylon 6) / EVOH / NY6 three-layer film (trade name: Heptax HP, film thickness 17 μm) manufactured by Gunze Limited, and a NY6 / MXD6 (polyamide MXD6) / NY6 three-layer film (trade name: Embron M, film thickness 15 μm) manufactured by Unitika Limited.

[0090] 1-4. Pressure-sensitive adhesive layer When the surface of the thermoplastic resin layer has adhesive properties, the thermoplastic resin layer may be directly adhered to the surface of the paper substrate, but it is preferable to have a pressure-sensitive adhesive layer between the paper substrate and the thermoplastic resin layer in order to prevent peeling during production, transportation, and display of the skin pack package.

[0091] The adhesive constituting the adhesive layer is not particularly limited, but is preferably a resin-based adhesive suitable for dry lamination and wet lamination. Specifically, the adhesive constituting the adhesive layer can be of a water-based, solvent-based, UV-based, or other type, with water-based adhesives being preferred. Among the water-based adhesives, at least one selected from the group consisting of acrylic adhesives, polyurethane adhesives, and isocyanate adhesives is preferred, with acrylic adhesives being more preferred.

[0092] The mass per unit area of ​​the pressure-sensitive adhesive layer (solid content equivalent) is 1 to 50 g / m ２ is preferable, and more preferably 5 to 20 g / m ２ The pressure-sensitive adhesive layer is preferably formed by coating the pressure-sensitive adhesive on the surface of the paper substrate or the surface of the thermoplastic resin layer so that the mass per unit area of ​​the pressure-sensitive adhesive layer is within the above range. For coating, a coating liquid containing the pressure-sensitive adhesive is preferably used, and a mixed coating liquid in which a curing agent is mixed with the coating liquid containing the pressure-sensitive adhesive is more preferably used.

[0093] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 5 to 100 μm, more preferably 8 to 30 μm, from the viewpoint of moldability.

[0094] 1-5. Other Layers The skin pack mount according to this embodiment may include layers other than those described above, as long as the effects of the present disclosure are not impaired. Examples of other layers include an ink layer made of ink and a laser-printed layer that can be printed by ultraviolet laser printing.

[0095] (Ink Layer) The ink layer is a layer formed by printing. The printing method is not particularly limited, and any method such as offset printing or inkjet printing can be used.

[0096] The ink layer can be provided on the surface of the thermoplastic resin layer opposite to the surface in contact with the paper substrate, between the thermoplastic resin layer and the paper substrate, on the coating layer, etc. Of these, the ink layer is preferably provided between the thermoplastic resin layer and the paper substrate. When the ink layer is disposed between the thermoplastic resin layer and the paper substrate, it is preferable that the ink layer is provided adjacent to the paper substrate, and that the thermoplastic resin layer is provided on the ink layer via an adhesive layer.

[0097] When the ink layer is provided on the coating layer, the ink layer may be provided anywhere on the coating layer, but from the viewpoint of preventing slippage of the skin pack backing, it is preferable that the ink layer be provided as part of the coating layer and in a position that does not come into contact with the ground when the skin pack packaging body is placed on an inclined surface.

[0098] (Laser Printing Layer) The laser printing layer is a printing layer containing titanium oxide. When the laser printing layer is irradiated with an ultraviolet laser, the titanium oxide in the printing layer changes color from white to black, and characters, patterns, etc. are printed. The discoloration of titanium oxide is thought to occur when the ionic valence of titanium oxide contained in the printing layer changes from tetravalent to trivalent, causing oxygen defects.

[0099] The laser printing layer can be provided on the surface of the thermoplastic resin layer opposite to the surface in contact with the paper substrate, between the thermoplastic resin layer and the paper substrate, on the coating layer, etc. Alternatively, the coating layer or the paper substrate may contain titanium oxide, so that the coating layer or the paper substrate also serves as the laser printing layer.

[0100] In addition, when the laser printing layer is provided on the coating layer, in order to ensure that the skin pack backing is non-slip, it is preferable that the laser printing layer is part of the coating layer and is provided in a position that does not come into contact with the ground when the skin pack packaging body is placed on an inclined surface.

[0101] The method for forming the laser printing layer is not particularly limited, and may be a coating method or a lamination method. However, a coating method is preferred because it is easy to provide the laser printing layer only in the desired locations and is easy to manufacture.

[0102] The content of titanium oxide in the laser printing layer is usually 0.1 g / m from the viewpoint of obtaining sufficient printing density. ２ or more, preferably 0.2 g / m ２ More preferably, 0.3 g / m ２ More preferably, 0.4 g / m ２ From the viewpoint of obtaining a print spot with excellent print clarity, suppressing an increase in cost due to the inclusion of more titanium oxide than necessary when the print density reaches a plateau, and suppressing the amount of smoke generated during ultraviolet laser irradiation (during printing), it is preferable that the amount of titanium oxide is 10 g / m ２ or less, more preferably 7.5 g / m ２ More preferably, 5 g / m or less ２ or less, and even more preferably 3.5 g / m ２ The following is the result.

[0103] If smoke occurs during irradiation with an ultraviolet laser, which is thought to be due to the scattering of titanium oxide, there is a risk that the discolored titanium oxide will fall off from the laser-printed layer, and if the discolored titanium oxide falls off from the laser-printed layer, the print clarity will tend to decrease. However, by setting the content of titanium oxide in the laser-printed layer to the above-mentioned upper limit or less, such smoke generation tends to be suppressed.

[0104] Furthermore, when a laser printing layer is provided between the thermoplastic resin layer and the paper substrate, the thermoplastic resin layer functions as a protective layer, which suppresses the generation of smoke associated with ultraviolet laser irradiation and also suppresses the detachment of titanium oxide associated with the generation of smoke, and this tends to result in a printed image with high print density and excellent print clarity for each point, which is even more effective.

[0105] 1-6. Manufacturing Method of Skin Pack Mount The method for manufacturing the skin pack mount according to this embodiment is not particularly limited, and any method such as a known method or a method based thereon can be used. An example of the manufacturing method is shown below.

[0106] (Preparation of Paper Base Material) First, a paper layer having a single layer or multilayer structure is obtained by single-layer or multi-layer papermaking of a paper material containing pulp. The obtained paper layer can be used as a paper base material as a single sheet. Furthermore, the paper layers can also be used as a paper base material as an interleaving paper by bonding them together with an adhesive layer as needed.

[0107] When preparing the paper stock, internal additives may be added to the pulp. Examples of internal additives include sizing agents, fillers, paper strength agents, retention aids, pH adjusters, drainage aids, water resistance agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments. Of these, the internal additive is preferably one or more selected from the group consisting of rosin-based sizing agents, paper strength agents, and aluminum sulfate.

[0108] The amount of rosin-based sizing agent added to 100 parts by mass of pulp when preparing paper stock is preferably 0.05 to 0.50 parts by mass.

[0109] The amount of paper strength agent added per 100 parts by mass of pulp when preparing the paper stock is not particularly limited, as long as the content of the paper strength agent relative to the total amount of the paper base material is within the above range, but is preferably 0.05 to 5.00 parts by mass, more preferably 0.10 to 4.00 parts by mass, even more preferably 0.40 to 3.00 parts by mass, still more preferably 0.80 to 2.00 parts by mass, and particularly preferably 1.00 to 1.80 parts by mass.

[0110] The amount of aluminum sulfate added to 100 parts by mass of pulp when preparing the paper stock is preferably 0.05 to 0.50 parts by mass.

[0111] Any wet paper machine can be appropriately selected and used for making the paper stock, and more specifically, examples of the paper machine include a twin-wire paper machine, a Fourdrinier paper machine, a gap former paper machine, a cylinder paper machine, and a short-wire paper machine.

[0112] In papermaking from stock, for example, the stock is cast onto a wire or the like, dewatered to obtain a wet paper, and if necessary, multiple wet papers are stacked, and this single-layer or multi-layer wet paper is pressed and dried. In this case, if multiple wet papers are not stacked, a single-layer base paper is obtained, and if multiple wet papers are stacked, a multi-layer base paper is obtained. When a multi-layer base paper is obtained, the above-mentioned paper strength agent may be applied between each layer during papermaking, and the layers may be stacked together in order to increase the interlayer strength.

[0113] When applying a paper strength agent, the mass of the paper strength agent per unit area (solid content equivalent) is not particularly limited as long as the content of the paper strength agent relative to the total amount of the paper base material is within the above range, but is preferably 0.10 to 5.00 g / m ２ , more preferably 0.40 to 2.00 g / m ２ is.

[0114] The paper produced by the paper machine is preferably transported on a felt and dried in a dryer. A multi-stage cylinder dryer may be used as a pre-dryer before the paper is dried in the dryer.

[0115] The resulting paper may be subjected to a surface treatment using a calendar to make the thickness and profile uniform. Any suitable calendaring machine can be selected and used for the calendaring treatment.

[0116] When the paper substrate is a single sheet, the obtained paper layer can be used as the paper substrate, and a coating layer and a thermoplastic resin layer can be provided to obtain a skin pack liner.

[0117] When the paper base material is a slip sheet, the method for producing the skin pack backing after obtaining paper layer A and paper layer B is not particularly limited, and examples include Method 1, in which paper layer A and paper layer B are bonded together via an adhesive layer to obtain a paper base material, and then a coating layer and a thermoplastic resin layer are provided; Method 2, in which a coating layer is provided on paper layer B, an adhesive layer and paper layer A are provided on the surface of paper layer B opposite to the surface that contacts the coating layer, and a thermoplastic resin layer is further provided on paper layer A; and Method 3, in which a thermoplastic resin layer is provided on paper layer A, an adhesive layer and paper layer B are provided on the surface of paper layer A opposite to the surface that contacts the thermoplastic resin layer, and a coating layer is further provided on paper layer B.

[0118] Alternatively, an interleaving paper serving as a paper substrate can be obtained by applying an adhesive coating liquid containing an aqueous solution or emulsion in which the resin contained in the adhesive layer is dissolved or dispersed in water to the surface of one of the paper layers, removing some or all of the water as necessary, and laminating the other paper layer to the coated surface. In this case, the adhesive coating liquid can be applied using a coater such as a blade coater, air knife coater, roll coater, bar coater, gravure coater, rod blade coater, lip coater, die coater, or curtain coater. The water is preferably removed by drying with hot air or by drying with infrared radiation, for example.

[0119] If necessary, a printing step of printing on the surface of the paper layer or a printing layer laminating step of providing a printed layer may be performed either before or after the laminating step of each paper layer.

[0120] (Formation of coating layer) The coating layer can be formed by applying a coating liquid in which a resin is dissolved or suspended in a solvent to one side of a paper substrate, and then drying to remove the solvent from the coating liquid.The coating liquid is preferably one in which a resin is dissolved in a solvent, and more preferably one in which a water-soluble resin is dissolved in water, because this makes it easier to adjust the surface roughness of the paper substrate.In addition, the coating liquid can be applied and dried using the same method as that used for applying and drying the adhesive coating liquid described above.

[0121] (Formation of Thermoplastic Resin Layer) The thermoplastic resin layer may be directly adhered to the paper substrate, or may be adhered to the paper substrate via an adhesive layer. In the latter case, it is preferable to apply a coating liquid containing an adhesive to the surface of the paper substrate, and then laminate the thermoplastic resin layer on the surface of the paper substrate via the adhesive layer. In this case, a film may be attached to the paper substrate as the thermoplastic resin layer.

[0122] (Processing) The skin pack mount obtained as described above may be cut to appropriate dimensions, taking into consideration the size and shape of the contents, and suitability for transportation and display. Cutting is preferably performed by punching, from the viewpoint of efficiently obtaining skin pack mounts of the same shape. Punching is preferably performed using a high-speed automatic punching machine, a flat-bed punching machine, or a rotary punching machine, and more preferably a high-speed automatic punching machine. By performing punching using a high-speed automatic punching machine or a flat-bed punching machine, skin pack mounts of shapes such as rectangles, rounded rectangles, and ellipses can be easily and efficiently obtained.

[0123] 2. Skin Pack Package A second embodiment of the present disclosure is a skin pack package including the skin pack mount, a storage item, and a resin film, with the storage item stored between the thermoplastic resin layer of the skin pack mount and the resin film. The skin pack package according to this embodiment is preferably one that hermetically stores the storage item.

[0124] The resin film can be appropriately selected depending on the type and shape of the stored items, but preferably has excellent adhesiveness and is releasable when the stored items are removed, since it must be adhered to the thermoplastic resin layer of the skin pack mount to store the stored items. Therefore, the resin film is preferably made of the thermoplastic resin used in the thermoplastic resin layer described above, and more preferably has a barrier layer when the contents are food, etc. The barrier layer used in the thermoplastic resin layer described above is preferably used as the barrier layer.

[0125] When the skin pack packaging according to this embodiment is to be stored, displayed, etc. by hanging, the skin pack packaging is provided with a hanging part. The hanging part is not particularly limited as long as it enables the skin pack packaging to be hung from a hanging rod, and may be, for example, a through-hole opened in the skin pack packaging so that a hanging rod can be passed through it, a part of the skin pack packaging cut into a hook shape so that it can be hung on a hanging rod, or a hanging device such as a hook and suction cup attached to the skin pack packaging.

[0126] The stored items are not particularly limited, and examples thereof include food, daily necessities, etc. Since the skin pack packaging can hermetically store the stored items, it is suitable for storing foods such as fresh foods such as vegetables, meat, and fresh fish, as well as processed foods thereof.

[0127] The present disclosure will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the present disclosure should not be interpreted as being limited by the specific examples shown below.

[0128] [Preparation of Paper Layer A1] 50 parts by mass of hardwood bleached kraft pulp (LBKP) and 50 parts by mass of softwood bleached kraft pulp (NBKP) were mixed to obtain a pulp slurry with a Canadian Standard Freeness (CSF) of 490 mL. A double-disc refiner was used for beating. To the obtained pulp slurry, 0.80 parts by mass (solids equivalent) of aluminum sulfate (manufactured by Asahi Chemical Industries, Ltd.), 0.1 parts by mass (solids equivalent) of a polyacrylamide-based paper strength agent ("Polystron 1430" manufactured by Arakawa Chemical Industries, Ltd.), and 0.12 parts by mass (solids equivalent) of an internal rosin sizing agent ("Sizepine N-817" manufactured by Arakawa Chemical Industries, Ltd.) were added to prepare a paper stock. Using this paper stock, all five layers (surface layer, undersurface layer, middle layer, undersurface layer, and undersurface layer) were set to the same basis weight, and the set basis weight was 450 g / m ２ The paper was made using a five-layer short wire paper machine to obtain paper layer A1.

[0129] [Preparation of Paper Layer A2] Paper layer A2 was obtained in the same manner as paper layer A1, except that in the preparation of the paper stock, the amount of paper strength agent added was changed to 0.50 parts by mass per 100 parts by mass of pulp (solid content equivalent).

[0130] [Preparation of Paper Layer A3] Paper layer A3 was obtained in the same manner as paper layer A1, except that in the preparation of the paper stock, the amount of paper strength agent added was changed to 1.50 parts by mass per 100 parts by mass of pulp (solid content equivalent).

[0131] [Preparation of Paper Layer A4] Paper layer A4 was obtained in the same manner as paper layer A1, except that in the preparation of the paper stock, the amount of paper strength agent added was changed to 2.00 parts by mass per 100 parts by mass of pulp (solid content equivalent).

[0132] [Preparation of Paper Layer A5] Paper layer A5 was obtained in the same manner as paper layer A1, except that in preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 560 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 parts by mass of pulp (solid content equivalent) was changed to 0.40 parts by mass.

[0133] [Preparation of Paper Layer A6] Paper layer A6 was obtained in the same manner as paper layer A1, except that in preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 620 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 parts by mass of pulp (solid content equivalent) was changed to 0.80 parts by mass.

[0134] [Preparation of Paper Layer A7] Paper layer A7 was obtained in the same manner as paper layer A1, except that in preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 620 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 parts by mass of pulp (solid content equivalent) was changed to 1.80 parts by mass.

[0135] [Preparation of coated paper layer A8] Basis weight: 520 g / m ２ A paper layer was produced in the same manner as Paper Layer A7, except that the amount of paper stock and the press pressure during papermaking were adjusted so that the surface of this paper layer was coated with starch ("GRS-T110" manufactured by Oji Cornstarch Co., Ltd.) adjusted to a 10% by mass aqueous solution in an amount of 0.50 g / m2 in terms of solid content. ２The coated paper layer A8 was obtained by coating with a bar coater so that the coated paper layer A8 had a thickness of 100 μm.

[0136] [Preparation of Paper Layer A9] Paper layer A9 was obtained in the same manner as paper layer A1, except that in the preparation of the paper stock, no paper strength agent was added to the pulp slurry.

[0137] [Preparation of Paper Layer A10] Paper layer A10 was obtained in the same manner as paper layer A1, except that in preparing the pulp slurry, the beating degree was adjusted so that the CSF was 380 mL.

[0138] [Preparation of Paper Layer B1 with Coating Layer] 50 parts by mass of hardwood bleached kraft pulp (LBKP) and 50 parts by mass of softwood bleached kraft pulp (NBKP) were mixed to obtain a pulp slurry with a Canadian Standard Freeness (CSF) of 490 mL. A double-disc refiner was used for beating. A stock was prepared by adding 0.80 parts by mass (solids equivalent) of aluminum sulfate (manufactured by Asahi Chemical Industries, Ltd.), 0.1 parts by mass (solids equivalent) of a polyacrylamide-based paper strength agent ("Polystron 1430" manufactured by Arakawa Chemical Industries, Ltd.), and 0.12 parts by mass (solids equivalent) of an internal rosin sizing agent ("Sizepine N-817" manufactured by Arakawa Chemical Industries, Ltd.) to 100 parts by mass (solids equivalent) of pulp. This stock was used to prepare a paper sheet with a set basis weight of 70 g / m. ２ A 10% by mass aqueous solution of oxidized starch (Oji Cornstarch Co., Ltd.'s "Ace A") was applied to the surface of the paper layer in a coating amount of 0.50 g / m2 in terms of solid content. ２ The coated paper layer B1 was obtained by coating with a bar coater so that the coated paper layer B1 became

[0139] [Preparation of Coated Paper Layer B2] The amount of oxidized starch coated on the surface of the paper substrate was 1.00 g / m2 in terms of solid content. ２ A coated paper layer B2 was obtained in the same manner as for the coated paper layer B1, except for the above change.

[0140] [Preparation of Coated Paper Layer B3] The amount of oxidized starch coated on the surface of the paper substrate was 1.50 g / m2 in terms of solid content. ２ A coated paper layer B3 was obtained in the same manner as for the coated paper layer B1, except for the above change.

[0141] [Preparation of coated paper layer B4] In preparing the paper stock, the amount of paper strength agent added was changed to 0.50 parts by mass per 100 parts by mass of pulp (solid content equivalent), but coated paper layer B4 was obtained in the same manner as coated paper layer B1.

[0142] [Preparation of coated paper layer B5] In preparing the paper stock, the amount of paper strength agent added was changed to 1.50 parts by mass per 100 parts by mass of pulp (solid content equivalent), but coated paper layer B5 was obtained in the same manner as coated paper layer B1.

[0143] [Preparation of coated paper layer B6] Coated paper layer B6 was obtained in the same manner as coated paper layer B1, except that in the preparation of the paper stock, the amount of paper strength agent added was changed to 2.00 parts by mass per 100 parts by mass of pulp (solid content equivalent).

[0144] [Preparation of coated paper layer B7] In preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 560 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 mass parts of pulp (solid content equivalent) was changed to 0.40 mass parts. Coated paper layer B7 was obtained in the same manner as coated paper layer B1.

[0145] [Preparation of coated paper layer B8] In preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 620 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 mass parts of pulp (solid content equivalent) was changed to 0.80 mass parts. Coated paper layer B8 was obtained in the same manner as coated paper layer B1.

[0146] [Preparation of coated paper layer B9] In preparing the pulp slurry, the degree of beating was adjusted so that the CSF was 620 mL, and in preparing the paper stock, the amount of paper strength agent added per 100 mass parts of pulp (solid content equivalent) was changed to 1.80 mass parts. Coated paper layer B9 was obtained in the same manner as coated paper layer B1.

[0147] [Preparation of Paper Layer B10] Paper layer B10 was prepared in the same manner as for coated paper layer B4, except that oxidized starch was not applied to the surface of the paper base material.

[0148] [Preparation of Paper Layer B11] Paper layer B11 was prepared in the same manner as coated paper layer B8, except that oxidized starch was not applied to the surface of the paper base material.

[0149] [Preparation of Coated Paper Layer B12] Coated paper layer B12 was obtained in the same manner as coated paper layer B1, except that no paper strength agent was added to the pulp slurry in preparing the paper stock.

[0150] [Preparation of Coated Paper Layer B13] The amount of oxidized starch coated on the surface of the paper substrate was 2.00 g / m2 in terms of solid content. ２ A coated paper layer B13 was obtained in the same manner as the coated paper layer B1, except for changing the above.

[0151] [Preparation of Coated Paper Layer B14] Coated paper layer B14 was obtained in the same manner as for coated paper layer B1, except that in preparing the pulp slurry, the beating degree was adjusted so that the CSF was 380 mL.

[0152] Example 1 One side of the paper layer A1 was melt-extrusion coated with MDPE ("8010" manufactured by ENEOS NUC Corporation) to a dry film thickness of 20 μm, and the paper layer B1 was laminated to the coated surface to obtain a two-layer paper substrate. Then, a coating liquid prepared by mixing 100 parts by mass of a water-based acrylic adhesive ("EM-575" manufactured by Arakawa Paint Co., Ltd.) and 3 parts by mass of a curing agent ("EM-550K" manufactured by Arakawa Paint Co., Ltd.) was applied to the paper layer A1 to a coating amount of 10 g / m after heat drying. ２ A three-layer film of PE / EVOH / PP ("Diamilon YF1966" manufactured by Mitsubishi Chemical Corporation, thickness 40 μm) was dry-laminated onto the adhesive layer so that the PP layer and the adhesive layer were adjacent to each other, thereby obtaining a mount for a skin pack.

[0153] Examples 2 to 9, Comparative Examples 1 to 5 Skin pack mounts were prepared in the same manner as in Example 1, except that the paper layer was changed to that shown in Table 1.

[0154] Example 10 A coating solution prepared by mixing 100 parts by mass of a water-based acrylic adhesive ("EM-575" manufactured by Arakawa Paint Co., Ltd.) and 3 parts by mass of a curing agent ("EM-550K" manufactured by Arakawa Paint Co., Ltd.) was applied to the surface of the paper layer A8 opposite to the surface coated with starch, and the coating amount after heat drying was 10 g / m ２ A three-layer film of PE / EVOH / PP ("Diamilon YF1966" manufactured by Mitsubishi Chemical Corporation, thickness 40 μm) was dry-laminated onto the adhesive layer so that the PP layer and the adhesive layer were adjacent to each other, thereby obtaining a mount for a skin pack.

[0155] The physical properties of the paper substrate and the skin pack mount were measured and evaluated by the following methods. The results are shown in Tables 1 and 2.

[0156] [Basis Weight] Basis weight was measured using a high-resolution balance (Sartorius Cubis MSU524S manufactured by Sartorius Japan K.K.) in accordance with JIS P 8124:2011 (Paper and paperboard - Method for measuring basis weight, published March 22, 2011).

[0157] [Thickness] Using a digital thickness measuring instrument ("No. 132" manufactured by Toyo Seiki Seisaku-sho, Ltd.), the thickness of 10 samples was measured in accordance with JIS P 8118:2014 ("Paper and paperboard -- Test methods for thickness, density and specific volume", published on November 20, 2014), and the arithmetic mean value was taken as the paper thickness.

[0158] [Surface roughness] The back surface of the skin pack mount was photographed at 12x magnification using a 3D shape measuring machine (Keyence Corporation "VR3200"). The entire area of ​​the obtained image was used as the reference surface, and waviness of wavelengths of 5 mm or more was removed using analysis software (Keyence Corporation "VR3000"). The arithmetic mean height Sa was measured in accordance with ISO 25178-2:2021 ("Geometric Product Specifications (GPS) - Surface Texture - Part 2: Terms, Definitions and Surface Texture Parameters", published April 2012), and this was used as the surface roughness of the coating layer on the side opposite the paper substrate.

[0159] [Tensile specific strength of skin pack liner] Using a horizontal tensile tester ("CODE SE-06" manufactured by L&W), the longitudinal and transverse tensile specific strengths of the skin pack liner were measured in accordance with JIS P 8113:2006 ("Paper and paperboard -- Test methods for tensile properties -- Part 2: Constant rate of extension method", published December 20, 2006), and their geometric mean values ​​were calculated.

[0160] [Degree of pulp fibrillation] The paper base material of the skin pack mount was peeled off by hand and cut into 4 cm square pieces. These pieces were immersed in ion-exchanged water, adjusted to a solids concentration of 2% by mass, and then soaked for 24 hours. Subsequently, a standard disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used to disintegrate the pulp into fibers for 20 minutes. If undisintegrated pulp remained, the disintegrator was again used for 20 minutes to disintegrate the pulp into fibers. The disintegration was performed in accordance with JIS P 8220-2:2012 ("Pulp - Disintegration methods - Part 2: Disintegration of mechanical pulp (20°C)", published April 20, 2012).

[0161] The fibrillation degree of the obtained fiber sample was measured using a fiber length measuring instrument ("New Valmet FS5" manufactured by Valmet Co., Ltd., equipped with a UHD base unit) in accordance with ISO 16065-2:2014 ("Pulp - Determination of fiber length by automated photometric methods - Part 2: Non-polarized method", published on January 15, 2007). At this time, the ratio of the projected portion of small fibers that were fluffy on the fiber surface to the entire projected fibers was calculated according to formula (1) to define the fibrillation degree.

[0162] [Evaluation of suppression of paper dust generation from skin pack liner] Using an automatic flat-bed die-cutter, rectangular pieces of paper measuring 280 mm in length (MD) x 180 mm in width (CD) were die-cut from 100 sheets of skin pack liner (550 mm length x 800 mm width) at a rate of 6,000 sheets / hour. The last 10 skin pack liner sheets die-cut were checked for the presence or absence of paper dust adhering to the thermoplastic resin layer and rated according to the following criteria: AA to B were evaluated as good, and C was evaluated as poor.

[0163] Evaluation criteria AA: 0 skin pack liner sheets with paper powder adhering to the thermoplastic resin layer A: 1 skin pack liner sheet with paper powder adhering to the thermoplastic resin layer B: 2 skin pack liner sheets with paper powder adhering to the thermoplastic resin layer C: 3 or more skin pack liner sheets with paper powder adhering to the thermoplastic resin layer

[0164] [Evaluation of slip resistance of skin pack mount] A 150 g weight (a rectangular shape of 150 mm length × 100 mm width × 10 mm height) was placed in the center of a skin pack mount (a rectangular shape of 280 mm length × 180 mm width), and the skin pack was packaged using a barrier film ("Cryovac" manufactured by Sealed Air) to produce a skin pack package.

[0165] A stainless steel plate (600 mm long x 300 mm wide) was fixed at an angle on a horizontal hard surface, and a barrier film (manufactured by Sealed Air; 550 mm long x 250 mm wide) was attached to the upper surface of the stainless steel plate. At this time, three types of slopes were formed on the stainless steel plate, with an inclination angle of 20 degrees, 23 degrees, or 26 degrees. A skin pack package was gently placed on this slope so that the barrier film and the skin pack mount were in contact, and it was observed whether the skin pack package slid off when released. Based on the angle of the slope at which the skin pack package slid off, it was evaluated according to the following criteria. AA to B were evaluated as good, and C was evaluated as poor.

[0166] Evaluation criteria AA: The skin pack package did not slide down even when placed on a slope with an inclination angle of 26 degrees. A: The skin pack package slid down from a slope with an inclination angle of 26 degrees, but did not slide down from a slope with an inclination angle of 23 degrees. B: The skin pack package slid down from a slope with an inclination angle of 23 degrees, but did not slide down from a slope with an inclination angle of 20 degrees. C: The skin pack package slid down from a slope with an inclination angle of 20 degrees.

[0167] [Evaluation of warpage of skin pack mount during skin pack packaging] A 150 g weight (a rectangular shape of 150 mm length × 100 mm width × 10 mm height) was placed in the center of a skin pack mount (a rectangular shape of 280 mm length × 180 mm width), and skin pack packaging was performed using a barrier film ("Cryovac" manufactured by Sealed Air). The change in the degree of warpage of the skin pack mount before and after skin pack packaging was evaluated using the following method.

[0168] First, the mount was placed flat on a horizontal hard surface, and the lift of each of the four corners of the mount was measured and the average value was calculated. The warpage of the mount before and after skin pack packaging was measured, and the difference was evaluated according to the following criteria. AA to B were evaluated as good, and C was evaluated as poor.

[0169] Evaluation criteria AA: The difference in warp of the skin pack liner before and after skin pack packaging is less than 1 mm. A: The difference in warp of the skin pack liner before and after skin pack packaging is 1 mm or more and less than 3 mm. B: The difference in warp of the skin pack liner before and after skin pack packaging is 3 mm or more and less than 6 mm. C: The difference in warp of the skin pack liner before and after skin pack packaging is 6 mm or more.

[0170] [Evaluation of drop impact resistance of skin pack mount] A 150 g weight (a rectangular shape of 150 mm length × 100 mm width × 10 mm height) was fixed to the center of a skin pack mount (a rectangular shape of 280 mm length × 180 mm width) with cloth gummed tape to prepare an evaluation sample.

[0171] The evaluation sample was placed at a height of 500 mm from the vinyl chloride floor so that the short side would touch the ground when dropped. The evaluation sample was then allowed to fall vertically onto the vinyl chloride floor, and the skin pack mount was visually inspected for the presence or absence of creases. This drop impact test was repeated, and the number of tests until a crease was formed on the evaluation sample was counted. The above procedure was performed on five evaluation samples, and the average number of tests (rounded to one decimal place) until a crease was formed on the skin pack mount was calculated and evaluated according to the following criteria: AA to B were evaluated as good, and C was evaluated as poor.

[0172] Evaluation criteria AA: The average number of tests before the skin pack mount is folded is 5.0 or more. A: The average number of tests before the skin pack mount is folded is 3.0 or more but less than 5.0. B: The average number of tests before the skin pack mount is folded is 2.0 or more but less than 3.0. C: The average number of tests before the skin pack mount is folded is less than 2.0.

[0173]

[0174]

[0175] REFERENCE SIGNS LIST 10: Skin pack backing 11: Thermoplastic resin layer 13: Paper substrate 15: Coating layer 20: Fiber 21: Fibril 23: Outer fibril

Claims

1. A skin pack liner having, in this order, a thermoplastic resin layer, a paper base material, and a coating layer, wherein the degree of fibrillation of the pulp in the paper base material is 1.0% or less, the coating layer contains a resin, the surface roughness of the coating layer on the side opposite to the paper base material is 1.50 to 4.20 μm, and the geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the skin pack liner is 37.0 N·m / g or more.

2. The mass per unit area of the resin in the coating layer is 0.10 to 1.90 g / m ２ The skin pack mount according to claim 1, 3. The skin pack liner according to claim 1, wherein the resin contained in the coating layer comprises at least one resin selected from the group consisting of water-soluble resins and water-dispersible resins.

4. The skin pack mount according to claim 3, wherein the water-soluble resin comprises one or more selected from the group consisting of oxidized starch, cationized starch, polyvinyl alcohol, and polyacrylamide.

5. A skin pack liner according to claim 1, wherein the geometric mean of the specific tensile strength in the longitudinal direction and the specific tensile strength in the transverse direction of the skin pack liner is 53.0 N·m / g or less.

6. The skin pack liner according to claim 1, wherein the paper base material contains a paper strength agent in an amount of 0.10% by mass or more based on the total amount of the paper base material.

7. The skin pack liner according to claim 1, wherein the paper substrate is a laminated paper having a paper layer A, an adhesive layer and a paper layer B in this order, or a single paper.

8. A skin pack packaging body comprising the skin pack liner according to any one of claims 1 to 7, a contained item, and a resin film, wherein the contained item is contained between the thermoplastic resin layer of the skin pack liner and the resin film.

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