Laminate paper

Abstract

To provide laminate paper that enables separation, in hot water and within a short time, of a paper base material and a thermoplastic resin layer containing a polyolefin resin, and allows suppression of an amount of residue containing the paper base material remaining in the thermoplastic resin layer.SOLUTION: Laminate paper 100 comprises a paper base material 10, a thermoplastic resin layer 30, and a separation layer 20 provided between the paper base material 10 and the thermoplastic resin layer 30, wherein the separation layer 20 contains a water-soluble resin and a water-insoluble resin, the water-insoluble resin having a softening temperature of 35°C or more and 70°C or less, and the thermoplastic resin layer 30 contains a polyolefin resin.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to laminated paper.

Background Art

[0002] Laminated materials obtained by laminating a thermoplastic resin and paper are used in various applications. In recent years, there has been an increasing interest in recycling from the viewpoint of reducing the environmental impact associated with the treatment of plastic waste.

[0003] Patent Document 1 discloses a synthetic resin laminated paper in which a thermoplastic synthetic resin film is provided on paper or cardboard via a water-soluble adhesive layer and which is easily peelable in water.

[0004] Patent Document 2 discloses a laminated paper in which a polyethylene layer is provided on at least one side of paper mainly composed of natural pulp via a mixed layer composed of polyvinyl alcohol and polyethyleneimine.

[0005] Patent Document 3 discloses a laminated paper including a base material layer made of a paper material and a synthetic resin layer. In the laminated paper disclosed in Patent Document 3, an adhesive layer is provided between the base material layer and the synthetic resin layer, and the main component constituting the adhesive layer is a water-soluble adhesive, a water-dispersible adhesive or a water-dissociable adhesive.

[0006] Patent Document 4 discloses a laminated paper in which polyethylene is laminated on one side of a base paper. The laminated paper disclosed in Patent Document 4 is an easily separable laminated paper in which a water-soluble resin is applied between the surface of the base paper and polyethylene.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] Conventionally, laminated paper in which a thermoplastic resin layer is laminated on a paper substrate has been known. In order to improve the separability of the laminated paper, a technique for separating the paper and the thermoplastic resin layer using an alkaline solution has been proposed. However, in this technique, since a strong alkaline solution is used, if the strong alkaline solution is discharged as it is, there is a concern about the impact on the environment. Further, in this technique, treatment steps such as neutralization treatment of the strong alkaline solution that becomes waste liquid after the separation treatment are increased before discharging it out of the system. For this reason, when separating the paper substrate and the thermoplastic resin layer, a technique that can separate them with water at room temperature or water heated to a predetermined temperature or higher without using a strong alkaline solution is required.

[0009] In order to separate the paper substrate and the thermoplastic resin layer, laminated paper in which a layer containing a water-soluble resin is provided between the paper substrate and the thermoplastic resin layer has been proposed. Such laminated paper may be able to separate the paper substrate and the thermoplastic resin layer with water at room temperature. However, water-soluble resins have a high affinity for water. For this reason, laminated paper in which the paper substrate and the thermoplastic resin layer are laminated via a water-soluble resin is likely to have reduced water resistance and moisture resistance. Therefore, laminated paper provided with a thermoplastic resin layer via a water-soluble resin layer, which can separate the paper substrate and the thermoplastic resin layer with water at room temperature, may have reduced adhesion between the paper substrate and the thermoplastic resin layer and may cause unintended peeling, for example, in a high-temperature and high-humidity environment (for example, a temperature of 40°C and a relative humidity of 95%RH).

[0010] In addition, in a laminated paper in which a layer containing a water-soluble resin is provided between a paper base material and a thermoplastic resin layer, techniques such as adding an adhesion improver to the water-soluble resin layer have also been proposed. However, depending on the device for improving the adhesion with the thermoplastic resin layer, the separation time between the paper base material and the thermoplastic resin layer becomes long, and in these techniques, there may be a large amount of paper material of the paper base material remaining on the thermoplastic resin layer side. Further, even when an adhesion improver is included in the water-soluble resin layer, if the adhesion improver has a high affinity for water, the adhesion between the paper base material and the thermoplastic resin layer in a high-temperature and high-humidity environment tends to decrease.

[0011] As described above, laminated paper is required to have improved practicality in a high-temperature and high-humidity environment and excellent recyclability that enables separation of the paper base material and the thermoplastic resin layer with heated water without using a strong alkaline solution, and there is still room for further improvement.

[0012] An object of the present invention is to provide a laminated paper capable of suppressing a decrease in adhesion between a paper base material and a thermoplastic resin layer containing a polyolefin resin in a high-temperature and high-humidity environment, and separating the paper base material and the thermoplastic resin layer with heated water in a short time, and capable of achieving both suppression of the amount of residue including the paper base material remaining on the thermoplastic resin layer.

Means for Solving the Problems

[0013] [1] A laminated paper, a paper base material, a thermoplastic resin layer, and a separation layer provided between the paper base material and the thermoplastic resin layer, wherein the separation layer contains a water-soluble resin and a water-insoluble resin, the water-insoluble resin has a softening temperature of 35°C or higher and 70°C or lower, the thermoplastic resin layer contains a polyolefin resin, a laminated paper.

[0014] [2] In the laminated paper according to [1], The ratio of the water-soluble resin to the water-insoluble resin satisfies the following mathematical formula (Equation 1) in terms of the mass ratio in terms of solid content: Laminated paper. The water-soluble resin: the water-insoluble resin = 3:7 to 5:5 ···(Equation 1)

[0015] [3] In the laminated paper according to [1] or [2], The water-insoluble resin is at least one selected from the group consisting of styrene-butadiene latex, polyurethane, and styrene-acrylic. Laminated paper.

[0016] [4] In the laminated paper according to any one of [1] to [3], The water-soluble resin is polyvinyl alcohol. Laminated paper.

[0017] [5] In the laminated paper according to any one of [1] to [4], The total coating amount of the water-soluble resin and the water-insoluble resin is 1 g / m 2 or more and 3 g / m 2 or less in terms of solid content. Laminated paper.

[0018] [6] In the laminated paper according to any one of [1] to [5], The content of the water-soluble resin and the water-insoluble resin in the entire separation layer is 70% by mass or more and 100% by mass or less in terms of solid content. Laminated paper.

[0019] [7] In the laminated paper according to any one of [1] to [6], The polyolefin resin has at least one of a structural unit derived from ethylene and a structural unit derived from propylene. Laminated paper.

[0020] [8] In the laminated paper according to any one of [1] to [7], which is a release paper or a wrapping paper, Laminated paper.

[0021] [9] In the laminated paper according to any one of [1] to [8], when the paper base material and the thermoplastic resin layer are separated in warm water at 40°C or higher, the amount of residue adhering to the thermoplastic resin layer is represented by the following mathematical formula (Formula 2), wherein the amount of residue is 6% by mass or less with respect to the total mass of the paper base material and the separation layer, Laminated paper. R = [{TP W -((TP T / 10 4 )×TP ρ ×L S )} / {L W -((TP T / 10 4 )×TP ρ ×L S )}]×100 ···(Formula 2) (In the above mathematical formula (Formula 2), R is the amount of residue (unit: mass %), TP W is the mass of the thermoplastic resin layer after separation (unit: g), TP T is the thickness of the thermoplastic resin layer (unit: μm), TP ρ is the density of the thermoplastic resin layer (unit: g / cm 3 ), L S is the area of the thermoplastic resin layer in the laminated paper before separation (unit: cm 2 ), L W is the mass of the laminated paper before separation (unit: g).)

Advantages of the Invention

[0022] According to one aspect of the present invention, it is possible to provide a laminated paper that can suppress a decrease in adhesion between a paper substrate and a thermoplastic resin layer containing a polyolefin resin in a high-temperature and high-humidity environment, and can separate the paper substrate and the thermoplastic resin layer with heated water in a short time, while suppressing the amount of residue containing the paper substrate remaining on the thermoplastic resin layer.

Brief Description of the Drawings

[0023]

Figure 1

Embodiments for Carrying Out the Invention

[0024] [Laminated Paper] The laminated paper according to this embodiment includes a paper substrate, a thermoplastic resin layer, and a separation layer provided between the paper substrate and the thermoplastic resin layer. The separation layer contains a water-soluble resin and a water-insoluble resin. The water-insoluble resin has a softening temperature of 35°C or higher and 70°C or lower, and the thermoplastic resin layer contains a polyolefin resin.

[0025] The inventor focused on the configuration of the separation layer provided between the paper substrate and the thermoplastic resin layer. The inventor found that by including a water-soluble resin and a water-insoluble resin in the separation layer and setting the softening temperature of the water-insoluble resin within a specific range, the adhesion between the paper substrate and the thermoplastic resin layer containing a polyolefin resin can be maintained even in a high-temperature and high-humidity environment (for example, a temperature of 40°C and a relative humidity of 95%RH), and the temperature at which the paper substrate and the thermoplastic resin layer start to separate can be adjusted. That is, the laminated paper according to this embodiment can suppress a decrease in adhesion between the paper substrate and the thermoplastic resin layer containing a polyolefin resin in a high-temperature and high-humidity environment, and can separate the paper substrate and the thermoplastic resin layer with heated water in a short time, while suppressing the amount of residue containing the paper substrate remaining on the thermoplastic resin layer.

[0026] Regarding this, the inventor of the present invention thinks as follows. Since the release layer contains a water-soluble resin, it becomes easy to separate the paper base material and the thermoplastic resin layer in warm water in a short time. However, as the resin component contained in the release layer, only the water-soluble resin tends to reduce the adhesion between the paper base material and the thermoplastic resin layer containing a polyolefin resin in a high-temperature and high-humidity environment. Therefore, by coexisting a water-soluble resin and a water-insoluble resin having a softening point of 35°C or higher in the release layer, the adhesion between the paper base material and the thermoplastic resin layer in a high-temperature and high-humidity environment is ensured. Further, by coexisting a water-soluble resin and a water-insoluble resin having a softening point of 70°C or lower in the release layer, water easily penetrates into the release layer due to the softening of the water-insoluble resin at the water temperature near the softening point of the water-insoluble resin. Thereby, near the softening point of the water-insoluble resin, since the water-soluble resin starts to dissolve and the paper base material and the thermoplastic resin layer start to separate, the separability between the paper base material and the thermoplastic resin layer is ensured. That is, since the release layer contains both a water-soluble resin and a water-insoluble resin having a softening temperature of 35°C or higher and 70°C or lower, the action of the water-soluble resin makes it easy to separate the paper base material and the thermoplastic resin layer in warm water in a short time, and the action of the water-insoluble resin having a softening temperature in a specific range suppresses the decrease in the adhesion between the paper base material and the thermoplastic resin layer in a high-temperature and high-humidity environment and ensures the ease of separation between the paper base material and the thermoplastic resin layer in warm water. Here, warm water refers to water having a temperature of 40°C or higher.

[0027] In the laminated paper according to the present embodiment, when the thermoplastic resin layer and the paper base material are separated, the thermoplastic resin layer and the paper base material are considered to be in a state close to being separated at the interface between the thermoplastic resin layer and the release layer, for example, with the paper base material separated from the thermoplastic resin layer together with the release layer.

[0028] The laminated paper according to this embodiment will be described with reference to the drawings. In the drawings, some parts are shown enlarged or reduced for ease of explanation. The laminated paper 100 shown in FIG. 1 includes a paper base material 10, a separation layer 20 laminated on one surface (the first paper base material surface 11) of the paper base material 10, and a thermoplastic resin layer 30 laminated on a surface (the first separation layer surface 21) opposite to the surface (the second separation layer surface 22) of the separation layer 20 on the paper base material 10 side. That is, in the laminated paper 100, the separation layer 20 is provided between the paper base material 10 and the thermoplastic resin layer 30, and the paper base material 10, the separation layer 20, and the thermoplastic resin layer 30 are sequentially laminated in this order in the thickness direction from the paper base material 10 toward the thermoplastic resin layer 30. The paper base material 10 and the separation layer 20 are in direct contact, and the separation layer 20 and the thermoplastic resin layer 30 are in direct contact. In the laminated paper 100 shown in FIG. 1, the separation layer 20 and the thermoplastic resin layer 30 are not provided on the second paper base material surface 12 opposite to the first paper base material surface 11 of the paper base material 10, and the second paper base material surface 12 is exposed. Further, the second thermoplastic resin layer surface 32 of the thermoplastic resin layer 30 is in contact with the separation layer 20, and the opposite first thermoplastic resin layer surface 31 is exposed. The separation layer 20 contains a water-soluble resin and a water-insoluble resin having a softening temperature of 35°C or higher and 70°C or lower. The thermoplastic resin layer 30 contains a polyolefin resin.

[0029] As described above, an example of the laminated paper according to the present embodiment has been described with reference to FIG. 1. However, the laminated paper according to the present embodiment is not limited thereto. The laminated paper according to the present embodiment can adopt various forms as long as it has the above configuration. For example, in the laminated paper 100, the release layer 20 and the thermoplastic resin layer 30 are provided on the first paper base material surface 11 side of the paper base material 10. However, not only on the first paper base material surface 11 side, but also on the second paper base material surface 12 side, the release layer 20 and the thermoplastic resin layer 30 may be provided. When the release layer 20 and the thermoplastic resin layer 30 are provided on both the first paper base material surface 11 and the second paper base material surface 12, the release layer 20 and the thermoplastic resin layer 30 on the first paper base material surface 11 side may be respectively referred to as the first release layer and the first thermoplastic resin layer, and the release layer 20 and the thermoplastic resin layer 30 on the second paper base material surface 12 side may be respectively referred to as the second release layer and the second thermoplastic resin layer. When the release layer 20 (second release layer) and the thermoplastic resin layer 30 (second thermoplastic resin layer) are also provided on the second paper base material surface 12, the release layer 20 (second release layer) provided on the second paper base material surface 12 may be in direct contact with the paper base material 10, and the release layer 20 (second release layer) and the thermoplastic resin layer 30 (second thermoplastic resin layer) provided on the second paper base material surface 12 may be in direct contact with the release layer 20 (second release layer). When the release layer 20 (second release layer) and the thermoplastic resin layer 30 (second thermoplastic resin layer) are also provided on the second paper base material surface 12, the thermoplastic resin layer 30 (first thermoplastic resin layer), the release layer 20 (first release layer), the paper base material 10, the release layer 20 (second release layer), and the thermoplastic resin layer 30 (second thermoplastic resin layer) may be provided in this order in the thickness direction.

[0030] Further, when the laminated paper 100 is applied to, for example, the use of release paper, a release agent layer (not shown) may be provided on the first thermoplastic resin layer surface 31. The release agent layer is not particularly limited, and may contain, for example, a silicone-based release agent. Further, when applying the laminated paper 100, for example, to the use of wrapping paper, a decorative layer (not shown) such as a printing layer may be provided on at least one of the first thermoplastic resin layer surface 31, the first paper base material surface 11, and the second paper base material surface 12 as necessary. The printing layer as the decorative layer may be provided on only one of these surfaces, or may be provided on a plurality of these surfaces.

[0031] <Paper base material> The paper base material is not particularly limited as long as it can support the separation layer. Examples of the paper base material include kraft paper, medium paper, high-quality paper, glassine paper, and coated paper (for example, art paper, clay-coated paper, and cast-coated paper, etc.). In the laminated paper according to the present embodiment, it is also preferable that the paper base material is an uncoated paper that is not, for example, coated paper. The uncoated paper refers to a paper base material that is a paper base material other than coated paper and is composed of a base paper portion that does not have a pigment coating layer described later. In this case, the paper base material is preferably specifically any one of kraft paper, medium paper, high-quality paper, and glassine paper, etc.

[0032] In this specification, the coated paper includes a base paper mainly composed of pulp fibers and a pigment coating layer provided on the base paper. The base paper is obtained by adding a target additive mainly composed of, for example, beaten pulp fibers by a known method. The base paper may have a single-layer structure or a multilayer structure. The pigment coating layer is provided on the base paper by a known method. The pigment coating layer may have a single-layer structure or a multilayer structure. The pigment coating layer contains, for example, an adhesive such as an aqueous resin in a range of 2 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of one or more pigments such as calcium carbonate, kaolin, clay, talc, satin white, titanium oxide, and plastic pigment. In this specification, the aqueous resin refers to a resin that can be dispersed in water or a resin that can be dissolved in water (that is, a water-soluble resin). The aqueous resin includes not only water-soluble resins but also resins that can be dispersed in water such as emulsion type and dispersion type. In this specification, the so-called sealer that can be applied during the production of the paper substrate is included in the paper substrate and is distinguished from the separation layer provided in the laminated paper according to this embodiment.

[0033] <Separation layer> The separation layer contains a water-soluble resin and a water-insoluble resin, and the water-insoluble resin has a softening temperature of 35°C or higher and 70°C or lower. The separation layer is preferably provided in direct contact with the paper substrate. In this specification, the water-soluble resin refers to a resin that dissolves 1% by mass or more in water at 25°C. The resin that can dissolve in water (water-soluble resin) described for the aforementioned paper substrate has the same meaning. Further, the water-insoluble resin represents a resin other than the water-soluble resin.

[0034] The content ratio of the water-soluble resin and the water-insoluble resin in the separation layer is not particularly limited as long as it can suppress the decrease in adhesion between the paper substrate and the thermoplastic resin layer containing a polyolefin resin in a high-temperature and high-humidity environment, and can separate the paper substrate and the thermoplastic resin layer in warm water in a short time, and can suppress the amount of residue containing the paper substrate remaining on the thermoplastic resin layer (hereinafter, this compatibility may be referred to as the compatibility of suppressing the decrease in adhesion between the paper substrate and the thermoplastic resin layer and suppressing the amount of residue containing the paper substrate). For example, the ratio of the water-soluble resin to the water-insoluble resin (water-soluble resin: water-insoluble resin) may satisfy the range of 2:8 to 7:3 in terms of the mass ratio in terms of solid content, or may satisfy the range of 2:8 to 6:4. From the viewpoint of achieving both the suppression of the decrease in adhesion between the paper substrate and the thermoplastic resin layer and the suppression of the amount of residue containing the paper substrate, it is preferable that the ratio of the water-soluble resin to the water-insoluble resin satisfies the following mathematical formula (Formula 1) in terms of the mass ratio in terms of solid content. The water-soluble resin: the water-insoluble resin = 3:7 to 5:5 ···(Formula 1)

[0035] (Water-soluble resin) Examples of the water-soluble resin include polyvinyl alcohol (unmodified polyvinyl alcohol and various modified polyvinyl alcohols), starch (such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch), and cellulose derivatives (such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose). These can be used alone or in combination of two or more kinds.

[0036] Among these, from the viewpoint of achieving both suppression of the decrease in adhesion between the paper base material and the thermoplastic resin layer and suppression of the amount of residue containing the paper base material, it is preferable that the water-soluble resin contains at least polyvinyl alcohol. From the same viewpoint, it is more preferable that the water-soluble resin is polyvinyl alcohol.

[0037] In this specification, polyvinyl alcohol is a concept including both unmodified polyvinyl alcohol and modified polyvinyl alcohol. When specifying the presence or absence of modification, it is described as unmodified polyvinyl alcohol and modified polyvinyl alcohol. In the following description, polyvinyl alcohol may be abbreviated as "PVA", unmodified polyvinyl alcohol as "unmodified PVA", and modified polyvinyl alcohol as "modified PVA".

[0038] PVA is obtained by polymerizing polyvinyl acetate from a monomer containing vinyl acetate and then saponifying the polyvinyl acetate. PVA is a resin mainly containing vinyl alcohol units obtained by saponifying polyvinyl acetate. As PVA, either one or both of unmodified PVA and modified PVA can be used. Also, PVA can be used alone. As PVA, two or more kinds having different saponification degrees of PVA, polymerization degrees of PVA, modification types of modified PVA, modification amounts of modified PVA, etc. can be used in combination. As PVA, commercially available PVA may be used, or synthesized PVA may be used.

[0039] Modified PVA is a resin obtained by introducing a modifying group into polyvinyl alcohol mainly composed of vinyl alcohol units obtained by saponifying polyvinyl acetate through copolymerization or post-reaction. Examples of modified PVA include silane-modified PVA, anionic-modified PVA (such as carboxy-modified PVA, sulfonic acid-modified PVA, and phosphoric acid-modified PVA), cationic-modified PVA, and modified PVA copolymerized with ethylene, α-olefins having 3 or more and 20 or less carbon atoms, vinyl ether, vinyl ester, and (meth)acrylamide and its salts. When using modified PVA as PVA, it is preferable to use at least one selected from the group consisting of anionic-modified PVA and ethylene-modified PVA which is a modified PVA copolymerized with ethylene, and more preferably to use at least one selected from the group consisting of carboxy-modified PVA and ethylene-modified PVA which is a modified PVA copolymerized with ethylene. The modification amount of modified PVA is, for example, 0.1 mol% or more and 20 mol% or less. The modification amount of modified PVA may be, for example, 0.5 mol% or more, or may be 1 mol% or more. The modification amount of modified PVA may be 15 mol% or less, or may be 10 mol% or less.

[0040] The saponification degree of PVA is represented by the percentage of the number of hydroxyl groups to the total number of the number of acetic acid groups and the number of hydroxyl groups in PVA. The saponification degree and the degree of polymerization of PVA are not particularly limited. The saponification degree of PVA may be 70% or more, may be 78% or more, may be 85% or more, or may be 95% or more. The saponification degree of PVA may be 100% or less, or may be 99% or less. The degree of polymerization of PVA may be 300 or more, or may be 500 or more. The degree of polymerization of PVA may be 3000 or less, may be 1000 or less, may be 800 or less, or may be 600 or less. The saponification degree and the degree of polymerization of PVA are determined by, for example, the method specified in JIS K 6726:1994. PVA may be used alone or in combination of two or more.

[0041] (Water-insoluble resin) The water-insoluble resin has a softening temperature of 35°C or higher and 70°C or lower. If the softening temperature of the water-insoluble resin is 70°C or lower, for example, when separating the paper substrate and the thermoplastic resin layer in warm water, the separation between the paper substrate and the thermoplastic resin layer becomes easy, and the amount of residue containing the paper substrate of the thermoplastic resin is likely to be suppressed. If the softening temperature of the water-insoluble resin is 35°C or higher, the separability of the paper substrate and the thermoplastic resin layer in warm water can be easily obtained while ensuring the adhesion between the paper substrate and the thermoplastic resin layer in a high-temperature and high-humidity environment. From the viewpoint of achieving both suppression of the decrease in the adhesion between the paper substrate and the thermoplastic resin layer and suppression of the amount of residue containing the paper substrate, the softening temperature of the water-insoluble resin is preferably 65°C or lower, and more preferably 60°C or lower.

[0042] The softening temperature of the water-insoluble resin is measured by the penetration method using thermomechanical analysis (TMA). The penetration method presses a needle-shaped indenter against a sample for measuring the softening temperature of the water-insoluble resin, raises the temperature under a constant load, measures the process of the needle-shaped indenter penetrating into the measurement sample, and measures the softening temperature from the deformation of the measurement sample. Such a measurement method can be specifically measured by a method conforming to JIS K 7196:1991. Details of the measurement method for the softening temperature of the water-insoluble resin are as described in the examples below.

[0043] Examples of the method for controlling the softening temperature of the water-insoluble resin include adjusting the type or composition ratio of the monomer components constituting the water-insoluble resin, and adjusting the molecular weight of the water-insoluble resin, etc. The softening temperature of the water-insoluble resin can be controlled by one or both of these. The water-insoluble resin is obtained by a known production method for the resin used as the water-insoluble resin.

[0044] The type of the water-insoluble resin is not particularly limited as long as it can achieve both suppression of the decrease in adhesion between the paper base material and the thermoplastic resin layer and suppression of the amount of residue including the paper base material. From the viewpoint of achieving both suppression of the decrease in adhesion between the paper base material and the thermoplastic resin layer and suppression of the amount of residue including the paper base material, for example, the type of the water-insoluble resin is preferably at least one selected from the group consisting of styrene-butadiene latex, polyurethane, and styrene-acrylic. As the water-insoluble resin, one kind alone may be used, or two or more kinds may be used in combination. Among these, the type of the water-insoluble resin is more preferably at least one selected from the group consisting of styrene-butadiene latex and polyurethane. The water-insoluble resin can also be used by combining two or more kinds having different types and softening temperatures of the water-insoluble resin. As the water-insoluble resin, a commercially available water-insoluble resin may be used, or a synthesized water-insoluble resin may be used.

[0045] In the separation layer, the contents of the water-soluble resin and the water-insoluble resin with respect to the entire separation layer are not particularly limited as long as it can achieve both suppression of the decrease in adhesion between the paper base material and the thermoplastic resin layer and suppression of the amount of residue including the paper base material. From the viewpoint of achieving both suppression of the decrease in adhesion between the paper base material and the thermoplastic resin layer and suppression of the amount of residue including the paper base material, in the separation layer, the contents of the water-soluble resin and the water-insoluble resin with respect to the entire separation layer are preferably 70% by mass or more and 100% by mass or less in terms of solid content. It is more preferably 80% by mass or more, further preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 99% by mass or more based on the total amount of the separation layer. If the contents of the water-soluble resin and the water-insoluble resin in the separation layer are 100% by mass (that is, the separation layer consists only of the water-soluble resin and the water-insoluble resin), the thermoplastic resin layer becomes easier to recycle.

[0046] The total coating amount of the water-soluble resin and the water-insoluble resin is not particularly limited as long as both the suppression of the decrease in the adhesion between the paper substrate and the thermoplastic resin layer and the suppression of the amount of residue including the paper substrate can be achieved simultaneously. From the viewpoint of achieving both the suppression of the decrease in the adhesion between the paper substrate and the thermoplastic resin layer and the suppression of the amount of residue including the paper substrate, the total coating amount of the water-soluble resin and the water-insoluble resin is preferably 1 g / m 2 or more and 3 g / m 2 or less in terms of solid content. Even if components other than the water-soluble resin and the water-insoluble resin are contained in the separation layer, the total coating amount of the water-soluble resin and the water-insoluble resin may be within the above range.

[0047] The separation layer may contain various additives such as inorganic fillers and colorants, if necessary.

[0048] <Thermoplastic resin layer> The thermoplastic resin layer contains a polyolefin resin. The thermoplastic resin layer is preferably provided in direct contact with the separation layer. The polyolefin resin is not particularly limited. Examples of the polyolefin resin include polymers polymerized from monomers containing olefin monomers having 2 or more and 18 or less carbon atoms.

[0049] Examples of the polyolefin resin include homopolymers of olefin monomers such as ethylene, propylene, butene, hexene, octene, decene, and 4-methyl-1-pentene. Examples of the polyolefin resin also include copolymers of olefin monomers selected from the group consisting of ethylene, propylene, butene, hexene, octene, decene, and 4-methylpentene. Copolymers of olefin monomers include, for example, copolymers of ethylene and at least one olefin monomer selected from the group consisting of α-olefins having 3 or more and 18 or less carbon atoms (e.g., propylene, butene, hexene, octene, decene, and 4-methylpentene). Copolymers of olefin monomers may use two or more olefin monomers in combination. The polyolefin resin may be a single resin or a combination of two or more resins.

[0050] Polyolefin resins include, for example, copolymers of one or more olefin monomers such as ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene, and one or more monomers having a hydroxyl group, carboxyl group, vinyl acetate structure, acid anhydride structure, etc. Polyolefin resins also include resins obtained by polymerizing olefin monomers such as ethylene, propylene, butene, hexene, octene, and 4-methyl-1-pentene, and introducing one or more structures such as a hydroxyl group, carboxyl group, vinyl acetate structure, and acid anhydride structure into the polymer.

[0051] The polyolefin resin is, for example, specifically, at least one selected from the group consisting of polyethylene (such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene), polypropylene, poly-1-butene, poly-2-butene, poly-1-hexene, poly-1-octene, poly(4-methyl-1-pentene), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, and ethylene-(meth)acrylate copolymer.

[0052] Among these, the polyolefin resin is preferably a resin having at least one of a structural unit derived from ethylene and a structural unit derived from propylene. Specifically, the polyolefin resin is more preferably at least one resin selected from the group consisting of polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, and even more preferably at least one resin selected from the group consisting of polyethylene and polypropylene.

[0053] The density of the polyolefin resin is not particularly limited. For example, it is preferably 0.85 g / cm 3 or more and 0.97 g / cm 3 or less. When the polyolefin resin is polyethylene, for example, the density is 0.91 g / cm 3 or more and 0.93 g / cm3 Low-density polyethylene with a density less than 0.93 g / cm 3 and greater than or equal to 0.942 g / cm 3 Medium-density polyethylene with a density less than 0.942 g / cm 3 and greater than or equal to 0.97 g / cm 3 Any of the above high-density polyethylene may be used. When the polyolefin resin is polypropylene, for example, it is preferably polypropylene with a density greater than or equal to 0.90 g / cm 3 and less than or equal to 0.91 g / cm 3 The density of the polyolefin resin can be measured in accordance with JIS K7112:1999.

[0054] The thickness of the thermoplastic resin layer is not particularly limited, and is preferably 10 μm or more and 30 μm or less. The thickness of the thermoplastic resin layer is more preferably 11 μm or more, and even more preferably 13 μm or more. The thickness of the thermoplastic resin layer is more preferably 28 μm or less, and preferably 25 μm or less.

[0055] In the thermoplastic resin layer, the content of the polyolefin resin is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass, based on the total amount of the thermoplastic resin layer. If the content of the polyolefin resin in the thermoplastic resin layer is 100% by mass (i.e., the thermoplastic resin layer consists only of the polyolefin resin), the thermoplastic resin layer containing the polyolefin resin becomes easier to recycle.

[0056] The thermoplastic resin layer may contain various additives such as inorganic fillers, antioxidants, ultraviolet absorbers, and stabilizers in addition to the polyolefin resin.

[0057] In the laminated paper according to this embodiment, when the paper base material and the thermoplastic resin layer are separated with warm water at 40°C or higher, the amount of residue adhering to the thermoplastic resin layer is preferably 6% by mass or less with respect to the total mass of the paper base material and the separation layer. The amount of this residue is more preferably 3% by mass or less, still more preferably 1% by mass or less, and even more preferably 0 (zero) % by mass. The residue adhering to the thermoplastic resin layer is a residue containing the paper base material. When the paper base material and the thermoplastic resin layer are separated, the amount of residue of the residue adhering to the thermoplastic resin layer is represented by the following formula (Formula 2).

[0058] R=[{TP W -((TP T / 10 4 )×TP ρ ×L S )} / {L W -((TP T / 10 4 )×TP ρ ×L S )}]×100 ···(Formula 2) (In the above formula (Formula 2), R is the amount of residue (unit: mass %), TP W is the mass of the thermoplastic resin layer after separation (unit: g), TP T is the thickness of the thermoplastic resin layer (unit: μm), TP ρ is the density of the thermoplastic resin layer (unit: g / cm 3 ), L S is the area of the thermoplastic resin layer in the laminated paper before separation (unit: cm 2 ), L W represents the mass of the laminated paper before separation (unit: g).)

[0059] If the amount of this residue is 6% by mass or less, it becomes easier to reuse the thermoplastic resin layer, and the yield of the thermoplastic resin layer containing a recyclable polyolefin resin improves.

[0060] (Use of laminated paper) The use of the laminated paper according to this embodiment is not particularly limited, and examples include release paper and wrapping paper. The laminated paper according to this embodiment may be applied to uses such as release paper or wrapping paper. When the laminated paper according to this embodiment is applied to the use of release paper or wrapping paper, the release paper or wrapping paper includes the laminated paper according to this embodiment. The release paper can be applied to general release sheet uses. As the release paper, for example, it can be used as release paper for protecting the adhesive layer of an adhesive sheet, or as process paper used in the process of forming a sheet-like material on the release surface of the release agent layer provided on the release paper. Specifically, the release paper can be applied as various process papers when producing various resin sheets, various resin materials, synthetic leather, or various composite materials, etc.

[0061] When applying the laminated paper according to this embodiment to the use of release paper, the laminated paper according to this embodiment itself may be applied as release paper, or it may be applied as a base material for release paper. When applying the laminated paper according to this embodiment as a base material for release paper, it is preferable to provide a release agent layer on the thermoplastic resin layer in the laminated paper according to this embodiment. For example, the release agent layer may be laminated so as to directly contact the thermoplastic resin layer in the laminated paper according to this embodiment. For example, an intermediate layer may be directed upward on the thermoplastic resin layer in the laminated paper according to this embodiment, and a release agent layer may be laminated on the intermediate layer. Examples of the intermediate layer include an easy-adhesion layer such as a primer layer. The release agent contained in the release agent layer is not particularly limited, and known release agents such as silicone-based release agents can be used. The silicone-based release agent is not particularly limited, and it can be used in any form of solvent type, solvent-free type, or emulsion type.

[0062] When applying the laminate paper according to this embodiment to the use of wrapping paper, the wrapping paper can be applied to the use of general wrapping paper. The form of the wrapping paper is not particularly limited, and it may be in any form such as sheet form, bag form, box form, cup form, and carton form. The wrapping paper is not particularly limited, and examples include moisture-proof wrapping paper. The moisture-proof wrapping paper can be used, for example, as a wrapping paper for wrapping various paper materials such as copy paper (PPC paper), coated paper, cast-coated paper, other general-purpose papers, and newsprint. In addition, examples of the wrapping paper include food wrapping paper. The food wrapping paper may be any wrapping paper that can wrap the food to be wrapped. Examples of the food to be wrapped include confectionery, dairy products, juice, fresh food, processed food, and frozen food. The food wrapping paper also includes, for example, the form of beverage containers such as milk cartons.

[0063] When applying the laminate paper according to this embodiment as a wrapping paper, for example, the laminate paper according to this embodiment itself may be applied as a wrapping paper, and at least one of the surface on the side opposite to the separation layer side of the paper base material in the laminate paper according to this embodiment (second paper base material surface) and the surface on the side opposite to the separation layer side of the thermoplastic resin layer (first thermoplastic resin layer surface) may be provided with a decorative layer such as a printing layer. Further, a printing layer may be provided on the surface on the separation layer side of the paper base material (first paper base material surface) or the surface on the thermoplastic resin layer side of the separation layer (first separation layer surface). By providing a printing layer as a decorative layer, information regarding the contents of the object to be packaged and other information can be displayed on the laminate paper by printing.

[0064] When providing a printing layer on any of the above layers of the laminate paper according to this embodiment, the printing method for forming the printing layer is not particularly limited. The printing layer can be formed, for example, by printing methods such as relief printing such as flexographic printing, intaglio printing such as gravure printing, planographic printing such as offset printing, and stencil printing such as screen printing.

[0065] [Manufacturing method of laminate paper] As an example of a preferred manufacturing method of the laminated paper according to the present embodiment, the following manufacturing method can be mentioned. The preferred manufacturing method of the laminated paper according to the present embodiment includes, for example, a step of preparing a paper substrate, a step of providing a separation layer by applying a coating liquid containing a water-soluble resin and a water-insoluble resin to at least one surface of the paper substrate, and a step of providing a thermoplastic resin layer containing a polyolefin resin by melt-extrusion laminating a polyolefin resin on the surface of the separation layer opposite to the paper substrate side.

[0066] In the step of preparing a paper substrate, the paper substrate described above with respect to the paper substrate may be prepared. The paper substrate can be obtained by a known manufacturing method.

[0067] The step of providing a separation layer includes a step of preparing a water-soluble resin and a water-insoluble resin having a softening temperature of 35°C or higher and 70°C or lower as described above with respect to the separation layer. The water-soluble resin may be prepared as a water-soluble resin solution in which the water-soluble resin is dissolved in an aqueous solvent (for example, water, etc.). As long as the water-soluble resin can be dissolved, the concentration of the water-soluble resin solution is not particularly limited. From the viewpoint of ease of handling and the like, it is preferable to prepare an emulsion-type water-insoluble resin as the water-insoluble resin having a softening temperature of 35°C or higher and 70°C or lower.

[0068] Next, the water-soluble resin and the water-insoluble resin prepared above are mixed and stirred to prepare a coating liquid for forming a separation layer containing the water-soluble resin and the water-insoluble resin, and the prepared coating liquid for forming a separation layer is applied to at least one surface of the paper substrate. When applying the coating liquid for forming a separation layer, the coating liquid for forming a separation layer may be diluted so as to achieve a target coating amount in terms of solid content. The method of applying the coating liquid for forming a separation layer is not particularly limited, and examples thereof include coating methods such as a bar coating method, a knife coating method, a roll knife coating method, a roll coating method, a blade coating method, a die coating method, a curtain coating method, and a gravure coating method. After applying the coating liquid for forming a separation layer to one surface of the paper substrate to form a coating film of the coating liquid for forming a separation layer, the coating film is dried, whereby a separation layer is provided on the substrate. As the drying conditions of the coating film, conditions under which the coating film can be dried may be adopted.

[0069] In the step of providing the separation layer, after providing the separation layer on the surface of the paper substrate, in order to enhance the adhesion between the separation layer and the thermoplastic resin layer, an easy adhesion treatment such as a corona treatment, a plasma treatment, and a flame treatment may be performed on the surface of the separation layer.

[0070] The step of providing the thermoplastic resin layer includes the step of preparing the polyolefin resin described in the above-mentioned thermoplastic resin layer. Next, the prepared polyolefin resin is melt-extrusion laminated on the surface of the separation layer opposite to the paper substrate side. The method of melt-extrusion laminating the polyolefin resin is not particularly limited, and for example, it is preferable to melt-extrusion laminate the polyolefin resin using a T-die. The extrusion temperature when melt-extrusion laminating the polyolefin resin may be set according to the type of the polyolefin resin. When the polyolefin resin is polyethylene, for example, it is preferably 290 °C or higher and 350 °C or lower. When the polyolefin resin is polypropylene, for example, it is preferably 240 °C or higher and 300 °C or lower. Here, the extrusion temperature when melt-extrusion laminating the polyolefin resin is the temperature of the polyolefin resin when it is extruded from the die. The extrusion temperature can be measured as the temperature of the polyolefin resin in the die of the extruder.

[0071] By going through the above steps, the laminated paper according to this embodiment is obtained.

[0072] [Method for Separating Laminated Paper] As an example of a preferred method for separating the laminated paper according to this embodiment, the following separation method can be mentioned. A preferred separation method for the laminated paper according to this embodiment includes, for example, a step of preparing the laminated paper according to this embodiment, and a step of separating the laminated paper into the paper base material and the thermoplastic resin layer in warm water at 40°C or higher.

[0073] The step of preparing the laminated paper prepares the laminated paper described with the above-mentioned laminated paper. The laminated paper can be obtained, for example, by the preferred manufacturing method of the above-mentioned laminated paper.

[0074] The step of separating the laminated paper separates the paper base material and the thermoplastic resin layer in warm water at 40°C or higher. The method for separating the paper base material and the thermoplastic resin layer is not particularly limited. From the viewpoint of separating the thermoplastic resin layer and the paper base material in a short time and making it easy to suppress the amount of residue containing the paper base material remaining in the thermoplastic resin layer, as the method for separating the paper base material and the thermoplastic resin layer, it is preferable to adopt a method of immersing the laminated paper in warm water at 40°C or higher and stirring it in the warm water. The time for the paper base material and the thermoplastic resin layer to separate in warm water at 40°C or higher is preferably 15 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less. The warm water at 40°C or higher includes tap water, industrial water, distilled water, ion-exchanged water, etc. From the viewpoint of simplifying the process, the pH of the warm water at 40°C or higher is, for example, preferably 6.5 or higher and 7.5 or lower. The upper limit of the temperature of the warm water at 40°C or higher is not particularly limited. The upper limit of the temperature of the warm water may be 100°C or lower, or 80°C or lower. The warm water at 40°C or higher may be 50°C or higher. The warm water at 40°C or higher may be, for example, 40°C or higher and 80°C or lower.

[0075] By going through the above steps, the laminated paper according to this embodiment has the thermoplastic resin layer containing a polyolefin resin separated from the paper base material. The separated thermoplastic resin layer and the separated paper base material can each be recycled. Further, by the preferable separation method of the laminated paper according to this embodiment, the residue (residue containing the paper base material) adhering to the separated thermoplastic resin layer is suppressed. For example, as the residue amount of the residue adhering to the thermoplastic resin layer, the residue amount represented by the above-mentioned mathematical formula (Formula 2) may be 6% by mass or less. Therefore, by the preferable separation method of the laminated paper according to this embodiment, the yield of the thermoplastic resin layer containing a recyclable polyolefin resin is improved.

[0076] The present invention is not limited to the above embodiment. The present invention can include modifications, improvements, etc. within the scope where the object of the present invention can be achieved.

Examples

[0077] Examples will be described below, but the present invention is not limited to these examples at all.

[0078] As materials for producing the laminated paper of each example and each comparative example, the following raw materials were prepared.

[0079] <Paper base material> 「P-1」: The paper base material was produced by the following procedure. First, kraft pulp in which the mass ratio of softwood (N) to hardwood (L) is N / L = 40 / 60 was beaten in water by the Shopper Regler method to a beating degree of 38°SR, and then diluted with water to obtain a pulp slurry having a concentration of about 1.0% by mass. Next, 0.4 part by mass of rosin sizing agent as a sizing agent and 0.2 part by mass of aluminum sulfate as a fixing agent were respectively added to 100 parts by mass of the pulp in this pulp slurry to prepare a pulp slurry after chemical addition. Next, this prepared pulp slurry was paper-made using a Fourdrinier multi-cylinder paper machine to obtain a paper base material having a basis weight of 81 g / m 2 The obtained paper base material had a thickness of 97 μm.

[0080] <Separation layer> (Water-soluble resin) "PVA-1": Ethylene-modified PVA (manufactured by Kuraray Co., Ltd., "Exceval RS-2817SB", saponification degree 95.5 - 97.5) "PVA-2": Unmodified PVA (manufactured by Kuraray Co., Ltd., "Kuraray Poval 3-98", saponification degree 98.0 - 99.0) "PVA-3": Unmodified PVA (manufactured by Kuraray Co., Ltd., "Kuraray Poval 3-88", saponification degree 87.0 - 89.0) "PVA-4": Carboxy-modified PVA (manufactured by Mitsubishi Chemical Corporation, "Gohsenex T-350", saponification degree 93.0 - 95.0)

[0081] (Water-insoluble resin) "SBR": Styrene-butadiene latex (manufactured by Nippon A&R Co., Ltd., "Smartex SN-309R", softening temperature 41°C) "UR": Urethane resin (manufactured by Dainichi Seiko Kogyo Co., Ltd., softening temperature 55°C) "St·Ac": Styrene-acrylic resin (manufactured by Starlight PMC Co., Ltd., "HE-1335", softening temperature 98°C)

[0082] <Thermoplastic resin layer> "LDPE": Low-density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., "SumikaSen L405", density 0.924 g / cm 3 )

[0083] <Example 1> First, as the water-soluble resin, ethylene-modified PVA (PVA-1) and, as the water-insoluble resin, styrene-butadiene latex (SBR) were prepared. PVA-1 was dissolved in water to prepare an aqueous solution of PVA-1. Next, an aqueous solution of PVA-1 was weighed so as to be 3 parts by mass in terms of solid content, and SBR was weighed so as to be 7 parts by mass in terms of solid content. Then, by mixing and stirring the two, a coating liquid for forming a separation layer was prepared. The mass ratio of PVA-1 to SBR in terms of solid content (PVA-1:SBR) is 3:7. Next, on one side of the paper base material (P-1), the coating liquid for forming the separation layer prepared above was coated with an applicator so that the total coating amount of PVA-1 and SBR in terms of solid content was 3 g / m 2 Thereafter, it was dried at 120 °C for 1 minute and 20 seconds to form a separation layer. Next, low-density polyethylene (LDPE) was heated and melted, and the molten polyethylene was extruded from a T-die at an extrusion temperature of 300 °C so as to directly contact the separation layer, thereby forming a thermoplastic resin layer with a thickness of 15 μm. In this way, the laminated paper of Example 1 laminated in the order of the paper base material, the separation layer, and the thermoplastic resin layer was obtained.

[0084] <Examples 2 to 8> According to Table 1, except that at least one of the conditions such as the types of the water-soluble resin and the water-insoluble resin used for the separation layer, the ratio of the water-soluble resin to the water-insoluble resin, and the total coating amount of the water-soluble resin and the water-insoluble resin was changed, the laminated papers of the respective examples were obtained in the same manner as in Example 1.

[0085] <Comparative Example 1> According to Table 1, except that no separation layer was provided, the laminated paper of Comparative Example 1 was obtained in the same manner as in Example 1.

[0086] <Comparative Example 2> Except that no water-insoluble resin was used for the separation layer, the laminated paper of Comparative Example 2 was obtained in the same manner as in Example 1.

[0087] <Comparative Examples 3 to 5> According to Table 1, except that the type of the water-soluble resin used for the separation layer was changed, the laminated papers of Comparative Examples 3 to 5 were obtained in the same manner as in Comparative Example 2.

[0088] <Comparative Example 6> Except that the water-insoluble resin used for the separation layer was changed to styrene acrylic resin (St·Ac), the laminated paper of Comparative Example 6 was obtained in the same manner as in Example 1.

[0089] <Comparative Examples 7, Comparative Example 8> According to Table 1, laminate papers of Comparative Example 7 and Comparative Example 8 were obtained in the same manner as Comparative Example 6, except that the type of water-soluble resin used for the separation layer was changed.

[0090] The measurements or evaluations in each example and each comparative example were carried out by the methods shown below.

[0091] <Softening temperature of non-water-soluble resin> A film-shaped non-water-soluble resin was prepared so that the thickness of the non-water-soluble resin became 150 μm. A sample for measuring the softening temperature was cut out from the film-shaped non-water-soluble resin. Using a thermomechanical analyzer (manufactured by Netzsch Japan Co., Ltd., "TMA4000S"), by the penetration method, using a needle-shaped indenter, in a nitrogen atmosphere, with a load of 50 g, a heating rate of 5 °C / min, and a measurement temperature range from -90 °C to 150 °C, the penetration temperature of the indenter was determined from the obtained TMA curve, and the softening temperature (unit: °C) was calculated.

[0092] <Evaluation of easy separability> The laminate paper obtained in each example was cut into a size of 50 mm × 50 mm to collect a sample for evaluating easy separability. The sample for evaluating easy separability was put into 1 liter of water at any one of the temperatures of 25 °C, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C, and stirred using a stirrer (manufactured by AS ONE Corporation, High Power Star Stirrer HPS-100) at a rotation speed of 420 rpm. The stirring time was carried out until the time when the paper base material peeled off from the thermoplastic resin layer. The time when the paper base material peeled off from the thermoplastic resin layer was recorded, and the evaluation of easy separability was carried out according to the following evaluation criteria. When the paper base material did not peel off from the thermoplastic resin layer, the stirring time was set to a maximum of 15 minutes.

[0093] (Evaluation criteria) "1": Within 2 minutes, no residue containing the paper base material adhering to the thermoplastic resin layer was observed, and all peeled off. "2": Exceeding 2 minutes and within 4 minutes, no residue containing the paper base material was observed from the thermoplastic resin layer, and all peeled off. "3": Exceeding 4 minutes and within 8 minutes, no residue containing the paper base material was observed from the thermoplastic resin layer, and all peeled off. "4": Beyond 8 minutes and within 15 minutes, no residue containing the paper substrate is observed in the thermoplastic resin layer, and all of it peels off. "5": Even after 15 minutes have passed, the paper substrate does not peel off from the thermoplastic resin layer. Even when rubbing the paper substrate adhering to the thermoplastic resin layer immediately after taking out the sample for evaluating easy separability from water at each temperature, the paper substrate is difficult to peel off.

[0094] <Residue amount evaluation> The laminated paper obtained in each example was cut into a size of 100 mm × 100 mm along the direction parallel to the thickness direction to collect a sample for evaluating the residue amount. The area of the thermoplastic resin layer in the collected sample for evaluating the residue amount is 10,000 mm 2 . The mass of the collected sample for evaluating the residue amount was measured. Then, the sample for evaluating the residue amount was put into 1 liter of warm water at a temperature of 50°C and stirred at a rotation speed of 420 rpm using a stirrer (manufactured by AS ONE Corporation, High Power Starler HPS-100). The stirring time was carried out until the paper substrate peeled off from the thermoplastic resin layer. When the paper substrate did not peel off from the thermoplastic resin layer, stirring was carried out for a maximum of 20 minutes. The thermoplastic resin layer separated from the sample for evaluating the residue amount was taken out from the warm water, and the mass of the thermoplastic resin layer was measured. From the mass of the sample for evaluating the residue amount measured before being put into the warm water and the mass of the thermoplastic resin layer measured after being taken out from the warm water, the residue amount of the residue adhering to the thermoplastic resin layer was calculated according to the above-mentioned formula (formula 2).

[0095] The value substituted for TP in formula (formula 2) ρ was taken as 0.924 g / cm for the density of the low-density polyethylene used for the thermoplastic resin layer. 3 Also, as the value substituted for TP in formula (formula 2) T , the thickness of the thermoplastic resin layer after being separated from the sample for evaluating the residue amount was measured. The thickness of the thermoplastic resin layer was measured at a total of 5 locations near the four corners and near the center of the thermoplastic resin layer, avoiding the portions where residues exist, and the average value was taken. When there are many residues adhering to the thermoplastic resin layer, the thickness of the thermoplastic resin layer was adopted as the thickness of the thermoplastic resin layer formed by extrusion from the above-mentioned T-die.

[0096] <Adhesion evaluation> The laminated paper obtained in each example was cut into pieces with a width of 15 mm and a length of 100 mm, and test pieces for adhesion evaluation were prepared to evaluate the adhesion between the thermoplastic resin layer and the paper substrate. A part of the prepared test pieces was left standing in an environment of 23°C and 50% RH for 1 day, and the remaining part of the prepared test pieces was left standing in an environment of 40°C and 95% RH for 7 days. After leaving the test pieces in their respective environments, the test pieces were peeled by hand to produce a part mainly containing the thermoplastic resin layer that became the starting point of peeling and a part mainly containing the paper substrate. Next, using a tensile testing machine (manufactured by Shimadzu Corporation, "Autograph AGS-20NX"), the part mainly containing the thermoplastic resin layer of the test piece and the part mainly containing the paper substrate were each gripped with the jaws of the tensile testing machine, and by the T-peel (a test method in accordance with JIS K6854-3:1999, while supporting the test piece, gripping each with the jaws, and peeling in the direction in which the part mainly containing the thermoplastic resin layer and the part mainly containing the paper substrate separated from each other), under the condition of a tensile speed of 0.3 m / min, the thermoplastic resin layer and the paper substrate were peeled, and the adhesion was evaluated according to the following evaluation criteria.

[0097] (Evaluation criteria) "A": Paper layer breakage occurred, indicating sufficient adhesion. "F": The paper substrate did not adhere to the thermoplastic resin layer (LDPE) and peeled off.

[0098] [Table 1]

[0099] [Table 2]

[0100] From the above results, it can be seen that the laminated paper of each example can separate the paper substrate and the thermoplastic resin layer containing a polyolefin resin in a short time compared with the laminates of each comparative example, and that the amount of residue containing the paper substrate remaining in the thermoplastic resin layer is suppressed in the laminated paper of each example compared with the laminates of each comparative example.

[0101] In addition, it can be seen that the laminated paper of each example containing a water-insoluble resin having a specific softening temperature in the separation layer is superior in the adhesion of the thermoplastic resin layer in a high-temperature and high-humidity environment (40 °C, 95% RH) compared with the laminated paper of each comparative example containing only a water-soluble resin in the separation layer.

[0102] After separating the thermoplastic resin in the same manner as the easy-separability evaluation for the laminated paper produced in Example 1, when the separation layer and the side surface (second thermoplastic resin layer surface) where the paper substrate was provided on the thermoplastic resin layer were analyzed by infrared spectroscopy (IR: Infrared spectroscopy), the presence of peaks derived from the resin used for the separation layer could not be confirmed on the second thermoplastic resin layer surface of the thermoplastic resin layer. Therefore, it was confirmed that the laminated paper of Example 1 was in a state where the paper substrate was separated from the thermoplastic resin layer together with the separation layer and separated at the interface between the thermoplastic resin layer and the separation layer.

Explanation of Signs

[0103] 10…Paper substrate, 11…First paper substrate surface, 12…Second paper substrate surface, 20…Separation layer, 21…First separation layer surface, 22…Second separation layer surface, 30…Thermoplastic resin layer, 31…First thermoplastic resin layer surface, 32…Second thermoplastic resin layer surface, 100…Laminated paper.

Claims

1. A laminated paper comprising: a paper substrate; a thermoplastic resin layer; and a separation layer provided between the paper substrate and the thermoplastic resin layer, wherein the separation layer contains a water-soluble resin and a water-insoluble resin, the water-insoluble resin has a softening temperature of 35°C or higher and 70°C or lower, and the thermoplastic resin layer contains a polyolefin resin. Laminated paper.

2. The laminated paper according to Claim 1, wherein the ratio of the water-soluble resin to the water-insoluble resin satisfies the following formula (Formula 1) in terms of the mass ratio in terms of solid content: Laminated paper. The water-soluble resin: the water-insoluble resin = 3:7 to 5:5... (Formula 1)

3. The laminated paper according to Claim 1 or Claim 2, wherein the water-insoluble resin is at least one selected from the group consisting of styrene-butadiene latex, polyurethane, and styrene-acrylic. Laminated paper.

4. The laminated paper according to Claim 1 or Claim 2, wherein the water-soluble resin is polyvinyl alcohol. Laminated paper.

5. The laminated paper according to Claim 1 or Claim 2, The total coating amount of the water-soluble resin and the water-insoluble resin is 1 g / m or more and 3 g / m or less in terms of solid content. ２ ２ ​​ Laminated paper.

6. The laminated paper according to Claim 1 or Claim 2, wherein the content of the water-soluble resin and the water-insoluble resin in the entire separation layer is 70% by mass or more and 100% by mass or less in terms of solid content. Laminated paper.

7. The laminated paper according to Claim 1 or Claim 2, wherein the polyolefin resin has at least one of a structural unit derived from ethylene and a structural unit derived from propylene. Laminated paper.

8. The laminated paper according to Claim 1 or Claim 2, which is release paper or wrapping paper. Laminated paper.

9. The laminated paper according to Claim 1 or Claim 2, when the paper substrate and the thermoplastic resin layer are separated in warm water at 40°C or higher, the amount of residue adhering to the thermoplastic resin layer is represented by the following formula (Formula 2), and the amount of residue is 6% by mass or less based on the total mass of the paper substrate and the separation layer. Laminated paper. R = [{TP Ｗ - ((TP Ｔ / 10 ４ ) × TP ρ × L Ｓ )} / {L Ｗ - ((TP Ｔ / 10 ４ ) × TP ρ × L Ｓ )}] × 100... (Equation 2) (In the formula (Formula 2), R is the residue amount (unit: mass %), TP Ｗ is the mass of the thermoplastic resin layer after separation (unit: g), TP Ｔ is the thickness of the thermoplastic resin layer (unit: μm), TP ρ is the density of the thermoplastic resin layer (unit: g / cm ３ ), L Ｓ is the area of the thermoplastic resin layer in the laminate paper before separation (unit: cm ２ ), L Ｗ represents the mass of the laminate paper before separation (unit: g). )

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