Backside moisture-proof paper for decorative board

Abstract

An object of the present application is to provide a backside moisture-proof paper for a decorative plate, which is a laminate using paper and can suppress a decrease in water vapor barrier properties even when a long period of time (at least 12 months) has elapsed since the production.SOLUTION: In the paper substrate 3, the proportion of pulps having lengths of 0. 4mm or more and 1mm or less is 60% or more, and the proportion of pulps having widths of 10 μm or more and 20 μm or less is 40% or more, based on the total number of pulps contained in the paper substrate 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a moisture-proof paper for decorative panels used in interior door panels, etc., which is attached to the back surface of the decorative panel to prevent warping of the decorative panel caused by moisture absorption and release due to changes in indoor temperature and humidity. [Background technology]

[0002] Conventionally, decorative panels used for applications such as interior door panels have generally been formed by laminating a decorative sheet printed with a solid print layer to provide hiding properties or a patterned layer to improve design to the surface of a multi-layered wood-based substrate such as plywood, medium-density fiberboard (MDF), veneer, board material, or other material. If the moisture content of a wood-based substrate is lower than the equilibrium moisture content of the wood-based substrate under ambient conditions, the surface of the decorative board where the decorative sheet is not attached will absorb moisture, causing the surface to expand. If the moisture content is higher than the equilibrium moisture content of the wood-based substrate, the surface of the decorative board where the decorative sheet is not attached will release moisture, causing shrinkage. However, the surface where the decorative sheet is attached will hardly absorb or release moisture, causing deformation (warping, dimensional changes) of the decorative board.

[0003] Known methods for preventing this deformation include applying paint to the back of a decorative board with a decorative sheet attached to the surface, attaching a synthetic resin sheet such as polyvinyl chloride, polyethylene, or polypropylene, or attaching a moisture-proof sheet made of paper / polyethylene / paper (for example, Patent Document 1).

[0004] Furthermore, when even higher moisture resistance is required, a method is known for preventing deformation of the decorative board, such as laminating a moisture-proof sheet having a vapor-deposited layer on a synthetic resin substrate. To achieve high moisture-proof performance, a vapor-deposited layer must be formed on a smooth surface, so synthetic resin substrates are generally chosen, and it is considered technically difficult to achieve high moisture-proof performance using a paper substrate.

[0005] However, in recent years, growing environmental awareness stemming from the problem of marine plastic waste has led to a growing trend toward a plastic-free society. From the perspective of reducing the amount of plastic used, the use of paper instead of plastic materials has been considered in various fields. For example, Patent Document 2 listed below discloses a laminate in which a barrier layer is laminated on paper. Furthermore, from the perspective of the Law for Promoting Effective Utilization of Resources, it is required to increase the ratio of paper to the entire laminate having barrier properties. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3206408 [Patent Document 2] Patent No. 6944022 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the present inventors have found that although a laminate in which a barrier layer is laminated on paper has good initial water vapor barrier properties, the water vapor barrier properties deteriorate over a long period of time after production. If the laminate is used for a long period of time in doors, sliding doors, partitions, etc. where there is a large difference in temperature and humidity environment between the two sides due to a decrease in the water vapor barrier, the degree of expansion and contraction on both sides will differ, and warping may occur in the decorative panel equipped with the laminate.

[0008] Therefore, the present disclosure aims to provide a laminate using paper, a moisture-proof paper for the back side of decorative panels, which can suppress a decrease in water vapor barrier properties even after a long period of time (at least 12 months) has passed since its manufacture.

[0009] Furthermore, the moisture-proof backside paper for decorative panels according to the present disclosure has high moisture-proofing performance, so that warping of the decorative panel can be prevented for a long period of time even when used in a place where there is a large difference in temperature and humidity environment on both sides, and by reducing the amount of plastic used, an environmentally friendly moisture-proof backside paper for decorative panels can be provided. [Means for solving the problem]

[0010] In order to solve the above problems, the present disclosure provides the following moisture-proof backside paper for decorative boards. [1] A moisture-proof backside paper for decorative panels, comprising at least a paper substrate, a first resin layer, and a water vapor barrier layer in this order, In the paper base material, the proportion of pulp having a length of 0.4 mm or more and 1 mm or less is 60% or more, and the proportion of pulp having a width of 10 μm or more and 20 μm or less is 40% or more, based on the total number of pulp contained in the paper base material. [2] The moisture-proof backside paper for decorative panels according to [1], further comprising a second resin layer on the surface of the water vapor barrier layer opposite the first resin layer. [3] The moisture-proof backside paper for decorative panels according to [1] or [2], wherein the thickness of the first resin layer is 0.3 μm or more and 10 μm or less. [4] The moisture-proof backside paper for decorative panels according to any one of [1] to [3], wherein the first resin layer contains at least one resin selected from the group consisting of polyvinyl alcohol-based resins and polyolefin resins having polar groups. [5] The moisture-proof backside paper for decorative boards according to any one of [1] to [4], wherein the second resin layer contains a polyolefin resin having a polar group. [6] The moisture-proof backside paper for decorative panels according to any one of [1] to [5], wherein the water vapor barrier layer is an aluminum vapor deposition layer. [7] A moisture-proof backside paper for decorative panels described in any one of [1] to [6], wherein the mass of the pulp component contained in the paper base material is 50 mass% or more based on the mass of the entire moisture-proof backside paper for decorative panels. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a laminate having high and stable water vapor barrier properties and a moisture-proof backside paper for decorative panels, which has a high paper component ratio. Furthermore, according to one aspect of the present invention, a moisture-proof backside paper for decorative boards can be provided that contributes to reducing the amount of plastic materials used.

[0012] In other words, according to one embodiment of the present invention, a moisture-proof backside paper for decorative panels can be provided that is a laminate using paper and that can suppress a decrease in water vapor barrier properties even after a long period of time (at least 12 months) has passed since its manufacture. Such moisture-proof paper for the back side of decorative panels has high moisture-proofing properties, so it can prevent warping of the decorative panels over a long period of time even when used in places where there is a large difference in temperature and humidity environment on both sides, and it is environmentally friendly and can reduce the amount of plastic used.

[0013] Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of a moisture-proof backside paper for decorative panels according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to FIG. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc., differ from the actual ones. Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not specify the materials, shapes, structures, etc. of the components to be described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0016] FIG. 1 is a schematic cross-sectional view showing the structure of moisture-proof backside paper 10 for decorative boards according to this embodiment. A moisture-proof backside paper 10 for decorative boards according to one embodiment of the present disclosure comprises a paper substrate 3, a first resin layer 1, a water vapor barrier layer 4, and a second resin layer 2, in this order.

[0017] <Moisture-proof paper 10 for the back of decorative panels> The moisture-proof backside paper 10 for decorative boards according to this embodiment is a moisture-proof paper that is pasted onto the backside of a decorative board used, for example, for an interior door panel, etc. In this embodiment, this moisture-proof backside paper 10 for decorative boards will hereinafter also be referred to simply as "moisture-proof paper 10." The moisture-proof paper 10 is used to prevent warping of the decorative board caused by moisture absorption and release due to changes in temperature and humidity in the room.

[0018] The moisture-proof backside paper 10 for decorative boards according to this embodiment is a moisture-proof backside paper for decorative boards that comprises, in this order, at least a paper base material 3, a first resin layer 1, and a water vapor barrier layer 4. In the paper base material 3, the proportion of pulp with a length of 0.4 mm to 1 mm is 60% or more, based on the total number of pulps contained in the paper base material 3, and the proportion of pulp with a width of 10 μm to 20 μm is 40% or more, based on the total number of pulps contained in the paper base material 3. The moisture-proof backside paper 10 for decorative boards according to this embodiment may further comprise a second resin layer 2 on the surface of the water vapor barrier layer 4 opposite to the first resin layer 1.

[0019] According to the moisture-proof back paper 10 for decorative panels, by having the proportion of pulp with a length of 0.4 mm or more and 1 mm or less and the proportion of pulp with a width of 10 μm or more and 20 μm or less in the paper base material 3 within the above numerical ranges, the long-term stability of the water vapor barrier properties of the moisture-proof back paper 10 for decorative panels can be improved, and the deterioration of the water vapor barrier properties can be suppressed even after a long period of time (at least 12 months) has passed since the moisture-proof back paper 10 for decorative panels was manufactured.

[0020] The inventors speculate that the reason for this effect is as follows. Specifically, even very slight dimensional changes in the paper substrate, which are insignificant in normal use, can cause defects such as cracks and pinholes in the water vapor barrier layer. These defects affect the long-term stability of the water vapor barrier property. Here, if a large amount of pulp less than 0.4 mm in length is present in the paper substrate, the pulp becomes dense and the distance between the pulp particles becomes short. This makes interfiber bonding more likely to occur, and pulp expansion and contraction spreads throughout the paper substrate through the interfiber bonds, making the dimensions more likely to change. Furthermore, if a large amount of pulp greater than 1 mm in length is present, the pulp particles become entangled. This increases the interfiber bonding area, making pulp expansion and contraction spread throughout the paper substrate, making the dimensions more likely to change. Furthermore, if a large amount of pulp less than 10 μm in width or greater than 20 μm in width is present, the paper substrate will absorb moisture and become more susceptible to dimensional changes.

[0021] In contrast, by using a paper base material 3 in which the proportion of pulp with a length of 0.4 mm to 1 mm is 60% or more, based on the total number of pulps contained in the paper base material 3, it is possible to prevent dimensional changes caused by pulp expansion and contraction from spreading to the entire paper base material 3. Furthermore, by using a paper base material 3 in which the proportion of pulp with a width of 10 μm to 20 μm is 40% or more, based on the total number of pulps contained in the paper base material 3, the amount of moisture absorbed by the paper base material 3 is reduced. As a result, even very slight dimensional changes in the paper base material 3 are reduced, and the water vapor barrier properties of the moisture-proof backside paper 10 for decorative boards remain stable over the long term.

[0022] Furthermore, by using the moisture-proof paper backside for decorative panels 10, it is possible to provide a moisture-proof paper that addresses the issues of eliminating plastic and marine litter, has a high ratio of paper components, and has stable and excellent water vapor barrier properties. Each layer will be explained below.

[0023] [Paper base material 3] The paper base material 3 may be paper whose main component is plant-derived pulp. Specific examples of the paper base material 3 include tissue paper, fine paper, art paper, cast-coated paper, kraft paper, titanium paper, linter paper, paperboard, gypsum board paper, coated paper, parchment paper, glassine paper, parchment paper, wax paper, and Japanese paper. Preferably, thin paper (so-called inter-sheet reinforced paper) in which synthetic resin is mixed with pulp (e.g., cellulose fiber), which is a paper component, to strengthen the inter-sheet strength, or paper impregnated with latex or synthetic resin is used.

[0024] The basis weight of the paper base material 3 is not particularly limited, but the basis weight of the paper base material 3 is preferably 20 g / m 2 If the paper substrate 3 has a basis weight of less than 200 g / m, it is too flexible and wrinkles tend to occur during processing. 2 If the basis weight is more than 20 g / m, peeling from the paper layer is likely to occur. 2 More than 200g / m 2 The following range is preferred: 20 g / m 2 More than 100g / m 2 The following range is more preferable: 20 g / m 2 More than 50g / m 2 The following ranges are more preferred: Furthermore, the surface of the paper substrate 3 may be subjected to a surface treatment such as corona treatment, plasma treatment, or flame treatment, if necessary.

[0025] The proportion of pulp having a length of 0.4 mm or more and 1 mm or less is preferably 65% ​​or more, and more preferably 70% or more, based on the total number of pulp pieces contained in the paper base material 3. The proportion of pulp having a length of 0.4 mm or more and 1 mm or less is preferably 90% or less, and more preferably 80% or less, based on the total number of pulp pieces contained in the paper base material 3.

[0026] The proportion of pulp having a length of less than 0.4 mm is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more, based on the total number of pulp pieces contained in the paper base material 3. The proportion of pulp having a length of less than 0.4 mm is preferably 30% or less, based on the total number of pulp pieces contained in the paper base material 3.

[0027] The proportion of pulp having a length of more than 1 mm is preferably 5% or more based on the total number of pulp pieces contained in the paper base material 3. The proportion of pulp having a length of more than 1 mm is preferably 20% or less based on the total number of pulp pieces contained in the paper base material 3, and more preferably 15% or less.

[0028] The proportion of pulp having a width of 10 μm or more and 20 μm or less is preferably 50% or more, and more preferably 55% or more, based on the total number of pulps contained in the paper base material 3. The proportion of pulp having a width of less than 10 μm is preferably 5% or more, based on the total number of pulps contained in the paper base material 3. The proportion of pulp having a width of less than 10 μm is preferably 15% or less, and more preferably 10% or less, based on the total number of pulps contained in the paper base material 3. The proportion of pulp having a width greater than 20 μm is preferably 20% or more, and more preferably 25% or more, based on the total number of pulps contained in the paper base material 3. The proportion of pulp having a width greater than 20 μm is preferably 60% or less, and more preferably 50% or less, based on the total number of pulps contained in the paper base material 3.

[0029] The length and width of the pulp are measured by the method described in the Examples below. The proportion of pulp having a length or width within the above numerical range is calculated by the method described in the Examples below.

[0030] A paper base material 3 in which the proportion of pulp with a length of 0.4 mm to 1 mm is 60% or more and the proportion of pulp with a width of 10 μm to 20 μm is 40% or more, based on the total number of pulps contained in the paper base material 3, can be obtained, for example, by the following method: First, prepare multiple types of pulp. Then, analyze the width and length distribution of each pulp. Then, obtain a mixture of each pulp while adjusting the proportion of each pulp according to the analysis results. Finally, obtain the paper base material 3 by papermaking this mixture.

[0031] The paper base material 3 may have a coating layer (not shown) on at least the side of the paper base material 3 that comes into contact with the first resin layer 1. When the paper base material 3 has a coating layer, the paper base material 3 may have at least a paper layer and a coating layer. The coating layer may be provided on both surfaces (i.e., the front and back surfaces) of the paper base material 3. The coating layer prevents the resin that constitutes the first resin layer 1 from seeping into the paper layer and also serves as a sealant that fills in unevenness in the paper layer, allowing the first resin layer 1 to be formed uniformly and without defects.

[0032] The coating layer may contain, for example, various copolymers such as styrene-butadiene, styrene-acrylic, and ethylene-vinyl acetate copolymers, polyvinyl alcohol resins, cellulose resins, paraffin (wax), etc. as binder resins. The coating layer may also contain, for example, clay, kaolin, calcium carbonate, talc, mica, etc. as fillers. The coating layer may also be a clay coating layer containing at least clay as a filler.

[0033] When the paper substrate 3 has a coating layer, the thickness of the coating layer is preferably 1.5 μm or more and 15 μm or less. The thickness of the coating layer is more preferably 1.8 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and particularly preferably 6 μm or more. The thickness of the coating layer is preferably 12 μm or less, and more preferably 10 μm or less. When the thickness of the coating layer is within the above range, the moisture-proof backside paper 10 for decorative panels can achieve better water vapor barrier properties.

[0034] The thickness of the paper substrate 3 is preferably 20 μm to 100 μm, more preferably 30 μm to 80 μm, and even more preferably 40 μm to 60 μm. When the thickness of the paper substrate 3 is within this range, the moisture-proof backside paper for decorative boards 10 can achieve better water vapor barrier properties not only initially (immediately after production) but also over a long period of time (at least 12 months after production). A thinner thickness reduces the moisture content of the paper substrate 3, making defects in the water vapor barrier layer 4 less likely. However, if the thickness is too thin, the paper substrate 3 is more likely to change in dimension during the coating and drying of the first resin layer 1, which can lead to poor appearance such as wrinkles in the moisture-proof backside paper for decorative boards 10. The thickness of the paper substrate 3 is preferably within this range in order to achieve both reduced defects in the water vapor barrier layer 4 and a good appearance for the moisture-proof backside paper for decorative boards 10.

[0035] The thickness of the coating layer is preferably 3% to 25%, and more preferably 5% to 20%, of the thickness of the paper substrate 3. When this ratio is within the above range, the moisture-proof backside paper 10 for decorative boards can achieve better water vapor barrier properties.

[0036] The mass of the pulp (paper component) contained in the paper base material 3 is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on the entire moisture-proof backside paper for decorative boards 10. If the mass of pulp is 50% by mass or more based on the entire moisture-proof backside paper for decorative boards 10, the amount of plastic material used can be sufficiently reduced, the entire moisture-proof backside paper for decorative boards 10 can be said to be made of paper, and it has excellent recyclability.

[0037] [First resin layer 1] The first resin layer 1 is provided on the surface of the paper base material 3 to improve adhesion between the paper base material 3 and the water vapor barrier layer 4 described later, and to improve the water vapor barrier properties of the backside moisture-proof paper 10 for decorative panels.

[0038] The first resin layer 1 preferably contains at least one resin selected from the group consisting of a polyolefin resin having a polar group, a polyvinyl alcohol resin, an acrylic resin, an epoxy resin, and a polyurethane resin. Examples of polyurethane resins include at least one of an acrylic urethane resin, a polyester polyurethane resin, and a polyether polyurethane resin. The first resin layer 1 preferably contains at least one resin selected from the group consisting of a polyvinyl alcohol resin and a polyolefin resin having a polar group, since this provides excellent water vapor barrier properties even after the moisture-proof backside paper for decorative boards 10 is bent.

[0039] When the first resin layer 1 contains a polyolefin resin having polar groups, the first resin layer 1 has excellent flexibility, can suppress cracking of the water vapor barrier layer 4 (described later) after bending (folding) the moisture-proof backside paper for decorative boards 10, and can improve adhesion between the first resin layer 1 and the water vapor barrier layer 4. Furthermore, when the first resin layer 1 contains a polyolefin resin having polar groups, the crystallinity of the polyolefin resin makes it possible to form a dense film, and water vapor barrier properties are exhibited. In other words, when the first resin layer 1 is formed from a polyolefin resin having polar groups, water vapor barrier properties are exhibited due to the crystallinity of the polyolefin resin, and the presence of polar groups enables adhesion to the water vapor barrier layer 4 to be exhibited.

[0040] The polyolefin resin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester.

[0041] As the polyolefin resin having a polar group, copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having a carboxyl group such as acrylic acid, methacrylic acid, maleic anhydride, etc.) or unsaturated carboxylic acid esters, and salts of carboxylic acids neutralized with basic compounds may be used, as well as copolymers of vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, polyamide compounds, etc.

[0042] Specific examples of polyolefin resins having a polar group include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, copolymers of acrylic acid esters and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.

[0043] When the first resin layer 1 contains a polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin has polar groups (hydroxyl groups) that readily bond with aluminum oxide present on the surface of the water vapor barrier layer 4, making it easier to improve adhesion between the water vapor barrier layer 4 and the first resin layer 1. Furthermore, such a first resin layer 1 has excellent flexibility, making it possible to prevent cracking of the water vapor barrier layer 4 after the moisture-proof backside paper for decorative boards 10 is bent (folded).

[0044] Polyvinyl alcohol-based resins are resins that contain vinyl alcohol as a constituent unit, and examples of polyvinyl alcohol-based resins include fully saponified polyvinyl alcohol resins, partially saponified polyvinyl alcohol resins, modified polyvinyl alcohol resins, and ethylene-vinyl alcohol copolymer resins.

[0045] The first resin layer 1 may contain components other than the above-mentioned resins, such as polyolefin resins other than the above-mentioned polyolefin resins having polar groups, silane coupling agents, organic titanate resins, polyester resins, polycarbonate resins, polyurea resins, polyamide resins, polyimide resins, melamine resins, and phenolic resins.

[0046] The thickness of the first resin layer 1 is, for example, preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and particularly preferably 1 μm or more. The thickness of the first resin layer 1 is preferably 10 μm or less, and more preferably 5 μm or less. If the thickness of the first resin layer is 0.3 μm or more, the unevenness of the paper base material 3 described above can be efficiently filled, allowing the water vapor barrier layer 4 described below to be laminated uniformly. Furthermore, if the thickness of the first resin layer 1 is 10 μm or less, the water vapor barrier layer 4 can be laminated uniformly while keeping costs down.

[0047] Examples of solvents contained in the coating liquid for forming the first resin layer 1 include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used alone or in combination. Among these, from the viewpoint of properties, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred. Furthermore, from the viewpoint of the environment, methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred.

[0048] The first resin layer 1 may be formed, for example, by applying a coating liquid containing the above-mentioned resin, a solvent, and the like onto the paper substrate 3 and then drying it.

[0049] The drying temperature for the coating liquid is preferably 105°C to 160°C, more preferably 110°C to 155°C, even more preferably 120°C to 150°C, and particularly preferably 130°C to 145°C. By setting the drying temperature at 105°C or higher, the moisture content of the moisture-proof backside paper for decorative laminates 10 can be reduced. The paper substrate 3 has the property of absorbing and desorbing moisture according to the humidity of the environment, changing its moisture content depending on the humidity. If the moisture content is suddenly reduced by high-temperature drying such as in an oven, when the paper substrate 3 is subsequently left in a humid environment, the moisture content will be lower than before high-temperature drying. In other words, the moisture absorption of the paper substrate 3 after high-temperature drying is reduced (the so-called paper hysteresis phenomenon).

[0050] However, if the drying temperature is too high, the paper base material 3 may shrink due to a sudden change in moisture content, resulting in wrinkles and other defects in appearance. Therefore, by setting the drying temperature to 160°C or less, it is possible to prevent wrinkles and other defects in appearance caused by the sudden shrinkage of the paper base material 3. Furthermore, the drying time of the coating film is preferably, for example, 0.1 to 2 minutes.

[0051] [Water vapor barrier layer 4] The water vapor barrier layer 4 may be, for example, a vapor-deposited layer of a metal or a vapor-deposited layer of an inorganic compound. Examples of metals include at least one of aluminum and silicon. Examples of inorganic compounds include metal oxides. Examples of metal oxides include at least one of aluminum oxide (AlOx) and silicon oxide (SiOx).

[0052] The thickness of the water vapor barrier layer 4 can be appropriately set depending on the intended use, but is preferably 10 nm to 300 nm, more preferably 20 nm to 100 nm, and even more preferably 30 nm to 100 nm. Setting the thickness of the water vapor barrier layer 4 to 10 nm or more makes it easier to ensure sufficient continuity of the water vapor barrier layer 4, while setting it to 300 nm or less sufficiently suppresses the occurrence of curling and cracking, making it easier to obtain sufficient water vapor barrier performance and flexibility. Furthermore, setting the thickness of the water vapor barrier layer 4 to 20 nm or more and 100 nm or less makes the water vapor barrier layer 4 less likely to crack, allowing for sufficient water vapor barrier properties to be obtained even after the moisture-proof backside paper for decorative boards 10 is folded.

[0053] The vapor deposition layer, the water vapor barrier layer 4, is preferably formed by vacuum deposition from the viewpoints of water vapor barrier performance and film uniformity. While known deposition methods include vacuum deposition, sputtering, and chemical vapor deposition (CVD), vacuum deposition is preferred due to its fast deposition rate and high productivity. Among vacuum deposition methods, electron beam heating is particularly effective because it allows for easy control of the deposition rate via the irradiation area and electron beam current, and allows for rapid heating and cooling of the deposition material.

[0054] [Second resin layer 2] The second resin layer 2 is provided on the surface of the water vapor barrier layer 4 so as to be in contact with the water vapor barrier layer 4. By providing the moisture-proof backside paper for decorative boards 10 with the second resin layer 2, it is possible to prevent the water vapor barrier layer 4 from being exposed to moisture and losing its water vapor barrier properties, and it is possible to suppress the deterioration of the water vapor barrier properties of the moisture-proof backside paper for decorative boards 10 over an extended period of time (at least 12 months). The second resin layer 2 may contain a polyolefin resin having a polar group.

[0055] The polyolefin resin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester.

[0056] Examples of polyolefin resins having polar groups include copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having a carboxyl group, such as acrylic acid or methacrylic acid) or unsaturated carboxylic acid esters, and salts of carboxylic acids neutralized with basic compounds. Other examples of polyolefin resins that can be used include copolymers of ethylene or propylene with vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, polyamide compounds, and the like.

[0057] Specific examples of polyolefin resins having a polar group include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, copolymers of acrylic acid esters and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.

[0058] By including a polyolefin resin having polar groups in the second resin layer 2, the second resin layer 2 has excellent flexibility, can prevent cracking of the water vapor barrier layer 4 after the moisture-proof backside paper for decorative boards 10 is bent (folded), and has excellent adhesion to the water vapor barrier layer 4. Furthermore, by including the polyolefin resin having the above-mentioned polar groups, a dense film can be formed due to the crystallinity of the polyolefin resin, and water vapor barrier properties are exhibited. Furthermore, the presence of polar groups enables adhesion to the water vapor barrier layer 4 to be exhibited. Furthermore, by including the polyolefin resin having the above-mentioned polar groups in the second resin layer 2, the moisture content of the moisture-proof backside paper for decorative boards 10 can be reduced, and deterioration of the water vapor barrier properties of the moisture-proof backside paper for decorative boards 10 over an extended period of time (after at least 12 months) can be more sufficiently suppressed.

[0059] The second resin layer 2 may contain other components in addition to the polyolefin resin having a polar group, such as a silane coupling agent, an organic titanate resin, a polyacrylic resin, a polyester resin, a polyurethane resin, a polycarbonate resin, a polyurea resin, a polyamide resin, a polyolefin resin emulsion, a polyimide resin, a melamine resin, and a phenolic resin.

[0060] The content of the polyolefin resin having a polar group in the second resin layer 2 is, for example, preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass, relative to the total mass of the second resin layer 2.

[0061] The thickness of the second resin layer 2 is, for example, preferably 0.05 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and particularly preferably 2 μm or more. The thickness of the second resin layer 2 is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. A thickness of the second resin layer 2 of 0.05 μm or more can more sufficiently prevent the deterioration of the water vapor barrier property of the moisture-proof backside paper for decorative boards 10 after a long period of time (after at least 12 months) has passed. Furthermore, a thickness of the second resin layer 2 of 20 μm or less can sufficiently exhibit adhesion to the water vapor barrier layer 4 and barrier property while suppressing costs. Furthermore, by setting the thickness of the second resin layer 2 to be 2 μm or more and 10 μm or less, the water vapor barrier layer 4 is more resistant to cracking, and sufficient water vapor barrier property can be obtained even after the moisture-proof backside paper for decorative boards 10 is folded.

[0062] In the moisture-proof backside paper for decorative panels 10, when the second resin layer 2 contains a polyolefin resin having a polar group, the thickness of the second resin layer 2 is 2 μm or more and 10 μm or less, and the thickness of the water vapor barrier layer 4 is 20 nm or more and 100 nm or less, the water vapor barrier layer 4 becomes less likely to crack, and the effect of obtaining sufficient water vapor barrier properties even after the moisture-proof backside paper for decorative panels 10 is particularly remarkable.

[0063] Examples of solvents contained in the coating liquid for forming the second resin layer 2 include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used alone or in combination. Among these, from the viewpoint of properties, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred. Furthermore, from the viewpoint of the environment, methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred.

[0064] The second resin layer 2 may be provided, for example, by applying a coating liquid containing the above-described polyolefin resin having a polar group, a solvent, and the like onto the water vapor barrier layer 4, followed by drying.

[0065] The melting point of the polyolefin resin having a polar group in the coating liquid is preferably 70°C to 160°C, more preferably 80°C to 120°C. If the melting point of the polyolefin resin having a polar group is high, there is a greater risk of blocking in a high-temperature environment. From the viewpoint of preventing blocking, it is preferable that the particle size of the polyolefin resin having a polar group is large so as to reduce the contact area. Although not particularly limited, the particle size of the polyolefin resin having a polar group is preferably 1 nm or more, more preferably 0.1 μm or more. The particle size of the polyolefin resin having a polar group is preferably 1 μm or less, more preferably 0.7 μm or less, and even more preferably 0.5 μm or less.

[0066] The drying temperature for the coating liquid is preferably 105°C to 160°C, more preferably 110°C to 155°C, even more preferably 120°C to 150°C, and particularly preferably 130°C to 145°C. By setting the drying temperature at 105°C or higher, the moisture content of the moisture-proof backside paper for decorative laminates 10 can be reduced. The paper substrate 3 has the property of absorbing and desorbing moisture according to the humidity of the environment, changing its moisture content depending on the humidity. If the moisture content is suddenly reduced by high-temperature drying such as in an oven, when the paper substrate 3 is subsequently left in a humid environment, the moisture content will be lower than before high-temperature drying. In other words, the moisture absorption of the paper substrate 3 after high-temperature drying is reduced (the so-called paper hysteresis phenomenon).

[0067] However, if the drying temperature is too high, the paper base material 3 may shrink due to a sudden change in moisture content, resulting in wrinkles and other defects in appearance. Therefore, by setting the drying temperature to 160°C or less, it is possible to prevent wrinkles and other defects in appearance caused by the sudden shrinkage of the paper base material 3. Furthermore, the drying time of the coating film is preferably, for example, 0.1 to 2 minutes.

[0068] The overall thickness of the moisture-proof backside paper 10 for decorative boards comprising the above layers is preferably 21 μm to 120 μm, more preferably 31 μm to 100 μm, and even more preferably 41 μm to 80 μm. When the overall thickness of the moisture-proof backside paper 10 for decorative boards is within the above range, the moisture-proof backside paper 10 for decorative boards can have better water vapor barrier properties not only initially (immediately after production) but also over a long period of time (at least 12 months after production).

[0069] [Effects of this embodiment] The moisture-proof backside paper 10 for decorative boards according to this embodiment has the following advantages. (1) The moisture-proof backside paper 10 for decorative panels according to this embodiment comprises at least a paper base material 3, a first resin layer 1, and a water vapor barrier layer 4, in that order, and in the paper base material 3, the proportion of pulp having a length of 0.4 mm or more and 1 mm or less is 60% or more, and the proportion of pulp having a width of 10 μm or more and 20 μm or less is 40% or more, based on the total number of pulps contained in the paper base material 3. With this configuration, even moisture-proof paper made of paper can prevent a decrease in water vapor barrier properties for a long period of time (at least 12 months).

[0070] (2) The moisture-proof backside paper 10 for decorative boards according to this embodiment may further include a second resin layer 2 on the surface of the water vapor barrier layer 4 opposite to the first resin layer 1. With this configuration, it is possible to prevent the water vapor barrier layer 4 from being exposed to moisture and the water vapor barrier properties from being reduced.

[0071] (3) The thickness of the first resin layer 1 constituting the moisture-proof backside paper 10 for decorative boards according to this embodiment may be 0.3 μm or more and 10 μm or less. With this configuration, the surface irregularities of the paper base material 3 can be efficiently filled, and the water vapor barrier layer 4 can be laminated uniformly while keeping costs down.

[0072] (4) The first resin layer 1 constituting the moisture-proof backside paper 10 for decorative panels in this embodiment may contain at least one resin selected from the group consisting of polyvinyl alcohol-based resins and polyolefin resins having polar groups. With this configuration, it is possible to improve the adhesion between the water vapor barrier layer 4 and the first resin layer 1, and also to suppress cracks in the water vapor barrier layer 4 that may occur after bending the backside moisture-proof paper 10 for decorative panels.

[0073] (5) The second resin layer 2 constituting the moisture-proof backside paper 10 for decorative boards according to this embodiment may contain a polyolefin resin having a polar group. With this configuration, it is possible to improve the adhesion between the water vapor barrier layer 4 and the second resin layer 2, and also to suppress cracks in the water vapor barrier layer 4 that may occur after bending the backside moisture-proof paper 10 for decorative panels.

[0074] (6) The water vapor barrier layer 4 constituting the moisture-proof backside paper 10 for decorative boards according to this embodiment may be an aluminum vapor deposition layer. With this configuration, a barrier layer having excellent barrier properties and flexibility can be easily formed.

[0075] (7) The mass of the pulp component contained in the paper base material 3 constituting the moisture-proof back paper 10 for decorative boards in this embodiment may be 50 mass% or more based on the total mass of the moisture-proof back paper 10 for decorative boards. With this configuration, the amount of plastic material used can be significantly reduced.

[0076] [Example] The present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples. <Preparation of moisture-proof paper on the backside of decorative panels> Example 1 Paper base material with a clay-coated layer (thickness: 5.9 μm) (thickness including clay-coated layer: 45 μm, proportion of pulp with length between 400 μm and 1000 μm: 72.5%, proportion of pulp with width between 10 μm and 20 μm: 57.2%, basis weight: 55 g / m 2 ) was prepared. Next, an aqueous dispersion of polyolefin resin containing a salt of a carboxyl group (polar group-containing polyolefin) (manufactured by Sumitomo Seika Chemicals Co., Ltd., product name: ZAIKXEN AC, particle size: less than 0.2 μm, solvent: water / IPA = 1 / 1 (mass ratio), solid content: 22.5 mass%) was applied to the surface of the paper substrate on the clay coating layer side using a gravure coater to form a first resin layer (thickness: 3 μm).

[0077] Subsequently, an aluminum (AL) vapor deposition layer (thickness: 50 nm) was formed on the first resin layer as a water vapor barrier layer by vacuum deposition, thereby obtaining the moisture-proof paper of Example 1. The method for measuring the proportion of pulp having a length of 400 μm or more and 1000 μm or less and the proportion of pulp having a width of 10 μm or more and 20 μm or less in the paper base material will be described later.

[0078] Example 2 The paper base material was a paper base material with a clay coat layer (thickness: 8.1 μm) (thickness including the clay coat layer: 50 μm, proportion of pulp with a length of 400 μm to 1000 μm: 68.4%, proportion of pulp with a width of 10 μm to 20 μm: 45.4%, basis weight: 60 g / m 2 The moisture-proof paper of Example 2 was obtained in the same manner as in Example 1, except that ) was used.

[0079] Example 3 The paper base material was a paper base material with a clay coat layer (thickness: 5.8 μm) (thickness including the clay coat layer: 53 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 68.5%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 42.8%, basis weight: 60 g / m 2 The moisture-proof paper of Example 3 was obtained in the same manner as in Example 1, except that a cellulose ester (manufactured by Sappi, product name: Hi-Fi Kraft Lux) was used.

[0080] Example 4 The paper base material was a paper base material (thickness including clay coat layer: 59 μm, percentage of pulp with length between 400 μm and 1000 μm: 61.5%, percentage of pulp with width between 10 μm and 20 μm: 53.9%, basis weight: 50 g / m 2 The moisture-proof paper of Example 4 was obtained in the same manner as in Example 1, except that ) was used.

[0081] Example 5 The paper base material was a paper base material (thickness including the clay coat layer: 75 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 71.0%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 68.7%, basis weight 60 g / m 2 The moisture-proof paper of Example 5 was obtained in the same manner as in Example 1, except that ) was used.

[0082] Example 6 In the same manner as in Example 1, a first resin layer was formed on the surface of the paper substrate on the clay coating layer side. Subsequently, in the same manner as in Example 1, an aluminum vapor deposition layer was formed on the first resin layer. Next, an aqueous dispersion of polyolefin resin containing a salt of a carboxyl group (polar group-containing polyolefin) (manufactured by Sumitomo Seika Chemicals Co., Ltd., product name: ZAIKXEN AC, particle size: less than 0.2 μm, solvent: water / IPA = 1 / 1 (mass ratio), solid content: 22.5 mass%) was applied using a gravure coater onto the surface of the AL vapor deposition layer opposite the first resin layer to form a second resin layer (thickness: 3 μm), and the moisture-proof paper of Example 6 was obtained.

[0083] Example 7 The paper base material was a paper base material with a clay coat layer (thickness: 8.1 μm) (thickness including the clay coat layer: 50 μm, proportion of pulp with a length of 400 μm to 1000 μm: 68.4%, proportion of pulp with a width of 10 μm to 20 μm: 45.4%, basis weight: 60 g / m 2 The moisture-proof paper of Example 7 was obtained in the same manner as in Example 6, except that ) was used.

[0084] Example 8 The paper base material was a paper base material with a clay coat layer (thickness: 5.8 μm) (thickness including the clay coat layer: 53 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 68.5%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 42.8%, basis weight: 60 g / m 2 The moisture-proof paper of Example 8 was obtained in the same manner as in Example 6, except that a cellulose ester (manufactured by Sappi, trade name: Hi-Fi Kraft Lux) was used.

[0085] Example 9 The paper base material was a paper base material (thickness: 59 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 61.5%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 53.9%, basis weight: 50 g / m 2 The moisture-proof paper of Example 9 was obtained in the same manner as in Example 6, except that ) was used.

[0086] Example 10 The paper base material was a paper base material (thickness: 75 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 71.0%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 68.7%, basis weight: 60 g / m 2 The moisture-proof paper of Example 10 was obtained in the same manner as in Example 6, except that ) was used.

[0087] Example 11 The moisture-proof paper of Example 11 was obtained in the same manner as Example 6, except that the first resin layer (thickness: 3 μm) was formed using a coating liquid containing a polyvinyl alcohol resin (degree of polymerization: 500) instead of an aqueous dispersion of a polyolefin resin containing a salt of a carboxyl group.

[0088] Example 12 The paper base material was a paper base material with a clay coat layer (thickness: 8.1 μm) (thickness including the clay coat layer: 50 μm, proportion of pulp with a length of 400 μm to 1000 μm: 68.4%, proportion of pulp with a width of 10 μm to 20 μm: 45.4%, basis weight: 60 g / m 2 The moisture-proof paper of Example 12 was obtained in the same manner as in Example 11, except that ) was used.

[0089] Example 13 The paper base material was a paper base material with a clay coat layer (thickness: 5.8 μm) (thickness including the clay coat layer: 53 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 68.5%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 42.8%, basis weight: 60 g / m 2 The moisture-proof paper of Example 13 was obtained in the same manner as in Example 11, except that a cellulose ester (manufactured by Sappi, trade name: Hi-Fi Kraft Lux) was used.

[0090] Example 14 Paper base material with a clay coat layer (thickness: 5.8 μm) (thickness including clay coat layer: 53 μm, proportion of pulp with length between 400 μm and 1000 μm: 68.5%, proportion of pulp with width between 10 μm and 20 μm: 42.8%, basis weight: 60 g / m 2 ) was prepared. Next, an aqueous polyurethane resin containing a polyurethane resin having an acid group and a polyamine compound was applied to the surface of the paper substrate on the clay coating layer side using a gravure coater to form a first resin layer (thickness: 3 μm). Subsequently, aluminum (AL) was deposited on the first resin layer by vacuum deposition to form an AL deposited layer (thickness: 50 nm) as a water vapor barrier layer. Next, an aqueous dispersion of polyolefin resin containing a salt of a carboxyl group (polar group-containing polyolefin) (manufactured by Sumitomo Seika Chemicals Co., Ltd., product name: ZAIKXEN AC, particle size: less than 0.2 μm, solvent: water / IPA = 1 / 1 (mass ratio), solids concentration: 22.5 mass%) was applied using a gravure coater to the surface of the AL vapor deposition layer opposite the first resin layer to form a second resin layer (thickness: 3 μm), and the moisture-proof paper of Example 14 was obtained.

[0091] Example 15 The moisture-proof paper of Example 15 was obtained in the same manner as Example 1, except that instead of the aluminum vapor deposition layer, a silica vapor deposition layer (thickness: 50 nm) was formed on the first resin layer by vacuum vapor deposition.

[0092] (Comparative Example 1) The paper base material was a paper base material (thickness: 67 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 62.7%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 30.8%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 1 was obtained in the same manner as in Example 1, except that ) was used.

[0093] (Comparative Example 2) The paper base material was a paper base material (thickness: 54 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 67.7%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 39.8%, basis weight: 55 g / m 2 A moisture-proof paper of Comparative Example 2 was obtained in the same manner as in Example 1, except that ) was used.

[0094] (Comparative Example 3) The paper base material was a paper base material (thickness: 50 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 54.3%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 49.4%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 3 was obtained in the same manner as in Example 1, except that ) was used.

[0095] Comparative Example 4 The paper base material was a paper base material with a clay coat layer (thickness: 5.3 μm) (thickness including the clay coat layer: 52 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 57.5%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 47.4%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 4 was obtained in the same manner as in Example 1, except that ) was used.

[0096] (Comparative Example 5) The paper base material was a paper base material (thickness: 27 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 47.8%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 35.7%, basis weight: 33 g / m 2 A moisture-proof paper of Comparative Example 5 was obtained in the same manner as in Example 1, except that ) was used.

[0097] (Comparative Example 6) The paper base material was a paper base material with a clay coat layer (thickness: 9.9 μm) (thickness including the clay coat layer: 52 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 53.6%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 18.3%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 6 was obtained in the same manner as in Example 1, except that ) was used.

[0098] (Comparative Example 7) The paper base material was a paper base material with a clay coat layer (thickness: 9.3 μm) (thickness including the clay coat layer: 51 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 56.2%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 28.0%, basis weight: 60 g / m 2A moisture-proof paper of Comparative Example 7 was obtained in the same manner as in Example 1, except that ) was used.

[0099] (Comparative Example 8) The paper base material was a paper base material (thickness: 35 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 54.4%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 26.2%, basis weight: 40 g / m 2 A moisture-proof paper of Comparative Example 8 was obtained in the same manner as in Example 1, except that ) was used.

[0100] (Comparative Example 9) The paper base material was a paper base material (thickness: 27 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 47.8%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 35.7%, basis weight: 33 g / m 2 A moisture-proof paper of Comparative Example 9 was obtained in the same manner as in Example 6, except that ) was used.

[0101] (Comparative Example 10) The paper base material was a paper base material with a clay coat layer (thickness: 9.9 μm) (thickness including the clay coat layer: 52 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 53.6%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 18.3%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 10 was obtained in the same manner as in Example 6, except that ) was used.

[0102] (Comparative Example 11) The paper base material was a paper base material (thickness: 35 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 54.4%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 26.2%, basis weight: 40 g / m 2 A moisture-proof paper of Comparative Example 11 was obtained in the same manner as in Example 6, except that ) was used.

[0103] (Comparative Example 12) The paper base material was a paper base material with a clay coat layer (thickness: 9.9 μm) (thickness including the clay coat layer: 52 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 53.6%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 18.3%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 12 was obtained in the same manner as in Example 11, except that ) was used.

[0104] (Comparative Example 13) The paper base material was a paper base material (thickness: 35 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 54.4%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 26.2%, basis weight: 40 g / m 2 A moisture-proof paper of Comparative Example 13 was obtained in the same manner as in Example 11, except that ) was used.

[0105] (Comparative Example 14) The paper base material was a paper base material (thickness: 67 μm, percentage of pulp with a length of 400 μm or more and 1000 μm or less: 62.7%, percentage of pulp with a width of 10 μm or more and 20 μm or less: 30.8%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 14 was obtained in the same manner as in Example 11, except that ) was used.

[0106] (Comparative Example 15) The paper base material was a paper base material with a clay coat layer (thickness: 9.9 μm) (thickness including the clay coat layer: 52 μm, proportion of pulp with a length of 400 μm or more and 1000 μm or less: 53.6%, proportion of pulp with a width of 10 μm or more and 20 μm or less: 18.3%, basis weight: 60 g / m 2 A moisture-proof paper of Comparative Example 15 was obtained in the same manner as in Example 15, except that ) was used.

[0107] <Measurement of water vapor permeability (initial)> The moisture-proof papers obtained in the examples and comparative examples were measured for water vapor permeability (unit: g / m) under conditions of 40°C and 90% RH by the Mocon method in accordance with JIS K7129-2. 2The moisture-proof paper used was one that had been produced within a few days. A PERMATRAN 3 / 34G (manufactured by MOCON) was used for the measurement. The measurement was carried out three times, and the average value was calculated. The results are shown in Tables 1 to 6.

[0108] <Measurement of water vapor permeability (after 12 months)> The moisture-proof papers obtained in the Examples and Comparative Examples were cut to A4 size and left in an environment of 23°C and 50% RH for 12 months. After leaving them for 12 months, the moisture vapor permeability of the moisture-proof paper (average value of three measurements) was determined using the same method as for measuring the water vapor permeability (initial). In addition, the difference (increase) between the water vapor permeability after leaving them for 12 months and the initial water vapor permeability was calculated. The results are shown in Tables 1 to 6. In this evaluation, the difference (increase) between the water vapor permeability after 12 months and the initial water vapor permeability was 4 g / m 2 If the time is less than 100 days, the deterioration of water vapor barrier properties can be suppressed even after a long period of time has passed since production, and the product is deemed to have passed the test.

[0109] <Calculation of the percentage of pulp with a length of 0.4 mm to 1 mm and the percentage of pulp with a length of 10 μm to 20 μm> Pulp dispersions were obtained from the paper base materials of the Examples and Comparative Examples by the following procedures 1 to 4. Five thousand pulps were randomly selected from the pulp in the dispersion, and the pulp length and width of the 5,000 pulps were measured. A fiber length distribution measuring device (manufactured by Phyto Turbo Co., Ltd., product name "MORFI NE") was used for the measurements. Each pulp is divided into several sections by imaginary lines where no bending is observed. The pulp length is the sum of the lengths of each section. The pulp width is the average width of the pulp at each imaginary line.

[0110] The percentage of pulp with a length of 0.4 mm or more and 1 mm or less out of 5,000 pulp pieces was calculated from the measurement results. This percentage was calculated for the three dispersions and the average value was calculated. In addition, the percentage of pulp with a width of 10 μm or more and 20 μm or less out of 5,000 pulp pieces was calculated. This percentage was calculated for the three dispersions and the average value was calculated. The results are shown in Tables 1 to 6.

[0111] Step 1: 0.3 g (3 tablets) of sodium hydroxide and 50 g of pure water were placed in a bottle to prepare a 0.6% aqueous solution of sodium hydroxide. Operation 2: 0.3 g of the paper substrate was added to the aqueous sodium hydroxide solution prepared in Operation 1 and stirred for 24 hours. Step 3: 2 mol / l (2N) hydrochloric acid was added to the bottle to neutralize the solution, and a mixed solution was obtained. Step 4: 4 g of the mixture obtained in Step 3 was taken with a dropper and placed in a 1 L plastic container. 800 g of pure water was added to dilute the mixture 200 times to obtain a dispersion in which pulp was dispersed.

[0112] [Table 1]

[0113] [Table 2]

[0114] [Table 3]

[0115] [Table 4]

[0116] [Table 5]

[0117] [Table 6]

[0118] As shown in Tables 1 to 3, the moisture-proof papers of Examples 1 to 15 have a paper base material in which, based on the total number of pulps, the proportion of pulp pieces with a length of 0.4 mm to 1 mm is 60% or more, and the proportion of pulp pieces with a width of 10 μm to 20 μm is 40% or more, and therefore can suppress deterioration of water vapor barrier properties even after a long period of time (at least 12 months) has passed since production.

[0119] This has enabled us to verify that it is possible to provide a moisture-proof paper for the back side of decorative panels that can prevent warping of the decorative panels over a long period of time, even when used in places where there is a large difference in temperature and humidity environments on both sides, and that is also environmentally friendly, which is the objective of this invention. [Explanation of symbols]

[0120] 1: 1st resin layer 2: Second resin layer 3:Paper base material 4: Water vapor barrier layer 10: Moisture-proof paper on the back of decorative panels (moisture-proof paper)

Claims

1. A moisture-proof backside paper for decorative panels, comprising at least a paper substrate, a first resin layer, and a water vapor barrier layer in this order, In the paper base material, the proportion of pulp having a length of 0.4 mm or more and 1 mm or less is 60% or more, and the proportion of pulp having a width of 10 μm or more and 20 μm or less is 40% or more, based on the total number of pulp contained in the paper base material.

2. The moisture-proof backside paper for decorative panels according to claim 1 , further comprising a second resin layer on the surface of the water vapor barrier layer opposite to the first resin layer.

3. The moisture-proof backside paper for decorative panels according to claim 1 or 2, wherein the thickness of the first resin layer is 0.3 μm or more and 10 μm or less.

4. The moisture-proof backside paper for decorative panels according to claim 1 or 2, wherein the first resin layer contains at least one resin selected from the group consisting of polyvinyl alcohol-based resins and polyolefin resins having polar groups.

5. The moisture-proof backside paper for decorative panels according to claim 2 , wherein the second resin layer contains a polyolefin resin having a polar group.

6. The moisture-proof backside paper for decorative panels according to claim 1 or 2, wherein the water vapor barrier layer is an aluminum vapor-deposited layer.

7. The moisture-proof backside paper for decorative panels according to claim 1 or claim 2, characterized in that the mass of the pulp component contained in the paper base material is 50 mass% or more based on the mass of the entire moisture-proof backside paper for decorative panels.

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