JP7658220B2 - Moisture-proof paper on the back side of decorative panels - Google Patents

Description

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

Conventionally, decorative panels used for applications such as interior door panels have generally been made by laminating a decorative sheet having a solid print layer for providing hiding properties or a picture pattern layer for improving design properties to the surface of a multi-layered wood-based substrate such as plywood, medium density fiberboard (MDF), veneer, board material, or other such substrate.
When the moisture content of a wood-based substrate is lower than the equilibrium moisture content of the substrate under outdoor conditions, the substrate will absorb moisture from the side of the decorative board that is not bonded to the decorative sheet, causing that side to expand; when the moisture content is higher than the equilibrium moisture content of the substrate, the substrate will release moisture and shrink, whereas the side to which the decorative sheet is bonded will absorb and release almost no moisture, causing the decorative board to deform (warp, change in dimensions).

Methods known to prevent this deformation include applying paint to the backside of the decorative board with a decorative sheet bonded to the front side, bonding a synthetic resin sheet such as polyvinyl chloride, polyethylene, or polypropylene, or bonding a moisture-proof sheet made of paper/polyethylene/paper.

Conventionally, there are known moisture-proof decorative sheets having a five-layer structure of protective resin layer/printed pattern layer/interleaf reinforced paper/synthetic resin layer/interleaf reinforced paper, and doors and other fittings to which a moisture-proof back sheet having a three-layer structure of interleaf reinforced paper/synthetic resin/interleaf reinforced paper is attached (see paragraphs [0013] to [0016] and figures 1 to 4 of Patent Document 1).

Patent No. 3206408

However, conventional moisture-proof decorative sheets and moisture-proof back sheets have insufficient moisture-proofing properties, and when used for long periods of time on doors, sliding doors, partitions, etc. where there is a large difference in temperature and humidity environments on both sides, the degree of expansion and contraction on both sides can differ, causing warping.
The present invention has been made to solve this problem, and provides a moisture-proof back paper for decorative boards that prevents warping even when used in places where there is a large difference in temperature and humidity environments on both sides.

The moisture-proof back paper for decorative boards according to one embodiment of the present invention is a moisture-proof back paper for decorative boards that is formed by laminating a moisture-proof layer on one side of a paper substrate, and is characterized in that the moisture-proof layer is provided on one side of the paper substrate in the following order: a layer containing a polyvinyl alcohol-based resin; a vapor deposition layer; and a layer containing a polyolefin having at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester.

In addition, the moisture-proof paper for decorative panels according to one embodiment of the present invention is characterized in that the thickness of the layer containing the polyvinyl alcohol-based resin is 1 μm or more and 5 μm or less.

The moisture-proof paper for decorative panels according to one embodiment of the present invention is characterized in that the thickness of the vapor deposition layer is 30 nm or more and 100 nm or less.

The moisture-proof paper for decorative panels according to one embodiment of the present invention is characterized in that the thickness of the layer containing the polyolefin is 2 μm or more and 10 μm or less.

The moisture-proof paper for decorative panels according to one embodiment of the present invention is characterized in that the weight of the paper base material is 50% by mass or more based on the entire moisture-proof layer.

The moisture-proof paper for decorative boards according to one aspect of the present invention is characterized in that the moisture-proof paper for decorative boards has an adhesive primer layer provided on the outer surface of the moisture-proof layer.

The moisture-proof paper for the back surface of a decorative board according to one aspect of the present invention is characterized in that the paper base material is a reinforced paper for paper-interleaving.

According to one embodiment of the moisture-proof backside paper for decorative boards of the present invention, moisture permeability can be significantly reduced, and even when used in a location where there is a large difference in temperature and humidity environment on both sides, warping of the decorative board can be prevented, for example.
Furthermore, according to one aspect of the present invention, it is possible to provide a moisture-proof paper backing for decorative panels that contributes to reducing the amount of plastic materials used.

1 is an explanatory diagram showing the cross-sectional shape of one embodiment of moisture-proof paper of the present invention. FIG. 2 is an explanatory diagram showing the cross-sectional shape of an embodiment of the moisture-proof paper using an adhesive primer layer of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
Here, 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 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 as described below. The technical idea of the present invention can be modified in various ways within the technical scope defined by the claims.

[Moisture-proof paper 10 for decorative panels]
FIG. 1 is a schematic cross-sectional view showing a moisture-proof backside paper 10 for decorative boards according to one embodiment.
The moisture-proof back surface paper 10 for decorative panels in one embodiment is used by adhering it to the back surface of a decorative panel used, for example, as an interior door panel, and is hereinafter also referred to 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 indoors.

As shown in FIG. 1, the moisture-proof paper 10 is roughly divided into two layers, with a moisture-proof layer 30 laminated on one side of a paper base material 20 .
The moisture-proof layer 30 is composed of a layer 40 containing a polyvinyl alcohol-based resin, a vapor-deposited layer 50, and a layer 60 containing a polyolefin having at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester, provided in this order.

[Moisture permeability of moisture-proof paper 10]
The moisture permeability of the moisture-proof paper 10 is preferably less than 5 g/ ^m2 ·24 hr, and more preferably less than 5 g/ ^m2 ·24 h, 4 g/ ^m2 ·24 h or less, or 3 g/ ^m2 ·24 h or less, and the lower limit is preferably 0 g/ ^m2 ·24 hr, or 0.1 g/ ^m2 ·24 hr or more, 0.3 g/ ^m2 ·24 hr or more, 0.5 g/ ^m2 ·24 hr or more, or 1.0 g/ ^m2 ·24 hr or more.

[Paper base material 20]
The paper base material 20 is not particularly limited, and may be appropriately selected depending on the application of the moisture-proof backside paper 10 for decorative boards.
Specific examples of the paper base material 20 include tissue paper, fine paper, art paper, cast coated paper, kraft paper, titanium paper, linter paper, paperboard, gypsum board paper, fine paper, coated paper, sulfate paper, glassine paper, parchment paper, paraffin paper, and Japanese paper.
Preferably, thin paper in which synthetic resin is mixed to increase the inter-sheet strength (so-called inter-sheet reinforced paper) or paper impregnated with latex or synthetic resin is used.

The basis weight is not particularly limited, but if it is 20 g/ ^m2 or less, it will be too soft and wrinkles will easily occur during processing, and if it is 200 g/m2 or ^more , it will easily peel off from the paper layer, so 20 to 200 g/ ^m2 is preferable, 20 to 100 g/ ^m2 is more preferable, and 20 to 50 g/ ^m2 is even more preferable.
Furthermore, the paper base material 20 may be subjected to surface treatment such as corona treatment, plasma treatment, or flame treatment, if necessary.

[Coat layer]
The paper base material 20 may be provided with a coating layer (not shown) at least on the side in contact with the layer 40 containing a polyvinyl alcohol-based resin described below.
By providing a coating layer, it is possible to prevent the layer 40 containing the polyvinyl alcohol-based resin from seeping into the paper, and it is also possible to act as a sealant to fill in unevenness in the paper, so that the layer 40 containing the polyvinyl alcohol-based resin can be formed uniformly without defects.

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, and may contain clay, kaolin, calcium carbonate, talc, mica, etc. as fillers.
The thickness of the coating layer is not particularly limited, but may be, for example, 1 to 10 μm, or 3 to 8 μm.

The weight of the paper base material 20 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 weight of the moisture-proof layer 30 .
When the weight of the paper base material 20 is 50% by mass or more based on the weight of the moisture-proof layer 30, the amount of plastic material used can be sufficiently reduced, and the paper can be said to be a moisture-proof paper for the back surface of a decorative board.

[Layer 40 containing polyvinyl alcohol-based resin]
The layer 40 containing a polyvinyl alcohol-based resin is provided on the surface of the paper substrate 20 in order to improve adhesion between the paper substrate 20 and a deposition layer 50, which will be described later.
The polyvinyl alcohol resin is, for example, a completely saponified polyvinyl alcohol resin, a partially saponified polyvinyl alcohol resin, a modified polyvinyl alcohol resin, an ethylene-vinyl alcohol copolymer resin, etc. The degree of polymerization of the polyvinyl alcohol resin is preferably 300 or more and 1,500 or less.
If the degree of polymerization is 300 or more, the barrier properties and flex resistance of the moisture-proof layer will be good, and if the degree of polymerization is 1500 or less, the viscosity of the coating liquid of the polyvinyl alcohol-based resin described below will be low, resulting in good coatability.

The layer 40 containing the polyvinyl alcohol-based resin can be provided by applying a coating liquid containing the above-mentioned polyvinyl alcohol-based resin and a solvent onto the paper substrate 20 and drying it.
Examples of the solvent contained in the coating liquid include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide. In particular, a mixed solvent of water and an alcohol such as methyl alcohol, ethyl alcohol, or isopropyl alcohol is preferred.
The coating liquid may contain additives such as a surfactant, a preservative, a storage stabilizer, a silane coupling agent, and an organic titanate.

Such a layer 40 containing a polyvinyl alcohol-based resin has excellent flexibility, can suppress cracking of the deposition layer 50, and can improve adhesion between the deposition layer 50 and the layer 40 containing a polyvinyl alcohol-based resin.

The thickness of the layer 40 containing the polyvinyl alcohol resin may be, for example, 1 μm or more, 2 μm or more, or 5 μm or less. If the thickness is 1 μm or more, the unevenness of the paper base material 20 described above can be efficiently filled, and the deposition layer 50 described later can be laminated evenly.
Furthermore, if the thickness is 5 μm or less, the deposition layer 50 can be laminated uniformly while keeping costs down.

[Deposition layer 50]
The deposition layer 50 is a layer formed by depositing a metal or an inorganic compound.
The deposition layer 50 may be obtained by depositing aluminum, or may contain aluminum oxide (A10x), silicon oxide (SiOx), or the like.

The thickness of the deposition layer 50 may be appropriately set depending on the intended use, but is preferably 30 nm or more, 50 nm or more, and may be 100 nm or less, 80 nm or less.
By making the thickness of the vapor deposition layer 50 30 nm or more, it is easy to ensure sufficient continuity of the vapor deposition layer 50, and by making the thickness 100 nm or less, the occurrence of curling and cracking can be sufficiently suppressed, and it is easy to achieve sufficient gas barrier performance and flexibility.

The deposition layer 50 is preferably formed by a vacuum deposition means from the viewpoints of oxygen gas barrier performance and film uniformity.
The film may be formed by known methods such as vacuum deposition, sputtering, and chemical vapor deposition (CVD), with the vacuum deposition being preferred due to its high film formation speed and high productivity.
Among the vacuum deposition methods, the deposition method using electron beam heating is particularly effective because the deposition rate can be easily controlled by the irradiation area and electron beam current, and the temperature of the deposition material can be raised and lowered in a short time.

[Polyolefin-containing layer 60]
The polyolefin-containing layer 60 is provided on the surface of the vapor-deposited layer 50 so as to be in contact with the vapor-deposited layer 50, and contains a polyolefin having at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester.

The layer 60 containing such a polyolefin has excellent flexibility, can suppress cracking of the vapor-deposited layer 50, and has excellent adhesion to the vapor-deposited layer 50.
Furthermore, by including the above-mentioned polyolefin, it is possible to obtain a moisture-proof layer 30 having excellent water vapor barrier properties.

The polyolefin-containing layer 60 may contain other components in addition to the above-mentioned polyolefins.
Examples of other components include silane coupling agents, organic titanates, polyacrylics, polyesters, polyurethanes, polycarbonates, polyureas, polyamides, polyolefin emulsions, polyimides, melamine, and phenols.

The content of the polyolefin in the polyolefin-containing layer 60 may be, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass.

The thickness of the layer 60 containing polyolefin may be, for example, 2 μm or more, 3 μm or more, 10 μm or less, 8 μm or less, or 5 μm or less.
Furthermore, if the thickness of the polyolefin-containing layer 60 is 10 μm or less, the adhesion to the deposition layer and the barrier properties can be sufficiently exhibited while keeping costs down.

The polyolefin-containing layer 60 can be provided by applying a coating liquid containing the above-mentioned polyolefin and a solvent onto the vapor deposition layer 50 and drying it.
Examples of the solvent contained in the coating liquid 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 lactone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used alone or in combination of two or more. Among these, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl lactone, and water are preferred from the viewpoint of properties.
From the environmental viewpoint, methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferable.

[Adhesion primer layer 70]
The adhesive primer layer 70 is provided for the purpose of ensuring sufficient adhesion with various laminating adhesives, such as isocyanate-curing urethane resins and modified vinyl acetate resin emulsions, which are used when laminating and adhering to the surface of various substrates.
Known materials for this purpose include various primers such as ester resins, urethane resins, acrylic resins, polycarbonate resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, and nitrocellulose resins. From these, a primer that matches the type of laminating adhesive is selected and used.
For example, when a modified vinyl acetate resin emulsion adhesive is used as the laminating adhesive, good adhesion can be obtained with a urethane adhesive primer.

Furthermore, if an inorganic fine powder such as silica is added to the adhesive primer layer 70, the surface of the adhesive primer layer 70 will be roughened, which will not only prevent blocking when the moisture-proof sheet is rolled up and stored, but will also improve adhesion to the laminating adhesive through an anchoring effect.
The adhesive primer layer 70 can be formed by using an adhesive composition, either alone or in combination, and applying the composition by a suitable coating method such as roll coating or gravure printing.

(Features and Effects of the Embodiments Based on the Present Invention)
The features of the embodiment according to the present invention are as follows.
(First characteristic point)
The first feature is that the moisture-proof back paper 10 for decorative panels is formed by laminating a moisture-proof layer 30 on one side of a paper base material 20, and the moisture-proof layer 30 is formed by providing, in this order, a layer 40 containing a polyvinyl alcohol-based resin, a vapor deposition layer 50, and a layer 60 containing a polyolefin having at least one type selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester on one side of the paper base material 20.

(Effect of the first characteristic point)
According to the first characteristic, the moisture permeability can be significantly reduced, and even when used in a location where there is a large difference in temperature and humidity environment on both sides, for example, warping of the decorative board can be prevented.
Furthermore, the first characteristic point can contribute to reducing the amount of plastic material used.
Specifically, as shown in Tables 1 and 2 described later, taking the Examples and Comparative Examples as examples, the moisture permeability (JIS Z 0208) is 5.0 g/ ^m2 ·24 hr or less, and therefore the moisture proof performance is far superior to that of a moisture proof sheet made of a synthetic resin such as polyvinyl chloride, polyethylene, or polypropylene, or a sheet made of paper/polyethylene/paper.
It also reduces the amount of plastic used and is highly recyclable.

(Second characteristic point)
The second characteristic is that the thickness of the layer 40 containing the polyvinyl alcohol-based resin is 1 μm or more and 5 μm or less.
(Effect of the second characteristic point)
According to the second characteristic, when the thickness of the layer 40 containing the polyvinyl alcohol-based resin is 1 μm or more, the unevenness of the paper base material 20 can be efficiently filled, and the vapor deposition layer 50 can be laminated evenly.
Furthermore, if the thickness is 5 μm or less, the deposition layer 50 can be laminated uniformly while keeping costs down.

(Third characteristic point)
A third characteristic point is that the thickness of the deposition layer 50 is 30 nm or more and 100 nm or less.
(Effect of the third characteristic point)
According to the third characteristic, by making the thickness of the vapor deposition layer 50 30 nm or more, it is easy to ensure sufficient continuity of the vapor deposition layer 50, and by making the thickness 100 nm or less, the occurrence of curling and cracking can be sufficiently suppressed, and it is easy to achieve sufficient gas barrier performance and flexibility.

(Fourth characteristic point)
A fourth characteristic point is that the thickness of the polyolefin-containing layer 60 is 2 μm or more and 10 μm or less.
(Effect of the fourth characteristic point)
In the fourth characteristic, the thickness of the polyolefin-containing layer 60 is set to 2 μm or more in order to protect the deposition layer as the outermost layer and to maintain water vapor barrier performance.
Furthermore, if the thickness is 10 μm or less, the adhesiveness to the deposition layer 50 and the barrier properties can be sufficiently exhibited while keeping costs down.

(Fifth characteristic point)
A fifth characteristic is that the weight of the paper base material 20 is 50% by mass or more based on the entire moisture-proof layer 30 .
(Effect of the fifth characteristic point)
According to the fifth characteristic, if the amount is 50 mass % or more, the amount of plastic material used can be sufficiently reduced, and the moisture-proof back surface paper 10 for decorative boards can be said to be made of paper.
That is, according to the fifth characteristic point, it contributes to reducing the amount of plastic materials used, and since it is composed of wood materials and paper components, it is also highly recyclable.

(Sixth characteristic point)
The sixth characteristic is that the moisture-proof backside paper 10 for decorative boards has an adhesive primer layer 70 provided on the outer surface of the moisture-proof layer 30 .
(Effect of the sixth characteristic point)
According to the sixth feature, the adhesive primer layer 70 can be used for laminating and adhering to the surface of various substrates. For example, the adhesive primer layer 70 ensures sufficient adhesion to various laminating adhesives such as isocyanate-curing urethane resins and modified vinyl acetate resin emulsions.
In addition, by adding, for example, inorganic fine powder to the adhesive primer layer 70, the surface of the adhesive primer layer 70 is roughened, which not only prevents blocking when the moisture-proof paper 10 for decorative panels is rolled up and stored, but also improves adhesion to the laminating adhesive through an anchoring effect.

(Seventh characteristic point)
The seventh characteristic is that in the moisture-proof backside paper 10 for decorative boards, the paper base material 20 is a reinforced inter-paper paper.
(Effect of the Seventh Feature)
According to the seventh characteristic point, by using inter-layer reinforced paper, peeling between the paper layers can be prevented in the event of long-term use or when unavoidable external forces are applied.

(Eighth characteristic point)
The eighth characteristic point is that the moisture permeability of the moisture-proof backside paper 10 for decorative boards is less than 5.0 g/m ² ·24 hr.
(Effect of the eighth characteristic point)
According to the eighth characteristic point, even if the laminate is used in a place where there is a large difference in temperature and humidity environment on both sides, for example, warping of the decorative board can be prevented.
Specifically, as shown in Tables 1 and 2 described later, taking the Examples and Comparative Examples as examples, the moisture permeability (JIS Z 0208) is less than 5.0 g/ ^m2 ·24 hr, and therefore the moisture proof performance is far superior to that of a moisture proof sheet made of a synthetic resin such as polyvinyl chloride, polyethylene, or polypropylene, or a sheet made of paper/polyethylene/paper.

(Ninth characteristic point)
A ninth characteristic point is that the degree of polymerization of the layer 40 containing the polyvinyl alcohol-based resin is 300 or more and 1,500 or less.
(Effect of the ninth characteristic point)
According to the ninth feature, by setting the degree of polymerization of the layer 40 containing a polyvinyl alcohol-based resin to be 300 or more, the barrier property and bending resistance of the moisture-proof layer are improved, and if the degree of polymerization is 1,500 or less, the viscosity of the coating liquid for the layer 40 containing a polyvinyl alcohol-based resin described later is reduced, resulting in improved coatability.

(Tenth characteristic point)
A tenth characteristic point is that the thickness of the layer 40 containing a polyvinyl alcohol-based resin is 1 μm or more and 5 μm or less.
(Effect of the 10th characteristic point)
According to the tenth characteristic point, by making the thickness of the layer 40 containing a polyvinyl alcohol-based resin 1 μm or more, the unevenness of the paper base material 20 can be efficiently filled, and the vapor deposition layer 50 can be laminated evenly.
Furthermore, if the thickness is 5 μm or less, the deposition layer 50 can be laminated uniformly while keeping costs down.

(Eleventh characteristic point)
An eleventh feature is that the thickness of the deposition layer 50 is not less than 30 nm and not more than 100 nm.
(Effects of the eleventh characteristic point)
According to the eleventh characteristic point, by making the thickness of the vapor deposition layer 50 30 nm or more, it is easy to ensure sufficient continuity of the vapor deposition layer 50, and by making the thickness 100 nm or less, the occurrence of curling and cracking can be sufficiently suppressed, and it is easy to achieve sufficient gas barrier performance and flexibility.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.
Example 1
A coating solution prepared by dissolving polyvinyl alcohol resin with a saponification degree of 98% and a polymerization degree of 500 in a water/1PA=8/2 solution at a solids concentration of 10% by mass was applied onto the surface of ³⁰ g/m2 inter-paper reinforced paper (manufactured by Tenma Tokushu Paper Co., Ltd.) as a paper substrate using a bar coater, and the coating solution was dried in an oven to form a layer containing polyvinyl alcohol resin.
The layer thickness was 3 μm.
Subsequently, Al was deposited on the layer containing the polyvinyl alcohol resin by vacuum deposition to give an Al deposited layer having a thickness of 50 nm.
Thereafter, a coating liquid containing a carboxyl group salt (product name: Chemipearl S500, manufactured by Mitsui Chemicals) was applied onto the vapor deposition layer using a bar coater and dried in an oven to form a layer containing polyolefin, thereby obtaining a moisture-proof layer.
The thickness of the layer containing the polyolefin was 3 μm.

Example 2
A moisture-proof layer was obtained in the same manner as in Example 1, except that the thickness of the layer containing the polyvinyl alcohol resin was 1 μm.
Example 3
A moisture-proof layer was obtained in the same manner as in Example 1, except that the thickness of the polyolefin-containing layer was 2 μm.

Example 4
A moisture-proof layer was obtained in the same manner as in Example 1, except that the thickness of the polyolefin-containing layer was 10 μm.
(Example 5)
A moisture-proof layer was obtained in the same manner as in Example 1, except that the vapor-deposited layer was made of silica and had a thickness of 30 nm.

Example 6
A moisture-proof layer was obtained in the same manner as in Example 1, except that the vapor-deposited layer was made of alumina and had a thickness of 30 nm.

(Comparative Example 1)
A moisture-proof layer was obtained in the same manner as in Example 1, except that a coating liquid containing a vinyl acetate-based polyolefin resin (product name: Chemipearl V300, manufactured by Mitsui Chemicals) was used instead of the coating liquid containing the polyvinyl alcohol resin.
(Comparative Example 2)
A moisture-proof layer was obtained in the same manner as in Example 1, except that no vapor deposition layer was provided.

(Comparative Example 3)
As a conventional moisture-proof sheet, a 30 g/ ^m2 inter-paper reinforced paper (manufactured by Tenmon Special Paper Co., Ltd.) with one side corona-treated was sandwich-laminated with 50 μm of molten polyethylene resin extruded from a T-die extruder to produce a moisture-proof sheet (inter-paper reinforced paper/polyethylene/inter-paper reinforced paper).

<Evaluation>
The moisture permeability of the moisture-proof sheets of the Examples and Comparative Examples prepared above was calculated in accordance with JIS Z 0208, and a comparison was made between the moisture permeabilities. The results are shown in Tables 1 and 2 below.

As is clear from the results in Tables 1 and 2, the moisture-proof sheets of the examples had significantly lower moisture permeability than the moisture-proof sheets of the comparative examples. The moisture-proof sheets of the present invention have been found to have improved moisture permeability due to the inclusion of a moisture-proof layer, and are expected to have the effect of reducing warping of the decorative panels caused by moisture absorption and release due to changes in temperature and humidity indoors compared to conventional products.

This enabled us to verify that it is possible to provide a moisture-proof paper for the back side of decorative boards that can prevent warping even when used in places where there is a large difference in temperature and humidity environments on both sides, which is the objective of this invention.

<Evaluation Results>
(Comparison between Examples 1 to 6 and Comparative Examples 1 to 3)
Using Tables 1 and 2, the moisture-proof decorative papers according to Examples 1 to 6 and the moisture-proof decorative papers according to Comparative Examples 1 to 3 were compared in terms of moisture permeability.
The moisture permeability of the moisture-proof decorative paper is deemed to be acceptable if it is 5 g/m ² ·24 hr or less, and as shown in Table 1, all of Examples 1 to 6 passed the criteria.
In contrast, all of Comparative Examples 1 to 3 failed, as shown in Table 2.
It can be assumed that the reason for this is that Comparative Example 1 does not have a "polyolefin-containing layer" in comparison with Examples 1 to 6.
It is presumed that the reason for the increase in moisture permeability in Comparative Example 2 compared to Examples 1 to 6 is the absence of a "vapor deposition layer." It is presumed that the reason for the increase in moisture permeability in Comparative Example 2 compared to Comparative Example 1 is the absence of a "vapor deposition layer."
It is presumed that the reason for this is that, in comparison with Examples 1 to 6, Comparative Example 3 does not have the "layer containing a polyvinyl alcohol-based resin," the "vapor deposition layer," and the "layer containing a polyolefin."

REFERENCE SIGNS LIST 10 Moisture-proof paper for decorative laminate back surface 20 Paper substrate 30 Moisture-proof layer 40 Layer containing polyvinyl alcohol-based resin 50 Vapor-deposited layer 60 Layer containing polyolefin 70 Adhesive primer layer

Claims (7)

A moisture-proof paper for decorative panels having a back surface formed by laminating a moisture-proof layer on one side of a paper base material,
The moisture-proof layer is a back-side moisture-proof paper for decorative panels, characterized in that it is formed by providing, on one side of the paper base material, a layer containing a polyvinyl alcohol-based resin, a vapor deposition layer, and a layer containing a polyolefin having at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and a carboxylic acid ester, in that order. The moisture-proof backside paper for decorative panels according to claim 1, characterized in that the thickness of the layer containing the polyvinyl alcohol-based resin is 1 μm or more and 5 μm or less. The moisture-proof back paper for decorative panels according to claim 1 or 2, characterized in that the thickness of the vapor deposition layer is 30 nm or more and 100 nm or less. The moisture-proof backside paper for decorative panels according to any one of claims 1 to 3, characterized in that the thickness of the layer containing polyolefin is 2 μm or more and 10 μm or less. The moisture-proof paper for the back side of decorative panels according to any one of claims 1 to 4, characterized in that the weight of the paper base material is 50% by mass or more based on the entire moisture-proof layer. The moisture-proof back paper for decorative boards according to any one of claims 1 to 5, characterized in that an adhesive primer layer is provided on the outer surface of the moisture-proof layer. The moisture-proof backside paper for decorative boards according to any one of claims 1 to 6, characterized in that the paper base material is a reinforced inter-paper paper.

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