JP7597170B2 - Laminated stretched film, substrate for decorative sheet, decorative sheet and decorative plate - Google Patents

Description

The present invention relates to a laminated stretched film, a substrate for a decorative sheet, a decorative sheet, and a decorative board.

Decorative sheets used for architectural interior materials and the surfaces of building fixtures, particularly those used in public places, are required to meet the technical standards for non-combustible materials set out in Article 108-2, Items 1 and 2 of the Enforcement Order of the Building Standards Act. Traditionally, decorative sheets that meet these technical standards for non-combustible materials have contained soft polyvinyl chloride resins. However, decorative sheets that contain soft polyvinyl chloride resins have had problems such as the generation of toxic gases when incinerated after disposal.

For this reason, decorative sheets using polyolefin resins have been proposed in recent years instead of polyvinyl chloride resins. However, although the generation of toxic gases during combustion is suppressed when polyolefin resins are used for decorative sheets, it has been difficult to meet the technical standards for non-combustible materials because polyolefin resins have excellent combustibility.
Decorative sheets using polyolefin resins that satisfy the technical standards for noncombustible materials set forth in the above-mentioned laws and regulations include, for example, the sheets described in Patent Documents 1 and 2. Patent Documents 1 and 2 disclose structures using polyolefin resin layers that contain inorganic fillers such as calcium carbonate.

JP 2013-010931 A JP 2011-122293 A

As a method for obtaining a decorative sheet made of a polyolefin resin that satisfies the technical standards for non-combustible materials, for example, a method for thinning the substrate of the decorative sheet, i.e., the substrate for the decorative sheet, can be mentioned. In addition, in order to impart design to the decorative sheet, a printing layer is generally provided on the surface of the substrate for the decorative sheet. In this case, when the substrate for the decorative sheet is fed into a printing machine, the substrate for the decorative sheet is required to have sufficient mechanical tensile strength in order to prevent the occurrence of misalignment of the printing position.
In this case, if a stretched film that has been uniaxially or biaxially stretched is used as the decorative sheet substrate, the decorative sheet substrate can be made thinner, improving the flame resistance of the decorative sheet, while at the same time increasing the elastic modulus of the decorative sheet substrate, thereby increasing the mechanical strength of the decorative sheet substrate per the same cross-sectional area, and further increasing the mechanical strength of the entire decorative sheet.

However, when the surface layer of the substrate for decorative sheets becomes hard by stretching, stress concentration occurs between the printed layer and the surface layer, and the printed layer and the surface layer are easily peeled off near the interface. In such a situation, there is a problem that the peel strength expressed by the peel test force between the transparent resin layer formed (laminated) on the substrate for decorative sheets via the printed layer and the substrate is significantly reduced.
Achieving both improved peel strength and increased strength through stretching is an issue in obtaining a decorative sheet that combines mechanical strength and durability in a thin decorative sheet substrate.

The present invention has been made with attention to the above-mentioned points, and aims to provide a laminated stretched film, a substrate for decorative sheet, a decorative sheet and a decorative board in which the mechanical strength of the substrate for decorative sheet is improved despite being a thin film by increasing the elastic modulus while maintaining a peel strength (interlayer adhesion strength) that can be evaluated by a peel test force between the substrate for decorative sheet and a laminate including a transparent resin layer and the like provided above a printed layer.

In order to solve the above problems, a laminated stretched film according to one embodiment of the present invention is a uniaxial or biaxial laminated stretched film having a plurality of layers whose resin material is mainly composed of a polypropylene-based resin, and when a first layer located at the outermost surface of the plurality of layers is defined as a surface layer and a layer other than the surface layer of the plurality of layers is defined as a core layer, the surface layer has a Martens hardness of 20 N/mm2 ^or more and less than 120 N/ ^mm2 and a peak intensity ratio in Raman spectroscopy of 1.0 or more and less than 6.0.
Moreover, a decorative sheet according to one embodiment of the present invention comprises a laminated stretched film according to the above embodiment as a substrate for a decorative sheet, and one or more transparent resin layers containing a polyolefin resin formed on the surface of the substrate for a decorative sheet on the side of the surface layer.

According to one aspect of the present invention, the peel strength (interlayer adhesion) between the substrate for decorative sheet and a laminate including a transparent resin layer provided above a printed layer, which can be evaluated by a peel test force, is maintained, while the elastic modulus of the substrate for decorative sheet is increased, thereby improving the mechanical strength of the substrate despite being a thin film.
In one aspect of the present invention, the substrate for decorative sheet is stretched uniaxially or biaxially, and the Martens hardness and the peak intensity ratio in Raman spectroscopy of the surface layer of the substrate for decorative sheet are adjusted, thereby suppressing stress concentration at the interface between the surface layer and the core layer, and sufficient peel strength is obtained.

1 is a cross-sectional view showing one configuration example of a decorative sheet according to an embodiment of the present invention.

An embodiment of the present invention will be described with reference to the drawings.
Here, the configuration shown in Fig. 1 is schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc. are different 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 is not limited to the materials, shapes, structures, etc. of the components described below. The technical idea of the present invention can be modified in various ways within the technical scope defined by the claims.

Figure 1 is a cross-sectional view showing the configuration of a decorative sheet 1 according to this embodiment. The decorative sheet 1 has a decorative sheet substrate 6 (hereinafter also referred to as substrate 6) made of a laminate containing multiple thermoplastic resin layers, and a printing layer 5, an adhesive layer 4, a transparent resin layer 3, and a surface protective layer 2 are formed in this order on one surface (front surface) of the substrate 6. In addition, the decorative sheet 1 has a concealing layer 7 and a primer layer 8 provided on the other surface (rear surface) of the substrate 6. The rear surface of the substrate 6 is also called the bottom surface.

The substrate 6 is made of a laminate of n substrate layers (n is any positive integer equal to or greater than 2). The substrate 6 includes a first substrate layer 6-1 (hereinafter referred to as surface layer 6-1) that is the outermost surface, and at least one of the second substrate layer 6-2 to the n-th substrate layer 6-n that are located below the surface layer 6-1. The second substrate layer 6-2 to the (n-1)-th substrate layer 6-(n-1) are also referred to as "core layers 6-2 to 6-(n-1)", and the n-th substrate layer 6-n that is the other surface of the substrate 6 is also referred to as "lowest layer 6-n". In addition, when the substrate 6 is made of two layers, the surface layer 6-1 and the core layer 6-2, the back surface of the core layer 6-2 is the other surface of the substrate 6. In addition, since the bottom layer 6-n may come into contact with the primer layer 8, it is preferable that the bottom layer 6-n has the same structure as the surface layer 6-1. By doing so, the adhesion between the substrate 6 and the primer layer 8 can be maintained.

The concealing layer 7 may be formed between the substrate 6 and the printing layer 5, or may be omitted. In particular, in this embodiment, since an inorganic pigment is mixed into the substrate 6 as described below, there is no problem in terms of design even if the concealing layer 7 is omitted. When the amount of pigment mixed into the substrate 6 is kept small, it is preferable to provide the concealing layer 7 as necessary.
The thickness of the decorative sheet 1 is preferably within a range of, for example, 49 μm to 360 μm. When the thickness of the decorative sheet 1 is within this range, the printing workability during the production of the decorative sheet 1 is improved, and the production costs can be reduced.
The surface (rear surface) of such a decorative sheet 1 on which the primer layer 8 is formed is attached to a base plate 9 made of, for example, a wood base material, thereby forming a decorative board.
Each part of the decorative sheet 1 will now be described in detail.

<Substrate>
The substrate 6 in this embodiment is made of a laminated stretched film that has been thinned by uniaxial or biaxial stretching.
By stretching the substrate 6, the Martens hardness and the peak intensity ratio in Raman spectroscopy of the surface layer of the substrate for decorative sheets are adjusted, and the peel strength (interlayer adhesion) that can be evaluated by the peel test force is improved. The thickness of the substrate 6 is preferably 20 μm or more and less than 60 μm, and more preferably 20 μm or more and 40 μm or less. When the thickness of the substrate 6 is in the range of 20 μm or more and less than 60 μm, the peel strength, mechanical properties (mechanical strength), and non-flammability of the decorative sheet 1 can be achieved at the same time. In addition, when the thickness of the substrate 6 is in the range of 20 μm or more and 40 μm or less, it is more preferable because the non-flammability is further improved.

The reason why the non-combustibility is improved by setting the thickness of the substrate 6 within the above numerical range is believed to be because the substrate 6 is thinned by stretching. Also, the reason why the mechanical properties (mechanical strength) are improved by setting the thickness of the substrate 6 within the above numerical range is believed to be because the elastic modulus of the substrate 6 is increased by stretching.
The noncombustibility of the substrate 6 is preferably such that, in a heat generation test using a cone calorimeter tester conforming to ISO 5660-1 in a state where the substrate 6 is laminated with a noncombustible substrate (not shown) made of a metal plate, an inorganic material, etc., the substrate 6 has a noncombustibility sufficient to satisfy the requirements set forth in Article 108-2, Items 1 and 2 of the Enforcement Order of the Building Standards Act. As in the examples described later, it is possible to impart a noncombustibility sufficient to satisfy the requirements set forth in Article 108-2, Items 1 and 2 of the Enforcement Order of the Building Standards Act.

As described above, the substrate 6 is constructed as a laminate of two or more substrate layers, and each substrate layer is formed from a resin material. The substrate 6 contains a polypropylene resin, which is a thermoplastic resin, as the main component of the resin material that constitutes the substrate layer. In this specification, the main component refers to a resin material that is contained in an amount of 70 parts by mass or more and 100 parts by mass or less, preferably 90 parts by mass or more and 100 parts by mass or less, based on 100 parts by mass of the resin material that constitutes the layer.

(Martens hardness of substrate 6)
The "Martens hardness" in this embodiment will be described below.
The Martens hardness in this embodiment is measured, for example, using a Martens hardness measuring device (Fisherscope HM2000; Fisher Instruments Co., Ltd.) conforming to ISO14577. The Martens hardness may be measured from the cross section of the substrate to avoid the influence of the core layer of the laminated substrate other than the surface layer during measurement. Specifically, the substrate may be embedded in a resin such as a cold-curing epoxy resin or a UV-curing resin and sufficiently cured, and then cut so that the cross section of the substrate appears and mechanically polished to obtain a measurement surface. In addition, a specific measurement method is to press an indenter into the measurement surface of the substrate of each sample, and calculate the Martens hardness from the indentation depth and the load. The measurement conditions are, for example, a test force of 10 mN, a test force load time of 10 seconds, and a test force holding time of 5 seconds.

(Peak Intensity Ratio of Substrate 6 in Raman Spectroscopy)
Hereinafter, the "peak intensity ratio in Raman spectroscopy" in this embodiment will be described.
In this embodiment, in order to measure the peak intensity ratio of the polypropylene film surface by Raman spectroscopy, the Raman scattered light is analyzed using a polarizing filter. Here, the value of the peak intensity ratio is expressed by the following formula (1).

In addition, S808 parallel and S841 parallel are defined as the peak intensity at 808 cm ^-1 and the peak intensity at 841 cm ^{-1 when the polarization direction and the MD direction (flow direction during film production) are parallel. S808 perpendicular is defined as the peak intensity at 808 cm-1} when the polarization direction and the MD direction are perpendicular, and S841 perpendicular is defined as the peak intensity at 841 cm ^-1 when the polarization direction and the MD direction are perpendicular. This peak intensity ratio is an indicator of the degree of molecular orientation.

[Surface layer]
The surface layer 6-1 forming the surface of the substrate 6 has a Martens hardness of 20 N/mm2 ^or more and 120
N/ ^mm2 or less, preferably 50N/mm2 ^or more and less than 120N/ ^mm2 , and the peak intensity ratio in Raman spectroscopy is 1.0 or more and less than 6.0. By doing so, stress concentration between the printing layer 5 and the surface layer 6-1 can be suppressed, resulting in sufficient peel strength. In addition, if the Martens hardness of the surface layer 6-1 is 50N/ ^mm2 or more, it is possible to obtain a stretched film that is preferable in terms of scratch resistance on the surface. If the Martens hardness is less than 20N/ ^mm2 , stress concentration occurs between the surface layer 6-1 and the core layers 6-2 to 6-(n-1), and the peel strength may be insufficient. In addition, if the Martens hardness is 120N/mm2 or ^more , stress concentration occurs between the printing layer 5 and the surface layer 6-1, and the peel strength may be insufficient.

In addition, even if the Martens hardness of the surface layer 6-1 is 20 N/mm2 ^{or more} and less than 120 N/ ^mm2 , when the peak intensity ratio in Raman spectroscopy is 6.0 or more, the cohesive force of the surface layer 6-1 is insufficient, so that in a peel test between the transparent resin layer 3 and the substrate 6, cohesive failure of the surface layer 6-1 may occur, resulting in insufficient peel strength. In addition, when the peak intensity ratio in Raman spectroscopy is less than 1.0, the cohesive force of the surface layer 6-1 is insufficient, so that in a peel test between the transparent resin layer 3 and the substrate 6, cohesive failure of the surface layer 6-1 may occur, resulting in insufficient peel strength. In contrast, by setting the peak intensity ratio in Raman spectroscopy to be 1.0 or more and less than 6.0, the peel strength between the transparent resin layer 3 and the substrate 6 becomes sufficient.
In this way, by making the Martens hardness of the surface layer 6-1 20 N/mm2 ^or more ^and less than 120 N/mm2 and making the peak intensity ratio in Raman spectroscopy 1.0 or more and less than 6.0, the peel strength between the stretched substrate 6 and the transparent resin layer 3 can be improved.

[Core layer]
When the substrate is put into the printer, in order to suppress the occurrence of misalignment of the printing position, the substrate is required to have sufficient mechanical tensile strength. Therefore, by making the Martens hardness of the core layers 6-2 to 6-(n-1) 60 N/mm ² or more and less than 150 N/mm ² , the substrate has a sufficiently high tensile strength even if it is a thin film. On the other hand, if the Martens hardness of the core layers 6-2 to 6-(n-1) is less than 60 N/mm ² , the substrate may not have sufficient tensile strength when stretched and thinned. In addition, if the Martens hardness is 150 N/mm ² or more, stress concentration occurs between the surface layer 6-1 and the core layers 6-2 to 6-(n-1), which is not preferable.
The Martens hardness values of the core layers 6-2 to 6-(n-1) may be greater than that of the surface layer 6-1. By making the Martens hardness values of the core layers 6-2 to 6-(n-1) greater than that of the surface layer 6-1, the substrate 6 can have sufficiently high peel strength and tensile strength.

[Bottom layer]
When recycling the decorative sheet 1, it is desirable to separate the decorative sheet 1 from, for example, the base plate 9. Therefore, the Martens hardness of the bottom layer 6-n is set to 20 N/mm2 or ^more and 120
By setting the Martens hardness to less than N/ ^mm2 and the peak intensity ratio in Raman spectroscopy to 1.0 or more and less than 6.0, the decorative sheet 1 can be easily separated from the base plate 9. On the other hand, if the Martens hardness of the bottom layer 6-n is less than 20 N/ ^mm2 or greater than 120 N/ ^mm2 , the decorative sheet 1 may not be easily separated from the base plate 9. Also, even if the peak intensity ratio in Raman spectroscopy is less than 1.0 or greater than 6.0, the decorative sheet 1 may not be easily separated from the base plate 9.

In addition, since the bottom layer 6-n of the substrate 6 may come into contact with the primer layer 8, by making the bottom layer 6-n of the substrate 6 have a structure similar to that of the surface layer 6-1, the adhesive strength (adhesion) between the substrate 6 and the primer layer 8 can also be improved.
As described above, by specifying the Martens hardness and the peak intensity ratio in Raman spectroscopy in the surface layer 6-1 of the substrate 6, it is possible to improve the peel strength (interlayer adhesion) between the substrate 6 and a laminate including the transparent resin layer 3 provided above the printing layer 5, which can be evaluated by a peel test force, and also to improve the mechanical strength of the thin-film substrate 6.

(Resin material)
As described above, the main component of the resin material constituting each of the base layers constituting the base material 6, ie, the surface layer 6-1 and each of the base layers which become the core layers 6-2 to 6-n, is a polypropylene-based resin.
The polypropylene-based resin may be a polypropylene copolymerized with one or more types of α-olefins. Examples of α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 9-methyl-1-decene, 11-methyl-1-dodecene, and 12-ethyl-1-tetradecene.
In order to improve the tensile modulus of elasticity of the base material 6, it is preferable to use highly crystalline polypropylene.

(Soft material)
The surface layer 6-1 may contain a resin material with low crystallinity as a soft material in order to adjust the Martens hardness after stretching or the peak intensity ratio in Raman spectroscopy.
A first example of a soft material is a polypropylene-based resin made of a propylene-α-olefin copolymer, which is an α-olefin copolymer of polypropylene. The propylene-α-olefin copolymer is a polypropylene-based resin produced by copolymerizing propylene with an α-olefin made of a linear olefin. Examples of α-olefins made of linear olefins include ethylene, butene, and pentene. This polypropylene-based resin made of a propylene-α-olefin copolymer is a polypropylene-based resin with a lower melting point than homopolypropylene.

Here, the copolymerization ratio of the α-olefin in the polypropylene-based resin consisting of a propylene-α-olefin copolymer is preferably 3% or more and less than 16% (the content of the α-olefin is 3 parts by mass or more and less than 16 parts by mass per 100 parts by mass of the polypropylene-based resin which is a propylene-α-olefin copolymer).
If the copolymerization ratio is 16% or more, the cohesive strength of the surface layer 6-1 decreases, and the required peel strength may not be obtained. If the copolymerization ratio is less than 3%, the cohesive strength of the surface layer 6-1 decreases, and the required peel strength may not be obtained.

A second example of the soft material is a polypropylene resin whose melting point is lowered compared to that of isotactic homopolypropylene by lowering the stereoregularity of the polypropylene resin. Here, the stereoregularity can be expressed by the mesopentad fraction. The mesopentad fraction representing the stereoregularity of the soft material is preferably 30% or more and less than 75%. If the mesopentad fraction is less than 30%, the cohesive force of the surface layer 6-1 is reduced, and the required peel strength may not be obtained. If the mesopentad fraction is 75% or more, the cohesive force of the surface layer 6-1 is reduced, and the required peel strength may not be obtained.
By appropriately blending the soft materials as exemplified above, it is possible to reliably adjust the Martens hardness of the surface layer 6-1 after stretching to 20 N/ ^mm2 or more and less than 120 N/ ^mm2 , and the peak intensity ratio in Raman spectroscopy to 1.0 or more and less than 6.0.

When the surface layer 6-1 contains a soft material, the surface layer 6-1 is preferably formed from a mixed resin in which 5 parts by mass or more of the soft material is mixed with 100 parts by mass of the resin (base resin) that is the main component constituting the surface layer 6-1. When the amount of the soft material mixed is less than 5 parts by mass, the softening effect due to the mixing of the soft material may not be easily achieved. When the amount of the soft material mixed is 80 parts by mass or more, the softening effect due to the mixing of the soft material is achieved, but the stickiness of the surface layer 6-1 may become a problem due to the heat treatment during the stretching of the substrate 6.
From the viewpoint of uniformity of the resin material forming the surface layer 6-1, it is preferable that the soft material is a material that is highly compatible with the resin material forming the surface layer 6-1. From this viewpoint, for example, when the surface layer 6-1 is made of a polypropylene-based resin, it is preferable that the soft material to be mixed is also a polypropylene-based resin.

(Inorganic pigments)
At least one of the base layers constituting the base material 6 preferably contains an inorganic pigment. By containing an inorganic pigment, the light transmittance of the base material 6 is reduced, and it is possible to prevent the pattern of the base plate 9 to which the decorative sheet 1 is attached from being transmitted through.
The amount of inorganic pigment mixed in the base layer containing the inorganic pigment is preferably 5 vol% or more and 50 vol% or less with respect to the resin material. When the amount of inorganic pigment mixed is 5 vol% or more and 50 vol% or less, the effect of improving non-combustibility due to the addition of the inorganic pigment is exhibited, and embrittlement of the base material 6 caused by the addition of too much inorganic pigment can also be suppressed.

The inorganic pigment contained is not particularly limited, but examples thereof include natural inorganic pigments and synthetic inorganic pigments.
Examples of natural inorganic pigments include earth pigments, calcined earth, and mineral pigments. Examples of synthetic inorganic pigments include oxide pigments, hydroxide pigments, sulfide pigments, silicate pigments, phosphate pigments, carbonate pigments, metal powder pigments, and carbon pigments.
One or a mixture of two or more synthetic inorganic pigments may be used.
It is not preferable to use an organic pigment as the pigment, since this would impair the non-flammability of the base material 6.

In order to obtain the concealing properties required from the viewpoint of the design of the decorative sheet 1, the substrate 6 preferably has a light transmittance of 40% or less. If the light transmittance exceeds 40%, sufficient concealing properties cannot be obtained to obtain the design properties of the decorative sheet 1. Note that the above-mentioned "sufficient concealing properties cannot be obtained" means, for example, that in a decorative board in which the surface of the decorative sheet 1 facing the primer layer 8 is attached to a substrate board 9 made of a wood substrate or the like, the pattern of the surface of the wood substrate or the like facing the primer layer 8 is visible from the surface protection layer 2 side through the decorative sheet 1. When it is visible in this way, the pattern of the printing layer 5 and the pattern of the substrate board 9 such as a wood substrate may be seen overlapping each other. When it is visible, it is preferable to provide a concealing layer 7.

<Printed layer>
The printing layer 5 is a layer on which a picture pattern is formed to impart design. The printing layer 5 can be provided on the surface layer 6-1 of the substrate 6 using a known printing method. When the substrate 6 can be prepared in a rolled state, printing for forming the printing layer 5 can be performed using a roll-to-roll printing device. The printing method is not particularly limited, but for example, gravure printing can be used in consideration of productivity and quality of the pattern.

The design pattern may be any pattern that takes into consideration the design depending on the location of use, such as flooring or wall material. For example, when obtaining a decorative sheet 1 with a wood-based design pattern, various wood grain patterns are often preferred for the design pattern, and a cork pattern may also be used in addition to the wood grain pattern. When obtaining a decorative sheet 1 that resembles a stone floor such as marble, the stone grain of marble is used for the design pattern. In addition to design patterns of natural materials, artificial design patterns based on these motifs or artificial design patterns such as geometric patterns are used as the design pattern of the printed layer 5.
The printing ink used to form the printed layer 5 is not particularly limited, but an ink suitable for the printing method is appropriately selected. In particular, it is preferable to select the printing ink taking into consideration the adhesion to the substrate 6, printability, and weather resistance of the decorative sheet 1.

The printing ink is appropriately added with pigments, colorants such as dyes, extender pigments, solvents, and binders that are contained in normal inks. Examples of pigments include condensed azo, insoluble azo, quinacridone, isoindoline, anthraquinone, imidazolone, cobalt, phthalocyanine, carbon, titanium oxide, iron oxide, and pearl pigments such as mica. The binder may be water-based, solvent-based, or emulsion type, and the curing method may be a one-liquid type, a two-liquid type consisting of a base agent and a curing agent, or a type cured by ultraviolet light or electron beams, and is not particularly limited. The most common method is a two-liquid type that uses a urethane-based base agent and a curing agent consisting of isocyanate. In addition, designs may be applied by vapor deposition or sputtering of various metals.
The thickness of the printed layer 5 is preferably 2 μm or more and 20 μm or less. When the thickness of the printed layer 5 is in this range, the printing can be made clear, the printing workability during the production of the decorative sheet 1 can be improved, and the production cost can be reduced.

<Adhesive Layer>
The adhesive layer 4 is provided for the purpose of strengthening the adhesion between the substrate 6 and the printed layer 5 and the transparent resin layer 3. Strong adhesion between the substrate 6 and the printed layer 5 and the transparent resin layer 3 can impart bending processability to conform to curved surfaces and right-angled surfaces to the decorative sheet 1. The adhesive layer 4 is preferably transparent.
The adhesive layer 4 is formed of, for example, an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, an epoxy adhesive, etc. As the adhesive constituting the adhesive layer 4, it is usually preferable to use a two-liquid curing type adhesive, in view of its cohesive strength, and in particular a urethane-based material obtained by reacting a polyol with an isocyanate. Note that the adhesive layer 4 may be omitted if sufficient adhesive strength can be obtained between the transparent resin layer 3 and the printing layer 5.

Any method can be selected as a method for bonding the substrate 6 and the printed layer 5 to the transparent resin layer 3 via the adhesive layer 4, and examples of such methods include lamination methods such as thermal lamination, extrusion lamination, and dry lamination.
The thickness of the adhesive layer 4 is preferably 1 μm or more and 20 μm or less. When the thickness of the adhesive layer 4 is in this range, the adhesive strength between the substrate 6 and the printed layer 5 and the transparent resin layer 3 is improved, the printing workability during the production of the decorative sheet 1 is improved, and the production cost can be reduced.

<Transparent resin layer>
The transparent resin layer 3 is, for example, a transparent resin sheet, and is bonded to the substrate 6 and the printing layer 5 by an adhesive layer 4. In the decorative sheet 1 shown in FIG. 1, the transparent resin layer 3 is a single layer, but a plurality of transparent resin layers 3 may be laminated. The transparent resin layer 3 of this embodiment is preferably composed mainly of a polyolefin resin. The main component refers to, for example, a resin material contained in an amount of 70 parts by mass or more and 100 parts by mass or less, preferably 90 parts by mass or more and 100 parts by mass or less, based on 100 parts by mass of the resin material constituting the transparent resin layer 3.

Examples of polyolefin resins constituting the transparent resin layer 3 include polypropylene, polyethylene, polybutene, and the like, as well as α-olefins (e.g., propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl Examples of the copolymer include a homopolymer or copolymer of two or more of α-olefins (e.g., 1-ethyl-1-hexene, 3-ethyl-1-hexene, 9-methyl-1-decene, 11-methyl-1-dodecene, 12-ethyl-1-tetradecene, etc.), and copolymers of ethylene or α-olefins with other monomers, such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-butyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-butyl acrylate copolymer. In addition, when improving the surface strength of the decorative sheet 1, it is preferable to use highly crystalline polypropylene.

The thickness of the transparent resin layer 3 is preferably 20 μm or more and 200 μm or less. When the thickness of the transparent resin layer 3 is within this range, the strength of the decorative sheet 1 is improved, the printing workability when manufacturing the decorative sheet 1 is improved, and manufacturing costs can be reduced.

<Surface protective layer>
The surface protective layer 2 is provided on the outermost surface of the decorative sheet 1 and has the functions of protecting the surface and adjusting the gloss. Examples of materials constituting the surface protective layer 2 include polyurethane resins, acrylic silicone resins, fluorine resins, epoxy resins, vinyl resins, polyester resins, melamine resins, aminoalkyd resins, and urea resins. The form of the resin material is not particularly limited, and may be aqueous, emulsion, or solvent-based. The curing method may be appropriately selected from one-liquid type, two-liquid type, ultraviolet curing method, and the like.

In particular, from the viewpoints of workability, price, and the cohesive strength of the resin itself, a urethane resin using isocyanate is suitable as the resin material that is the main component of the surface protection layer 2. The isocyanate can be appropriately selected from, for example, tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), diphenylmethane diisocyanate (MDI), lysine diisocyanate (LDI), isophorone diisocyanate (IPDI), methylhexane diisocyanate (HTDI), methylcyclohexanone diisocyanate (HXDI), trimethylhexamethylene diisocyanate (TMDI), etc. Among them, hexamethylene diisocyanate (HMDI), which has a linear molecular structure, is suitable as the isocyanate from the viewpoint of weather resistance. In addition, when improving the surface hardness, it is preferable to use a resin that is cured by active energy rays such as ultraviolet rays and electron beams. These resins can be used in combination with each other; for example, a hybrid of a thermosetting type and a photocurable type can be used to improve surface hardness, suppress cure shrinkage, and improve adhesion.

The thickness of the surface protection layer 2 is preferably 3 μm or more and 20 μm or less. When the thickness of the surface protection layer 2 is within this range, it is possible to provide sufficient gloss while protecting the surface of the decorative sheet 1, and it is also possible to improve the printing workability during the production of the decorative sheet 1 and reduce production costs.

<Hidden Layer>
The concealing layer 7 is formed for the purpose of maintaining the concealing property for the base plate 9 in a decorative board in which the surface of the primer layer 8 side of the decorative sheet 1 is attached to a base plate 9 such as a wooden base material. The concealing layer 7 is formed, for example, by printing ink in the same manner as the printing layer 5. As the pigment to be contained in the ink, for example, an opaque pigment, titanium oxide, iron oxide, etc. are preferably used. In addition, in order to improve the concealing property of the pattern of the base plate 9 made of a wooden base material to which the decorative sheet 1 is attached in the concealing layer 7, it is also possible to add metals such as gold, silver, copper, and aluminum to the ink, and generally it is preferable to add flaky aluminum. Note that, as described above, the concealing layer 7 can be omitted when any of the base layers of the base material 6 is opaque and has concealing property.
The thickness of the concealing layer 7 is preferably 2 μm or more and 20 μm or less. When the thickness of the concealing layer 7 is in this range, the concealing properties for the base plate 9 are maintained, the printing workability during the production of the decorative sheet 1 is improved, and the production cost can be reduced.

<Primer layer>
The primer layer 8 is provided to improve adhesion between the decorative sheet 1 and the base plate 9 in a decorative board in which the surface of the decorative sheet 1 facing the primer layer 8 is attached to the base plate 9 .
The primer layer 8 can basically use the same material (printing ink) as the printed layer 5. In particular, considering that the decorative sheet 1 will be wound up in web form since it will be applied to the back surface of the decorative sheet 1, it is preferable to add an inorganic filler such as silica, alumina, magnesia, titanium oxide, barium sulfate, etc. to the printing ink. This can prevent blocking from occurring when the decorative sheet 1 is wound up, and can increase adhesion with the adhesive.

When the base plate 9 is a wood base material, the primer layer 8 is preferably formed from a resin material such as an ester resin, a urethane resin, an acrylic resin, a polycarbonate resin, a vinyl chloride-vinyl acetate copolymer, a polyvinyl butyral resin, or a nitrocellulose resin. These resin materials can be used alone or in combination to form an adhesive composition, and can be formed using an appropriate coating method such as roll coating or gravure printing. In this case, it is preferable to use a urethane-acrylate resin as the resin material constituting the primer layer 8. In other words, it is particularly preferable to form the primer layer from a resin consisting of a copolymer of an acrylic resin and a urethane resin, and an isocyanate.

The thickness of the primer layer 8 is preferably 0.1 μm or more and 20 μm or less. When the thickness of the primer layer 8 is in this range, the adhesion between the decorative sheet 1 and the base plate 9 is improved, the printing workability when manufacturing the decorative sheet 1 is improved, and the manufacturing cost can be reduced. Furthermore, when the bottom layer 6-n of the base material 6 is made of the same material and has the same structure as the surface layer 6-1, the interlayer adhesion between the base material 6 and the primer layer 8 can be improved, and therefore the adhesion between the decorative sheet 1 and the base plate 9 can be improved.
The decorative sheet 1 using the substrate 6 according to this embodiment uses a substrate formed by stretching and thinning a resin film whose main component is a polypropylene-based resin, which is a thermoplastic resin. This improves the mechanical strength of the thinned substrate 6 while maintaining the peel strength (interlayer adhesion) that can be evaluated by a peel test force between the substrate 6 and a laminate including a transparent resin layer 3 provided above the printed layer 5.

In addition, the decorative sheet 1 according to this embodiment has a multi-layer structure in which the polypropylene resin layers constituting the stretched film are laminated, and the Martens hardness of the surface layer 6-1 is 20 N/mm2 ^or more and less ^than 120 N/mm2, and the peak intensity ratio in Raman spectroscopy is 1.0 or more and less than 6.0.
According to this configuration, in this embodiment, the peel strength (interlayer adhesion) between the substrate 6 and a laminate including the transparent resin layer 3 provided above the printing layer 5, which can be evaluated by a peel test force, is maintained, while the elastic modulus of the substrate 6 is increased, thereby making it possible to improve the mechanical strength of the substrate despite being a thin film.
In other words, according to this embodiment, a decorative sheet 1 can be obtained that is thin yet has improved mechanical strength by increasing the elastic modulus of the substrate 6 while maintaining the peel strength (interlayer adhesion strength) that can be evaluated by a peel test force between the substrate 6 and a laminate including a transparent resin layer 3 provided above the printing layer 5.

Furthermore, since the substrate 6 can be thinned by stretching, it is also possible to improve non-flammability.
Here, when the substrate 6 is composed of three or more substrate layers, that is, when the core layers 6-2 to 6-n are two or more layers, it is preferable that the bottom layer (n-th layer) 6-n is made of the same material as the surface layer 6-1. That is, the Martens hardness of the bottom layer (n-th layer) 6-n is set to 20 N/
It is preferable that the compressive strength is 100 N ^/mm2 or more and less than 120 N/ ^mm2 , and that the peak intensity ratio in Raman spectroscopy is 1.0 or more and less than 6.0.
This configuration can improve the adhesion between the primer layer 8 and the bottom layer 6-n.

[Example]
The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
First, the first embodiment will be described.
The decorative sheet of Example 1 was formed by the steps shown below.
(Step of forming resin sheet for transparent resin layer)
First, a resin material was prepared by adding a hindered phenol-based antioxidant, a benzotriazole-based ultraviolet absorber, and a hindered amine-based light stabilizer to a homopolypropylene resin. Here, the homopolypropylene resin used had a mesopentad fraction of 97.8%, an MFR (melt flow rate) of 15 g/10 min (230°C), and a molecular weight distribution MWD (Mw/Mn) of 2.3. In addition, the hindered phenol-based antioxidant (
Irganox 1010 (manufactured by BASF) was added to the homopolypropylene resin at 500 PPM. Benzotriazole-based ultraviolet absorber (Tinuvin 328 (manufactured by BASF) was added to the homopolypropylene resin at 2000 PPM. Hindered amine-based light stabilizer (Chimasorb 944 (manufactured by BASF) was added to the homopolypropylene resin at 2000 PPM. Such resin materials were extruded using a melt extruder to form a transparent resin sheet made of polypropylene with a thickness of 80 μm to be used as a transparent resin layer.
Subsequently, both sides of the obtained transparent resin sheet were subjected to a corona treatment, so that the wetting tension of the surface of the transparent resin sheet was set to 40 dyn/cm or more.

(Substrate forming process)
The substrate was constructed from three substrate layers, with the first layer being the surface layer, the second layer being the core layer, and the third layer being the bottom layer. The substrate, in which the three layers, the first to third layers, were laminated, was formed by forming a film by extrusion and stretching. In other words, the substrate for decorative sheet was constructed from three layers made of polypropylene-based resin.
A layer serving as a precursor of the first surface layer was formed to a thickness of 12 μm using resin A as the material. Next, a layer serving as a precursor of the second core layer was formed to a thickness of 108 μm on the layer serving as the precursor of the first surface layer using resin C to which an inorganic pigment was added as the material. A layer serving as a precursor of the third layer was laminated thereon using resin B as the material.
This resulted in the formation of a laminated resin precursor with a total thickness of 132 μm for the three layers.

Next, this laminated resin precursor was stretched four times by uniaxial stretching to form a base material having a thickness of 33 μm (surface layer: 3 μm, core layer: 27 μm, bottom layer: 3 μm).
[Resin A]
Resin material: Random PP (polypropylene)
[Resin B]
Resin material: Homo PP (polypropylene)
[Resin C]
Resin material: Polypropylene copolymer with 4% ethylene content

(Printing layer forming process)
A print layer was formed on the surface layer of the substrate by gravure printing using a two-component urethane ink (V180; manufactured by Toyo Ink Mfg. Co., Ltd.) to which 0.5% by mass of a hindered amine light stabilizer (Chimasorb 944; manufactured by BASF) was added based on the binder resin content of the ink.

(Transparent resin layer formation process)
Next, a dry lamination adhesive (Takelac A540, manufactured by Mitsui Chemicals, Inc.; coating amount 2 g/m ² ) was applied as an adhesive layer to the surface layer side of the substrate on which the printing layer was formed. A transparent resin sheet was attached via an adhesive layer to the front surface of the substrate on which the layer was formed by dry lamination to form a transparent resin layer.
In this manner, the decorative sheet constituting Example 1 was formed.
In Example 1, the surface layer of the substrate had a Martens hardness of 110 and a peak intensity ratio of 5.5 in Raman spectroscopy, and the core layer had a Martens hardness of 52 and a peak intensity ratio of 5.5 in Raman spectroscopy. The Martens hardness of the bottom layer was 159 and the peak intensity ratio in Raman spectroscopy was 6.1.

Example 2
A decorative sheet constituting Example 2 was formed in the same manner as in Example 1, except that the above-mentioned resin A material was used as the material for the bottom layer.
In Example 2, the surface layer of the substrate had a Martens hardness of 110 and a peak intensity ratio by Raman spectroscopy of 5.5, the core layer had a Martens hardness of 52 and a peak intensity ratio by Raman spectroscopy of 1.7, and the bottom layer had a Martens hardness of 109 and a peak intensity ratio by Raman spectroscopy of 5.3.

Example 3
The decorative sheet constituting Example 3 was formed in the same manner as Example 1, except that the material for the surface layer was the above-mentioned resin A, the material for the core layer was the above-mentioned resin B, and the material for the bottom layer was the above-mentioned resin A.
In Example 3, the surface layer of the substrate had a Martens hardness of 110 and a peak intensity ratio measured by Raman spectroscopy of 5.5, the core layer had a Martens hardness of 96 and a peak intensity ratio measured by Raman spectroscopy of 5.1, and the bottom layer had a Martens hardness of 109 and a peak intensity ratio measured by Raman spectroscopy of 5.3.

Example 4
The decorative sheet constituting Example 4 was formed in the same manner as Example 1, except that the material for the surface layer was the above-mentioned resin C, the material for the core layer was the above-mentioned resin B, and the material for the bottom layer was the above-mentioned resin C.
In Example 4, the surface layer of the substrate had a Martens hardness of 54 and a peak intensity ratio by Raman spectroscopy of 1.9, the core layer had a Martens hardness of 103 and a peak intensity ratio by Raman spectroscopy of 5.5, and the bottom layer had a Martens hardness of 54 and a peak intensity ratio by Raman spectroscopy of 2.1.

Example 5
The decorative sheet constituting Example 5 was formed in the same manner as Example 1, except that the material of resin C described above was used as the material of the surface layer, the material of resin C described above was used as the material of the core layer, and the material of resin C described above was used as the material of the bottom layer.
In Example 5, the surface layer of the substrate had a Martens hardness of 56 and a peak intensity ratio by Raman spectroscopy of 1.9, the core layer had a Martens hardness of 52 and a peak intensity ratio by Raman spectroscopy of 1.7, and the bottom layer had a Martens hardness of 55 and a peak intensity ratio by Raman spectroscopy of 1.7.

<Comparative Example 1>
The decorative sheet constituting Comparative Example 1 was formed in the same manner as in Example 1, except that the material of resin B described above was used as the material for the surface layer, the material of resin B described above was used as the material for the core layer, and the material of resin B described above was used as the material for the bottom layer.
In Comparative Example 1, the surface layer of the substrate had a Martens hardness of 160 and a peak intensity ratio by Raman spectroscopy of 6.2, the core layer had a Martens hardness of 92 and a peak intensity ratio by Raman spectroscopy of 5.2, and the bottom layer had a Martens hardness of 159 and a peak intensity ratio by Raman spectroscopy of 6.1.

<Comparative Example 2>
The decorative sheet constituting Comparative Example 2 was formed in the same manner as in Example 1, except that the material for the surface layer was Resin D described below, the material for the core layer was Resin B described above, and the material for the bottom layer was Resin D described below.
[Resin D]
Resin material: polypropylene copolymer with ethylene content of 15% In Comparative Example 2, the surface layer of the substrate had a Martens hardness of 16 and a peak intensity ratio measured by Raman spectroscopy of 1.8, the core layer had a Martens hardness of 97 and a peak intensity ratio measured by Raman spectroscopy of 5.3, and the bottom layer had a Martens hardness of 18 and a peak intensity ratio measured by Raman spectroscopy of 1.7.

<Comparative Example 3>
The decorative sheet constituting Comparative Example 3 was formed in the same manner as in Example 1, except that the material for the surface layer was the above-mentioned resin B, the material for the core layer was the above-mentioned resin C, and the material for the bottom layer was the above-mentioned resin B.
In Comparative Example 3, the surface layer of the substrate had a Martens hardness of 160 and a peak intensity ratio by Raman spectroscopy of 6.5, the core layer had a Martens hardness of 58 and a peak intensity ratio by Raman spectroscopy of 2, and the bottom layer had a Martens hardness of 161 and a peak intensity ratio by Raman spectroscopy of 6.7.

The configurations of each example and each comparative example are shown in Table 1. Table 1 also lists the evaluation results.

<Method of measuring Martens hardness>
In each example and each comparative example, the Martens hardness was measured using a Martens hardness tester. Specifically, the Martens hardness was measured using a Martens hardness measuring device (Fisherscope HM2000; Fisher Instruments Co., Ltd.) conforming to ISO14577. The decorative sheets of each example and each comparative example were measured from the cross-section of the substrate to avoid the influence of the core layer of the laminated substrate other than the surface layer during measurement. Specifically, the substrate was embedded in a resin such as a cold-curing type epoxy resin or a UV-curing resin and sufficiently cured, and then cut so that the cross-section of the substrate appeared and mechanically polished to obtain a measurement surface. The specific measurement method was to press an indenter into the measurement surface of the substrate of each decorative sheet, and calculate the Martens hardness from the indentation depth and the load. In addition, the measurement was performed under the following measurement conditions: test force 10 mN, test force load time 10 seconds, and test force retention time 5 seconds.

<Method of measuring peak intensity ratio in Raman spectroscopy>
In each of the examples and comparative examples, the peak intensity ratio of the polypropylene film surface was measured by Raman spectroscopy. Specifically, the Raman scattered light was analyzed using a polarizing filter. Here, the value of the peak intensity ratio is expressed by the following formula (2).

In addition, S808 parallel and S841 parallel are defined as the peak intensity at 808 cm ^-1 and 841 cm ^-1 when the polarization direction and MD direction (flow direction during film production) are parallel. S808 perpendicular is defined as the peak intensity at 808 cm- ¹ when the polarization direction and MD direction are perpendicular, and S841 perpendicular is defined as the peak intensity at 841 cm ^-1 when the polarization direction and MD direction are perpendicular.

<Performance evaluation of decorative sheets>
The decorative sheets of each Example and Comparative Example were subjected to an evaluation of performance.
[Peel test (180 degree peel test)]
The peel test (180-degree peel test) is a test for evaluating the adhesive strength (adhesion) between the transparent resin layer and the substrate as peel strength. The peel test was carried out in accordance with JIS K 6854-2 using the decorative sheets of each Example and Comparative Example.
The evaluation is as follows:
○: Good (within specifications) (12N/inch or more)
×: Bad (out of spec) (peel strength less than 12 N/inch)

[Elasticity measurement (tensile test)]
The decorative sheets of each of the Examples and Comparative Examples were pulled at 50 mm/min using a Tensilon universal material testing machine to measure the elastic modulus.
The evaluation of the elastic modulus is as follows.
○: Very good (elastic modulus 800 MPa or more)
△: Good (elastic modulus 500 MPa or more and less than 800 MPa)
×: Poor (elastic modulus less than 500 MPa)

As can be seen from the peel test results shown in Table 1, in the decorative sheets of Examples 1 to 5, the peel strength (interlayer adhesion) that can be evaluated by the peel test force between the substrate and the laminate including a transparent resin layer provided above the printed layer was sufficient.
Furthermore, as shown in Table 1, the decorative sheets of Examples 1 to 5 had a sufficient elastic modulus.

1 Decorative sheet 2 Surface protective layer 3 Transparent resin layer 4 Adhesive layer 5 Printed layer 6 Substrate 6-1 Surface layer (surface substrate layer)
6-2 to 6-n Core layer 7, masking layer 8, primer layer 9, substrate plate

Claims (8)

A uniaxially or biaxially stretched laminate film is used as the substrate in a laminate having at least a substrate, a printed layer, an adhesive layer, and a transparent resin layer in this order, the laminate having a plurality of layers whose resin material is mainly composed of a polypropylene-based resin,
When the first layer located at the outermost surface of the plurality of layers is defined as a surface layer, and the layers other than the surface layer of the plurality of layers are defined as a core layer,
The surface layer has a Martens hardness of 20 N/ ^mm2 or more and less than 120 N/ ^mm2 , and a peak intensity ratio, as defined by the following formula (1), measured by Raman spectroscopy of 1.0 or more and less than 6.0,
The surface layer is made of a random propylene resin,
The layers other than the bottom layer of the core layer are made of a copolymer of ethylene and propylene ,
The core layer has a Martens hardness of 52 N/mm2 ^or more and less than 150 N/mm2 ^,
the Martens hardness value of the core layer is smaller than the Martens hardness value of the surface layer;
The printed layer is a layer formed of a urethane-based ink,
The adhesive layer is a layer formed of a polyurethane adhesive,
The laminated stretched film is characterized in that the transparent resin layer is a layer formed of a polyolefin resin .

In formula (1), S808 parallel represents the peak intensity at 808 cm ⁻¹ when the polarization direction and the MD direction (flow direction during film production) are parallel, S841 parallel represents the peak intensity at 841 cm −1 when the polarization direction and the MD direction are parallel, S808 perpendicular represents the peak intensity at 808 cm ⁻¹ when the polarization direction and the MD direction are perpendicular, and S841 perpendicular represents the peak intensity at ⁸⁴¹ cm ⁻¹ when the polarization direction and the MD direction are perpendicular . a bottom layer, the bottom layer being made of a polypropylene-based resin as a main component of a resin material, below the core layer;
The laminated stretched film according to claim 1, characterized in that the bottom layer has a Martens hardness of 20 N/ ^mm2 or more and less than 120 N/ ^mm2 , and a peak intensity ratio in Raman spectroscopy defined by the following formula (1) of 1.0 or more and less than 6.0.

In formula (1), S808 parallel represents the peak intensity at 808 cm ⁻¹ when the polarization direction and the MD direction (flow direction during film production) are parallel, S841 parallel represents the peak intensity at 841 cm −1 when the polarization direction and the MD direction are parallel, S808 perpendicular represents the peak intensity at 808 cm ⁻¹ when the polarization direction and the MD direction are perpendicular, and S841 perpendicular represents the peak intensity at ⁸⁴¹ cm ⁻¹ when the polarization direction and the MD direction are perpendicular . The core layer has a Martens hardness of 52 N/mm ² 3. The laminated stretched film according to claim 1 or 2, The surface layer has a Martens hardness of 110 N/mm ² The laminated stretched film according to any one of claims 1 to 3, wherein The laminated stretched film according to any one of claims 1 to 4 , characterized in that the surface layer has a Martens hardness of 50 N/ ^mm2 or more and less than 120 N/ ^mm2 . A substrate for decorative sheets, comprising the laminated stretched film according to any one of claims 1 to 5 . 7. A decorative sheet comprising the substrate for decorative sheet according to claim 6 and one or more transparent resin layers containing a polyolefin resin formed on the surface of the substrate for decorative sheet on the side of the surface layer. A decorative board comprising the decorative sheet according to claim 7 laminated to a base board made of a wood material.

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