JP7673473B2 - Wood base material, decorative material, and method for manufacturing wood base material - Google Patents

Description

This invention relates to wood substrates, decorative materials, and methods for manufacturing wood substrates.

Wood substrates are obtained by heating and pressurizing a mixture of wood materials such as wood flour, wood chips, and wood fibers with an adhesive. These wood substrates are called particle boards, medium density fiberboards, etc., depending on the type of wood material, and are used for a wide range of purposes, such as undercoats for floors and walls, fittings, and furniture.
Conventionally, urea resin adhesives, melamine resin adhesives, or phenol resin adhesives have been used as adhesives for wood substrates together with hardeners containing formaldehyde. Since formaldehyde is a harmful substance that causes sick house syndrome, its emission from wood substrates has become a problem, and various measures to reduce the amount of emission have been considered. However, with conventional techniques, it has been difficult to completely suppress the emission of formaldehyde.
In response to this, a method has been proposed in the past to use an adhesive containing powdered sugars and powdered polycarboxylic acid as the main components as a formaldehyde-free adhesive, mix this with plant fibers, and mold it under heat and pressure to produce a fiberboard (see paragraph [0017] of Patent Document 1). Also, a method has been proposed in the past to use an adhesive containing polyvinyl alcohol and water as a formaldehyde-free adhesive to produce a laminate containing a wood substrate (see paragraph [0015] and Figure 1 of Patent Document 2).

JP 2016-55620 A Patent No. 5553279

However, the wood substrates using the above-mentioned conventional adhesives are not practically sufficient in terms of mechanical properties such as bending strength and water resistance.
Therefore, an object of the present invention is to provide a wood base material that does not contain harmful substances that cause sick house syndrome and has practical mechanical strength and water resistance, a decorative material that includes this wood base material, and a method for producing this wood base material.

A wood substrate according to one embodiment of the present invention comprises a wood material having at least one of a powdered and chipped form and a thermoplastic resin composition, the wood substrate comprising a skin layer and a core layer, and characterized in that the skin layer and the core layer each have a normalized C-H area calculated from an absorption spectrum obtained by Fourier infrared spectroscopy measurement using the following formula (1) in the range of 0.07 to 1.00:
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
(Here, in formula (1), S _C-H represents the area value of the peak derived from either the _CH2 group or the _CH3 group in the wave number region of 2700 cm ^-1 or more and 3000 cm ^-1 or less, S _O-H represents the area value of the peak derived from the OH group in the wave number region of 3000 cm ^-1 or more and 3500 cm ^-1 or less, and S _C-OH represents the area value of the peak derived from the C-OH group in the wave number region of 900 cm ^-1 or more and 1200 cm ^-1 or less.)

In addition, the wood base material according to one embodiment of the present invention is characterized in that the normalized C-H area measured for each of the skin layer and the core layer is within the range of 0.08 to 0.35.
In addition, a wood substrate according to one embodiment of the present invention is characterized in that the wood substrate comprises the skin layer, the core layer, and the skin layer in that order, and the thickness ratio of each of the layers (skin layer:core layer:skin layer) is within the range of 1:0.1:1 to 1:18:1.
In addition, the wood base material according to one embodiment of the present invention is characterized in that the thickness of the skin layer is within the range of 2 mm or more and 19 mm or less.
In addition, a wood base material according to one embodiment of the present invention is characterized in that, when the normalized C-H area of the skin layer is A _S and the normalized C-H area of the core layer is A _C , A _S > A _C.
In addition, in one embodiment of the wood base material of the present invention, the skin layer and the core layer each have a mass ratio of the wood material to the thermoplastic resin composition (wood material/thermoplastic resin composition) in the range of 95/5 to 70/30.
A wood base material according to one embodiment of the present invention is characterized in that it contains a mushroom bed as a raw material.
In addition, a wood substrate according to one embodiment of the present invention is characterized in that the thermoplastic resin composition contains polyethylene.
In addition, a wood substrate according to one embodiment of the present invention is characterized in that the thermoplastic resin composition contains an acid-modified polyolefin.

The decorative material according to one aspect of the present invention is characterized in that a decorative substrate is laminated onto the above-mentioned wood substrate.

The method for producing a wood substrate according to one aspect of the present invention is a method for producing the above-mentioned wood substrate, and is characterized by having a step of mixing a wood material having at least one of a powdered and chipped shape with a thermoplastic resin composition to obtain a raw material mixture for the wood substrate, and a step of heating and pressurizing the raw material mixture to form the wood substrate.

According to one aspect of the present invention, it is possible to provide a wood substrate that does not contain harmful substances that cause sick house syndrome and has practical mechanical strength and water resistance, a decorative material that includes the wood substrate, and a method for manufacturing the wood substrate.

FIG. 1 is a schematic diagram showing a method for producing a wood base material according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing the structure of a wood base material according to a first embodiment of the present invention. 1 is an infrared absorption spectrum of a typical wood material. 1 is an infrared absorption spectrum of a wood base material according to a first embodiment of the present invention. 4 is a schematic cross-sectional view showing the structure of a decorative material according to a second embodiment of the present invention. FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Here, the drawings are 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 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.

[First embodiment]
A schematic diagram for explaining a method for manufacturing a wood substrate according to an embodiment of the present invention is shown in Fig. 1. A metal plate 2 is placed on the bottom surface of a jig 1 for manufacturing a wood substrate, which has a storage section cut out to a predetermined size (for example, a 10 cm x 10 cm square), and a releasable metal plate 3 is placed on top of the metal plate 2.
Next, a raw material mixture 6 containing a wood material 4 having at least one of a powder and chip form and a powdered thermoplastic resin composition 5 is placed into the storage portion of the jig 1 for producing a wood substrate, and a releasable metal plate 3 is placed on the raw material mixture 6.
Next, a thickness adjusting metal plate 7 is placed on the jig 1 for producing a wooden substrate, and the raw material mixture 6 is pressed down from above with a metal weight 8 via a releasable metal plate 3 .
Finally, a press top plate 9 set under predetermined conditions is heated and pressurized from above the raw material mixture 6 via a metal weight 8, forming a skin layer 11 according to this embodiment. Another skin layer 11 is also formed in a similar manner.
After the pair of skin layers 11 are thus formed, the metal plate 2, the releasable metal plate 3, and the skin layer 11 are layered in this order on the bottom surface of the jig 1 for producing a wooden substrate.
Next, a raw material mixture 6 containing a wood material 4 having at least one of a powdered and chipped form and a powdered thermoplastic resin composition 5 is placed in the storage portion of the jig 1 for producing a wooden substrate, and a skin layer 11 and a release metal plate 3 are placed in this order on the raw material mixture 6. Here, the raw material mixture 6 sandwiched between the skin layers 11 becomes the core layer 12 in the wooden substrate 10.
Next, the thickness adjusting metal plate 7 is placed on the jig 1 for producing the wooden substrate, and the raw material mixture 6 is pressed down from above with a metal weight 8 via the skin layer 11 and the releasable metal plate 3 .
Finally, a press top plate 9 set under predetermined conditions is used to apply heat and pressure from above the raw material mixture 6 via a metal weight 8 to form the wood base material 10 according to this embodiment.

FIG. 2 is a schematic cross-sectional view showing the structure of the wood substrate 10 according to this embodiment.
As shown in Fig. 2, the wood substrate 10 according to this embodiment is configured to include skin layers 11 that form the front and back surfaces of the wood substrate 10, and a core layer 12 that is located at the center of the wood substrate 10 and is sandwiched between the skin layers 11. That is, the wood substrate 10 according to this embodiment includes a skin layer 11 formed from a wood material 4 and a thermoplastic resin composition 5, and a core layer 12 formed from a wood material 4 and a thermoplastic resin composition 5. In the wood substrate 10, it is preferable that the skin layer 11 and the core layer 12 are in contact with each other.
The wood base material 10 is called a particle board, a medium density fiberboard, or the like depending on the type of wood material 4, and is used for a wide range of purposes such as underlayment for floors and walls, fittings, and furniture.
In this way, the wood base material 10 according to the present embodiment does not contain harmful substances such as formaldehyde that cause sick house syndrome, and therefore, it is possible to suppress the emission of harmful substances such as formaldehyde that cause sick house syndrome from inside the wood base material 10.
The materials constituting the wood base material 10 will now be described.

(Wood material 4)
The wood material 4 has at least one of a powder and chip shape. Here, there is generally no definition of size or shape for "powder" and "chip shape." In this embodiment, the size (average particle size) is generally in the range of several tens of microns to several centimeters. In order to stably produce the wood base material 10, it is desirable for the average particle size of the wood material 4 to be in the range of 1 to 5 mm.
Examples of the wood material 4 include wood flour, wood fiber, and wood crushed into chips, and examples of the raw material that can be used include thinned wood, sawdust, and waste wood.
Furthermore, materials other than wood may also be used as the wood material 4, such as bamboo, hemp, coconut fiber, and walnut shells, as long as they contain cellulose components similar to wood.
As a raw material for the wood material 4, for example, used mushroom beds that are generated in large quantities during mushroom cultivation are suitable. The mushroom bed is a culture medium used in mushroom cultivation, and is made by mixing wood chips and sawdust with nutrients such as bran and rice bran. It is estimated that around 300,000 tons of mushroom beds are discarded annually in Japan after mushroom cultivation, making them a promising source of biomass, but recycling is currently not progressing well, and using them as a wood raw material (wood material 4) is beneficial in reducing the environmental load.
As the wood substrate 10 containing a mushroom bed, the mushroom bed may be used alone as the wood material 4, or the mushroom bed may be used in combination with other wood materials 4. Here, the term "wood substrate containing a mushroom bed" refers to a wood substrate 10 in which the proportion of the mushroom bed in the volume of the entire wood material 4 is within a range of 1% or more and 100% or less.

(Method for manufacturing wood material 4)
For example, when trying to obtain wood material 4 from waste wood, many foreign objects such as concrete fragments, metal fragments, paper, etc. can be contained. Foreign objects can be removed by known methods such as magnetic sorting, air sorting, specific gravity sorting, etc. Coarse particles are adjusted in size by known methods such as cutting and crushing, and particles in the range of approximately several tens of microns to several centimeters are used.
Furthermore, when attempting to obtain wood material 4 from a mushroom bed, it is desirable to sterilize it by a known method before use.

(Mass ratio of wood material 4 to thermoplastic resin composition 5)
The mass ratio of the wood material 4 to the thermoplastic resin composition 5 (wood material/thermoplastic resin composition) is desirably in the range of 95/5 to 70/30 in each of the skin layer 11 and the core layer 12. If the content of the wood material 4 is greater than the above value (95/5), sufficient bending strength cannot be imparted to the wood substrate 10. On the other hand, if the content of the wood material 4 is less than the above value (70/30), the wood substrate 10 is likely to deform when heated and pressurized, which is not preferable.
The mass ratio of the wood material 4 to the thermoplastic resin composition 5 (wood material/thermoplastic resin composition) is more preferably in the range of 85/15 to 70/30 in each of the skin layer 11 and the core layer 12. By setting the content of the wood material 4 within the above numerical range, a wood substrate 10 with greater bending strength can be obtained.

Regarding the mass ratio of the wood material 4 to the thermoplastic resin composition 5 (wood material/thermoplastic resin composition), it is desirable to increase the proportion of the thermoplastic resin composition 5 in the skin layer 11 more than in the core layer 12. Increasing the proportion of the thermoplastic resin composition 5 improves the water resistance of the skin layer 11 (particularly the skin layer 11 that constitutes the surface layer of the wood substrate 10). In addition, for example, the content of the thermoplastic resin composition 5 in the skin layer 11 is desirably in the range of 1.1 to 2 times the content of the thermoplastic resin composition 5 in the core layer 12, and more desirably in the range of 1.3 to 1.8 times.

(Thermoplastic resin composition 5)
The thermoplastic resin composition 5 is a powder-like composition having an average particle size of several tens of microns to 1 millimeter. The particle size of the thermoplastic resin composition 5 is not particularly limited, but it is preferable that the particle size is similar to that of the wood material 4 because it is easier to mix with the wood material 4. If the particle size of the thermoplastic resin composition 5 is too small, it will slip through the wood material 4 and accumulate at the bottom, and if it is too large, it will accumulate at the top of the wood material 4, resulting in a non-uniform wood substrate 10, which is undesirable. Therefore, the particle size (average particle size) of the thermoplastic resin composition 5 is more preferably in the range of 1 micron (μm) to 1 millimeter. In addition, the particle size (average particle size) of the thermoplastic resin composition 5 is preferably in the range of 30 microns (μm) to 300 microns (μm) inclusive, taking into consideration ease of handling, etc.
The thermoplastic resin composition 5 can be made of various materials such as polyester, polyamide, polyolefin, ethylene-propylene-diene rubber, ethylene vinyl acetate, and silicone rubber, but polyethylene is preferred in terms of the mechanical strength and water resistance of the wood base material 10.
The thermoplastic resin composition 5 may be used alone or in combination with a plurality of different types. In terms of the mechanical strength of the wood substrate 10, it is preferable that the thermoplastic resin composition 5 contains polyethylene in an amount of 50 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the entire thermoplastic resin composition 5. It is more preferable that the thermoplastic resin composition 5 contains polyethylene in an amount of 80 parts by mass or more and 100 parts by mass or less.
The polyethylene added to the thermoplastic resin composition 5 is not particularly limited, and may be appropriately selected from existing materials such as high-density polyethylene (polyethylene with a specific gravity of about 0.92 to 0.96), low-density polyethylene (polyethylene with a specific gravity of about 0.91 to 0.92), very low-density polyethylene (polyethylene with a specific gravity of less than 0.9), and linear low-density polyethylene (polyethylene with a specific gravity of less than 0.94), taking into consideration the reactivity during heating and pressurization and the fluidity of the raw material mixture 6. Of the above-mentioned materials, it is more desirable to use high-density polyethylene in order to obtain a wood substrate 10 with high bending strength.

The polyethylene used in this embodiment may be biomass-derived polyethylene. Biomass-derived polyethylene is produced by polymerizing monomers containing biomass-derived ethylene. Since biomass-derived ethylene is used as the raw material monomer, the polymerized polyethylene is biomass-derived. Note that the raw material monomer for polyethylene may not contain 100% by mass of biomass-derived ethylene.

The thermoplastic resin composition 5 may be used alone, or may be mixed with other known thermoplastic resin compositions 5. Materials to be mixed with the thermoplastic resin composition 5 are not particularly limited, but examples include acid-modified resins and organic peroxides.

(Acid-modified resin)
The acid-modified resin is used to improve the adhesion between the wood material 4 and the thermoplastic resin composition 5. When the main component of the thermoplastic resin composition 5 is polyethylene, the acid-modified resin is preferably an acid-modified polyolefin because of its ease of compatibility (high compatibility). In particular, maleic acid-modified polyethylene is preferably used as the acid-modified resin. Here, the above-mentioned "main component" refers to a component that accounts for 50% by mass or more of the total mass of the thermoplastic resin composition 5.

(Amount of Acid-Modified Resin Added)
The amount of the acid-modified resin added is preferably within the range of 3 parts by mass to 40 parts by mass relative to 100 parts by mass of the total thermoplastic resin composition. If the amount of the acid-modified resin added is less than 3 parts by mass, the effect of improving the adhesion between the wood material 4 and the thermoplastic resin composition 5 is insufficient, and sufficient strength may not be imparted to the wood substrate 10. If the amount of the acid-modified resin added exceeds 40 parts by mass, the effect of improving the adhesion is limited and only a slight improvement can be confirmed.
The amount of the acid-modified resin added is more preferably within the range of 5 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the entire thermoplastic resin composition.

(Organic peroxides)
The organic peroxide may be used to radically crosslink the thermoplastic resins contained in the thermoplastic resin composition 5 when the raw material mixture 6 is heated and pressurized. In addition, if a material having radical crosslinking properties is used for the acid-containing resin, the acid-containing resin and the thermoplastic resin can be reliably crosslinked by adding the organic peroxide to the thermoplastic resin composition 5. When radical crosslinking is formed between the thermoplastic resins or between the acid-containing resin and the thermoplastic resin, the crosslinked structure improves the mechanical strength of the entire wood substrate 10. In other words, by adding the organic peroxide to the thermoplastic resin composition 5, it is possible to form a three-dimensional network (bond) by radical crosslinking between the thermoplastic resin contained in the thermoplastic resin composition 5, the acid-containing resin, and the wood material 4. This improves the mechanical strength of the entire wood substrate 10.
The organic peroxide is not particularly limited, and may be appropriately selected from existing materials such as peroxyketals, dialkyl peroxides, diacyl peroxides, peroxyesters, etc., taking into consideration reactivity and stability. Organic peroxides are a type of radical crosslinking agent, and examples of such organic peroxides include hydroperoxides, diacyl peroxides, peroxydicarbonates, peroxyesters, peroxycarbonates, dialkyl peroxides, and ketone peroxides.

(Amount of organic peroxide added)
The amount of the organic peroxide added is preferably within a range of 0.01 parts by mass or more and 5 parts by mass or less based on 100 parts by mass of the entire thermoplastic resin composition.
If the amount of organic peroxide added is less than 0.01 parts by mass, the reactivity of the raw material mixture 6 when heated and pressurized is insufficient, and therefore the amount does not contribute to improving the strength of the wood substrate 10. If the amount of organic peroxide added is more than 5 parts by mass, the amount of decomposition products produced during the reaction increases, which may cause deformation of the wood substrate 10, and is therefore undesirable.

(Additives)
An additive such as wax may be mixed into the thermoplastic resin composition 5. Adding wax as an additive further improves the water resistance of the wood substrate 10. In addition, an additive such as wax also serves as a lubricant for uniformly mixing the wood material 4 and the thermoplastic resin composition 5, or multiple types of thermoplastic resin compositions 5.

(Method for producing thermoplastic resin composition 5)
The thermoplastic resin composition 5 can be prepared in a powder form by a known method. When a plurality of types of materials are mixed with the thermoplastic resin composition 5, they are mixed by a known method. The thermoplastic resin composition 5 may be heated during mixing to weld the particles of the thermoplastic resin composition 5 together. However, if the particles are larger than 150 μm, the number of particles decreases and the surface area decreases, making it difficult to mix uniformly with the wood material 4, which is not desirable.
In addition, the thermoplastic resin composition 5 can be made by powdering resin pellets produced by a known method using a known method such as mechanical crushing or freeze crushing. When mixing a thermoplastic resin composition containing a mixture of resin pellets and powder, the resin pellets and powder may be mixed and then crushed, or the resin pellets may be crushed and then mixed into powder. For example, if a powder of polyethylene and a powder of an acid-modified polyolefin are mixed, a process such as freeze crushing is not required when crushing the thermoplastic resin composition 5, and a powder of the thermoplastic resin composition 5 can be easily obtained.

The thermoplastic resin composition 5 can be obtained by, for example, using a single-screw kneader or a batch kneader to heat and knead multiple types of thermoplastic resin pellets, followed by mechanical crushing or freeze-pulverization. For example, polyethylene pellets and acid-modified polyolefin pellets can be heat-kneaded in a single-screw kneading extruder, pelletized, and the kneaded pellets can be freeze-pulverized to obtain a powder of the thermoplastic resin composition 5. In other words, multiple types of thermoplastic resin compositions 5 can be kneaded by an extrusion method to obtain a powder of the thermoplastic resin composition 5. In addition, by mixing multiple types of powdered thermoplastic resin compositions 5, the thermoplastic resin compositions 5 can be mixed more uniformly, and therefore a wood substrate 10 with excellent in-plane uniformity of bending strength can be obtained.

(Wood base material 10)
The wood substrate 10 is formed by heating and pressurizing a raw material mixture 6 containing a wood material 4 having at least one of a powdered and chipped form and a powdered thermoplastic resin composition 5. The wood substrate 10 thus formed has a multilayer structure having at least one skin layer 11 and one core layer 12. Here, the skin layer 11 is a water-resistant layer. By providing this skin layer 11, water absorption in the core layer 12 is reduced, and the entire wood substrate 10 can be prevented from expanding and deforming.
In addition, if it is considered that moisture absorption occurs simultaneously from the front and back of the wood base material 10, warping of the wood base material 10 due to swelling becomes a problem, so it is desirable to have a three-layer structure as shown in Figure 2, with skin layers 11 having the same properties on the front and back of the wood base material 10.
The thickness of the wood substrate 10 is preferably within a range of 5 mm to 40 mm. If the thickness of the wood substrate 10 is thinner than 5 mm, the bending strength of the wood substrate 10 is weak (low), which is not practical. If the thickness of the wood substrate 10 is thicker than 40 mm, the weight of the wood substrate 10 is heavy, which makes it difficult to handle during construction work.
The thickness of the skin layer 11 on one side (e.g., the front side) of the wood substrate 10 may be thicker or thinner than the thickness of the skin layer 11 on the other side (e.g., the back side) of the wood substrate 10. The thickness of the skin layer 11 on one side (e.g., the front side) of the wood substrate 10 and the thickness of the skin layer 11 on the other side (e.g., the back side) of the wood substrate 10 may be the same.

The thickness of each of the skin layer 11 and the core layer 12 constituting the wood substrate 10 is preferably 2 mm or more. If the thickness of each of the skin layer 11 and the core layer 12 is less than 2 mm, it is difficult to produce a uniform skin layer 11 and a core layer 12 because they are too thin. As shown in FIG. 2, when the wood substrate 10 has a three-layer structure with the skin layer 11 on the front and back sides, the thickness ratio of the skin layer 11 to the core layer 12 (skin layer 11:core layer 12) is preferably within a range of 1:0.1 to 1:18. In other words, as shown in FIG. 2, when the wood substrate 10 has a structure in which the skin layer 11, the core layer 12, and the skin layer 11 are sequentially provided, the thickness ratio of each layer (skin layer 11:core layer 12:skin layer 11) is preferably within a range of 1:0.1:1 to 1:18:1.
In addition, since the total thickness of the wood base material 10, which is the sum of the skin layer 11 and the core layer 12, is desirably 40 mm or less, the skin layer 11 is desirably 19 mm or less.

The skin layer 11 and the core layer 12 constituting the wood substrate 10 are preferably adjusted so that A _{S >} A C, where A S is the normalized C-H area of the skin layer 11 calculated from the absorption spectrum obtained in Fourier infrared spectroscopy, as described later, and A _C is the normalized C- _H area of the core layer 12. The size of each normalized C-H area is qualitatively proportional to the component amount (content ratio) of the thermoplastic resin composition 5 added to the skin layer 11 and the core layer 12, respectively. Therefore, the problem of the present application can be solved even if the component amount (content ratio) of the thermoplastic resin composition 5 in the core layer 12 is the same as the component amount (content ratio) of the thermoplastic resin composition 5 in the skin layer 11. However, in that case, the component amount (content ratio) of the thermoplastic resin composition 5 in the core layer 12 becomes larger (larger) than necessary, which may increase the production cost. Therefore, by adjusting the component amounts (content ratio) of the thermoplastic resin composition 5 so that A _S >A _C , it is possible to reduce the production cost while maintaining both the mechanical strength and water resistance.

Here, we will explain Fourier infrared spectroscopy. First, infrared spectroscopy is a measurement method that obtains information about the chemical structure and state of a substance by measuring the infrared light absorbed by the substance, utilizing the principle that the amount of infrared light, which is light with a wavelength of 2.5 μm to 25 μm, absorbed by the substance changes based on the vibration and rotational motion of the molecules of the substance. A specific measurement method is to irradiate the substance with infrared light from a light source, generate an interference wave by synthesizing the divided transmitted light and reflected light, and calculate the light intensity of each wave number component from the signal intensity of the interference wave to measure the infrared spectrum. In particular, in this embodiment, the calculation of the interference wave is performed using the Fourier transform method, and the measurement is performed by Fourier infrared spectroscopy, which is a method of measuring infrared spectra. A graph in which the wave number obtained by the above method is plotted on the horizontal axis and the measured absorbance (or transmittance) on the vertical axis is called an infrared absorption spectrum (or infrared transmission spectrum), and a unique pattern is recognized for each substance. In this case, the absorbance on the vertical axis changes as the peak intensity value at a given wavenumber in proportion to the concentration and thickness of the substance, and in the case of crystalline substances, the amount of crystalline or amorphous parts, making it possible to perform quantitative analysis from the height and area of the peak.

Figure 3 shows an example of an infrared absorption spectrum of a typical wood material 4. In wood material 4, the peak of OH groups derived from cellulose is strongly present in the wave number region of 3000 cm ^-1 to 3500 cm ^-1 , and the peak of C-OH groups is strongly present in the wave number region of 900 cm ^-1 to 1200 cm ^-1 . The peak area values are labeled S _O-H and S _C-OH , respectively, and are corrected using the baseline shown by the dashed line as the background. In other words, the ranges surrounded by the solid and dashed lines in Figure 3 are the area values of the peaks of OH groups and C-OH groups.
In this embodiment, the area value of each peak was calculated by averaging values obtained by measuring at 10 different measurement positions within the same sample.

Figure 4 shows an example of the infrared absorption spectrum of the wood substrate 10 of this embodiment. In addition to the peaks derived from the wood material 4, the peaks of the _CH2 and _CH3 groups derived from the thermoplastic resin composition 5 are strongly present in the region of wave numbers from 2700 cm ^-1 to 3000 cm ^-1 . The area value of the peak is indicated as S _C-H , and is corrected using the baseline shown by the dashed line as the background. In other words, the ranges surrounded by the solid and dashed lines in Figure 4 are the area values of the peaks of the OH group, the C-OH group, and the _CH2 and _CH3 groups.

The normalized C-H area A _S of the skin layer 11 and the normalized C-H area A _c of the core layer 12, calculated from the area values of the respective peaks using the following formula (1), are adjusted to be within the range of 0.07 to 1.00. Specifically, the content ratio of the wood material 4 and the thermoplastic resin composition 5 is adjusted to adjust the values of the normalized C-H area A _S and the normalized C-H area A _c, respectively.
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
When the normalized C-H area A _s and the normalized C-H area A _c are each less than 0.07, the proportion of the wood material 4 is too high, making it difficult to impart bending strength and water resistance necessary for practical use. On the other hand, when the normalized C-H area A _s and the normalized C-H area A _c are each more than 1.00, the proportion of the thermoplastic resin composition 5 is too high, making it easy for deformation of the wood substrate 10 to occur during heating and pressurization, which is not preferable. In addition, if the wood material 4 and the thermoplastic resin composition 5 are not mixed uniformly, the normalized C-H area A _s and the normalized C-H area A _c may locally be greater than 1.00. If the wood material 4 and the thermoplastic resin composition 5 are not mixed uniformly, the bending strength and water resistance of the wood substrate 10 will vary, which is not preferable.

It is more preferable that the normalized C-H area A _S of the skin layer 11 and the normalized C-H area A _c of the core layer 12 are each within the range of 0.08 to 0.35. If each normalized C-H area is within the above numerical range, it is possible to obtain a good wood substrate 10 that has higher bending strength, improved water resistance, and is less likely to deform.
Furthermore, the area ratio (A _S /A _c ) of the normalized C-H area A _S to the normalized C-H area A _c is preferably in the range of more than 1 and not more than 4, and more preferably in the range of 1.1 to 1.8. When this normalized C-H area ratio (A _S /A _c ) is within the above numerical range, excellent water resistance can be imparted to the entire wood substrate 10 while the amount of thermoplastic resin composition 5 added to the core layer 12 can be reduced to the minimum necessary, thereby reducing production costs.

(Production conditions of wood base material 10)
Various known methods can be used for the heating and pressurization used in producing the wood substrate 10, but press molding using a frame mold as shown in Fig. 1 is suitable for producing the wood substrate 10. The heating temperature is usually in the range of 120°C to 250°C and must be equal to or higher than the melting point of the thermoplastic resin composition 5, but if the heating temperature exceeds 250°C, significant thermal deterioration of the wood material 4 may occur. The pressing pressure is usually in the range of 10 kgf/ ^cm2 to 400 kgf/ ^cm2 , and a value appropriately set depending on the desired density of the wood substrate 10 is used.
The density and shape of the wood substrate 10 obtained above are appropriately determined depending on the application, but the density is preferably in the range of 0.5 g/ ^cm3 to 1.2 g/ ^cm3 , particularly 0.6 g/ ^cm3 to 1.1 g/ ^cm3 . If the density of the wood substrate 10 is less than 0.5 g/ ^cm3 , the bending strength is significantly reduced and it is not practical. On the other hand, if the density of the wood substrate 10 is more than 1.2 g/ ^cm3 , the weight of the wood substrate 10 is too large, making it difficult to handle during construction.

When manufacturing the wood substrate 10, a releasable metal plate 3 as shown in FIG. 1 may be used. The material of the releasable metal plate 3 may be a film with releasability, but if smoothness of the wood substrate 10 is required, a hard metal material is more preferable. The material of the releasable metal plate 3 may be any material that does not adhere to the thermoplastic resin composition 5, the metal plate 2, and the metal weight 8, and for example, a fluorine-coated material is preferably used. In addition, fine metal particles may be sprayed onto the surface of the releasable metal plate 3 to provide irregularities. The releasability is improved by forming an irregular structure on the surface of the releasable metal plate 3. In addition, the releasability can be further improved by combining an irregular structure and a fluorine coating on the releasable metal plate 3.

In this embodiment, a metal plate 2 or a metal weight 8 that has been subjected to a non-adhesive treatment may be used instead of the releasable metal plate 3. In other words, the surface of the metal plate 2 or the surface of the metal weight 8 may be subjected to a non-adhesive treatment that prevents the thermoplastic resin composition 5 from adhering thereto, and it is more preferable if an uneven structure is formed by fluorine coating or thermal spraying.

(Modification)
In this embodiment, the method for producing the wood base material 10 includes first creating two separate skin layers 11 by heating and pressurizing, and then sandwiching the raw material mixture 6 that will become the core layer 12 between the two skin layers 11 and heating and pressurizing again to produce the wood base material 10. However, the present invention is not limited to this method.
For example, first, the raw material mixture 6 that will become the skin layer 11, the raw material mixture 6 that will become the core layer 12, and the raw material mixture 6 that will become the skin layer 11 may be laminated in this order, and then the two types and three layers of raw material mixture 6 may be heated and pressurized simultaneously to produce the wood base material 10.
Thus, in the manufacturing method of the wood substrate 10 according to this embodiment, the skin layer 11 may be formed in the first heating and pressing process and the core layer 12 may be formed in the second heating and pressing process, or both the skin layer 11 and the core layer 12 may be formed in the first heating and pressing process.

[Second embodiment]
The second embodiment will be described with reference to FIG.
The second embodiment is a decorative material 14 in which a decorative layer 13 having a design property is laminated on the wood substrate 10 according to the first embodiment described above with reference to FIG.
According to this embodiment, by laminating the design layer 13 on the wood base material 10, it is possible to impart design properties.
That is, the wood base material 10 can be used as a decorative material by itself, but in order to impart even more excellent design to the wood base material 10, a design layer 13 such as paper or film having a design such as a picture may be laminated onto the wood base material 10 to form a decorative material 14, as shown in FIG. 5 .

<Actions and other details>
(1) The wood substrate 10 of this embodiment includes a wood material 4 having at least one of a powder and chip shape, and a thermoplastic resin composition 5. The wood substrate 10 has a skin layer 11 and a core layer 12. The normalized C-H area of each of the skin layer 11 and the core layer 12, calculated from the absorption spectrum obtained by Fourier infrared spectroscopy measurement using the following formula (1), is in the range of 0.07 to 1.00.
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
In formula (1), S _C-H represents the area value of the peak derived from either a _CH2 group or a _CH3 group in the wave number region of 2700 cm ^-1 or more and 3000 cm ^-1 or less, S _O-H represents the area value of the peak derived from an OH group in the wave number region of 3000 cm ^-1 or more and 3500 cm ^-1 or less, and S _C-OH represents the area value of the peak derived from a C-OH group in the wave number region of 900 cm ^-1 or more and 1200 cm ^-1 or less.
With this configuration, since the thermoplastic resin composition 5 is used as an adhesive instead of formaldehyde, which causes sick house syndrome, it is possible to provide a wood base material 10 that does not emit harmful substances.
Furthermore, since the wood base material 10 contains the thermoplastic resin composition 5, the thermoplastic resin composition 5 itself has high water resistance, which imparts excellent water resistance to the wood base material 10.
Furthermore, since the wood base material 10 is a laminated structure including at least the skin layer 11 and the core layer 12, it has excellent mechanical properties such as bending strength.

(2) In the wood substrate 10 of this embodiment, the normalized C-H areas A _S and A _C measured for the skin layer 11 and the core layer 12, respectively, may be within a range of 0.08 to 0.35.
With this configuration, since a thermoplastic resin composition is used as an adhesive instead of formaldehyde, which causes sick house syndrome, it is possible to provide a wood base material 10 that does not emit harmful substances.
Furthermore, if the normalized C-H areas A _S and A _C are within the above-mentioned numerical ranges, it is possible to obtain a good wood substrate 10 that has stronger bending strength and improved water resistance and is less prone to deformation.

(3) The wood substrate 10 of this embodiment has a skin layer 11, a core layer 12, and a skin layer 11 in that order, and the thickness ratio of each layer (skin layer:core layer:skin layer) may be within a range of 1:0.1:1 to 1:18:1.
With such a structure, the wood substrate 10 has a multi-layer structure and is therefore excellent in bending strength and water resistance.

(4) In the wood substrate 10 of this embodiment, the skin layer 11 may have a thickness in the range of 2 mm or more and 19 mm or less.
With such a configuration, it is possible to provide a wood base material 10 that satisfactorily fulfills the role of the skin layer 11, the overall thickness of the wood base material 10 is not too large, and there are no problems with workability during construction.

(5) In the wood substrate 10 of this embodiment, when the normalized C-H area of the skin layer 11 is A _S and the normalized C-H area of the core layer 12 is A _C , A _S >A _C may be satisfied.
With this configuration, the thermoplastic resin composition 5 can be used as an adhesive instead of formaldehyde, which causes sick house syndrome, and the wood base material 10 has good water resistance.

(6) In the wood substrate 10 of this embodiment, the mass ratio of the wood material 4 to the thermoplastic resin composition 5 (wood material 4/thermoplastic resin composition 5) in each of the skin layer 11 and the core layer 12 may be within a range of 95/5 to 70/30.
With this configuration, it is possible to reliably provide a wood substrate 10 with stronger bending strength.

(7) In the wood substrate 10 of this embodiment, the wood material 4 may contain a mushroom bed as a raw material.
With such a configuration, it is possible to provide a wood substrate 10 that is beneficial in reducing the environmental impact.

(8) In the wood substrate 10 of this embodiment, the thermoplastic resin composition 5 may contain polyethylene.
Such a configuration can provide a wood substrate 10 that has both good bending strength and water resistance. Furthermore, when the wood substrate 10 contains biomass-derived polyethylene, the wood substrate 10 can be provided with benefits in terms of reducing the environmental impact.

(9) In the wood substrate 10 of this embodiment, the thermoplastic resin composition 5 may contain an acid-modified polyolefin.
With this configuration, it is possible to provide a wood substrate 10 having better bending strength.

(10) The decorative material 14 of this embodiment is obtained by laminating a decorative substrate (decorative layer 13) having a design onto the wood substrate 10 of this embodiment.
With this configuration, it is possible to provide a decorative material 14 that has better bending strength and water resistance than conventional decorative materials.

[Example]
Below, examples 1 to 20 of the wood base material according to the first embodiment of the present invention and comparative example 1 will be described. Note that the present invention is not limited to the following examples 1 to 20.

Example 1
The thermoplastic resin composition of Example 1 was a single high-density polyethylene resin (HDPE) pellet. The resin pellet was mechanically pulverized to obtain a powdered thermoplastic resin composition. The average particle size of the powder of the thermoplastic resin composition was 100 μm.
The wood material used was a washed and dried mushroom bed (average particle size: 2 mm) after harvesting. The wood material and the thermoplastic resin composition were dry-mixed in a mass ratio (wood material/thermoplastic resin composition) of 85/15 to obtain a raw material mixture for the wood substrate.
This raw material mixture was introduced into an aluminum mold and heated and pressed in a hot press to obtain one skin layer with a thickness of 4 mm (pressing conditions: 40 kgf/ ^cm2 , 200°C for 10 minutes, base material density: 0.8 g/ ^cm3 ). Another 4 mm skin layer was obtained in the same manner, and then the raw material mixture to become the core layer was placed between the two skin layers and heated and pressed. In this way, a three-layered wood base material of Example 1 was obtained, in which a skin layer of 4 mm, a core layer of 4 mm, and a skin layer of 4 mm were laminated in sequence.

Example 2
In Example 2, a wood base material was obtained in the same manner as in Example 1, except that the thickness of the skin layer was changed to 2 mm and the thickness of the core layer was changed to 5 mm.

Example 3
In Example 3, a wood base material was obtained in the same manner as in Example 1, except that the thickness of the skin layer was changed to 2 mm and the thickness of the core layer was changed to 36 mm.

Example 4
In Example 4, a wood base material was obtained in the same manner as in Example 1, except that the thickness of the skin layer was changed to 19 mm and the thickness of the core layer was changed to 2 mm.

Example 5
The thermoplastic resin composition of Example 5 was a low-density polyethylene resin (LDPE) pellet alone. A wood base material was obtained in the same manner as in Example 1.

Example 6
The thermoplastic resin composition of Example 6 was a linear low density polyethylene resin (LLDPE) pellet alone. A wood base material was obtained in the same manner as in Example 1.

(Example 7)
The thermoplastic resin composition of Example 7 was polypropylene resin (PP) pellets alone. A wood base material was obtained in the same manner as in Example 1.

(Example 8)
In Example 8, the mass ratio of the wood material to the thermoplastic resin composition for the skin layer (wood material/thermoplastic resin composition) was changed from "85/15" in Example 1 to "96/4," and otherwise the wood base material was obtained in the same manner as in Example 1.

(Example 9)
In Example 9, the mass ratio of the wood material to the thermoplastic resin composition for the skin layer (wood material/thermoplastic resin composition) was changed from "85/15" in Example 1 to "90/10," and otherwise the wood base material was obtained in the same manner as in Example 1.

(Example 10)
In Example 10, the mass ratio of the wood material to the thermoplastic resin composition for the skin layer (wood material/thermoplastic resin composition) was changed from "85/15" in Example 1 to "80/20," and otherwise the wood base material was obtained in the same manner as in Example 1.

Example 11
In Example 11, the mass ratio of the wood material to the thermoplastic resin composition for the skin layer (wood material/thermoplastic resin composition) was changed from "85/15" in Example 1 to "70/30," and otherwise the wood base material was obtained in the same manner as in Example 1.

Example 12
In Example 12, the mass ratio of the wood material to the thermoplastic resin composition for the skin layer (wood material/thermoplastic resin composition) was changed from "85/15" in Example 1 to "65/35," and otherwise the wood base material was obtained in the same manner as in Example 1.

Example 13
In Example 13, the mass ratio of the wood material to the thermoplastic resin composition (wood material/thermoplastic resin composition) for each of the skin layer and core layer was changed from "85/15" in Example 1 to "70/30," and otherwise the wood base material was obtained in the same manner as in Example 1.

(Example 14)
In Example 14, the mass ratio of the wood material to the thermoplastic resin composition (wood material/thermoplastic resin composition) for each of the skin layer and core layer was changed from "85/15" in Example 1 to "65/35," and otherwise the wood base material was obtained in the same manner as in Example 1.

(Example 15)
The components and masses of the thermoplastic resin composition of Example 15 are as follows.
(1) High density polyethylene resin 97 parts by weight (2) Acid modified polyolefin 3 parts by weight The above (1) and (2) were heated and mixed in a batch type mixer, and then mechanically crushed to obtain a powdered thermoplastic resin composition. The wood substrate of Example 15 was obtained in the same manner as in Example 1 except for the above.

(Example 16)
The components and masses of the thermoplastic resin composition of Example 16 are as follows.
(1) 80 parts by weight of high density polyethylene resin (2) 20 parts by weight of acid-modified polyolefin The above (1) and (2) were heated and mixed in a batch mixer, and then mechanically crushed to obtain a powdered thermoplastic resin composition. The wood substrate of Example 16 was obtained in the same manner as in Example 1 except for the above.

(Example 17)
The components and masses of the thermoplastic resin composition of Example 17 are as follows.
(1) 60 parts by weight of high density polyethylene resin (2) 40 parts by weight of acid-modified polyolefin The above (1) and (2) were heated and mixed in a batch-type mixer, and then mechanically crushed to obtain a powdered thermoplastic resin composition. The wood substrate of Example 17 was obtained in the same manner as in Example 1 except for the above.

(Example 18)
In Example 18, a wood base material was obtained in the same manner as in Example 1, except that the thickness of the skin layer was changed to 2 mm and the thickness of the core layer was changed to 40 mm.

(Example 19)
In Example 19, a wood base material was obtained in the same manner as in Example 1, except that the thickness of the skin layer was changed to 20 mm and the thickness of the core layer was changed to 2 mm.

(Example 20)
The thermoplastic resin composition of Example 20 was a single high-density polyethylene resin (HDPE) pellet. The resin pellet was mechanically pulverized to obtain a powdered thermoplastic resin composition. The average particle size of the powder of the thermoplastic resin composition was 100 μm.
The wood material used was a washed and dried mushroom bed (average particle size: 2 mm) after harvesting. The wood material and the thermoplastic resin composition were dry-mixed in a mass ratio (wood material/thermoplastic resin composition) of 85/15 to obtain a raw material mixture for the wood substrate.
The raw material mixture was introduced into an aluminum mold and heated and pressed in a hot press to obtain one skin layer with a thickness of 6 mm (pressing conditions: 40 kgf/ ^cm2 , 200°C for 10 minutes, base material density: 0.8 g/ ^cm3 ). The raw material mixture was then placed on top of the skin layer and heated and pressed. In this way, a two-layered wood base material with a skin layer of 6 mm and a core layer of 6 mm was obtained as in Example 20.

(Comparative Example 1)
In Comparative Example 1, a wood base material was obtained in a manner similar to that used for producing a so-called particle board.
Specifically, the wood material and adhesive were mixed using a drum blender, and the mixture was allowed to fall and spread in a natural state without applying external forces such as pressure or suction. A urea resin adhesive was used as the adhesive, and the wood material and adhesive were mixed at a mass ratio (wood material/adhesive) of 85/15. The mixture was then compacted to obtain a wood substrate.

(Evaluation of wood-based materials)
For the above Examples 1 to 20 and Comparative Example 1, Fourier infrared spectroscopy, mechanical strength, water resistance, and substrate deformation were evaluated.

(Fourier type infrared spectroscopy)
The Fourier infrared spectrometry was performed using a PerkinElmer Fourier infrared spectrometry device (Spectrum Spotlight 400) to obtain an absorption spectrum from 4000 cm ⁻¹ to 400 cm ⁻¹ . From the obtained absorption spectrum, the normalized C-C area of each of the skin layer and the core layer was calculated using the following formula (1).
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
In formula (1), S _C-H represents the area value of the peak derived from either a _CH2 group or a _CH3 group in the wave number region of 2700 cm ^-1 or more and 3000 cm ^-1 or less, S _O-H represents the area value of the peak derived from an OH group in the wave number region of 3000 cm ^-1 or more and 3500 cm ^-1 or less, and S _C-OH represents the area value of the peak derived from a C-OH group in the wave number region of 900 cm ^-1 or more and 1200 cm ^-1 or less.
In the Fourier infrared spectroscopic measurement, when the normalized C—H area of each of the skin layer and the core layer is in the range of 0.07 or more and 1.00 or less, it is judged to be acceptable.

(Mechanical strength)
The mechanical strength was measured as bending strength by a method conforming to JIS A 5908. The evaluation criteria for mechanical strength with respect to the measured values (unit: N/mm ² ) were set as follows, based on the standard values of the JIS.
The mechanical strength was evaluated according to the following four-level scale: "◎", "good", "△", and "×", with "◎", "good", and "△" being acceptable and "×" being unacceptable.
◎: 15 or more (pass)
○: 13 or more but less than 15 (pass)
△: 8 or more but less than 13 (pass)
×: Less than 8 (failed)

(water resistance)
The water resistance was measured by measuring the water absorption thickness swelling rate according to a method in accordance with JIS A 5908. The evaluation criteria for water resistance for the measured value (unit: %) were set as follows, based on the standard values of the JIS.
The water resistance was evaluated according to the following four-level scale: "◎", "good", "△", and "×", with "◎", "good", and "△" being acceptable and "×" being unacceptable.
◎: Less than 5 (pass)
○: 5 or more but less than 8 (pass)
△: 8 or more but less than 12 (pass)
×: 12 or more (fail)

(Substrate deformation)
The substrate deformation is a state in which the substrate surface is partially swollen, and is mainly caused by the retention of gas generated inside the substrate during pressing. Since the substrate deformation is clearly reflected by the state of the substrate edge, the appearance of the substrate edge was visually evaluated.
The evaluation criteria for the substrate deformation were as follows: 3-level evaluation of "good", "defective", and "poor", with "good" and "defective" being acceptable and "poor" being unacceptable.
〇: No voids (passed)
△: Traces of voids (passed)
×: Voids present (failed)

(Evaluation Results)
The evaluation results of the wood base materials are as shown in Table 1 below.
In addition, the "raw material blend ratio" in the examples in the table indicates the mass ratio defined as (wood material/thermoplastic resin composition), and the "raw material blend ratio" in the comparative examples in the table indicates the mass ratio defined as (wood material/adhesive).

(Evaluation results of Fourier infrared spectroscopy)
Only Comparative Example 1 failed the evaluation by Fourier infrared spectroscopy. Wood substrates containing polyolefin in the thermoplastic resin composition as in Examples 1 to 20 have characteristic peaks in the region of 2700 cm ^-1 to 3000 cm ^-1 , so the normalized C-H area of each of the skin layer and the core layer is large. In addition, the normalized C-H area calculated for the wood material alone is 0.05, so that the peak caused by the adhesive of Comparative Example 1 is hardly detected in the region of 2700 cm ^-1 to 3000 cm ^-1 .
Comparing Examples 1 to 20, the skin layers of Examples 14 and 12, in which the amount of thermoplastic resin composition in the skin layer is large, have the largest normalized C-H area, while the skin layer of Example 8, in which the amount of thermoplastic resin composition in the skin layer is small, has the smallest normalized C-H area.

(Mechanical strength evaluation results)
In terms of mechanical strength, all of Examples 1 to 20 and Comparative Example 1 passed the test. Of these, eight of Examples 4 to 9, 17, and 19 were given an evaluation result that included "△". In Examples 4 and 19, the core layer was extremely thinner than the skin layer, which is thought to have reduced mechanical strength. In Examples 5 to 7, LDPE, LLDPE, and PP were used as the base resin, respectively, which is thought to have reduced mechanical strength compared to HDPE. In Examples 8 to 9, the proportion of wood material in the skin layer was high, which is thought to have reduced mechanical strength. In Example 17, 40 parts of acid-modified polyolefin were blended, and the content of the base resin was relatively low, which is thought to have reduced mechanical strength.

(Water resistance evaluation results)
The only example that failed the water resistance test was Comparative Example 1. The conventional method using an adhesive has poorer water resistance than Examples 1 to 20 of the present invention. Comparing Examples 1 to 20, there are 12 examples including Examples 1 to 9 and 18 to 20 that are rated "△".
Examples 1 to 9 and 18 to 19 are material formulations that do not contain acid-modified polyolefin, and the ratio of the thermoplastic resin composition in the skin layer in Examples 1 to 9 and 18 is 15 parts or less, so it is believed that the water resistance was insufficient. Comparing Examples 10 to 17, it is believed that Examples 15 to 17 contain acid-modified polyolefin, so that the water resistance is improved. Examples 10 to 12 are examples in which the ratio of the thermoplastic resin composition in only the skin layer is increased to 20 parts, 30 parts, and 35 parts, but the water resistance is improved because the absorption of moisture from the front and back sides is suppressed. However, since the water resistance of the core layer is poor, the water resistance is inferior to Examples 13 and 14 in which the ratio of the thermoplastic resin composition in the core layer is also increased to 30 parts and 35 parts.
In addition, when comparing Examples 10 and 20, the thermoplastic resin composition ratio in the skin layer of both is 20 parts, but Example 20 has a skin layer only on the surface layer, and the water resistance of the back surface is insufficient, so that the water resistance is inferior to Example 10.

(Evaluation results of substrate deformation)
In terms of substrate deformation, all of Examples 1 to 20 and Comparative Example 1 passed the test. Among them, only Example 14 had an evaluation result of "△".
In Example 14, the skin layer, the core layer, and both layers contained 35 parts of thermoplastic resin composition, which is thought to have made the substrate more susceptible to deformation due to the relatively high content of thermoplastic resin composition.

(Overall evaluation results)
As a comprehensive evaluation result, Examples 1 to 20 were "passed" in all evaluation items, and as is clear from Table 1, it was shown that the wood base material of the present invention has excellent mechanical strength and water resistance, and there is no problem with substrate deformation. In Examples 18 to 19, the wood base material was thick at 42 mm, and the wood base material was heavy and difficult to handle during construction work, but it was not a problem in practical use.

1... Jig for making wooden substrate, 2... Metal plate (bottom), 3... Releaseable metal plate, 4... Wooden material, 5... Thermoplastic resin composition, 6... Raw material mixture, 7... Metal plate for thickness adjustment, 8... Metal weight, 9... Press top plate, 10... Wooden substrate, 11... Skin layer, 12... Core layer, 13... Design layer, 14... Decorative material

Claims (14)

A wood substrate comprising a wood material having at least one of a powder form and a chip form and a thermoplastic resin composition,
The wood base material comprises a skin layer and a core layer,
a normalized C-H area calculated from an absorption spectrum obtained by Fourier infrared spectrometry using the following formula (1) for each of the skin layer and the core layer is in the range of 0.07 or more and 1.00 or less,
The wood base material is characterized in that, when the normalized C-H area of the skin layer is AS and the normalized C-H area of the core layer is AC, AS and AC are different from each other .
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
(Here, in formula (1), S _C-H represents the area value of the peak derived from either the _CH2 group or the _CH3 group in the wave number region of 2700 cm ^-1 or more and 3000 cm ^-1 or less, S _O-H represents the area value of the peak derived from the OH group in the wave number region of 3000 cm ^-1 or more and 3500 cm ^-1 or less, and S _C-OH represents the area value of the peak derived from the C-OH group in the wave number region of 900 cm ^-1 or more and 1200 cm ^-1 or less.) The wood substrate according to claim 1, characterized in that the normalized C-H area measured for each of the skin layer and the core layer is within the range of 0.08 to 0.35. The wood base material includes the skin layer, the core layer, and the skin layer in this order,
3. The wood base material according to claim 1, wherein the thickness ratio of each layer (skin layer:core layer:skin layer) is within a range of 1:0.1:1 to 1:18:1. The wood base material includes the skin layer, the core layer, and the skin layer in this order,
3. The wood base material according to claim 1, wherein the skin layer and the core layer have different thicknesses . 5. The wood base material according to claim 1 , wherein the skin layer has a thickness in the range of 2 mm to 19 mm. The wood base material according to any one of claims 1 to 5 , characterized in that, when the normalized C-H area of the skin layer is AS and the normalized C-H area of the core layer is AC, AS>AC. The wood base material according to any one of claims 1 to 6, characterized in that the mass ratio of the wood material to the thermoplastic resin composition (wood material/thermoplastic resin composition) in each of the skin layer and the core layer is within a range of 95/5 to 70/30. The wood substrate according to any one of claims 1 to 7 , characterized in that the wood material contains a mushroom bed as a raw material. The wood substrate according to any one of claims 1 to 8 , characterized in that the thermoplastic resin composition contains polyethylene. The wood substrate according to any one of claims 1 to 9 , characterized in that the thermoplastic resin composition contains an acid-modified polyolefin. The wood substrate according to any one of claims 1 to 9 , characterized in that the thermoplastic resin composition contains only one type of acid-modified polyolefin. A wood substrate comprising a wood material having at least one of a powder form and a chip form and a thermoplastic resin composition,
The wood base material comprises a skin layer and a core layer,
a normalized C-H area calculated from an absorption spectrum obtained by Fourier infrared spectrometry using the following formula (1) for each of the skin layer and the core layer is in the range of 0.07 or more and 1.00 or less,
The wood base material is characterized in that , when the normalized C-H area of the skin layer is AS and the normalized C-H area of the core layer is AC, AS>AC .
Standardized C-H area = S _C-H / (S _O-H + S _C-OH ) ... Formula (1)
(Here, in formula (1), S _C-H represents the area value of the peak derived from either the _CH2 group or the _CH3 group in the wave number region of 2700 cm ^-1 or more and 3000 cm ^-1 or less, S _O-H represents the area value of the peak derived from the OH group in the wave number region of 3000 cm ^-1 or more and 3500 cm ^-1 or less, and S _C-OH represents the area value of the peak derived from the C-OH group in the wave number region of 900 cm ^-1 or more and 1200 cm ^-1 or less.) A decorative material comprising the wood substrate according to any one of claims 1 to 12 and a decorative substrate laminated thereon. A method for producing a wood substrate according to any one of claims 1 to 12 , comprising the steps of:
A step of mixing a wood material having at least one of a powder form and a chip form with a thermoplastic resin composition to obtain a raw material mixture for a wood base material;
and heating and pressurizing the raw material mixture to form a wood base material.

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