Wood base material, decorative material, and method for producing wood base material

Abstract

To provide a wooden base material which does not contain a harmful substance causing a sick house syndrome, and has practical mechanical strength and water resistance, a decorative material, and a method for manufacturing a wooden base material.SOLUTION: A wooden base material 20 contains a wooden material 11 having at least one of a powder shape and a chip shape, and a thermoplastic resin composition 12, wherein the wooden base material 20 sequentially includes a skin layer 21, a core layer 22 and the skin layer 21, and when the density of the skin layer 21 is represented by ρs and the density of the core layer 22 is represented by ρc, ρs / ρc is within a range of 1.0 or more and 2.4 or less, and each of the ρs and the ρc is within a range of 0.5 g / cm3 or more and 1.2 g / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wood substrate, a decorative material, and a method for producing a wood substrate. [Background technology]

[0002] 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.

[0003] In response to this, a method has been proposed in the past to use an adhesive containing powdered sugars and powdered polycarboxylic acid as its 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

[0017] and Figure 1 of Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-55620 A [Patent Document 2] Patent No. 5553279 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 suppresses the emission of harmful substances such as formaldehyde that cause sick house syndrome and that 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. [Means for solving the problem]

[0006] A wood base material according to one embodiment of the present invention comprises a wood material in at least one of a powdered and chipped form, and a thermoplastic resin composition, the wood base material comprising a skin layer, a core layer, and a skin layer in this order, the skin layer having a density of ρs and the core layer having a density of ρc, the ratio ρs / ρc being in the range of 1.0 to 2.4, and each of ρs and ρc being 0.5 g / cm 3 More than 1.2g / cm 3 It is characterized by being within the following range.

[0007] In addition, in one embodiment of the wood base material of the present invention, the normalized CH area of ​​each of the skin layers and the core layer, calculated from the absorption spectrum obtained by Fourier infrared spectroscopy using the following formula (1), is in the range of 0.07 to 1.00, and the normalized CH area of ​​the skin layer is A S , the normalized CH area of ​​the core layer is A C In this case, A S >A C It is characterized in that: Standardized CH area=S C-H / (S O―H +S C-OH )...Equation (1) (Here, in formula (1), S C-H is a wave number of 2700 cm -1 More than 3000cm -1The area value of the peak derived from either the CH2 group or the CH3 group in the following region, S O-H is a wave number of 3000 cm -1 More than 3500cm -1 The area value of the peak derived from the OH group in the following region, S C-OH is a wave number of 900 cm -1 More than 1200cm -1 The area values ​​of the peaks derived from C-OH groups in the following regions are shown below.)

[0008] Furthermore, the wood base material according to one embodiment of the present invention is characterized in that the ratio of the thicknesses of the skin layer, the core layer and the skin layer (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, in one embodiment of the wood base material of the present invention, each of the skin layers and the core layer is characterized in that the mass ratio of the wood material to the thermoplastic resin composition (wood material / thermoplastic resin composition) is within 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 a polyolefin resin. 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.

[0009] A 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.

[0010] Furthermore, a method for producing a wood substrate according to one aspect of the present invention is a method for producing the above-mentioned wood substrate, which is characterized by the steps of: mixing a wood material having at least one of a powdered and chipped form with a thermoplastic resin composition to obtain a raw material mixture for the wood substrate; and heating and pressurizing the raw material mixture to form the wood substrate. Effect of the Invention

[0011] According to one aspect of the present invention, it is possible to provide a wood base material that suppresses the emission of harmful substances such as formaldehyde that cause sick building syndrome and has practical mechanical strength and water resistance, a decorative material that includes this wood base material, and a method for manufacturing this wood base material. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a method for producing a wood base material according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing the structure of a wood base material according to a first embodiment of the present invention. [Diagram 3] 1 is an infrared absorption spectrum of a typical wood material. [Figure 4] 1 shows an infrared absorption spectrum of a wood base material according to a first embodiment of the present invention. [Diagram 5] FIG. 4 is a schematic cross-sectional view showing the structure of a decorative material according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] [First embodiment] Fig. 1 is a schematic diagram for explaining a method for producing a wood substrate according to an embodiment of the present invention. Fig. 2 shows a wood substrate 20 according to a first embodiment of the present invention. The wood substrate 20 is called a particle board, a medium density fiberboard, or the like depending on the type of wood material 11, and is used for a wide range of applications such as undercoat materials for floors and walls, fittings, and furniture. As shown in Fig. 1, the wood base material 20 is formed by heating and pressurizing a raw material mixture 10 containing a wood material 11 having at least one of a powdered and chipped form and a powdered thermoplastic resin composition 12. The wood base material 20 does not contain harmful substances such as formaldehyde that cause sick house syndrome. Therefore, the emission of harmful substances such as formaldehyde that cause sick house syndrome from inside the wood base material 20 can be suppressed.

[0015] The configuration of the wood base material 20 according to this embodiment will be described in detail below. 2, the wood substrate 20 according to this embodiment includes a skin layer 21 that forms the front and back surfaces of the wood substrate 20, and a core layer 22 that is located at the center of the wood substrate 20 and is sandwiched between the skin layers 21. That is, the wood substrate 20 according to this embodiment includes a skin layer 21 that is formed from a wood material 11 and a thermoplastic resin composition 12, and a core layer 22 that is formed from a wood material 11 and a thermoplastic resin composition 12. In the wood substrate 20, it is preferable that the skin layer 21 and the core layer 22 are in contact with each other. In this way, the wood base material 20 according to this 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 20. The materials constituting the wood base material 20 will be described below.

[0016] (Density of wood base material 20) With respect to the density of the wood substrate 20, ρs / ρc is within the range of 1.0 to 2.4, preferably 1.0 to 2.0, and more preferably 1.0 to 1.5, where ρs is the density of the skin layer 21 and ρc is the density of the core layer 22. If ρs / ρc exceeds 2.4, the weight of the skin layer 21 will increase, which may cause deformation of the substrate. If ρs / ρc is less than 1, the strength of the skin layer 21 will be low, which may result in insufficient mechanical strength. The density ρs of the skin layer 21 and the density ρc of the core layer 22 are each 0.5 g / cm 3 More than 1.2g / cm 3 Within the range of 0.6 g / cm 3 More than 1.1g / cm 3 It is preferable that ρs and ρc are each within the following range: 0.5 g / cm 3 If these conditions are not met, the wood base material 20 may not have sufficient strength. In addition, ρs and ρc are 1.2 g / cm 3 If it is larger, the weight of the wood base material 20 will be too large, and handling during construction may become difficult.

[0017] (Wood material 11) The wood material 11 has at least one of a powder and chip shape. Here, the terms "powder" and "chip" do not generally have definitions of size or shape. In this embodiment, the term refers to a size (average particle size) in the range of approximately several tens of microns to several centimeters. The average particle size of the wood material 11 in this embodiment is preferably within the range of 10 μm to 3 mm, for example.

[0018] Examples of the wood material 11 include wood powder, 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 11, such as bamboo, hemp, coconut fiber, and walnut shells, as long as they contain cellulose components similar to wood.

[0019] A suitable raw material for the wood material 11 is, for example, used mushroom beds that are generated in large quantities during mushroom cultivation. The mushroom beds are culture media used in mushroom cultivation, and are 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 has not progressed at present. In this embodiment, when a mushroom bed is used as the wood material 11, the ratio of the mushroom bed to the total volume of the wood material 11 may be within the range of 1% to 100%, and preferably within the range of 50% to 100%. If the mushroom bed content is within the above numerical range, the production cost can be reduced compared to the case where normal wood chips are used.

[0020] (Manufacturing method of wood material 11) For example, when trying to obtain wood material 11 from waste wood, it contains a lot of foreign matter such as concrete fragments, metal fragments, paper, etc. Foreign matter 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 11 from a mushroom bed, it is desirable to sterilize it by a known method before use.

[0021] (Mass ratio of wood material 11 to thermoplastic resin composition 12) The mass ratio of the wood material 11 to the thermoplastic resin composition 12 (wood material / thermoplastic resin composition) in each of the skin layer 21 and the core layer 22 is desirably within the range of 95 / 5 to 70 / 30. If the content of wood material 11 is greater than the above-mentioned value (95 / 5), sufficient bending strength (mechanical strength) cannot be imparted to wood base material 20. On the other hand, if the content of wood material 11 is less than the above-mentioned value (70 / 30), deformation of wood base material 20 tends to occur during heating and pressurization, which is not preferable. The mass ratio of the wood material 11 to the thermoplastic resin composition 12 (wood material / thermoplastic resin composition) is more preferably in the range of 85 / 15 to 70 / 30 in each of the skin layer 21 and the core layer 22. By setting the content of the wood material 11 within the above numerical range, a wood substrate 20 with greater bending strength can be obtained.

[0022] With regard to the mass ratio between the wood material 11 and the thermoplastic resin composition 12 (wood material / thermoplastic resin composition), it is desirable to increase the proportion of the thermoplastic resin composition 10 in the skin layer 21 more than in the core layer 22. Increasing the proportion of the thermoplastic resin composition 10 improves the water resistance of the skin layer 21 (particularly the skin layer 21 constituting the surface layer of the wood base material 20). Furthermore, for example, the content of the thermoplastic resin composition 10 in the skin layer 21 is desirably in the range of more than 1 time and not more than 2 times the content of the thermoplastic resin composition 10 in the core layer 22, and more desirably in the range of 1.3 times or more and not more than 1.8 times.

[0023] (Thermoplastic resin composition 12) The thermoplastic resin composition 12 is a powder-like composition having an average particle size of several tens of microns to 1 mm. The particle size of the thermoplastic resin composition 12 is not particularly limited, but it is preferable that the particle size is similar to that of the wood material 11 in order to facilitate mixing. If the particle size of the thermoplastic resin composition 12 is too small, it will slip through the wood material 11 and accumulate at the bottom, and if it is too large, it will accumulate at the top of the wood material 11, resulting in an uneven wood substrate 20, which is undesirable. Therefore, the particle size (average particle size) of the thermoplastic resin composition 12 is more preferably within the range of 1 to 5 mm. In addition, the particle size (average particle size) of the thermoplastic resin composition 12 is preferably within the range of 30 microns (μm) to 300 microns (μm) in consideration of ease of handling, etc. The thermoplastic resin composition 12 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 20. Examples of polyolefin resins that can be used in this embodiment include, in addition to polyethylene and polypropylene, polyolefin resins such as polymethylpentene, polybutene, ethylene-propylene copolymer, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer; polyolefin-based resins such as olefin-based copolymer resins such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-(meth)acrylic acid (ester) copolymer, and ethylene-unsaturated carboxylic acid copolymer metal neutralized product (ionomer); and mixtures, copolymers, composites, laminates, and the like of two or more of these. The thermoplastic resin composition 12 may be used alone or in combination with a plurality of different types. In terms of the mechanical strength of the wood substrate 20, it is preferable that the thermoplastic resin composition 12 contains polyolefin resin or the like in an amount of 50 parts by mass to 100 parts by mass, based on 100 parts by mass of the entire thermoplastic resin composition 12. It is more preferable that the thermoplastic resin composition 12 contains polyolefin resin or the like in an amount of 80 parts by mass to 100 parts by mass. The polyethylene added to the thermoplastic resin composition 12 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 10. Of the above-mentioned materials, it is more preferable to use high density polyethylene in order to obtain a wood substrate 20 with high bending strength.

[0024] The polyethylene used in the present embodiment may be biomass-derived polyethylene. Biomass-derived polyethylene is obtained by polymerizing a monomer containing biomass-derived ethylene. Since biomass-derived ethylene is used as the raw material monomer, the polymerized polyethylene is derived from biomass. Note that the raw material monomer of polyethylene may not contain 100% by mass of biomass-derived ethylene.

[0025] The thermoplastic resin composition 12 may be a single material, or may be mixed with a known thermoplastic resin composition 12. The material to be mixed with the thermoplastic resin composition 12 is not particularly limited, but examples thereof include acid-modified resins and organic peroxides.

[0026] (Acid-modified resin) The acid-modified resin is used to improve the adhesion between the wood material 11 and the thermoplastic resin composition 12 . Examples of the acid-containing resin that can be used include maleic anhydride-modified polyolefins such as maleic anhydride-modified polyethylene and maleic anhydride polypropylene, ethylene (meth)acrylic acid copolymers, and itaconic anhydride-modified polyethylenes. Among the above-mentioned materials, maleic anhydride-modified polyolefins are preferred as the acid-containing resins, and maleic anhydride-modified polyethylenes are more preferred, in view of compatibility (adhesiveness) with the wood material 11 containing cellulose.

[0027] (Amount of acid-modified resin added) The amount of the acid-containing resin added is preferably in the range of 5 parts by mass to 50 parts by mass, and more preferably in the range of 10 parts by mass to 40 parts by mass, based on 100 parts by mass of the entire thermoplastic resin composition. If the amount of the acid-containing resin added is less than 5 parts by mass, the adhesion between the wood material 11 and the thermoplastic resin composition 12 will be insufficient, making it impossible to impart sufficient strength to the wood substrate 20. If the amount of the acid-containing resin added is more than 50 parts by mass, the strength of the wood substrate 20 will often decrease, which is not preferable. Furthermore, when the adhesion between the wood material 11 and the thermoplastic resin composition 12 is insufficient, the entire surface of the wood chips, etc. that make up the wood material 11 cannot be covered with the thermoplastic resin composition 12, so that moisture that has penetrated into the wood material 11 causes the entire wood base material 20 to absorb water and expand, reducing the water resistance of the entire wood base material 20.

[0028] (organic peroxide) The thermoplastic resin composition 12 may further contain an organic peroxide. The organic peroxide may be used for radical crosslinking the thermoplastic resins contained in the thermoplastic resin composition 12 in the heating and pressurizing step of the raw material mixture 10. In addition, if a material having radical crosslinking properties is used for the acid-containing resin, crosslinking can be caused between the acid-containing resin and the thermoplastic resin by adding the organic peroxide to the thermoplastic resin composition 12. When radical crosslinking is formed between thermoplastic resins or between the acid-containing resin and the thermoplastic resin, the mechanical strength of the entire wood substrate 20 is improved due to the crosslinked structure.

[0029] 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 thereof include hydroperoxides, diacyl peroxides, peroxydicarbonates, peroxyesters, peroxycarbonates, dialkyl peroxides, and ketone peroxides.

[0030] (Amount of organic peroxide added) The amount of the organic peroxide added is preferably within the 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 10 when heated and pressurized will be insufficient, and will not contribute to improving the strength of the wood base material 20. If the amount of organic peroxide added is more than 5 parts by mass, the amount of decomposition products produced during the reaction will increase, which may cause deformation of the wood base material 20, and is therefore undesirable. Furthermore, by adding an organic peroxide to the thermoplastic resin composition 12, it becomes possible to form a three-dimensional network (bonds) by radical crosslinking between the thermoplastic resin contained in the thermoplastic resin composition 12, the acid-containing resin, and the wood material 11. This improves the mechanical strength of the entire wood substrate 20.

[0031] (Additives) An additive such as wax may be mixed into the thermoplastic resin composition 12. Adding wax as an additive further improves the water resistance of the wood substrate 20. In addition, an additive such as wax also serves as a lubricant to uniformly mix the wood material 11 and the thermoplastic resin composition 12, or multiple types of thermoplastic resin compositions 12.

[0032] (Method of producing thermoplastic resin composition 12) The thermoplastic resin composition 12 can be prepared by various known methods. For example, the particles of the thermoplastic resin composition 12 may be heated during mixing to fuse them together. However, if the particles are larger than 150 μm, the number of particles decreases and the surface area decreases, which makes it difficult to mix uniformly with the wood material 11, and this is not desirable. The thermoplastic resin composition 12 can also be prepared 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 may be crushed and then mixed. 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 12, and a powder of the thermoplastic resin composition 12 can be easily obtained.

[0033] The thermoplastic resin composition 12 can be powdered by, for example, mechanical crushing or freeze-pulverization after heating and kneading multiple types of thermoplastic resin pellets using a single-screw kneader or a batch kneader. For example, polyethylene pellets and acid-modified polyolefin pellets are heated and kneaded in a single-screw kneading extruder, pelletized, and the kneaded pellets are freeze-pulverized to obtain a powder of the thermoplastic resin composition 12. In other words, multiple types of thermoplastic resin compositions 12 may be kneaded by an extrusion method to obtain a powder of the thermoplastic resin composition 12. In addition, by mixing multiple types of powdered thermoplastic resin compositions 12, the thermoplastic resin compositions 12 can be mixed more uniformly, so that a wood substrate 20 with excellent in-plane uniformity of bending strength can be obtained.

[0034] (Wood base material 20) The wood substrate 20 is formed by heating and pressurizing a raw material mixture 10 containing a wood material 11 having at least one of a powdered and chipped form and a powdered thermoplastic resin composition 12. As shown in Fig. 2, the wood substrate 20 thus formed has a multilayer structure having at least one skin layer 21 and at least one core layer 22. Here, the skin layer 21 is a water-resistant layer. By providing this skin layer 21, water absorption in the core layer 22 is reduced, and the entire wood substrate 20 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 20, warping of the wood base material 20 due to swelling becomes a problem, so it is desirable to use a three-layer structure as shown in Figure 2, with skin layers 21 having the same properties on the front and back of the wood base material 20. The thickness of the wood base material 20 is preferably within a range of 5 mm to 40 mm. If the thickness of the wood base material 20 is thinner than 5 mm, the bending strength of the wood base material 20 is weak (low) and is not practical. If the thickness of the wood base material 20 is thicker than 40 mm, the weight of the wood base material 20 is heavy and difficult to handle during construction work. The thickness of the skin layer 21 on one side (e.g., the front side) of the wooden substrate 20 may be thicker or thinner than the thickness of the skin layer 21 on the other side (e.g., the back side) of the wooden substrate 20. The thickness of the skin layer 21 on one side (e.g., the front side) of the wooden substrate 20 and the thickness of the skin layer 21 on the other side (e.g., the back side) of the wooden substrate 20 may be the same.

[0035] The thickness of each of the skin layer 21 and the core layer 22 constituting the wood base material 20 is preferably 2 mm or more. If the thickness of each of the skin layer 21 and the core layer 22 is less than 2 mm, it is difficult to produce a uniform skin layer 21 and core layer 22 because they are too thin. As shown in FIG. 2, when the wood base material 20 has a three-layer structure with the skin layer 21 on the front and back sides, the thickness ratio of the skin layer 21 to the core layer 22 (skin layer 21:core layer 22) is preferably within a range of 1:0.1 to 1:18. In other words, as shown in FIG. 2, when the wood base material 20 has a structure including the skin layer 21, the core layer 22, and the skin layer 21 in sequence, the thickness ratio of each layer (skin layer 21:core layer 22:skin layer 21) is preferably within a range of 1:0.1:1 to 1:18:1. Moreover, since the total thickness of the wood base material 20, which is the sum of the skin layer 21 and the core layer 22, is desirably 40 mm or less, it is desirable for the skin layer 21 to be 19 mm or less.

[0036] The skin layer 21 and the core layer 22 constituting the wood base material 20 are each formed by measuring the normalized CH area of ​​the skin layer 21 calculated from an absorption spectrum obtained by Fourier infrared spectroscopy, which will be described later. S , the normalized CH area of ​​the core layer 22 is A C In this case, A S >A C It is desirable to adjust the normalized CH area so that it is equal to or smaller than the amount of the thermoplastic resin composition 12 added to the skin layer 21 and the core layer 22. The size of each normalized CH area is qualitatively proportional to the amount (content ratio) of the thermoplastic resin composition 12 added to the skin layer 21 and the core layer 22, respectively. Therefore, the problem of the present application can be solved even if the amount (content ratio) of the thermoplastic resin composition 12 in the core layer 22 is made the same as the amount (content ratio) of the thermoplastic resin composition 12 in the skin layer 21. However, in that case, the amount (content ratio) of the thermoplastic resin composition 12 in the core layer 22 becomes larger (larger) than necessary, which may increase the production cost. Therefore, the amount (content ratio) of the thermoplastic resin composition 12 is adjusted to be equal to or smaller than the amount (content ratio) of the thermoplastic resin composition 12 added to the skin layer 21 and the core layer 22. S >A C By adjusting the thickness so as to be equal to or smaller than the thickness of the resin, it is possible to reduce the manufacturing cost while maintaining both the mechanical strength and the water resistance.

[0037] Here, Fourier infrared spectrometry will be described. First, infrared spectrometry is a measurement method that obtains information about the chemical structure and state of a substance by measuring 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. Particularly, in this embodiment, the calculation of the interference wave is performed using the Fourier transform method, and the measurement is performed by Fourier infrared spectrometry, which is a method for measuring an infrared spectrum. 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 or thickness of the substance, or, in the case of a crystalline substance, the amount of crystalline or amorphous parts, making it possible to perform quantitative analysis from the height or area of ​​the peak.

[0038] FIG. 3 shows an example of the infrared absorption spectrum of a typical wood material 11. Wood material 11 has a peak of OH groups derived from cellulose at a wave number of 3000 cm. -1 More than 3500cm -1 The C-OH group peak at wavenumber 900 cm is in the following region. -1 More than 1200cm -1 The peak areas are S O-H、 S C-OH The baseline shown by the dashed line is used as the background for correction. In other words, the ranges enclosed by the solid and dashed lines in Figure 3 are the area values ​​of the peaks of the OH group and the C-OH group. 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.

[0039] 4 shows an example of the infrared absorption spectrum of the wood substrate 20 of this embodiment. In addition to the peak derived from the wood material 11, the peaks of the CH2 group and CH3 group derived from the thermoplastic resin composition 12 are observed at a wave number of 2700 cm. -1 More than 3000cm -1 It is strongly present in the following region. The area value of the peak is S C-H The baseline shown by the dashed line is used as the background for correction. In other words, the areas surrounded by the solid and dashed lines in Figure 4 represent the area values ​​of the peaks of the OH group, the C-OH group, the CH2 group, and the CH3 group.

[0040] The normalized CH area A of the skin layer 21 calculated from the area values ​​of each peak using the following formula (1) S and the normalized CH area A of the core layer 22 c It is preferable to adjust the normalized CH area A so that the normalized CH area A is within the range of 0.07 to 1.00. Specifically, the content ratio of the wood material 11 and the thermoplastic resin composition 12 is adjusted so that the normalized CH area A S and normalized CH area A c Adjust the values ​​of each. Standardized CH area=S C-H / (S O―H +S C-OH )...Equation (1) Normalized CH area product A S and normalized CH area A c When the normalized CH area A is less than 0.07, the proportion of the wood material 11 is too high, making it difficult to provide the bending strength and water resistance required for practical use. S and normalized CH area A c When each of the normalized CH area A and the normalized CH area B exceeds 1.00, the proportion of the thermoplastic resin composition 12 is too high, which is undesirable since the wood base material 20 is likely to deform when heated and pressurized. S and normalized CH area A c may each be greater than 1.00. If the wood material 11 and the thermoplastic resin composition 12 are not mixed uniformly, the bending strength and water resistance of the wood base material 20 will vary, which is not preferable.

[0041] Normalized CH area A of skin layer 21 S and the normalized CH area A of the core layer 22 c More preferably, each of the normalized CH areas is within the range of 0.08 to 0.35. If each normalized CH area is within the above numerical range, it is possible to obtain a good wood base material 20 that has a higher bending strength, is more water resistant, and is less likely to deform. In addition, the normalized CH area A S and the normalized CH area A c The area ratio (A S / A c The normalized CH area ratio (A) is preferably in the range of more than 1 and not more than 4, and more preferably in the range of 1.5 or more and not more than 3. S / A c ) within the above-mentioned numerical range, excellent water resistance can be imparted to the entire wood base material 20, while the amount of thermoplastic resin composition 12 added to the core layer 22 can be reduced to the minimum necessary, thereby reducing production costs.

[0042] (Manufacturing conditions for wood base material 20) Various known methods of heating and pressing can be used to manufacture the wooden substrate 20, but press molding using a frame mold as shown in Fig. 1 is suitable for manufacturing the wooden substrate 20. The heating temperature is usually within the range of 120°C to 250°C, and must be equal to or higher than the melting point of the thermoplastic resin composition 12. However, if the heating temperature exceeds 250°C, significant thermal degradation of the wooden material 11 may occur. The pressing pressure is usually 10 kgf / cm 2 More than 400kgf / cm 2 The value is within the following range and is appropriately set depending on the desired density of the wood base material 20.

[0043] 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 10 containing a wood material 11 having at least one of a powder and chip form and a powdered thermoplastic resin composition 12 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 10. Next, a thickness adjusting metal plate 7 is placed on the jig 1 for producing a wooden base material, 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 21 according to this embodiment. Another skin layer 21 is also formed in a similar manner. After the pair of skin layers 21 are thus formed, the metal plate 2, the releasable metal plate 3, and the skin layer 21 are layered in this order on the bottom surface of the jig 1 for producing a wooden base material. Next, a raw material mixture 10 containing a wood material 11 having at least one of a powdered and chipped form and a powdered thermoplastic resin composition 12 is placed in the storage portion of the jig 1 for producing a wooden substrate, and a skin layer 21 and a releasable metal plate 3 are placed in this order on the raw material mixture 10. Here, the raw material mixture 10 sandwiched between the skin layers 21 becomes a core layer 22 in the wood substrate 20. Next, the thickness adjusting metal plate 7 is placed on the jig 1 for producing the wooden base material, and the raw material mixture 10 is pressed from above with a metal weight 8 via the skin layer 21 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 10 via a metal weight 8, forming the wood base material 20 according to this embodiment.

[0044] When manufacturing the wood substrate 20, 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 having releasability, but when smoothness of the wood substrate 20 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 12, 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. By forming irregularities on the surface of the releasable metal plate 3, the releasability is improved. In addition, by using an uneven structure and a fluorine coating in combination on the releasable metal plate 3, it is possible to further improve the releasability.

[0045] 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 12 from adhering thereto, and it is more preferable that an uneven structure is formed by fluorine coating or thermal spraying.

[0046] (Modification) In this embodiment, the method for producing the wood base material 20 includes first creating two skin layers 21 by heating and pressurizing, and then sandwiching the raw material mixture 10 that will become the core layer 22 between the two skin layers 21 and heating and pressurizing again to produce the wood base material 20. However, the present invention is not limited to this method. For example, first, raw material mixture 10 that will become skin layer 21, raw material mixture 10 that will become core layer 22, and raw material mixture 10 that will become skin layer 21 may be laminated in this order, and then the two types and three layers of raw material mixture 10 may be heated and pressurized simultaneously to produce wood base material 20. Thus, in the manufacturing method of the wood base material 20 according to this embodiment, the skin layer 21 may be formed in a first heating and pressing process and the core layer 22 may be formed in a second heating and pressing process, or both the skin layer 21 and the core layer 22 may be formed in the first heating and pressing process.

[0047] [Second embodiment] The second embodiment will be described with reference to FIG. The second embodiment is characterized in that a decorative material 14 is formed by laminating a design layer 13 having a design effect on the wood base material 20 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 20, it is possible to impart design properties. That is, the wood base material 20 can be used as a decorative material by itself, but in order to give the wood base material 20 even more excellent design, a design layer 13 such as paper or film with a design such as a picture may be laminated onto the wood base material 20 to form a decorative material 14, as shown in Figure 5.

[0048] <Other effects> (1) The wooden substrate 20 of this embodiment includes a wooden material 11 having at least one of a powdery and chip-like shape, and a thermoplastic resin composition 12. The wooden substrate 20 includes a skin layer 21, a core layer 22, and a skin layer 21 in this order. When the density of the skin layer 21 is ρs and the density of the core layer 22 is ρc, ρs / ρc is in the range of 1.0 to 2.4, and each of ρs and ρc is 0.5 g / cm. 3 More than 1.2g / cm 3 It is within the following range. With this configuration, since the thermoplastic resin composition 12 is used as an adhesive instead of formaldehyde, which causes sick house syndrome, it is possible to provide a wood base material 20 that does not emit harmful substances. Furthermore, when ρs and ρc are within the above-mentioned ranges, it is possible to obtain a favorable wood base material 20 that has a higher bending strength, is more water-resistant, and is less prone to deformation.

[0049] (2) In the wood base material 20 of this embodiment, the normalized CH area calculated from the absorption spectrum obtained by Fourier infrared spectroscopy using the following formula (1) is in the range of 0.07 to 1.00 for each of the skin layers 21 and the core layer 22, and the normalized CH area of ​​the skin layer 21 is A S , the normalized CH area of ​​the core layer 22 is A C In this case, A S >A Cmay be also possible. Standardized CH area=S C-H / (S O―H +S C-OH )...Equation (1) Here, in formula (1), S C-H is a wave number of 2700 cm -1 More than 3000cm -1 The area value of the peak derived from either the CH2 group or the CH3 group in the following region, S O-H is a wave number of 3000 cm -1 More than 3500cm -1 The area value of the peak derived from the OH group in the following region, S C-OH is a wave number of 900 cm -1 More than 1200cm -1 The area values ​​of the peaks derived from C-OH groups in the following regions are shown. With this configuration, since the thermoplastic resin composition 12 is used as an adhesive instead of formaldehyde, which causes sick house syndrome, it is possible to provide a wood base material 20 that does not emit harmful substances. In addition, the normalized CH area A S , A C Within the above range, it is possible to obtain a favorable wood base material 20 that has a higher bending strength, is more water-resistant, and is less prone to deformation.

[0050] (3) In the wood base material 20 of this embodiment, the ratio of thicknesses of the skin layer 21, the core layer 22 and the skin layer 21 (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 base material 20 has a multi-layer structure and is therefore excellent in bending strength and water resistance.

[0051] (4) In the wood base material 20 of this embodiment, the skin layer 21 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 20 that functions adequately as the skin layer 21, the overall thickness of the wood base material 20 is not too large, and there are no problems with workability during construction.

[0052] (5) In the wood base material 20 of this embodiment, each skin layer 21 and core layer 22 may have a mass ratio of the wood material 11 to the thermoplastic resin composition 12 (wood material 11 / thermoplastic resin composition 12) within a range of 95 / 5 to 70 / 30. With this configuration, it is possible to reliably provide a wood base material 20 with greater bending strength.

[0053] (6) In the wood base material 20 of this embodiment, the wood material 11 may contain a mushroom bed as a raw material. With such a configuration, it is possible to provide a wood base material 20 that is beneficial in reducing the environmental impact.

[0054] (7) In the wood substrate 20 of this embodiment, the thermoplastic resin composition 12 may contain a polyolefin resin. Such a configuration can provide a wood base material 20 that has both good bending strength and water resistance. Furthermore, when the wood base material 20 contains polyethylene derived from biomass, the wood base material 20 can be provided with benefits in terms of reducing the environmental impact.

[0055] (8) In the wood substrate 20 of this embodiment, the thermoplastic resin composition 12 may contain an acid-modified polyolefin. With such a configuration, it is possible to provide a wood base material 20 with better bending strength.

[0056] (9) The decorative material 14 of this embodiment is obtained by laminating a decorative substrate (decorative layer 13) having a design onto the wood substrate 20 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.

[0057] [Example] Below, examples 1 to 23 and comparative examples 1 to 5 of the wood base material according to the first embodiment of the present invention will be explained. Note that the present invention is not limited to the following examples 1 to 23.

[0058] 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 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 with a heat press device to obtain one skin layer with a thickness of 4 mm (pressing conditions: 40 kgf / cm 2 , 200°C for 10 minutes, substrate density: 0.8g / cm 3 After obtaining another 4 mm skin layer in the same way, the raw material mixture for the core layer was placed between the two skin layers until the density of the core layer was 0.8 g / cm3. 3 The mixture was heated and pressed to obtain a three-layered wood substrate of Example 1, in which a skin layer of 4 mm, a core layer of 4 mm, and a skin layer of 4 mm were laminated in that order.

[0059] Example 2 In Example 2, the density of the skin layer is 1.2 g / cm 3 , the density of the core layer is 0.5g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0060] Example 3 In Example 3, the density of the skin layer is 0.5 g / cm 3 , the density of the core layer is 0.5g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0061] Example 4 In Example 4, the density of the skin layer is 1.2 g / cm 3 , the density of the core layer is 1.2g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0062] Example 5 In Example 5, the density of the skin layer is 0.9 g / cm 3 , the density of the core layer is 0.75g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0063] Example 6 In Example 6, 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.

[0064] Example 7 In Example 7, 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.

[0065] Example 8 In Example 8, 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.

[0066] Example 9 The thermoplastic resin composition of Example 9 was a low-density polyethylene resin (LDPE) pellet alone, and a wood base material was obtained in the same manner as in Example 1.

[0067] Example 10 The thermoplastic resin composition of Example 10 was a linear low-density polyethylene resin (LLDPE) pellet alone. A wood base material was obtained in the same manner as in Example 1 except for the above.

[0068] Example 11 The thermoplastic resin composition of Example 11 was polypropylene resin (PP) pellets alone. A wood base material was obtained in the same manner as in Example 1 except for the above.

[0069] 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 "96 / 4," and otherwise the wood base material was obtained in the same manner as in Example 1.

[0070] Example 13 In Example 13, 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.

[0071] Example 14 In Example 14, 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.

[0072] Example 15 In Example 15, 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.

[0073] Example 16 In Example 16, 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.

[0074] (Example 17) In Example 17, 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.

[0075] (Example 18) In Example 18, 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.

[0076] (Example 19) The components and masses of the thermoplastic resin composition of Example 19 are as follows. (1) High density polyethylene resin 97 parts by weight (2) Acid-modified polyolefin: 3 parts by mass The above (1) and (2) were heated and kneaded in a batch kneader, and then mechanically pulverized to obtain a powdered thermoplastic resin composition. A wood substrate of Example 19 was obtained in the same manner as in Example 1 except for the above.

[0077] (Example 20) The components and masses of the thermoplastic resin composition of Example 20 are as follows. (1) High density polyethylene resin 80 parts by weight (2) Acid-modified polyolefin: 20 parts by mass The above (1) and (2) were heated and kneaded in a batch kneader, and then mechanically pulverized to obtain a powdered thermoplastic resin composition. A wood substrate for Example 20 was obtained in the same manner as in Example 1 except for the above.

[0078] Example 21 The components and masses of the thermoplastic resin composition of Example 21 are as follows. (1) High density polyethylene resin 60 parts by weight (2) Acid-modified polyolefin 40 parts by mass The above (1) and (2) were heated and kneaded in a batch kneader, and then mechanically pulverized to obtain a powdered thermoplastic resin composition. A wood substrate for Example 21 was obtained in the same manner as in Example 1 except for the above.

[0079] Example 22 In Example 22, 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.

[0080] (Example 23) In Example 23, 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.

[0081] Comparative Example 1 In Comparative Example 1, the density of the skin layer was 0.4 g / cm 3 , the density of the core layer is 0.4g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0082] Comparative Example 2 In Comparative Example 2, the density of the skin layer was 1.3 g / cm 3 , the density of the core layer is 1.3 g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0083] Comparative Example 3 In Comparative Example 3, the density of the skin layer was 1.3 g / cm 3 , the density of the core layer is 0.5g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0084] Comparative Example 4 In Comparative Example 4, the density of the skin layer was 0.5 g / cm 3 , the density of the core layer is 1.2g / cm 3 A wood base material was obtained in the same manner as in Example 1, except for the above.

[0085] Comparative Example 5 In Comparative Example 5, a wood base material was obtained in the same manner as in the case of 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 the application of external forces such as pressure or suction. 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 base material.

[0086] (Evaluation of wood-based materials) The mechanical strength, water resistance, and substrate deformation were evaluated for the above-mentioned Examples 1 to 23 and Comparative Examples 1 to 5. The Fourier infrared spectroscopy was measured by the following method.

[0087] (Fourier type infrared spectroscopy) The Fourier-type infrared spectroscopy was performed using a PerkinElmer Fourier-type infrared spectrometer (Spectrum Spotlight 400) at 4000 cm -1 From 400cm -1 From the obtained absorption spectrum, the normalized CC area of ​​each of the skin layer and the core layer is calculated using the following formula (1). Standardized CH area=S C-H / (S O―H +S C-OH )...Equation (1) Here, in formula (1), S C-H is a wave number of 2700 cm -1 More than 3000cm -1 The area value of the peak derived from either the CH2 group or the CH3 group in the following region, S O-H is a wave number of 3000 cm -1 More than 3500cm -1 The area value of the peak derived from the OH group in the following region, S C-OH is a wave number of 900 cm -1 More than 1200cm -1 The area values ​​of the peaks derived from C-OH groups in the following regions are shown.

[0088] (Mechanical strength) The mechanical strength was measured by bending strength according to the method of JISA5908. Measured value (unit: N / mm 2 The evaluation criteria for mechanical strength for the above-mentioned materials are as follows, based on the JIS standard values: The mechanical strength was evaluated based on the following four-level scale: "◎", "good", "△", and "×", with "◎", "good", and "△" being pass marks and "×" being fail marks. ◎:15 or more (pass) 〇: 13 or more and less than 15 (pass) △: 8 or more but less than 13 (pass) ×: Less than 8 (failed)

[0089] (water resistance) Water resistance was measured by measuring the water absorption thickness swelling rate according to a method conforming to JISA 5908. The evaluation criteria for water resistance for the measured value (unit: %) are as follows, based on the JIS standard values. The water resistance was evaluated based on 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)

[0090] (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 substrate deformation were as follows: 3-level evaluation of "good", "△", and "×", with "good" and "△" being pass and "×" being fail. 〇: No voids (passed) △: Traces of voids (passed) ×: Voids present (failed)

[0091] (Evaluation Results) The evaluation results of the wood-based substrates are as shown in Table 1 below. In addition, the "raw material blend ratio" in Examples 1 to 23 and Comparative Examples 1 to 4 in the table indicates the mass ratio of (wood material / thermoplastic resin composition), and the "raw material blend ratio" in Comparative Example 5 in the table indicates the mass ratio of (wood material / adhesive).

[0092] [Table 1]

[0093] (Mechanical strength evaluation results) The two cases that failed the mechanical strength were Comparative Examples 1 and 4, which are considered to be due to the low density of the skin layer. In addition, when comparing Examples 1 to 23 and Comparative Examples 2 and 3, the nine cases that included "△" in the evaluation results were Examples 3, 8 to 13, 21, and 23. It is considered that the density of the core layer and the skin layer was low in Example 3. It is considered that the core layer was extremely thinner than the skin layer in Examples 8 and 23, which reduced the mechanical strength. It is considered that the mechanical strength was reduced compared to HDPE in Examples 9 to 11, because LDPE, LLDPE, and PP were used as the base resins, respectively. It is considered that the proportion of wood material in the skin layer was high in Examples 12 to 13, which reduced the mechanical strength. It is considered that the mechanical strength was reduced in Example 21, which contains 40 parts of acid-modified polyolefin, because the content of the base resin was relatively low.

[0094] (Water resistance evaluation results) The only one that failed the water resistance test was Comparative Example 5. The conventional method using an adhesive has poorer water resistance than Examples 1 to 23 of the present invention. Comparing Examples 1 to 23 and Comparative Examples 1 to 4, 19 cases, including Examples 1 to 13, 22 to 23, and Comparative Examples 1 to 4, include a grade of "△". In Examples 1 to 13, 22 to 23 and Comparative Examples 1 to 4, the material formulation does not contain an acid-modified polyolefin, and the thermoplastic resin composition is 15 parts or less, so it is considered that the water resistance was insufficient. In Examples 19 to 21, compared with Example 1, it is considered that the water resistance is improved because the acid-modified polyolefin is contained. In Examples 14 to 16, the proportion of the thermoplastic resin composition in only the skin layer is increased to 20 parts, 30 parts, and 35 parts, and 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 17 and 18 in which the proportion of the thermoplastic resin composition in the core layer is also increased to 30 parts and 35 parts.

[0095] (Evaluation results of substrate deformation) In terms of substrate deformation, only Comparative Examples 2 and 3 failed. Examples 1 to 23 and Comparative Examples 1, 4, and 5 passed. Among them, Examples 2, 4, and 18 had evaluation results that included "△". In Examples 2 and 4, only the skin layer or both the skin layer and the core layer have a density of 1.2 g / cm 3 It is considered that Example 18 contains 35 parts of the thermoplastic resin composition in both the skin layer and the core layer, and therefore the content of the thermoplastic resin composition is relatively high, which makes the substrate more likely to deform.

[0096] (Overall evaluation results) As a comprehensive evaluation result, Examples 1 to 23 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 22 and 23, the thickness of the wood base material exceeds 40 mm, so the wood base material is heavy and workability is deteriorated, but it is within a range that does not cause any practical problems. [Explanation of symbols]

[0097] Reference Signs List 1: Jig for making wooden substrate, 2: Metal plate (bottom surface), 3: Releaseable metal plate, 7: Metal plate for adjusting thickness, 8: Metal weight, 9: Press top plate, 10: Raw material mixture, 11: Wooden material, 12: Thermoplastic resin composition, 13: Design layer, 14: Decorative material, 20: Wooden substrate, 21: Skin layer, 22: Core layer

Claims

1. 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 includes a skin layer, a core layer, and a skin layer in this order. When the density of the skin layer is ρs and the density of the core layer is ρc, ρs / ρc is in the range of 1.0 to 2.4, and each of ρs and ρc is 0.5 g / cm ３ 1.2g / cm or more ３ Within the following range: A wood substrate characterized in that the mass ratio of the wood material to the thermoplastic resin composition contained in the skin layer (wood material / thermoplastic resin composition) is different from the mass ratio of the wood material to the thermoplastic resin composition contained in the core layer (wood material / thermoplastic resin composition).

2. 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 layers and the core layer is in the range of 0.07 or more and 1.00 or less, The wood base material according to claim 1, 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. Normalized C-H area = S Ｃ－Ｈ / (S Ｏ―Ｈ +S Ｃ－ＯＨ ) …………Formula (1) (Here, in formula (1), S Ｃ－Ｈ The wave number is 2700 cm －１ More than 3000cm －１ CH in the following areas ２ Group, CH ３ The area value of the peak derived from any one of the groups, S Ｏ－Ｈ is a wave number of 3000 cm －１ More than 3500cm －１ The area value of the peak derived from the OH group in the following region, S Ｃ－ＯＨ The wave number is 900 cm －１ More than 1200cm －１ The area values ​​of the peaks derived from C-OH groups in the following regions are shown below.)

3. The wood base material according to claim 1 or 2, characterized in that the ratio of the thicknesses of the skin layer, the core layer, and the skin layer (skin layer:core layer:skin layer) is within the range of 1:0.1:1 to 1:18:

1.

4. The wood base material according to claim 1 or 2, characterized in that the ratio of the thickness of each layer in the skin layer, the core layer, and the skin layer (skin layer:core layer:skin layer) is within the range of 1:0.1:1 to 1:2.5:1, or within the range of 1:18:1 to 1:20:

1.

5. The wood base material according to claim 1 or 2, characterized in that the ratio of the thickness of each layer in the skin layer, the core layer, and the skin layer (skin layer:core layer:skin layer) is within the range of 1:0.1:1 to 1:18:1 (excluding 1:5:1).

6. 6. The wood base material according to claim 1, wherein the skin layer has a thickness in the range of 2 mm to 19 mm.

7. The wood base material according to any one of claims 1 to 6, characterized in that each of the skin layers and the core layer has 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.

8. 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.

9. The wood substrate according to any one of claims 1 to 8, characterized in that the thermoplastic resin composition contains a polyolefin resin.

10. The wood substrate according to any one of claims 1 to 9, characterized in that the thermoplastic resin composition contains an acid-modified polyolefin.

11. The wood base material according to any one of claims 1 to 10, wherein the ρc is within a range of 0.75 g / cm 3 or more and 1.2 g / cm 3 or less.

12. The wood base material according to claim 1, wherein the ρs is within a range of 0.5 g / cm 3 or more and 0.9 g / cm 3 or less.

13. A decorative material comprising the wood substrate according to any one of claims 1 to 12 and a decorative substrate laminated thereon.

14. 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; The method for producing a wood substrate comprises heating and pressurizing the raw material mixture to form a wood substrate.

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