Modified softwood material, method for producing modified softwood material, and woody decorative material

Abstract

This modified softwood material includes a softwood material and a polymer in contact with the softwood material. The density of the modified softwood material is greater than 0.33 g / cm3 and no greater than 0.85 g / cm3, and the compressive strength in the radial direction of the modified softwood material is greater than 2.5 MPa and no greater than 30 MPa.

Description

Modified softwood material, manufacturing method for modified softwood material, and wood decorative material

[0001] The present disclosure relates to modified softwood materials, methods for producing modified softwood materials, and wood decorative materials.

[0002] Modified wood has been known in the past, in which properties such as strength and dimensional stability of wood have been changed by modifying the wood.

[0003] For example, Non-Patent Document 1 discloses modified eucalyptus wood in which styrene or methyl methacrylate is injected into the cell cavity of eucalyptus wood and polymerized to fill the cell cavity. Also, Non-Patent Document 2 discloses modified poplar wood in which the surface of the cell cavity of poplar wood is coated with a polymer.

[0004] Denise Ortigosa Stolf et al., "Wood-Polymer Composite: Physical and Mechanical Properties of Some Wood Species Impregnated with Styrene and Methyl Methacrylate", Materials Research, 2004, Vol. 7, No. 4, p.611-617.Dengkang Guo et al., "Improving physical properties of wood-polymer composites by building stable interface structure between swelled "cell walls and hydrophobic polymer", Wood Science and Technology, 2021, 55, p. 1401-1417.

[0005] The present disclosure aims to provide modified softwood that has higher strength than softwood while minimizing the increase in density relative to softwood.

[0006] The modified softwood according to the present disclosure includes a softwood and a polymer in contact with the softwood. ３ Greater than 0.85 g / cm３ and the radial compressive strength of the modified softwood is greater than 2.5 MPa and less than 30 MPa.

[0007] A method for producing modified softwood according to the present disclosure includes injecting an emulsion containing water as a solvent and polymer particles into softwood, and removing the solvent from the softwood.

[0008] According to the modified softwood material of the present disclosure, it is possible to provide a modified softwood material that has a higher strength than softwood material while suppressing an increase in density compared to softwood material.

[0009] FIG. 1A is a diagram showing an SEM image of a cross section of a cell wall in a modified softwood material according to embodiment 1, in which a polymer is provided on the surface of the cell lumen side of the cell wall. FIG. 1B is a schematic cross-sectional view showing a cross section of the cell lumen of a tubular cell in a modified softwood material according to embodiment 1. FIG. 2A is a schematic cross-sectional view showing a cross section perpendicular to the fiber direction of a tubular cell of a plant-based material. FIG. 2B is a diagram showing SEM images of cell wall cross sections in earlywood and latewood of a softwood material. FIG. 3A is a schematic see-through perspective view of a tubular cell, showing an untreated state before polymer injection. FIG. 3B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of a tubular cell, showing an untreated state before polymer injection. FIG. 3C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of a tubular cell, showing an untreated state before polymer injection. FIG. 3D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of a tubular cell, showing an untreated state before polymer injection. FIG. 4A is a schematic see-through perspective view of a tubular cell, showing a state in which a polymer is in contact with almost the entire inner surface of the cell wall. FIG. 4B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with almost the entire inner surface of the cell wall. FIG. 4C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with almost the entire inner surface of the cell wall. FIG. 4D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with almost the entire inner surface of the cell wall. FIG. 5A is a schematic see-through perspective view of a tubular cell, showing a state in which the polymer is in contact with approximately half of the inner surface of the cell wall. FIG. 5B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with approximately half of the inner surface of the cell wall. FIG. 5C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with approximately half of the inner surface of the cell wall. FIG. 5D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which the polymer is in contact with approximately half of the inner surface of the cell wall. FIG. 6A is a schematic see-through perspective view of a tubular cell, showing a state in which the polymer is in contact with a portion of the inner surface of the cell wall.6B is a cross-sectional view showing a cross-sectional structure perpendicular to the fiber direction of a tubular cell, showing a state in which a polymer is in contact with part of the inner surface of the cell wall. FIG. 6C is a cross-sectional view showing a cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which a polymer is in contact with part of the inner surface of the cell wall. FIG. 6D is a cross-sectional view showing a part of a cross-sectional structure parallel to the fiber direction of a tubular cell, showing a state in which a polymer is in contact with part of the inner surface of the cell wall. FIG. 7A is a schematic cross-sectional view showing an example of a step of immersing a softwood material in an emulsion in the method for producing a modified softwood material according to the first embodiment. FIG. 7B is a schematic cross-sectional view showing another example of a step of immersing a softwood material in an emulsion in the method for producing a modified softwood material according to the first embodiment. FIG. 7C is a schematic cross-sectional view showing a step of removing a solvent from a softwood material in the method for producing a modified softwood material according to the first embodiment. FIG. 8A is a schematic cross-sectional view showing a cross-section perpendicular to the fiber direction of a tubular cell of an untreated softwood material. FIG. 8B is a schematic cross-sectional view showing the area of ​​the cell wall in a cross-section of the cell lumen of the softwood material of FIG. 8A. Figure 8C is a schematic cross-sectional view showing the area of ​​voids in a cross-section of a cell lumen of the softwood of Figure 8A. Figure 9A is a schematic cross-sectional view showing a cross-section perpendicular to the fiber direction of a tubular cell of a modified softwood. Figure 9B is a schematic cross-sectional view showing the area of ​​an apparent cell wall including a cell wall and a polymer in a cross-section of a cell lumen of the modified softwood of Figure 9A. Figure 9C is a schematic cross-sectional view showing the area of ​​voids in a cross-section of a cell lumen of the modified softwood of Figure 9A.

[0010] (Knowledge that forms the basis of this disclosure) In order to curb global warming, curbing the increase in carbon dioxide, a greenhouse gas, has become an important global issue. Therefore, in order to move towards a decarbonized society that aims to curb the increase in carbon dioxide, attention is being paid to forest resources that can absorb carbon dioxide, a greenhouse gas, and storable timber. In order to sustainably obtain the effects of timber as described above, it is necessary to cycle "cut, use, plant," and therefore there is a demand for the development of uses for timber and the creation of high added value.

[0011] Wood has various properties, such as strength, dimensional stability, weather resistance, and abrasion resistance, that vary depending on the tree species, so it is necessary to consider the appropriate use. Examples of uses include exterior building materials, interior building materials, furniture, and acoustic materials. High-strength wood has a wide range of potential uses, so depending on the tree species, excessive harvesting has progressed and depletion has become a problem. On the other hand, low-strength wood has become a problem due to the increase in stockpiles and the abandonment of artificial forests.

[0012] One major application requiring high-strength wood is building materials. Flooring materials, in particular, require numerous strength and durability characteristics. These include dent resistance to withstand heavy loads such as office furniture, surface hardness to resist scratches caused by falling objects, resistance to deterioration even when exposed to hot water, and resistance to peeling caused by repeated friction from furniture with casters. Among flooring materials, decorative materials, being exposed on the surface of flooring components, also require high design quality. In addition, especially for interior building materials, it is desirable for them to be free of harmful substances. Furthermore, lightweight high-strength wood can reduce transportation costs and be easier to handle during construction, leading to the potential for expanded use. Given this background, there is a need for a safe method that uses almost no highly harmful VOCs to preserve the lightweight advantages of wood while retaining its distinctive design and improving its strength.

[0013] Indicators of wood's mechanical properties include, for example, compressive properties, tensile properties, and bending properties. Of these mechanical properties, compressive properties can be evaluated from stress-strain curves obtained using commercially available autograph testing machines, universal testing machines, tension-compression testing devices, and compression testing machines. Compressive properties generally include compressive strength, compressive modulus, and buckling strain, which can be quantitatively compared and evaluated. Compressive strength can be calculated from the upper yield point of the stress-strain curve, compressive modulus can be calculated from the slope of the stress-strain curve, and buckling strain is the magnitude of strain up to the upper yield point. Considering the practical uses of wood as described above, improving the compressive strength of wood will greatly contribute to expanding its applications.

[0014] For example, softwood is known as a type of wood with low strength. In contrast, hardwood is known as a type of wood with high strength. Specifically, softwood is softer than hardwood, and is more susceptible to dents from impacts and scratches from friction. For example, hardwood is called hardwood, while softwood is called softwood. This is because softwood has a different cellular structure than hardwood.

[0015] However, the inventors considered that softwoods are easier to use industrially for the following reasons. For example, softwoods grow straighter and have fewer branches than hardwoods. This allows for stable procurement of homogeneous raw materials. Softwoods also have a higher porosity and lower density than hardwoods. In other words, softwoods are lighter than hardwoods. Softwoods also have fewer cell types and a simpler tissue structure than hardwoods. This means that the differences in properties between different species of softwoods are relatively small.

[0016] In recent years, modified hardwoods, which are chemically modified to alter properties such as strength and dimensional stability, have attracted attention. For example, Non-Patent Document 1 discloses modified eucalyptus wood, a type of hardwood, in which styrene or methyl methacrylate is injected into the cell cavities of eucalyptus, a type of hardwood, and polymerized to fill the cell cavities. Wood modified in this manner and materials containing it are called WPC (Wood-Polymer Composites, or Wood-Plastic Composites). However, because WPCs fill almost all of the intracellular voids, they suffer from the problem of losing the lightweight nature that is one of wood's advantages. Another issue is that the appearance of WPCs is similar to that of resin products, and they lose the mellow luster characteristic of wood. This is due to the similar refractive indices of wood cells and polymers. Designability is an essential factor for industrial use of wood.

[0017] For example, Non-Patent Document 2 discloses modified poplar wood, a type of hardwood, in which the surface of the cell lumen of the cell wall is coated with a polymer. However, Non-Patent Document 2 does not describe or suggest modified softwood wood. It also proposes a modification process consisting of Step 1, in which N-methylol acrylate and hydroxyethyl methacrylate are impregnated into the cell wall and a grafting reaction is carried out to introduce and fix carbon-carbon double bonds into the cell wall, and Step 2, in which the fixed carbon-carbon double bonds are used as active sites to polymerize vinyl monomers such as polystyrene. N-methylol acrylate and hydroxyethyl methacrylate, which contain OH groups, penetrate into the cell wall while cleaving hydrogen bonds derived from OH groups in components such as cellulose that make up the poplar cell wall. According to this method, the grafting reaction proceeds not only on the cell wall surface but throughout the entire cell wall, making it possible to introduce a large number of active sites. However, the formation of multipoint hydrogen bonds between wood components is the main reason for the high strength of wood. Therefore, from the perspective of improving strength, it is undesirable for chemicals to penetrate between wood components and break the hydrogen bonds. Furthermore, in order to obtain the modified poplar wood described in Non-Patent Document 2, highly harmful volatile organic compounds are used, which poses safety issues when using modified poplar wood in industrial applications.

[0018] The present inventors conducted extensive research to achieve the above-mentioned object and discovered that by injecting an emulsion containing water as a dispersing medium into wood cells, removing the water, and then heating the cell, it is possible to obtain modified softwood in which a polymer is formed in contact with the surface of the cell wall facing the lumen while leaving voids in the cell lumen, leading to the present disclosure. The modified softwood according to the present disclosure has higher strength than softwood while suppressing an increase in density.

[0019] Each aspect of the present disclosure will be described below.

[0020] The modified softwood according to the first aspect includes a softwood and a polymer in contact with the softwood. The density of the modified softwood is 0.33 g / cm３ Greater than 0.85 g / cm ３ and the compressive strength in the radial direction of the modified softwood is greater than 2.5 MPa and less than 30 MPa. The radial direction of the modified softwood is the direction from the center of the annual ring of the modified softwood to the outside of the modified softwood.

[0021] The modified softwood material of the second aspect is the modified softwood material of the first aspect, wherein in the second aspect, the softwood material comprises a cell cavity and a cell wall surrounding the cell cavity, and the polymer may be in contact with at least a portion of the surface of the cell wall that is in contact with the cell cavity.

[0022] The modified softwood material of the third aspect is the modified softwood material of the second aspect, and in the third aspect, the polymer filling rate, which is the ratio of the area of ​​the polymer to the area of ​​the cell lumen in the cross section of the cell lumen, may be 10% or more and 60% or less.

[0023] The modified softwood material of the fourth aspect is the modified softwood material of any one of the first to third aspects, and in the fourth aspect, the polymer content in the modified softwood material may be 5 wt% or more and 65 wt% or less.

[0024] The modified softwood material of the fifth aspect is the modified softwood material of any one of the first to fourth aspects, and in the fifth aspect, the spring constant of the polymer calculated by force curve measurement with an atomic force microscope (AFM) may be 0.3 N / m or more and 0.8 N / m or less.

[0025] The modified softwood material according to a sixth aspect is the modified softwood material according to any one of the first to fifth aspects, and in the sixth aspect, the polymer may be a thermoplastic resin.

[0026] A modified softwood material according to a seventh aspect is the modified softwood material according to any one of the first to sixth aspects, and in the seventh aspect, the polymer may comprise at least one selected from the group consisting of vinyl acetate resin, acrylic resin, and styrene-acrylic copolymer resin.

[0027] The modified softwood material according to the eighth aspect is the modified softwood material according to any one of the first to seventh aspects, and in the eighth aspect, the softwood material may be cedar.

[0028] A modified softwood according to a ninth aspect is the modified softwood according to any one of the first to seventh aspects, and in the ninth aspect, the softwood may be Japanese cypress, and the density of the modified softwood is 0.49 g / cm ３ Greater than 0.85 g / cm ３ The modified softwood may have a compressive strength of greater than 6 MPa and less than or equal to 30 MPa.

[0029] A method for producing modified softwood according to a tenth aspect includes injecting an emulsion containing water as a solvent and polymer particles into softwood, and removing the solvent from the softwood.

[0030] The method for producing modified softwood material according to the eleventh aspect is the method for producing modified softwood material according to the tenth aspect, and in the eleventh aspect, injecting the emulsion into the softwood material may include immersing the softwood material in the emulsion and removing the softwood material immersed in the emulsion from the emulsion.

[0031] The modified softwood material of the twelfth aspect is the modified softwood material of any one of the first to ninth aspects, and in the twelfth aspect, the softwood material includes a cell cavity and a cell wall surrounding the cell cavity, and the cell cavity may include a polymer and voids.

[0032] A modified softwood according to a thirteenth aspect is the modified softwood according to any one of the first to ninth and twelfth aspects, and in the thirteenth aspect, the density of the modified softwood is 0.40 g / cm ３ It may be more than that.

[0033] A modified softwood according to a fourteenth aspect includes a softwood and a polymer in contact with the softwood. The softwood includes a cell lumen and a cell wall surrounding the cell lumen. The cell lumen includes the polymer and voids. The polymer does not impregnate the cell wall.

[0034] Here, "the polymer is not impregnated into the cell wall" means that the polymer used for modification is not present between cell wall components such as cellulose, hemicellulose, and lignin, and the cell wall itself is not swollen compared to its state before modification.

[0035] A wood decorative material according to a fifteenth aspect includes a softwood material and a polymer in contact with the softwood material. ３ Greater than 0.85 g / cm ３ and the compressive strength of the wood decorative material in the radial direction is greater than 2.5 MPa and less than or equal to 30 MPa.

[0036] Hereinafter, modified softwood materials and methods for producing the same according to embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0037] (Embodiment 1) Fig. 1A is a diagram showing an SEM image of a cross section of a cell wall in which a polymer 7 is provided on the surface of the cell wall 2 facing the cell lumen 4 in a modified softwood material 10 according to embodiment 1. Fig. 1B is a schematic cross section showing a cross section of the cell lumen 4 of a tubular cell in the modified softwood material according to embodiment 1. Fig. 1B is a schematic diagram showing the state in which a polymer 7 is provided on the surface of the cell wall 2 facing the cell lumen 4 in Fig. 1A.

[0038] As shown in Figures 1A and 1B, the modified softwood material 10 according to the first embodiment comprises a softwood material including cell walls 2 and a polymer 7 in contact with the surface of the cell walls 2 of the softwood material facing the cell lumen 7. The cell lumen 4 is surrounded by the lattice-like cell walls 2 of the softwood material and arranged in a lattice pattern. In this modified softwood material 10, the polymer 7 provided on the surface of the cell walls 2 facing the cell lumen 4 forms a membrane, reducing the voids in the cell lumen 4 while leaving them there, thereby suppressing an increase in density and maintaining the lightweight characteristic of softwood. Furthermore, the polymer 7 suppresses buckling and cracking of the cell walls 2, resulting in a higher strength than softwood material.

[0039] This modified softwood has a density of 0.33 g / cm ３ Greater than 0.85 g / cm ３and the compressive strength in the radial direction (i.e., along the radius of the modified softwood) is greater than 2.5 MPa and less than or equal to 30 MPa.

[0040] According to the modified softwood material of the first embodiment, it is possible to provide a modified softwood material that has a higher strength than softwood material while suppressing an increase in density compared to softwood material.

[0041] The elements that make up the modified softwood material according to the first embodiment will be described below.

[0042] <Coniferous wood> Examples of coniferous wood that can be used include cedar, cypress, red pine, black pine, yew, ginkgo, Japanese yew, Japanese kaya, larch, Japanese cedar, sawara, hemlock, Doga sawara, Abies sachalinensis, juniper, hiba, Himekomatsu, fir, agathis, Scots pine, Caribbean pine, pine, Clinky pine, Southern yellow pine, Ponderosa pine, Radiata pine, lodgepole pine, spruce, Japanese holly, Western red cedar, Western hemlock, Japanese cypress, Japanese cypress, Japanese red pine, Honsun, Japanese larch, Mexican pine, Mexican cypress, redwood, etc. Note that the above descriptions are merely examples, and coniferous wood is not limited to these.

[0043] Fig. 2A is a schematic cross-sectional view showing a cross section perpendicular to the fiber direction of tubular cells of a plant material. Fig. 2B is a diagram showing SEM images of cross sections perpendicular to the fiber direction of tubular cells in earlywood 5 and latewood 6 of coniferous wood. Fig. 2B shows an SEM image of cedar, a type of coniferous wood.

[0044] As shown in Figure 2B, coniferous wood is a collection of various tubular cells approximately 1 to 6 mm in length. The relatively white-appearing portions of the grain that make up the annual rings of coniferous wood are called earlywood 5 (or summer grain, or early wood) and are composed of cells that grow rapidly from spring to early summer. On the other hand, the relatively dark brown portions of the grain are called latewood 6 (or winter grain, or late wood) and are composed of cells that grow rapidly from early summer to late summer. The cells that make up earlywood 5 and latewood 6 differ significantly. Earlywood 5 has a large cell outer diameter of up to approximately 70 μm, a thin cell wall, and a large void 3 formed in the cell lumen 4, with the thinnest cells being less than 1 μm thick. Therefore, high porosity and low density are thought to be the causes of its low strength. Latewood 5, on the other hand, has a small cell outer diameter of less than 10 μm and a thick cell wall, with the thickest cells being nearly 5 μm thick, resulting in low porosity.

[0045] <Polymer> The polymer is in contact with the softwood. For example, the polymer is in contact with at least a portion of the surface of the cell wall of the softwood that faces the lumen. In other words, the polymer is in contact with at least a portion of the surface of the cell wall that faces the lumen. The polymer may also be a membrane formed along the surface of the cell wall that faces the lumen.

[0046] Figure 3A is a schematic perspective view of a tubular cell 1 when no polymer is in contact (i.e., when untreated), Figure 3B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of the tubular cell 1 when no polymer is in contact, Figure 3C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when no polymer is in contact, and Figure 3D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when no polymer is in contact.

[0047] Figure 4A is a schematic perspective view of a tubular cell 1 when polymer 7 is in contact with almost the entire inner surface of the cell wall 2; Figure 4B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of the tubular cell 1 when polymer 7 is in contact with almost the entire inner surface of the cell wall 2; Figure 4C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when polymer 7 is in contact with almost the entire inner surface of the cell wall 2; and Figure 4D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when polymer 7 is in contact with almost the entire inner surface of the cell wall 2.

[0048] Figure 5A is a schematic perspective view of a tubular cell 1 when polymer 7 is in contact with approximately half of the inner surface of cell wall 2, Figure 5B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of tubular cell 1 when polymer 7 is in contact with approximately half of the inner surface of cell wall 2, Figure 5C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of tubular cell 1 when polymer 7 is in contact with approximately half of the inner surface of cell wall 2, and Figure 5D is a cross-sectional view showing a portion of the cross-sectional structure parallel to the fiber direction of tubular cell 1 when polymer 7 is in contact with approximately half of the inner surface of cell wall 2.

[0049] Figure 6A is a schematic perspective view of a tubular cell 1 when polymer 7 is in contact with part of the inner surface of the cell wall 2; Figure 6B is a cross-sectional view showing the cross-sectional structure perpendicular to the fiber direction of the tubular cell 1 when polymer 7 is in contact with part of the inner surface of the cell wall 2; Figure 6C is a cross-sectional view showing the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when polymer 7 is in contact with part of the inner surface of the cell wall 2; and Figure 6D is a cross-sectional view showing part of the cross-sectional structure parallel to the fiber direction of the tubular cell 1 when polymer 7 is in contact with part of the inner surface of the cell wall 2.

[0050] Contact with at least a portion of the surface of the cell lumen side of the cell wall of softwood does not necessarily mean contact of the polymer 7 over almost the entire inner surface of the cell wall 2 as shown in Figures 4A to 4D. It may also be contact of the polymer 7 over about half of the inner surface of the cell wall 2 as shown in Figures 5A to 5D, or contact of the polymer 7 with only a portion of the inner surface of the cell wall 2 as shown in Figures 6A to 6D.

[0051] Furthermore, the polymer does not need to be in uniform contact with the surface of the cell wall facing the lumen; for example, as shown in Figures 5A to 5D, there may be areas where the polymer is locally abundant or sparse. The amount of polymer in contact with the surface of the cell wall facing the lumen also does not need to be uniform; for example, in multiple cross sections perpendicular to an arbitrary position in the fiber direction of a tubular cell, the polymer may be formed so as to completely fill the voids in some cross sections, while no polymer is formed at all in other cross sections. Furthermore, in a cross section perpendicular to the fiber direction of a tubular cell, some of the cell walls may have the polymer formed so as to completely fill the voids, some cell walls have the polymer formed on the surface facing the lumen, and some cell walls have no polymer formed at all.

[0052] In other words, the main structure of the cross-sections of the multiple tubular cells that make up the coniferous wood material should be a structure in which the cell wall has a hollow structure as shown in Figure 1B, and the polymer is in contact with the surface of the cell wall on the lumen side.

[0053] For example, the spring constant of the polymer calculated by measuring a force curve using an atomic force microscope is 0.3 N / m or more and 0.8 N / m or less. The spring constant of the polymer will be described in detail later.

[0054] The polymer may be, for example, a thermoplastic resin. Examples of thermoplastic resins include vinyl acetate resin, acrylic resin, styrene-based resin, styrene-acrylic copolymer resin, polyolefin-based resin, polyvinyl chloride resin, polyurethane resin, ABS resin, polyamide resin, polyacetal resin, polycarbonate resin, polyester resin, polyvinyl alcohol, and polyethylene glycol. The thermoplastic resin may be a copolymer of multiple components or a mixture of multiple thermoplastic resins. It can be used as a dispersion of resin particles such as an emulsion. From the viewpoint of film-forming properties and film hardness after impregnation, vinyl acetate resin, acrylic resin, and styrene-acrylic copolymer resin are preferred. Furthermore, polymers made of thermoplastic resins are independent of the components that make up the polymer. It is believed that if the strength of the polymer is equivalent, the strength of the modified softwood will also be equivalent. On the other hand, if the strength of the polymer is low, the strength of the modified softwood will not be improved. For example, soft rubber-like resins such as silicone, which are one type of thermosetting resin, have a low spring constant and therefore cannot improve the strength of the modified softwood. For this reason, impregnating softwood with a silicone emulsion is not desirable for the purpose of providing a modified softwood that has higher strength than softwood while suppressing an increase in density relative to the softwood itself. Furthermore, the properties of the components that make up the polymer are thought to be reflected to some extent in the properties of the modified softwood. For example, if the polymer contains a large amount of flame-retardant components, the flame retardancy of the modified softwood will also be enhanced.

[0055] <Density> The density of the modified softwood material can be determined by, for example, measuring the length of each of the three sides of the rectangular parallelepiped sapwood of the modified softwood material and calculating the volume (cm ３ ) and divided by the separately measured weight (g) to obtain the density (g / cm ３ ) can be calculated.

[0056] The density of the modified softwood material according to the first embodiment is 0.33 g / cm ３ Greater than 0.85 g / cm ３ The following is the result.

[0057] For example, if the softwood is cedar, the density of the modified softwood is preferably 0.34 g / cm ３ 0.85g / cm or more３ More preferably, 0.35 g / cm ３ 0.85g / cm or more ３ The following is the result.

[0058] For example, when the softwood material is cypress, the density of the modified softwood material is 0.49 g / cm ３ Greater than 0.85 g / cm ３ When the softwood is Japanese cypress, the density of the modified softwood is preferably 0.50 g / cm ３ 0.85g / cm or more ３ More preferably, it is 0.51 g / cm or less. ３ 0.85g / cm or more ３ The following is the result.

[0059] <Compressive strength in the radial direction (also called the radial direction or R direction) of the wood's annual rings, the tangential direction (T direction), and the fiber direction (L direction) of the wood's annual rings, with the strength generally being highest in the fiber direction. When utilizing the beauty of the wood grain as a flooring material, flat grain wood is used, so the compressive strength in the radial direction is important. The modified softwood material according to the first embodiment has a compressive strength in the radial direction of greater than 2.5 MPa and not more than 30 MPa.

[0060] For example, when the softwood material is cedar, the radial compressive strength is preferably 2.6 MPa or more and 30 MPa or less, more preferably 3 MPa or more and 30 MPa or less.

[0061] For example, when the coniferous wood is Japanese cypress, the radial compressive strength is greater than 6 MPa and less than 30 MPa. The radial compressive strength is preferably greater than 6.1 MPa and less than 30 MPa. The radial compressive strength is more preferably greater than 6.5 MPa and less than 30 MPa.

[0062] The radial direction is specifically the direction from the center of the growth ring of the softwood to the outside. In other words, the radial direction.

[0063] Compressive strength can be evaluated from a stress-strain curve obtained using, for example, a commercially available autograph testing machine, universal testing machine, tension-compression testing device, or compression testing machine. Compressive strength may also be evaluated by measuring with a micro-compression testing machine while observing under a microscope. Measurements using a micro-compression testing machine are particularly effective when the softwood sample is thin, small, or has uneven grain orientation.

[0064] Furthermore, since compressive strength also varies depending on the size of the measurement sample, the ratio of early and late wood to the density of the measurement sample, and the inclination of the annual rings of the measurement sample, it is preferable to make evaluations using samples with the same size, density, and inclination of the annual rings as much as possible when measuring compressive strength. The measurement sample is, for example, a cubic block of 1 cm or 2 mm square.

[0065] The radial compressive strength of the modified softwood according to the first embodiment measured by the above-described method is, for example, an index representing the strength of the modified softwood. More specifically, the upper yield point in the stress-strain curve of the modified softwood indicates that damage such as buckling or cracking of the cell walls has occurred in the modified softwood.

[0066] <Polymer filling ratio> The polymer filling ratio indicates the ratio of the area of ​​the polymer to the area of ​​the cell lumen in a cross section of the cell lumen. The polymer filling ratio is, for example, 10% or more and 60% or less.

[0067] The polymer filling rate can be determined, for example, by observing a cross section perpendicular to the fiber direction of the tubular cells of the softwood before modification and a cross section perpendicular to the fiber direction of the tubular cells of the modified softwood after modification using a scanning electron microscope (SEM).

[0068] <Polymer Content> The weight percentage (wt%) of the polymer after modification relative to the weight of the modified softwood is calculated as the polymer content. The polymer content in the modified softwood is, for example, 5 wt% or more and 65 wt% or less. The polymer content in the modified softwood is preferably 7 wt% or more and 63 wt% or less. The polymer content in the modified softwood is more preferably 9 wt% or more and 60 wt% or less. The polymer content in the modified softwood can be adjusted by adjusting the concentration of polymer particles in the emulsion impregnated in the modification process. The polymer content in the modified softwood can also be adjusted by increasing the number of impregnations, such as by impregnating the softwood with emulsion, removing the solvent, and then impregnating the softwood with emulsion again.

[0069] <Spring constant of polymer> For example, the spring constant of the polymer calculated by force curve measurement using an atomic force microscope is 0.3 N / m or more and 0.8 N / m or less, preferably 0.4 N / m or more and 0.8 N / m or less, and more preferably 0.5 N / m or more and 0.8 N / m or less.

[0070] By using the spring constant k, the longitudinal elastic modulus (Young's modulus) E (N / m ２ ) can be calculated as follows: E = kL / A (1) where A is the cross-sectional area (m ２ ), and L represents the length (m). The spring constant k (N / m) is an index of the hardness and resistance to deformation of a component. For example, when the same force (N) is applied, a component with a large spring constant is hard and resistant to deformation, while a component with a small spring constant is soft and easy to deform. In a heterogeneous composite material composed of multiple materials, the compressive strength measurement described above calculates an average value for the bulk of the composite material. However, since the spring constant can be calculated locally using techniques such as force curve measurement with an atomic force microscope, the hardness of a specific material component of the composite material can be calculated by calculating the spring constant of that specific material component. In other words, in the present disclosure, the hardness of the polymer of the modified softwood can be calculated by calculating the spring constant.

[0071] For example, using an atomic force microscope probe, the spring constant k is 0.4 N / m and the thickness L is 1×10 －７ When measuring the force curve of a polymer film of 1.0 m, the contact cross-sectional area A between the probe and the polymer film is 1 × 10 －１７ m ２ Then, from equation (1), the Young's modulus of the polymer film is E = 4 × 10 ９ N / m ２ In reality, since the contact area between the probe and the polymer film cannot be measured, a theoretical calculation formula for a contact model (such as the JKR model) that assumes the shape of the probe tip is spherical is fitted to the force curve, and the elastic modulus can be calculated from the fitting parameters.

[0072] In addition, the local elastic modulus of the plant material can be measured by polishing a cross section perpendicular to the fiber direction of the tubular cells of the plant material and performing quantitative nanomechanical mapping (PF-QNM) measurements using a Bruker AXS MultiMode 8 scanning probe microscope. In this measurement, the elastic modulus of the cedar cell wall was 7 to 9 GPa, and the elastic modulus of the polymer portion with a spring constant of 0.5 N / m was 5 × 10 ９ N / m ２ It was.

[0073] <Polymer Film Thickness> The polymer film thickness is not limited, but is, for example, 0.1 μm to 30 μm, preferably 0.1 μm to 10 μm. The polymer film thickness can be controlled by changing the solids concentration of the emulsion or the polymer concentration in the solvent in the manufacturing method of modified softwood material described below.

[0074] <Method for manufacturing modified softwood> The method for manufacturing modified softwood according to the first embodiment includes the following steps. Figures 7A to 7C are schematic cross-sectional views showing the steps of the method for manufacturing modified softwood according to the first embodiment. (1) A step of injecting an emulsion containing water as a solvent and polymer particles into softwood. (2) A step of removing the solvent from the softwood.

[0075] (1) Step of injecting emulsion into softwood Various methods can be used for the step of injecting an emulsion containing water as a solvent and polymer particles into softwood. For example, the emulsion may be applied to the softwood and then injected. Alternatively, the softwood may be immersed in the emulsion and then injected. The softwood immersed in the emulsion may be injected under reduced pressure. Alternatively, the softwood immersed in the emulsion may be degassed under reduced pressure and then injected under a pressurized environment. Furthermore, a combination of these methods may be used for injection.

[0076] The step of injecting the emulsion into the softwood may include: (1-1) a step of immersing the softwood in the emulsion; and (1-2) a step of removing the immersed softwood from the emulsion.

[0077] 7A and 7B are schematic cross-sectional views showing an example of a step of immersing softwood in an emulsion in the method for producing modified softwood according to the first embodiment.

[0078] <Emulsion> As shown in Figure 7A, the emulsion 12 into which the softwood is immersed contains water as a solvent 16 and polymer particles 14. The polymer particles 14 are dispersed in the solvent 16, for example. The emulsion 12 is, for example, an oil-in-water (o / w) emulsion. By using water as the solvent 16, the possibility of the sustained release of highly harmful volatile organic compounds can be reduced. This reduces the possibility that industrial materials (e.g., building materials) using modified softwood will cause sick building syndrome.

[0079] It is known that in emulsions, polymer particles fuse together due to the evaporation of the dispersion medium, forming a continuous film. The fusion of polymer particles begins when the polymer particles deform at temperatures higher than the minimum film-forming temperature (MFT) of the emulsion. For emulsions that do not contain plasticizers, the MFT is often similar to the glass transition temperature (Tg) of the polymer particles. For emulsions that contain plasticizers, the MFT can be significantly reduced depending on the type of plasticizer. By subjecting the polymer that has formed a film to a temperature higher than the MFT, the fusion of polymer particles is further promoted, polymer chains interdiffuse, and a dense, high-strength film is formed.

[0080] As shown in Figure 7B, only the solvent 16 penetrates the cell wall 2. The polymer particles 14 dispersed in the emulsion 12 increase in local concentration on the surface of the cell wall 2 facing the lumen, and fuse together on the surface of the cell wall facing the lumen, forming a fused product (specifically, partially fused polymer particles) 15.

[0081] It is known that solids do not penetrate wood cell walls, and the polymer particles contained in the emulsion do not penetrate the cell walls of softwood. Therefore, when the emulsion comes into contact with the surface of the cell lumen of the softwood cell wall, only the dispersant water is absorbed into the cell wall, and the polymer particles contained in the locally concentrated emulsion fuse together.

[0082] The solvent used in the emulsion is a solvent capable of penetrating the cell wall. The use of a solvent can prevent the voids in the cell lumen from being completely filled with the polymer. Water is more preferably used as the solvent from the viewpoints of toxicity to the human body, environmental impact, and VOC reduction. From the same viewpoint, a green solvent may also be used. Specific examples of green solvents include ethanol obtained by saccharifying sugarcane, corn, cellulose materials, etc.; 1,3-butanediol and glycerin, which are extracts from natural products; biodegradable 3-methoxy-3-methyl-1-butanol; and ethylene glycol, propylene glycol, and their derivatives, which are used as regenerating solvents for various materials such as plastic products. When a water-soluble polymer is used, the polymer is likely to penetrate into the cell wall, causing an increase in density and darkening of the material. When a highly polar green solvent is used, discoloration due to the elution of wood extractives and lignin leaching is likely to occur. Therefore, it is more preferable to use an aqueous dispersion of the polymer, such as an emulsion.

[0083] (2) Step of Removing Solvent from Softwood Fig. 7C is a schematic cross-sectional view showing the step of removing the solvent from the softwood, whereby the solvent 16 is removed and the polymer 7 is formed.

[0084] In the present disclosure, after the emulsion is injected into the softwood, the water solvent may be removed by any method, such as drying by blowing air with a fan or the like, drying under reduced pressure, drying by heating, or a combination of multiple methods.

[0085] The upper limit of the heating temperature in the present disclosure may be any temperature at which the wood does not undergo significant changes such as carbonization, burning, or deterioration of appearance, and may be, for example, 300°C or lower.

[0086] The lower limit of the heating temperature in the present disclosure may be equal to or higher than the minimum film-forming temperature (MFT) of the emulsion. If the temperature of the environment in which the emulsion is injected is higher than the MFT, the heating step does not significantly promote fusion and film formation of the polymer particles, but it is desirable to perform the heating step to remove moisture. For example, the heating may be performed at 40°C or higher, 60°C or higher, or 110°C or higher. The heating temperature may be adjusted appropriately to develop the desired wood color.

[0087] These processes can produce modified softwoods in which the softwood is contacted with a polymer.

[0088] Emulsions are widely recognized as adhesives in the wood, construction, and wood research industries. However, the modification of softwood by injecting an emulsion into the cell lumen and forming a polymer on the lumen-facing surface of the cell wall, as disclosed herein, has not been reported and would not be easily conceived by even a person skilled in the art.

[0089] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely illustrative and the present disclosure is not limited to the following examples.

[0090] (Example 1) <Impregnation> Cylinder sapwood (10 mm x 10 mm x 2 mm) was immersed in emulsion Polysol AP-3140 (manufactured by Resonac Co., Ltd.) as an impregnation agent, and the pressure was reduced to 0.01 MPa or less (100 hPa (approximately 0.1 atm)) at room temperature and held for 10 minutes. After returning to normal pressure, the pressure was increased to 0.85 MPa (8500 hPa (approximately 8.5 atm)) and held for 2 hours.

[0091] <Drying> The rectangular sapwood of the modified softwood impregnated with the emulsion was removed, the excess emulsion was wiped off, and the material was dried at room temperature and atmospheric pressure for 24 hours, followed by heat drying at 110°C and atmospheric pressure for 60 hours. The main components of the impregnation agent used are shown in Table 2. Heating at a temperature higher than the Tg of the polymer softens the polymer particles, promoting fusion between the polymer particles and entanglement and interdiffusion of the polymer chains. In addition, this heat drying process volatilizes traces of moisture and additives such as plasticizers remaining in the polymer, forming a denser, continuous coating. Depending on the type of polymer, heating may cause crosslinking of the polymer chains, resulting in the formation of a stronger film.

[0092] Example 2 A modified softwood material according to Example 2 was obtained in the same manner as in Example 1, except that heat drying was not carried out.

[0093] (Examples 3, 4 and 7) Modified softwood materials according to Examples 3, 4 and 7 were obtained in the same manner as in Example 1, except that the impregnation agents shown in Table 1 were used. Polysol AP-6750 used in Example 3, Polysol AP-4690N used in Example 4, and Polysol BX-8004 used in Example 7 were all manufactured by Resonac Co., Ltd. The main components of each impregnation agent used are shown in Table 2.

[0094] Example 5 A modified softwood material according to Example 5 was obtained in the same manner as in Example 1, except that the impregnation agent shown in Table 1 was used and heat drying was not performed.

[0095] (Example 6) Modified softwood according to Example 6 was obtained in the same manner as in Example 1, except that the impregnation agent shown in Table 1 was used and the impregnation procedure was carried out twice, with the aim of producing a modified softwood with a high polymer content.

[0096] (Examples 8 and 9) Modified softwoods according to Examples 8 and 9 were obtained in the same manner as in Example 1, except that the impregnation agents shown in Table 1 were used and the impregnation agents were diluted with distilled water, with the aim of producing modified softwoods with a low polymer content.

[0097] Example 10 A modified softwood material according to Example 10 was obtained in the same manner as in Example 1, except that Japanese cypress was used instead of Japanese cedar.

[0098] Example 11 A modified softwood material according to Example 11 was obtained in the same manner as in Example 1, except that Japanese cypress was used instead of Japanese cedar and that the impregnation agent shown in Table 1 was used.

[0099] Comparative Examples 1 and 2 In Comparative Example 1, unmodified (untreated) cedar was used, and in Comparative Example 2, unmodified (untreated) cypress was used.

[0100] (Comparative Example 3) Modified softwood according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the impregnating agent used was the agent shown in Table 1, which contained an aqueous dispersion of inorganic particles, instead of an emulsion, and that heat drying was not performed. The Seahoster KEW-10 used in Comparative Example 3 was manufactured by Nippon Shokubai Co., Ltd. The main components of the impregnating agent used are shown in Table 2.

[0101] Comparative Examples 4 and 5 Modified softwood materials according to Comparative Examples 4 and 5 were obtained in the same manner as in Example 1, except that the impregnation agents shown in Table 1 were used and that heat drying was not performed.

[0102]

[0103]

[0104] <Density> The density was calculated for each rectangular parallelepiped sapwood of the modified softwood obtained in the Examples and the softwood or modified softwood obtained in the Comparative Examples. The density was calculated by measuring the length of each of the three sides and calculating the volume (cm ３ ) and divided by the separately measured weight (g).

[0105] <Polymer content> For each rectangular sapwood of the modified softwood obtained in the examples and the softwood or modified softwood obtained in the comparative examples, the polymer content P (wt%) of the modified softwood was calculated using the following formula (2).

[0106]

[0107] In formula (2), P represents the polymer content. ０is the density of the softwood before modification, d １ represents the density of the modified softwood after modification. The softwood obtained in Comparative Examples 1 and 2 did not contain a polymer, so P = 0. Similarly, the modified softwood obtained in Comparative Example 3 also did not contain a polymer, so P = 0.

[0108] Formula (2) calculates the weight percentage (wt%) of the modified polymer to the weight of the modified softwood as the polymer content P. The weight of the modified polymer is calculated by multiplying the density d of the modified softwood by the weight percentage (wt%) of the modified softwood. １ The volume after modification is V １ From the weight after modification multiplied by , the density before modification d ０ The volume before modification is V ０ The weight of the modified softwood is obtained by subtracting the weight before modification multiplied by the density d of the modified softwood. １ The volume after modification is V １ The volume of the cell lumen decreases before and after the modification, but the total volume including the voids remains unchanged. ０ and the volume after modification V １ It is the same as (V １ =V ０ Therefore, in formula (2), the polymer content P (wt%) can be expressed as an equation that does not include the volume.

[0109] <Compressive Strength and Compressive Modulus> Compressive properties were measured in accordance with JIS Z2101:2009 as follows. Rectangular sapwood of the modified softwood was cut into 2 mm cubes as measurement samples. Taking into account the anisotropy of softwood, the wood grain was cut out so that it was parallel to the measurement surface. A load was applied in the radial direction of the annual rings using a flat compression jig, and a compression test was performed using a universal testing machine (manufactured by Shimadzu Corporation). The displacement rate was 1 mm / min, and compression was continued until the sample length was 70% of its pre-compression length. Compressive strength was calculated from the upper yield point of the obtained stress-strain curve, and compressive modulus was calculated from the slope.

[0110] Table 3 shows the density of the modified softwood, the polymer content of the modified softwood, the compressive strength in the radial direction of the annual rings, and the compressive modulus in the tangential direction of the annual rings.

[0111]

[0112] As shown in Table 3, the modified softwood materials according to Examples 1 to 11 have a polymer in contact with at least a portion of the surface of the cell lumen of the cell wall of the softwood material, and a density of 0.40 g / cm ３ 0.81g / cm or more ３ The compressive strength in the radial direction was 4 MPa or more and 27.2 MPa or less. The polymer content was 9.3 wt % or more and 59.3 wt % or less. The modified cedar softwood materials of Examples 1 to 9 had higher compressive strength than the cedar softwood material of Comparative Example 1 or the modified cedar softwood materials of Comparative Examples 3 to 5. The modified cypress softwood materials of Examples 10 and 11 had higher compressive strength than the cypress softwood material of Comparative Example 2.

[0113] The compressive strength of softwood modified with inorganic particle dispersion water instead of emulsion did not change because no coating was formed on the cell wall surface.

[0114] <Polymer filling rate> The end grain surface of the modified softwood sample was polished using a microtome to prepare a cross section for observation of the cell wall. As a pretreatment for observation, Pt-Pd was vapor-deposited onto the observation surface using an ion sputtering device E-1030 (Hitachi High-Technologies). Scanning electron microscope (SEM) images from late wood to late wood were obtained using a 3D real surface view microscope VE-8800 (Keyence).

[0115] 8A is a schematic cross-sectional view showing a cross section perpendicular to the fiber direction of a tubular cell of softwood before modification (untreated). FIG. 8B is a schematic cross-sectional view showing the cell wall area A of a tubular cell of softwood before modification (untreated) in a cross section perpendicular to the fiber direction. ００ 8C is an example of a schematic cross-sectional view showing the area A of voids in a cross section perpendicular to the fiber direction of tubular cells of softwood before modification (untreated). ０１ 9A is a schematic cross-sectional view showing a cross section perpendicular to the fiber direction of a tubular cell of a modified softwood material. FIG. 9B is a schematic cross-sectional view showing the apparent cell wall area A including the cell wall and polymer in a cross section perpendicular to the fiber direction of a tubular cell of a modified softwood material after modification. １０9C is an example of a schematic cross-sectional view showing the area A of the remaining voids in a cross section perpendicular to the fiber direction of the tubular cells of the modified softwood material after modification. １１ 1 is an example of a schematic cross-sectional view showing the

[0116] An example of a method for calculating the polymer loading of the modified softwood material of the present disclosure is described below.

[0117] First, the area A of the cell wall in a cross section perpendicular to the fiber direction of the tubular cells of the unmodified (untreated) softwood ００ (Fig. 8B) and the area of ​​the gap A ０１ (Fig. 8C) and (Fig. 8D) are calculated using image processing software. Secondly, for the modified softwood after modification, the apparent cell wall area A, including the cell wall and polymer in the cross section perpendicular to the fiber direction of the tubular cell, is calculated. １０ (FIG. 9B) and the area A of the remaining void １１ (FIG. 9C) is calculated. Third, the polymer filling rate F of the modified softwood is calculated using the following formula (3).

[0118]

[0119] Equation (3) is the cross-sectional area A of the void space of the cell lumen before modification (untreated). ０１ The proportion (area %) of the cross-sectional area of ​​the polymer after modification to the area of ​​the voids in the cell lumen before modification (untreated) is calculated as the polymer filling rate F of the modified softwood. ０１ Cross-sectional area A of the void space of the cell lumen after modification １１ The total cross-sectional area of ​​the voids and cell walls (apparent cell walls) is the same before and after modification (A ００ +A ０１ = A １０ +A １１ ).

[0120] <Polymer Film Thickness> The thickness of the polymer in the lumen of the cell wall can be measured, for example, from an SEM image of the cell wall cross section. Image processing software can be used to determine the number of pixels in the scale bar in the image. Using this value, the number of pixels representing the cell wall thickness in the image can be converted into the actual cell wall thickness, allowing for measurement. As an example, an SEM image of the earlywood of the sample in Example 1 is shown in Figure 1A. The cross-sectional SEM image in Figure 1A reveals that polymer 7 with a film thickness of 0.1 to 10 μm is formed along the lumen of the cell wall 2. The thickness of 10 randomly selected locations of the polymer 7 visible in the cross-sectional SEM image in Figure 1A was measured using the method described above, and the average polymer film thickness was 5.3 μm.

[0121] <Spring Constant of Polymer> The emulsion was applied to a glass substrate (length 76 mm, width 26 mm, thickness 1 mm) and dried at room temperature and atmospheric pressure for 24 hours to obtain a polymer. The emulsions used in Examples 1, 3, 4, 6, 7, 8, and 9 were then dried by heating at 110°C for 20 hours. The obtained polymer was subjected to force curve measurement using an atomic force microscope under the following conditions to evaluate the spring constant of the polymer. Measurement device: Seiko Instruments Inc. atomic force microscope SPI3800N-SPA300HV (AFM) Measurement mode: AFM mode (force curve measurement) Probe: Olympus OMCL-AC200TR-R3 (material: Si, spring constant: 9 N / m, tip curvature radius R: 7 (nm) Measurement area: 1 μm × 1 μm Measurement atmosphere: air Measurement temperature: room temperature (23°C)

[0122] The density, polymer content, compressive strength, polymer loading, and polymer spring constant are shown in Table 4.

[0123]

[0124] As shown in Table 4, the modified softwood materials according to Examples 1 to 11 have a polymer in contact with at least a portion of the surface of the cell lumen of the cell wall of the softwood material, and a density of 0.40 g / cm ３ 0.81g / cm or more ３The compressive strength in the radial direction was 4 MPa or more and 27.2 MPa or less, the polymer filling rate was 10% or more and 60% or less, and the spring constant of the polymer calculated by force curve measurement using an atomic force microscope was 0.3 N / m or more and 0.8 N / m or less.

[0125] The polymer filling rate of modified softwood is not 100%, and there are voids in the cell lumen. This maintains the lightweight property that is a characteristic of wood. In modified softwood produced by the method of the present disclosure, the polymers that come into contact with at least a portion of the surface of the cell lumen side of the cell wall are all formed in the same way by fusion between polymer particles, so it is thought that the polymer densities will be similar values. Therefore, ideally, there is a linear correlation between the polymer content (wt%) and polymer filling rate (%) of modified softwood. In fact, when linear regression was performed on the values ​​of polymer content (wt%) and polymer filling rate (%) listed in Table 4, the coefficient of determination, R ２ The value is greater than 0.95. According to the regression equation obtained by this linear regression, even if the polymer filling rate (%) is about 10%, the effect of improving the compressive strength in the radial direction can be obtained.

[0126] The modified softwood material according to the present disclosure has a higher strength than softwood material while suppressing an increase in density compared to softwood material, and can therefore be used in applications such as architectural interior materials such as flooring and structural materials.

[0127] 1 tubular cell 2 cell wall 3 cavity 4 cell lumen 5 earlywood 6 latewood 7 polymer 10 modified softwood 12 emulsion 14 polymer particles 15 fusion product 16 solvent (water)

Claims

1. A modified softwood comprising a softwood and a polymer in contact with the softwood, wherein the modified softwood has a density of 0.33 g / cm ３ Greater than 0.85 g / cm ３ and the modified softwood has a radial compressive strength of more than 2.5 MPa and not more than 30 MPa.

2. The modified softwood material according to claim 1, wherein the softwood material comprises a cell cavity and a cell wall surrounding the cell cavity, and the polymer is in contact with at least a portion of the surface of the cell wall that is in contact with the cell cavity.

3. The modified softwood material according to claim 2, wherein the polymer filling rate, which is the ratio of the area of ​​the polymer to the area of ​​the cell lumen in a cross section of the cell lumen, is 10% or more and 60% or less.

4. The modified softwood according to claim 1, wherein the content of the polymer in the modified softwood is 5 wt % or more and 65 wt % or less.

5. The modified softwood material according to claim 1, wherein the spring constant of the polymer calculated by force curve measurement using an atomic force microscope is 0.3 N / m or more and 0.8 N / m or less.

6. The modified softwood material of claim 1, wherein the polymer is a thermoplastic resin.

7. The modified softwood material according to claim 1, wherein the polymer comprises at least one selected from the group consisting of vinyl acetate resin, acrylic resin, and styrene-acrylic copolymer resin.

8. The modified softwood material according to claim 1, wherein the softwood material is cedar.

9. The coniferous wood is cypress, and the density is 0.49 g / cm ３ Greater than 0.85 g / cm ３ 2. The modified softwood material of claim 1, wherein the compressive strength is greater than 6 MPa and less than or equal to 30 MPa.

10. A method for producing a modified softwood comprising: injecting an emulsion containing water as a solvent and polymer particles into a softwood; and removing the solvent from the softwood.

11. The method of producing a modified softwood material as described in claim 10, wherein injecting the emulsion into the softwood material includes: immersing the softwood material in the emulsion; and removing the softwood material immersed in the emulsion from the emulsion.

12. The modified softwood of claim 1, wherein the softwood comprises a cell lumen and a cell wall surrounding the cell lumen, the cell lumen comprising the polymer and a void space.

13. The density is 0.40 g / cm ３ The modified softwood material according to claim 1, wherein 14. A modified softwood comprising: a softwood; and a polymer in contact with said softwood, said softwood comprising a cell cavity and a cell wall surrounding said cell cavity, said cell cavity comprising said polymer and a void space, and said polymer does not impregnate said cell wall.

15. A wood decorative material comprising a softwood and a polymer in contact with the softwood, wherein the density of the wood decorative material is 0.33 g / cm ３ Greater than 0.85 g / cm ３ and the compressive strength of the wood decorative material in the radial direction is greater than 2.5 MPa and less than 30 MPa.

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