Base material for flooring material, flooring material, and manufacturing method of flooring material

Abstract

To provide a base material for flooring material with excellent soundproofing and hardly warping, and applicable to flooring materials for underfloor heating using softwood plywood, a flooring material provided with the base material for flooring material, and a method of manufacturing the flooring material.SOLUTION: A plywood 11 includes seven layers, and seven softwood planks are stacked so that the fiber direction (first direction) of the first, third, fifth, seventh layers 11a, 11c, 11e, and 11g is perpendicular to the fiber direction (second direction) of the second, fourth, and sixth layers 11b, 11d, and 11f. On the back of the plywood 11, there are formed multiple first grooves 41 extending in the second direction from the back surface to the second layer 11b and multiple second grooves 42 extending in the first direction perpendicular to the second direction and reaching the fourth layer 11d from the rear surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a base material for flooring materials, a flooring material, and a method for manufacturing a flooring material.

Background Art

[0002] Conventionally, a soundproof flooring material for floor heating, which includes a base material provided with a decorative layer on the front surface and a cushioning material on the back surface and is constructed on a floor heating panel, has been proposed (for example, refer to Patent Document 1 below). In Patent Document 1, the base material for the flooring material is configured by a back-grooved plywood in which a plurality of grooves extending parallel to each other are formed on the back surface of the plywood. In the above flooring material, a plurality of back grooves formed on the back surface of the base material for the flooring material facilitate uniform heat transfer to the surface of the flooring material, and also impart flexibility to the flooring material to improve the soundproofing property.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, although a South Sea wood plywood such as lauan plywood has been used as the base material for the above flooring material, in recent years, it has become difficult to obtain South Sea wood plywood itself in terms of depletion of raw materials and prevention of environmental destruction, and replacement with softwood plywood has been attempted. Since softwood plywood is softer than hardwood plywood such as lauan plywood, if the base material of the flooring material is replaced with softwood plywood, the flooring material will lack surface strength and be easily damaged. Therefore, in some cases, medium density fiberboard is attached to the surface of softwood plywood to enhance the surface strength.

[0005] However, medium density fiberboard is more likely to absorb moisture and expand and contract compared to plywood. Therefore, in a base material where medium density fiberboard is attached to the surface of plywood to enhance the surface strength, it is more likely to warp than a base material consisting only of plywood. In particular, when the base material is composed of a back groove processed plywood like the soundproof flooring material for floor heating described in Patent Document 1, although the sound insulation performance can be improved by a plurality of back grooves, the fibers that can counter the dimensional changes due to moisture absorption or desorption of the medium density fiberboard are cut off by the back grooves, making the base material more likely to warp. Also, in the above-mentioned soundproof flooring material for floor heating, since it is constructed on a floor heating panel and the temperature change is large, the base material is more likely to warp. On the other hand, because a cushioning material is provided, the flooring material cannot be pressed against and fixed to the floor heating panel, and the warp of the base material cannot be suppressed. Further, if the thickness of the plywood is increased to counter the medium density fiberboard in order to suppress warping, there is a problem that the rigidity of the entire base material becomes too high and the desired sound insulation performance cannot be obtained.

[0006] The present invention has been made in view of such points, and its object is to provide a base material for flooring with excellent sound insulation that is less likely to warp even when using softwood plywood and is applicable to flooring for floor heating, a flooring material provided with the same, and a method for manufacturing the flooring material.

Means for Solving the Problems

[0007] In order to achieve the above object, in this invention, the number of plies of plywood is set to 7 plies, and seven softwood thin plates are laminated so that the fiber directions of the first, third, fifth, and seventh layers (first direction) and the fiber directions of the second, fourth, and sixth layers (second direction) are orthogonal to each other. On the back surface of the plywood, a plurality of first grooves extending in the second direction and reaching the second layer from the back surface, and a plurality of second grooves extending in the first direction orthogonal to the second direction and reaching the fourth layer from the back surface are formed.

[0008] Specifically, the first invention is a base material for a floor material having a surface strengthening layer made of medium density fiberboard adhered to the surface of a plywood. The plywood is a coniferous plywood having first to seventh layers made of seven coniferous thin plates laminated and adhesively integrated in order from the front surface side to the back surface side such that the fiber directions of adjacent two plates are orthogonal to each other. On the back surface of the plywood, a plurality of first grooves extending in a second direction orthogonal to a first direction which is the fiber direction of the first layer are formed at a first groove interval, and a plurality of second grooves extending in the first direction are formed at a second groove interval. The first grooves extend from one end to the other end of the plywood in the second direction, and the groove bottoms are located within the second layer. The second grooves extend from one end to the other end of the plywood in the first direction, and the groove bottoms are located within any one of the third to fifth layers. The first to third layers are, in the order of the third layer, the second layer, and the first layer, thinner in thickness while higher in density. The fifth to seventh layers are, in the order of the fifth layer, the sixth layer, and the seventh layer, thinner in thickness while higher in density. The thicknesses of the first and seventh layers are equal to or less than the thickness of the surface strengthening layer, and the thicknesses of the third and fifth layers are greater than the thickness of the surface strengthening layer.

[0009] In the first invention, the number of plies of the plywood is set to 7 plies, and a plurality of first grooves with a depth reaching from the back surface to the second layer are formed on the back surface of the plywood. As the plywood for the base material of the flooring material, those with 3 plies or 5 plies are often used. However, in the first invention, since the number of plies of the plywood is set to 7 plies, the locations adhered with the adhesive (the interfaces between the layers made of softwood thin plates) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood is set to 7 plies, the first grooves reaching from the back surface to the second layer are deeper than when the first grooves are formed in the same way in 3-ply plywood or 5-ply plywood. With such deep plurality of first grooves, the rigidity of the plywood decreases and the flexibility increases, making it easier to absorb the impact force. Further, in the first invention, not only the first grooves but also a plurality of second grooves extending in a direction (the first direction) orthogonal to the extending direction (the second direction) of the first grooves are formed on the back surface of the plywood. By forming the second grooves in this way, the rigidity of the plywood decreases and the flexibility increases compared to the case where only the first grooves are formed, making it easier to absorb the impact force. That is, when the base material for the flooring material according to the first invention is used, the flooring material has the required sound insulation performance and is excellent in soundproofing.

[0010] Moreover, in the first invention, since the plurality of first grooves extending in a direction (the second direction) orthogonal to the fiber direction (the first direction) of the first layer of the plywood do not reach the first layer, the fibers of the first layer are not cut off. With such a configuration, in the first invention, even when the medium density fiberboard adhered to the surface of the plywood tries to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer extending in the first direction. As a result, it becomes difficult for the base material of the flooring material to expand and contract in the first direction due to moisture absorption or desorption, and the warping in the first direction is suppressed.

[0011] Furthermore, in the first invention, since the plurality of second grooves extending in a direction (first direction) orthogonal to the fiber direction (second direction) of the second layer do not reach the second layer, the fibers of the second layer extending in the second direction that can counter the dimensional changes due to moisture absorption or desorption of the medium-density fiberboard adhered to the surface of the plywood are not cut off. With such a configuration, in the first invention, even if the medium-density fiberboard adhered to the surface of the plywood attempts to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer extending in the second direction. As a result, it becomes difficult for the base material for flooring to expand and contract in the second direction due to moisture absorption or desorption, and warping in the second direction is suppressed. That is, according to the base material for flooring according to the first invention, not only is warping in the fiber direction (first direction) of the first layer suppressed, but warping in the orthogonal direction (second direction) is also suppressed.

[0012] Also, in the first invention, the plywood becomes thinner and has a higher density from the middle in the thickness direction toward the outermost layer. With such a configuration, the surface strength of the base material for flooring is improved.

[0013] As described above, according to the first invention, it is possible to provide a base material for flooring with excellent sound insulation properties that is less likely to warp even when using softwood plywood and is applicable to floor heating floor materials.

[0014] The second invention is characterized in that, in the first invention, the softwood thin plates constituting the first, third, fifth, and seventh layers are each composed of a single veneer, while the softwood thin plates constituting the second, fourth, and sixth layers are formed by splicing a plurality of veneers in the first direction, and the second layer has no knot holes with a size in the first direction larger than the first groove interval.

[0015] In the second invention, each layer of the plywood is composed of softwood veneers. Although softwoods have more knots than hardwoods, if the softwood veneer constituting the second layer has a knot hole with a size in the first direction larger than the groove interval (the first groove interval) of the first groove, the fibers of the second layer extending in the second direction that can counter the dimensional changes due to moisture absorption or desorption of the medium-density fiberboard will be cut off by the knot hole. As a result, it is impossible to counter the dimensional changes due to moisture absorption or desorption of the medium-density fiberboard, and there is a risk of partial warping occurring in the second direction. However, according to the second invention, since the second layer does not have a knot hole with a size in the first direction larger than the first groove interval, an effect of suppressing warping in the second direction can be expected.

[0016] The third invention is characterized in that, in the second invention, the first layer is constituted by a part without knot holes of softwood or by a part with knot holes of softwood and filling the knot holes with putty so that there are no knot holes, and the second layer is constituted by a part without knot holes of softwood or by a part with knot holes of softwood and filling the knot holes with plugs so that there are no knot holes.

[0017] The inventors of the present application conducted a verification test on the correlation between the presence or absence of knot holes in the first to third layers of the plywood and the Brinell hardness of the floor material surface. As a result of the verification test, it was found that if there are knot holes in the first or second layer constituting the surface layer portion of the plywood, the Brinell hardness of the floor material surface is lower than the desired hardness, and even if there are knot holes in the third layer, if there are no knot holes in the first and second layers, the Brinell hardness of the floor material surface is above the desired hardness. That is, it was found that if the floor material is formed with knot holes remaining in the first and second layers of the plywood, the floor material may be easily damaged. In addition, if there are knot holes in the first and second layers constituting the surface layer portion of the plywood, it may deteriorate the surface properties of the floor material and lead to a decrease in the design quality of the floor material. In particular, when a thin (for example, 1.5 mm or less) medium-density fiberboard is used as the surface strengthening layer in order to minimize the influence of warping as much as possible, if there are knot holes near the surface layer of the plywood, the influence of the knot holes (such as unevenness) will be manifested up to the decorative material through the surface strengthening layer made of the thin medium-density fiberboard, increasing the risk of deteriorating the design quality of the floor material.

[0018] Therefore, in the third invention, the first and second layers are configured to have no knots. Specifically, the first layer is composed of a knot-free part of a coniferous tree or, if it is composed of a part with knots in a coniferous tree, the knots are filled with putty and disappeared to make it knot-free. Also, the second layer is composed of a knot-free part of a coniferous tree or, if it is composed of a part with knots in a coniferous tree, the knots are made to disappear by burying wood treatment. The burying wood treatment means a treatment of drilling a hole including a knot and filling the hole without gaps with wood (buried wood) having the same shape as the drilled hole to make the knot disappear. In the third invention, by configuring the first and second layers to have no knots in this way, the floor material produced using the base material for floor material is made difficult to be damaged and has good surface properties. Therefore, by using the base material for floor material according to the third invention, a floor material that is difficult to be damaged and has good surface properties can be provided.

[0019] The fourth invention is characterized in that, in the first invention, the medium density fiberboard is made mainly of hardwood xylem fibers.

[0020] In the fourth invention, since the false conduit fibers of coniferous trees have a significantly higher porosity and water absorption rate than the hardwood xylem fibers, a medium density fiberboard (hardwood MDF) made mainly of hardwood xylem fibers is used as the surface strengthening layer. By using hardwood xylem fibers as the medium density fiberboard constituting the surface strengthening layer in this way, the water absorption rate of the surface strengthening layer can be kept low, and dimensional changes can be suppressed.

[0021] The fifth invention is characterized in that, in the first invention, on one of the two opposite side surfaces of the base material for floor material, a concave groove part serving as a female joint is formed in the middle part in the thickness direction, and on the other side, a convex rib part serving as a male joint is formed in the middle part in the thickness direction. In the base material for floor material, the front convex part adjacent to the front side of the concave groove part, the back convex part adjacent to the back side of the concave groove part, and the convex rib part are formed so as to straddle a plurality of layers of the plywood.

[0022] In the fifth invention, this actual processing is performed on the peripheral side surface of the base material for the flooring material, and the convex portions (front-side convex portion, back-side convex portion, rib portion) protruding outside the female and male fruits are formed such that the female and male fruits necessarily straddle a plurality of layers of the plywood. The convex portions of the female and male fruits are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the fifth invention, it is possible to provide a base material for the flooring material in which the convex portions of the female and male fruits are less likely to chip.

[0023] The sixth invention is characterized in that, in the fifth invention, the female fruit is formed such that the groove bottom corner of the concave groove portion is located within one of the layers rather than at the adhesive portion between the layers of the plywood.

[0024] In the sixth invention, the female fruit is formed such that the groove bottom corner of the concave groove portion of the female fruit is located within one of the layers so as not to be located at the adhesive portion between any of the layers of the plywood. When the groove bottom corner of the concave groove portion of the female fruit is located at the adhesive portion between the layers of the plywood, the plywood is likely to peel at a certain layer when the rib portion of the male fruit is inserted, but according to the above configuration, such peeling can be suppressed.

[0025] The seventh invention is a flooring material including a base material for the flooring material and a cushioning material adhered to the back surface of the base material for the flooring material, wherein the base material for the flooring material is a base material for the flooring material according to any one of the first to sixth inventions.

[0026] According to the seventh invention, by providing the base material for the flooring material according to any one of the first to sixth inventions, it is possible to provide a flooring material with excellent sound insulation properties that is applicable to floor heating flooring and is less likely to warp even when using softwood plywood.

[0027] The eighth invention is a method for manufacturing a floor material, comprising a floor material base material with a surface strengthening layer made of medium density fiberboard adhered to the surface of a plywood, and a cushioning material adhered to the back surface of the floor material base material. The method includes the following steps: laminating seven coniferous tree thin plates of equal thickness in order such that an aqueous adhesive is interposed between each pair of them and the fiber directions of adjacent two coniferous tree thin plates are perpendicular to each other, and then performing hot press in the thickness direction to form a plywood having first to seventh layers made of the coniferous tree thin plates laminated and adhesively integrated in order from the front surface side to the back surface side (a plywood forming step); after sanding the surface of the plywood, adhering the surface strengthening layer to the surface to obtain the floor material base material (a surface strengthening layer adhering step); forming a plurality of first grooves extending in a second direction perpendicular to a first direction which is the fiber direction of the first layer on the back surface of the plywood at a first groove interval, and forming a plurality of second grooves extending in the first direction at a second groove interval (a groove processing step); and adhering a cushioning material to the back surface of the plywood after the groove processing step (a cushioning material adhering step). The first grooves extend from one end to the other end of the plywood in the second direction, and the groove bottoms are located within the second layer. The second grooves extend from one end to the other end of the plywood in the first direction, and the groove bottoms are located within any one of the third to fifth layers.

[0028] In the eighth invention, a plurality of first grooves with a depth reaching from the back surface to the second layer are formed on the back surface of a plywood with seven plies. As the plywood for the base material of the flooring material, those with three or five plies are often used. However, in the eighth invention, since the number of plies of the plywood is seven plies, the locations adhered with the aqueous adhesive (the interfaces between the layers made of softwood thin plates) increase compared to three-ply or five-ply plywood, so the strength is improved compared to three-ply or five-ply plywood. Also, since the number of plies of the plywood is seven plies, the first grooves reaching from the back surface to the second layer become deeper compared to the case where the first grooves are formed in the same way in three-ply or five-ply plywood. With such deep plurality of first grooves, the rigidity of the plywood decreases and the flexibility increases, making it easier to absorb the impact force. Further, in the eighth invention, not only the first grooves but also a plurality of second grooves extending in a direction (the first direction) orthogonal to the extending direction (the second direction) of the first grooves are formed on the back surface of the plywood. By forming the second grooves in this way, the rigidity of the plywood decreases and the flexibility increases compared to the case where only the first grooves are formed, making it easier to absorb the impact force. That is, according to the eighth invention, it is possible to provide a flooring material having the required sound insulation performance and excellent soundproofing properties.

[0029] Also, in the eighth invention, a plurality of first grooves extending in a direction (the second direction) orthogonal to the fiber direction (the first direction) of the first layer of the plywood are not made to reach the first layer so that the fibers of the first layer are not cut off by the first grooves. By forming the first grooves in this way, even when the medium density fiberboard adhered to the surface of the plywood tries to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer extending in the first direction. Thereby, it is possible to manufacture a flooring material that is difficult to expand and contract in the first direction due to moisture absorption or desorption and is less likely to warp in the first direction.

[0030] Furthermore, in the eighth invention, a plurality of second grooves extending in a direction (the first direction) orthogonal to the fiber direction (the second direction) of the second layer are not formed in the second layer, and the fibers of the second layer extending in the second direction, which can counter the dimensional change due to moisture absorption or desorption of the medium density fiberboard, are not cut off by the second grooves. By forming the second grooves in this way, even if the medium density fiberboard adhered to the surface of the plywood expands and contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer extending in the second direction. As a result, it is possible to manufacture a flooring material that is difficult to expand and contract in the second direction due to moisture absorption or desorption and is less likely to warp in the second direction. That is, according to the eighth invention, it is possible to manufacture a flooring material that is less likely to warp not only in the fiber direction (the first direction) of the first layer but also in the orthogonal direction (the second direction).

[0031] Also, in the eighth invention, while a plywood with a normal number of plies of 3 or 5 is often used for the base material of the flooring material, the number of plies of the plywood is set to 7 and it is adhered with an aqueous adhesive. Therefore, in the eighth invention, compared with the case of forming a 3-ply or 5-ply plywood, the laminate of softwood thin plates is hot-pressed in a state of higher moisture content, and the formed plywood becomes thinner and denser from the middle to the outermost layer in the thickness direction. According to the eighth invention, by using a plywood having such a configuration, it is possible to provide a flooring material with excellent surface strength.

[0032] As described above, according to the eighth invention, it is possible to provide a flooring material that is less likely to warp even when using a softwood plywood and has excellent sound insulation properties applicable to floor heating flooring.

[0033] The ninth invention is the same as the eighth invention, except that the softwood thin plates constituting the first, third, fifth, and seventh layers are each composed of a single veneer, while the softwood thin plates constituting the second, fourth, and sixth layers are formed by splicing a plurality of veneers in the first direction, and the second layer is characterized in that it has no knot holes and its size in the first direction is larger than the first groove interval.

[0034] In the ninth invention, a plywood is formed by laminating and integrating seven coniferous tree thin plates. Although coniferous trees have more knots than broad-leaved trees, if the coniferous tree thin plate constituting the second layer has a knot hole with a size in the first direction larger than the groove interval (the first groove interval) of the first groove, the fibers of the second layer extending in the second direction that can resist dimensional changes due to moisture absorption or desorption of the medium-density fiberboard will be cut off by the knot hole, so it cannot resist dimensional changes due to moisture absorption or desorption of the medium-density fiberboard, and there is a risk of partial warping in the second direction. However, according to the ninth invention, since there is no knot hole in the second layer with a size in the first direction larger than the first groove interval, the effect of suppressing warping in the second direction can be expected.

[0035] The tenth invention is characterized in that, in the ninth invention, the first layer is constituted by a part without knot holes of a coniferous tree or is constituted by a part with knot holes of a coniferous tree and the knot holes are filled with putty so as to have no knot holes, and the second layer is constituted by a part without knot holes of a coniferous tree or is constituted by a part with knot holes of a coniferous tree and the knot holes are filled with plugs so as to have no knot holes.

[0036] In the tenth invention, the first and second layers are configured to have no knot holes. Specifically, when the first layer is constituted by a part without knot holes of a coniferous tree or is constituted by a part with knot holes of a coniferous tree, the knot holes are filled with putty and disappeared to make it have no knot holes. Also, the second layer is configured to have no knot holes by filling the knot holes with plugs when it is constituted by a part without knot holes of a coniferous tree or is constituted by a part with knot holes of a coniferous tree. In the tenth invention, by configuring the first and second layers in this way so as to have no knot holes, the floor material made using the base material for floor materials is made difficult to be damaged and has good surface properties. Therefore, by using the base material for floor materials according to the tenth invention, a floor material that is difficult to be damaged and has good surface properties can be provided.

[0037] The eleventh invention is characterized in that, in the eighth invention, the medium-density fiberboard is made mainly from hardwood fibers.

[0038] In the 11th invention, since the tracheary element fibers of coniferous trees have a significantly higher porosity and water absorption rate than the xylem fibers of broad-leaved trees, medium-density fiberboard made from the xylem of broad-leaved trees (broad-leaved tree MDF) is used as the surface strengthening layer. By using the xylem fibers of broad-leaved trees as the medium-density fiberboard constituting the surface strengthening layer in this way, the water absorption rate of the surface strengthening layer can be kept low, and dimensional changes can be suppressed.

[0039] The 12th invention further includes, in the 8th invention, a main processing step of forming a concave groove portion serving as a female joint in the middle portion in the thickness direction on one of the two opposite side surfaces of the base material for the floor material, and forming a convex rib portion serving as a male joint in the middle portion in the thickness direction on the other side. In the main processing step, the front convex portion adjacent to the front side of the concave groove portion, the back convex portion adjacent to the back side of the concave groove portion, and the convex rib portion form the female joint and the male joint so as to straddle a plurality of layers of the plywood, respectively.

[0040] In the 12th invention, the main processing is performed on the peripheral side surface of the base material for the floor material, and the convex portions (front convex portion, back convex portion, convex rib portion) protruding outside the female joint and the male joint are formed so as to straddle a plurality of layers of the plywood. The convex portions of the female joint and the male joint are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the 12th invention, a floor material in which the convex portions of the female joint and the male joint are less likely to chip can be provided.

[0041] The 13th invention is characterized in that, in the 12th invention, in the main processing step, the female joint is formed such that the groove bottom corner portion of the concave groove portion is located within one of the layers rather than in the adhesive portion between the layers of the plywood.

[0042] In the 13th invention, the female fruit is processed so that the groove bottom corner of the concave groove portion of the female fruit is located within one of the layers, rather than in the adhesive portion between any of the layers of the plywood. If the groove bottom corner of the concave groove portion of the female fruit is located in the adhesive portion between the layers of the plywood, when the convex rib portion of the male fruit is inserted, the plywood is likely to peel off at the layer where the groove bottom corner is located. However, by processing as described above, such peeling can be suppressed.

Effect of the Invention

[0043] As described above, according to the present invention, since the number of plies of the plywood is set to 7 plies, and a plurality of first grooves extending in the second direction and reaching the second layer from the back surface, and a plurality of second grooves extending in the first direction orthogonal to the second direction and reaching the fourth layer from the back surface are formed on the back surface of the plywood, it is possible to provide a base material for a flooring material with excellent sound insulation that is less likely to warp even when using softwood plywood and is applicable to a flooring material for floor heating, a flooring material including the same, and a method for manufacturing the flooring material.

Brief Description of the Drawings

[0044]

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Embodiments for Carrying Out the Invention

[0045] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are merely preferred examples in essence and are not intended to limit the scope of the present invention, its applications, or its uses.

[0046] 《Embodiment 1 of the Invention》 -Configuration of the Floor Material- The floor material 1 is, for example, constructed on top of a floor heating panel within a building such as a house. As shown in FIGS. 1 to 3, the floor material 1 is formed in a rectangular shape and includes a base material (base material for floor material) 10, a decorative material 20 adhered to the surface of the base material 10, and a cushioning material 30 adhered to the back surface of the base material 10. In this embodiment, the floor material 1 is formed, for example, to have dimensions of 1850 mm × 303 mm and a thickness of 10 mm or more and 16 mm or less. Note that the size of the floor material 1 can be changed as appropriate.

[0047] The decorative material 20 is formed of a resin-based decorative sheet having a thickness of about 0.1 mm to 0.2 mm. As the resin-based decorative sheet, a resin film that contains almost no moisture, such as an olefin resin film, a PET (polyethylene terephthalate) resin film, or a vinyl chloride resin film, can be used. For example, wood grain, stone grain, abstract patterns, etc. are printed on the decorative material 20. Note that, in addition to the resin-based decorative sheet, decorative papers such as coated paper or resin-impregnated paper, and thin sheet materials such as thin veneer sheets for wood can also be used as the decorative material 20. Note that the thickness of the decorative material 20 is set to be about 0.1 mm to 0.8 mm.

[0048] The cushioning material 30 can be any material having cushioning properties. In this embodiment, the cushioning material 30 is composed of a polyurethane foam with a thickness of about 1 mm to 3 mm.

[0049] [Configuration of the base material] The base material 10 includes a plywood 11 and a surface strengthening layer 12 adhered to the surface of the plywood 11. The base material 10 is formed in a rectangular shape in plan view, and by performing this actual processing, female joints 13 and male joints 14 are formed on the peripheral side surfaces.

[0050] 〈Detailed configuration of the plywood〉 The plywood 11 is a seven-layered softwood plywood in which seven softwood thin plates are laminated and adhesively integrated with an adhesive interposed therebetween. The plywood 11 includes first to seventh layers 11a to 11g composed of softwood thin plates arranged in order from the front surface side to the back surface side. The softwood thin plates constituting each layer 11a to 11g of the plywood 11 are composed of one or more veneers obtained by cutting softwood logs with a rotary lathe. As the softwood thin plates, for example, thin plates such as cypress, cedar, larch, spruce, red pine, radiata pine, and spruce can be used. In this embodiment, cypress thin plates are used.

[0051] As the adhesive, for example, water-based adhesives such as vinyl acetate-based, water-based vinyl urethane-based, acrylic-based, isocyanate-based, urea-based, phenol-based, ethylene vinyl acetate copolymer-based, and polyvinyl alcohol-based adhesives can be used. Note that, if necessary, a curing agent such as an isocyanate-based or melamine-based curing agent may be added to the adhesive.

[0052] The seven softwood veneers constituting the first layer 11a to the seventh layer 11g of the plywood 11 are equal in thickness and size. The thickness of the softwood veneer used for the plywood 11 is preferably 1.0 mm or more and 1.5 mm or less. If the thickness of the softwood veneer is less than 1.0 mm, it is difficult to stably cut from the log, and when drying the cut veneer, the plane cannot be maintained, and the strength to uniformly apply the adhesive to both sides cannot be ensured, so it is not preferable. On the other hand, if the thickness of the softwood veneer is more than 1.5 mm, the back cracking during cutting becomes large, and after lamination and integration, not only does the portion compressed by hot pressing without being reinforced by the aqueous adhesive become large, but also the thermal conductivity deteriorates in the uncompressed portion, so it is not preferable. The size of the softwood veneer can be designed in various ways according to the size of the flooring material 1. In this embodiment, for example, in order to manufacture the flooring material 1 with a size of 1850 mm × 303 mm, a softwood veneer with a size of 1900 mm × 345 mm and a thickness of 1.3 mm is used.

[0053] The softwood veneers constituting the first layer 11a, the third layer 11c, the fifth layer 11e, and the seventh layer 11g (odd layers) are composed of a single veneer cut so that the fibers extend in the length direction (the first direction) of the plywood 11. On the other hand, the softwood veneers constituting the second layer 11b, the fourth layer 11d, and the sixth layer 11f (even layers) are formed by splicing a plurality of veneers cut so that the fibers extend in the width direction (the second direction) of the plywood 11 in a direction orthogonal to the fiber direction (see FIG. 6). The number of veneers to be spliced is not particularly limited, but in the first embodiment, the softwood veneers constituting the even layers are formed by splicing two veneers.

[0054] As a result, in the odd layers 11a, 11c, 11e, 11g of the plywood 11, the fibers extend in the length direction (the first direction), and in the even layers 11b, 11d, and the sixth layer 11f, the fibers extend in the width direction (the second direction). That is, the plywood 11 is configured such that the fiber directions of adjacent two layers (two sheets) of the first to seventh layers 11a to 11g (softwood veneers) are orthogonal to each other.

[0055] Although plywood with 3 or 5 plies is often used as the base material for floor coverings, the plywood 11 in this embodiment has 7 plies, which is more than usual. Although details will be described later, the plywood 11 is formed by laminating 7 softwood thin plates with an aqueous adhesive interposed between each of them and then performing hot press. Therefore, the plywood 11 of this embodiment is hot-pressed in a state with a higher moisture content than the 3-ply or 5-ply plywood commonly used as the base material for floor coverings. As it is hot-pressed in a state with more moisture from the middle to the outermost layer in the thickness direction, the thickness becomes thinner and the density becomes higher from the middle to the outermost layer in the thickness direction. Also, in the second and third layers, since the aqueous adhesive is applied and impregnated on both sides, it is hot-pressed in a state with a lot of moisture, so it is further compressed and the compressed state is fixed by the impregnated adhesive.

[0056] Specifically, in the plywood 11 of this embodiment using softwood thin plates with a thickness of 1.3 mm, the thickness of the first layer 11a and the seventh layer 11g is about 1.1 mm, the thickness of the second layer 11b and the sixth layer 11f is about 1.2 mm, and the third layer 11c to the fifth layer 11e remain at their original thickness of 1.3 mm without being substantially compressed. That is, in the first to third layers 11a to 11c, the thickness becomes thinner and the density becomes higher in the order of the third layer 11c, the second layer 11b, and the first layer 11a. Also, in the fifth to seventh layers 11e to 11g, the thickness becomes thinner and the density becomes higher in the order of the fifth layer 11e, the sixth layer 11f, and the seventh layer 11g. Also, the thickness of the first layer 11a and the seventh layer 11g is equal to or less than the thickness of the surface strengthening layer 12 (1.2 mm in this embodiment) described later, and the thickness of the third layer 11c to the fifth layer 11e is greater than the thickness of the surface strengthening layer 12.

[0057] (First groove, second groove) On the back surface of the plywood 11, a plurality of first grooves 41 and a plurality of second grooves 42 are formed. Both the first groove 41 and the second groove 42 are formed to improve the sound insulation of the floor covering 1. In addition, when the floor covering 1 is installed on the floor heating panel, the first and second grooves 41, 42 also have the effect of making heat transfer to the surface of the floor covering 1 easier and more uniform.

[0058] The first groove 41 is a groove extending from one end to the other end in the width direction of the plywood 11. In this embodiment, the first groove 41 is formed so that its cross-sectional shape is rectangular. The first groove 41 is formed such that the groove width is 1.0 mm or more and 2.0 mm or less, and the groove interval (the length between adjacent first grooves 41, the first groove interval) is 10 mm or more and 50 mm or less. In this embodiment, the first groove 41 is formed such that the groove width is 1.5 mm and the groove interval is 10.2 mm. Further, the first groove 41 is formed to a depth (6.9 mm in this embodiment) such that the groove bottom is located within the second layer 11b.

[0059] The second groove 42 is a groove extending from one end to the other end in the length direction of the plywood 11. In this embodiment, the second groove 42 is formed so that its cross-sectional shape is rectangular. The second groove 42 is formed such that the groove width is 2.0 mm or more and 4.0 mm or less, and the groove interval (the length between adjacent second grooves 42, the second groove interval) is 35 mm or more and 100 mm or less. In this embodiment, the second groove 42 is formed such that the groove width is 3.0 mm and the groove interval is 47 mm. Further, the second groove 42 is formed to a depth (5.0 mm in FIG. 3) such that the groove bottom is located within any one of the third to fifth layers 11c to 11e (the fourth layer 11d in FIG. 3).

[0060] Note that the cross-sectional shapes of the first groove 41 and the second groove 42 are not limited to rectangular shapes, and any shape may be used. Also, the groove depths of the first groove 41 and the second groove 42 are not limited to those described above. For the first groove 41, it is sufficient that the groove bottom is within the second layer 11b, and for the second groove 42, it is sufficient that the groove bottom is within any one of the third layer 11c to the fifth layer 11e. The groove widths and pitches of the first groove 41 and the second groove 42 are not limited to those exemplified in this embodiment. The reason why it is sufficient that the groove bottom of the second groove 42 is within any one of the third layer 11c to the fifth layer 11e will be described later.

[0061] 〈Detailed Configuration of Surface Reinforcement Layer〉 The surface reinforcement layer 12 has a thickness of 0.8 mm or more and 1.3 mm or less and a density of 0.6 g / cm 3 or more and 0.9 g / cm 3It is composed of the following medium - density fiberboard (MDF) and is adhered to the surface of the plywood 11 with an adhesive. In the first embodiment, the surface strengthening layer 12 is composed of broad - leaf tree MDF with broad - leaf tree wood fibers as the main component. Also, in the first embodiment, for the surface strengthening layer 12, broad - leaf tree MDF with a size of 1850 mm × 303 mm and a thickness of 1.2 mm is used, and chamfering is performed at the corners of the upper surface and the side surface of the broad - leaf tree MDF. As the adhesive used for adhesion to the plywood 11, any adhesive may be used. It may be laminated and integrated by cold - press using a soft adhesive such as an aqueous vinyl urethane - based adhesive, or it may be laminated and integrated by hot - press after cold - press using a soft adhesive such as an aqueous vinyl urethane - based adhesive. Also, it may be laminated and integrated by hot - press using a non - aqueous soft adhesive such as PUR hot melt.

[0062] 〈Detailed Configuration of Female and Male Joints〉 As shown in FIGS. 4 and 5, the following processing is performed on the peripheral side surface of the base material 10. Specifically, on one of the two opposite side surfaces (long - side surfaces 10a, 10a and short - side surfaces 10b, 10b) of the base material 10, a female joint 13 is formed, and on the other side, a male joint 14 that can be fitted to the female joint 13 is formed.

[0063] The female joint 13 is formed by notching the base material 10 so that the middle part in the thickness direction of the long - side surface 10a and the short - side surface 10b of the base material 10 becomes a concave groove part 13a. The concave groove part 13a is a groove extending from one end to the other end in the length direction of each side surface 10a, 10b. In this embodiment, the cross - sectional shape of the concave groove part 13a is formed in a rectangular shape, but the cross - sectional shape of the concave groove part 13a is not limited to this, and it may be trapezoidal or other shapes. By notching the concave groove part 13a on the long - side surface 10a and the short - side surface 10b of the base material 10, a front - side convex part 13b is formed adjacent to the front side of the concave groove part 13a, and a back - side convex part 13c is formed adjacent to the back side of the concave groove part 13a.

[0064] The male fruit 14 is formed by notching the base material 10 such that the middle portions in the thickness direction of the long-side surface 10a and the short-side surface 10b of the base material 10 become the convex rib portions 14a. The convex rib portions 14a are protrusions extending from one end to the other end in the length direction of each of the side surfaces 10a and 10b. In the present embodiment, the cross-sectional shape of the convex rib portions 14a is formed in a rectangular shape, but the cross-sectional shape of the convex rib portions 14a is not limited to this, and any shape may be used as long as it fits into the concave groove portion 13a.

[0065] The female fruit 13 and the male fruit 14 are each formed such that the convex portions protruding outward (the front-side convex portion 13b and the back-side convex portion 13c in the female fruit 13, and the convex rib portion 14a in the male fruit 14) straddle a plurality of layers of the plywood 11. Specifically, in the present embodiment, the front-side convex portion 13b of the female fruit 13 is formed so as to straddle two layers, i.e., the first layer 11a and the second layer 11b, of the plywood 11. Further, the back-side convex portion 13c of the female fruit 13 is formed so as to straddle three layers, i.e., the fifth layer 11e to the seventh layer 11g, of the plywood 11. Also, the convex rib portion 14a of the male fruit 14 is formed so as to straddle four layers, i.e., the second layer 11b to the fifth layer 11e, of the plywood 11.

[0066] With such a configuration, the convex portions 13b, 13c, and 14a of the female fruit 13 and the male fruit 14 are brittle and easily chipped. However, by configuring them to straddle a plurality of layers of the plywood 11 as described above, they will necessarily include the fibers extending in the length direction (the first direction) of the flooring material 1 and the fibers extending in the width direction (the second direction) of the flooring material 1, making them less likely to chip.

[0067] Also, in the present embodiment, by forming the female fruit 13 as described above, the groove bottom corner x of the concave groove portion 13a of the female fruit 13 is located within the layer (in the present embodiment, the front-side groove bottom corner x is within the second layer 11b, and the back-side groove bottom corner x is within the fifth layer 11e) rather than at the adhesive portion between the layers of the plywood 11. If the groove bottom corner x of the concave groove portion 13a of the female fruit 13 is located at the adhesive portion between the layers of the plywood 11, the plywood 11 is likely to peel at a certain layer interface when the convex rib portion 14a of the male fruit 14 is inserted. However, according to the above configuration, such peeling can be suppressed.

[0068] -Method for manufacturing a flooring material- The manufacturing method of the flooring material 1 will be described below.

[0069] The flooring material 1 is manufactured by performing a base material forming step S1, a decorative material bonding step S2, and a cushioning material bonding step S3.

[0070] [Base material forming step] The base material forming step S1 includes a plywood forming step S11, a surface strengthening layer bonding step S12, and a cutting process (grooving process) S13.

[0071] First, the plywood forming step S11 is performed. In the plywood forming step S11, first, a softwood log is cut by a rotary lathe so that the thickness is 1.3 mm and the length in the fiber direction is 1900 mm. Four first veneers with a length in the fiber direction of 1900 mm and a length in the direction perpendicular to the fiber of 345 mm, and six second veneers with a length in the fiber direction of 345 mm and a length in the direction perpendicular to the fiber of 950 mm are prepared. The four first veneers are used as four softwood thin plates for the odd layers 11a, 11c, 11e, 11g. Also, by splicing two second veneers in the direction perpendicular to the fiber, three softwood thin plates for the even layers 11b, 11d, 11f are formed (see FIG. 6).

[0072] Here, for the softwood thin plate for the second layer 11b, a knot-free second veneer with a size in the first direction larger than the groove interval (the first groove interval) of the first groove 41 is used. Two such knot-free second veneers may be selected and spliced in the direction perpendicular to the fiber to form the softwood thin plate for the second layer 11b, or a knot-free one among the three softwood thin plates formed for the even layers 11b, 11d, 11f may be used as the softwood thin plate for the second layer 11b. Also, in order to make the softwood thin plate for the second layer 11b knot-free, the softwood thin plates for the second layer 11b and the sixth layer 11f and the softwood thin plate for the fourth layer 11d may be prepared separately, and a knot-free one may be used as the softwood thin plates for the second layer 11b and the sixth layer 11f. Also, by using knot-free ones for all of the softwood thin plates for the even layers 11b, 11d, 11f, the softwood thin plate for the second layer 11b may be made knot-free.

[0073] In addition, in the first embodiment, the first layer 11a and the second layer 11b that constitute the surface layer portion of the plywood 11 are configured to have no knots. Here, the "no knots" means not only those composed of the knot-free part of the softwood log, but also those composed of the part with knots in the softwood log, but with the knots disappeared by a predetermined process. In the first embodiment, the processes for disappearing the knots are different between the first layer 11a and the second layer 11b. The first layer 11a makes the knots disappear by a putty process of embedding putty into the knots. On the other hand, the second layer 11b makes the knots disappear by a plugging process of drilling a hole including the knot and filling the hole without a gap with wood (plug) having the same shape as the drilled hole. The putty process may be performed after plywood forming, and the plugging process may be performed when preparing the second veneer, or may be performed after splicing the second veneer in the fiber orthogonal direction to form a softwood thin plate for the second layer 11b.

[0074] In order to make the first layer 11a and the second layer 11b have no knots as described above, it is ideal that all the softwood thin plates for the first to seventh layers 11a to 11g are composed of the knot-free part of the softwood, but it is not realistic because softwood has many knots. It is preferable to separately prepare the softwood thin plates for the odd-numbered layers 11a, 11c, 11e, 11g and the softwood thin plates for the even-numbered layers 11b, 11d, 11f, and configure the softwood thin plates for the even-numbered layers 11b, 11d, 11f to have no knots by the plugging process before plywood forming. According to such a plywood manufacturing method, since only two types of softwood thin plates need to be prepared, the procurement of materials is easy and the workability is excellent.

[0075] Also, the softwood veneers for the even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b and the sixth layer 11f, and for the fourth layer 11d. Only the softwood veneers for the second layer 11b and the sixth layer 11f may be configured to have no missing knots by plugging treatment before plywood forming. According to such a plywood manufacturing method, it is necessary to prepare three types of softwood veneers. However, since the objects of the plugging treatment are only the softwood veneers for the second layer 11b and the sixth layer 11f, the treatment cost can be suppressed. Further, after plywood forming, since the second layer 11b has no missing knots regardless of which surface of the plywood 11 is the front (the first layer 11a side), there is no need to distinguish between the front and back of the plywood 11, and the manufacturing becomes easy.

[0076] Furthermore, the softwood veneers for the even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b, and for the fourth layer 11d and the sixth layer 11f. Only the softwood veneers for the second layer 11b may be configured to have no missing knots by plugging treatment before plywood forming. According to such a plywood manufacturing method, it is necessary to prepare three types of softwood veneers. However, since the object of the plugging treatment is only the softwood veneers for the second layer 11b, the treatment cost can be minimized.

[0077] Next, the seven prepared softwood veneers for the first to seventh layers 11a to 11g are laminated in the order of the seventh layer 11g, the sixth layer 11f, the fifth layer 11e, the fourth layer 11d, the third layer 11c, the second layer 11b, and the first layer 11a while interposing an aqueous adhesive.

[0078] Specifically, first, a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (the first veneer) for the seventh layer 11g, which is the lowermost layer, on top of a softwood thin plate for the sixth layer 11f (formed by joining two second veneers). Then, a softwood thin plate (the first veneer) for the fifth layer 11e is placed directly on top of the softwood thin plate for the sixth layer 11f, and a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (formed by joining two second veneers) for the fourth layer 11d on top of that. Then, a softwood thin plate (the first veneer) for the third layer 11c is placed directly on top of the softwood thin plate for the fourth layer 11d, and a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (formed by joining two second veneers) for the second layer 11b on top of that. And finally, a softwood thin plate (the first veneer) for the first layer 11a is placed directly on top of the softwood thin plate for the second layer 11b.

[0079] The seven softwood thin plates laminated as described above are hot-pressed in the lamination direction to form a plywood 11 that is adhesively integrated. Thus, in this embodiment, since the number of laminations of the plywood 11 is set to 7 plies and it is adhered with a water-based adhesive, compared to the case of forming a 3-ply or 5-ply plywood, the laminate of softwood thin plates is hot-pressed in a state with a higher moisture content, and the formed plywood 11 becomes thinner and denser from the middle to the outermost layer in the thickness direction.

[0080] After the plywood forming step S11, a surface strengthening layer adhesion step S12 is performed. As described above, when the first veneer constituting the softwood thin plate for the first layer 11a is made of one with a knot hole, before the surface strengthening layer adhesion step S12, putty treatment is performed to fill the knot hole in the first layer 11a to eliminate the knot hole.

[0081] In the surface strengthening layer bonding step S12, first, the surface of the plywood 11 is sanded to smooth the surface. Then, a surface strengthening layer 12 made of hardwood MDF is bonded to the surface of the plywood 11. Specifically, an adhesive (for example, a soft adhesive such as an aqueous vinyl urethane-based adhesive or a non-aqueous soft adhesive such as PUR hot melt) is applied to the surface of the plywood 11, and the surface strengthening layer 12 is placed thereon. Then, the plywood 11 and the surface strengthening layer 12 are pressed in the lamination direction (cold press for a soft adhesive such as an aqueous vinyl urethane-based adhesive, and hot press for a non-aqueous soft adhesive such as PUR hot melt) to bond and integrate them.

[0082] After the surface strengthening layer bonding step S12, a cutting process step S13 is performed. The cutting process step S13 includes a groove processing step S14 and a main processing step S15.

[0083] In the groove processing step S14, a first groove 41 and a second groove 42 are formed by cutting on the back surface of the plywood 11. The first groove 41 is a groove having a predetermined width with a groove width of 1.0 mm or more and 2.0 mm or less (1.5 mm in the first embodiment), and a depth from the back surface of the plywood 11 to the second layer 11b (6.9 mm in the first embodiment) and having a rectangular cross-sectional shape extending in the width direction (the second direction). A plurality of such first grooves 41 are formed at a predetermined pitch of 10 mm or more and 50 mm or less (10.2 mm pitch in the first embodiment). The second groove 42 is a groove having a predetermined width with a groove width of 2.0 mm or more and 4.0 mm or less (3.0 mm in the first embodiment), a depth from the back surface of the plywood 11 to any one of the third to fifth layers 11c to 11e (the fourth layer 11d in FIG. 3 in the first embodiment) (5.0 mm in FIG. 3 of the first embodiment), and a rectangular cross-sectional shape extending in the length direction (the first direction). A plurality of such second grooves 42 are formed at a predetermined pitch of 35 mm or more and 100 mm or less (47 mm pitch in the first embodiment).

[0084] In the main processing step S15, female fruits 13 and male fruits 14 are formed by cutting (main processing) on the peripheral side surfaces (two long side surfaces 10a and two short side surfaces 10b) of the plywood 11.

[0085] Specifically, the female mating part 13 is formed by notching the base material 10 such that the intermediate portions in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 become concave groove portions 13a. At this time, the front convex portion 13b on the front side and the back convex portion 13c on the back side of the concave groove portion 13a form the female mating part 13 so as to straddle a plurality of layers of the plywood 11. Specifically, the female mating part 13 is formed such that the front convex portion 13b straddles two layers, namely the first layer 11a and the second layer 11b, and the back convex portion 13c straddles three layers, namely the fifth layer 11e to the seventh layer 11g. Also, the female mating part 13 is formed such that the groove bottom corner portion x of the concave groove portion 13a is located not in the adhesive portion between the layers of the plywood 11 but within the layer (in this embodiment, the front groove bottom corner portion x is within the second layer 11b, and the back groove bottom corner portion x is within the fifth layer 11e).

[0086] Also, the male mating part 14 is formed by notching the base material 10 such that the intermediate portions in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 become rib portions 14a. At this time, the rib portions 14a form the male mating part 14 so as to straddle a plurality of layers of the plywood 11. Specifically, the male mating part 14 is formed such that the rib portions 14a straddle four layers, namely the second layer 11b to the fifth layer 11e.

[0087] As described above, in the base material forming step S1, the plywood forming step S11, the surface strengthening layer adhesion step S12, and the cutting process (grooving process) S13 are executed to form the base material 10.

[0088] In the decorative material adhesion step S2, a decorative material 20 (a resin decorative sheet in this embodiment) is adhered to the surface of the base material 10 (the surface of the surface strengthening layer 12) formed in the base material forming step S1 with an adhesive.

[0089] In the cushioning material adhesion step S3, a cushioning material 30 (a non-woven fabric in this embodiment) is adhered to the back surface of the base material 10 (the back surface of the plywood 11) formed in the base material forming step S1 with an adhesive.

[0090] By performing the above base material forming step S1, decorative material adhesion step S2, and cushioning material adhesion step S3, the floor material 1 is manufactured.

[0091] - Test - The following Tests 1 to 8 were conducted on the floor material 1 according to this embodiment manufactured as described above. Test 1 is a test for confirming the sound insulation performance and dimensional stability of the floor material 1. Tests 2 to 4 are Brinell hardness tests for confirming the influence of knots on the surface hardness of the floor material 1. Tests 5 and 6 are lightweight floor impact sound tests for confirming the influence of grooves on the sound insulation performance (sound insulation performance) of the floor material 1. Tests 7 and 8 are tests for confirming the influence of the groove depth of the second groove 42 on the warping of the floor material 1 in the width direction (warping in the second direction). Test 7 is a dry-wet repeated test, and Test 8 is an 80°C heat durability test.

[0092] [Test 1] Similar to the floor material 1, test specimens 1-1 to 1-3 measuring 470 mm × 918.5 mm and including a base material 10, a decorative material 20, and a buffer material 30 were prepared. A sound insulation test and a water absorption length change rate test were conducted, and the lightweight floor impact sound and the water absorption length expansion rate were measured. The test specimens 1-1 to 1-3 have different configurations of the base material 10 as follows. Note that the test specimen 1-1 has the same configuration as the floor material 1 of this embodiment. The test specimen 1-2 is obtained by changing the plywood 11 of the floor material 1 of this embodiment to a 5-ply softwood plywood (hinoki plywood). The test specimen 1-3 is obtained by changing the plywood 11 of the floor material 1 of this embodiment to a 5-ply lauan plywood.

[0093] As a result of the sound insulation test, the reduction amount of the lightweight floor impact sound at the center frequencies of 250 Hz and 500 Hz was the best for the test specimen 1-1 and the worst for the test specimen 2. That is, it can be seen that the floor material 1 of this embodiment is superior in sound insulation performance to the floor materials using 5-ply softwood plywood (hinoki plywood) and lauan plywood.

[0094] Also, as a result of the water absorption length change rate test, although there was no significant difference in the water absorption length change rate among the test specimens 1-1 to 1-3, the warping in the length direction was the smallest for the test specimen 1-1 and the largest for the test specimen 1-2. Also, the warping in the width direction was the smallest for the test specimen 1-1 and the largest for the test specimen 1-2. That is, it can be seen that the floor material 1 of this embodiment is less likely to warp than the floor materials using 5-ply softwood plywood (hinoki plywood) and lauan plywood.

[0095] [Tests 2 to 4] (Test 2) Test specimens 2-1 to 2-8, each measuring 150 mm × 150 mm and comprising a base material 10 and a decorative material 20, were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness.

[0096] Test specimens 2-1 to 2-8 each have a different configuration of the base material 10. Specifically, test specimens 2-1 to 2-8 are each formed by laminating seven coniferous wood thin plates measuring 150 mm × 150 mm and 1.3 mm thick with the fiber directions alternating orthogonally while interposing an aqueous adhesive, and then hot-pressing to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of broad-leaved tree MDF and a decorative material 20 made of an olefin decorative sheet with a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane-based adhesive.

[0097] For test specimens 2-1 to 2-4, artificial through-holes with a diameter of 30 mm (assuming knots) were formed in the central part of the coniferous wood thin plates constituting the second layer 11b, and the first layer 11a was configured to have no knots by puttying. On the other hand, for test specimens 2-5 to 2-8, both the first layer 11a and the second layer 11b were configured to have no knots.

[0098] Also, for test specimens 2-1 to 2-4, the thickness of the surface strengthening layer 12 was made different for each. Specifically, it was 1.0 mm for test specimen 2-1, 1.3 mm for test specimen 2-2, 1.5 mm for test specimen 2-3, and 2.7 mm for test specimen 2-4. Similarly, for test specimens 2-5 to 2-8, the thickness of the surface strengthening layer 12 was also made different for each. Specifically, it was 1.0 mm for test specimen 2-5, 1.3 mm for test specimen 2-6, 1.5 mm for test specimen 2-7, and 2.7 mm for test specimen 2-8.

[0099] The Brinell hardness test was conducted in accordance with the test method described in "Measurement of Surface Hardness (Brinell Hardness)" of JIS Z 2101 "Test Methods for Wood", and the Brinell hardness at the central part of the surface of test specimens 2-1 to 2-8 (the position corresponding to the artificial through-hole in test specimens 2-1 to 2-4) was measured.

[0100] The results of Test 2 are shown in Fig. 7. When the Brinell hardness is 11 N / mm 2 or more in the above cases is marked as "○", 9.8 N / mm 2 or more and less than 11 N / mm 2 is marked as "△", and less than 9.8 N / mm 2 is marked as "×". From the results of Test 2, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the floor material 1 of the present embodiment, if there are knots (perforations in Test 2) in the second layer 11b of the plywood 11, it was found that the Brinell hardness does not reach the value (11 N / mm 2 ) required for the floor material 1.

[0101] (Test 3) Similar to the floor material 1, test pieces 3-1 to 3-8 of 150 mm × 150 mm each having a base material 10, a decorative material 20, and a buffer material 30 were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness. Note that the test pieces 3-1 to 3-8 are those in which the thickness of the softwood thin plates constituting the first layer 11a and the seventh layer 11g of the plywood 11 of the test pieces 2-1 to 2-8 was changed to 1.7 mm, and the other configurations are the same as those of the test pieces 2-1 to 2-8.

[0102] The results of Test 3 are shown in Fig. 8, and the same results as those of Test 2 shown in Fig. 7 were obtained. That is, from the results of Tests 2 and 3, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the floor material 1 of the present embodiment, if there are knots (perforations in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness does not reach the value (11 N / mm 2 ) required for the floor material 1, and it was found that even if the first layer 11a of the plywood 11 is made thicker, it has no significant effect on the Brinell hardness.

[0103] (Test 4) Similar to the flooring material 1, test specimens 4-1 to 4-6 with a size of 150 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness. For test specimens 4-1 to 4-3, artificial through-holes (assuming knots) with a diameter of 30 mm formed in the center of the softwood thin plate constituting the second layer 11b of the plywood 11 of test specimens 2-1 to 2-3 were formed in the center of the softwood thin plate constituting the third layer 11c, and both the first layer 11a and the second layer 11b were configured to have no knots. Test specimens 4-4 to 4-6 were configured such that none of the first to third layers 11a to 11c had knots in test specimens 4-1 to 4-3.

[0104] The results of Test 4 are shown in Fig. 9. For all of test specimens 4-1 to 4-6, the Brinell hardness on the surface was 2 equal to or greater than the value required for the flooring material 1 (11 N / mm 2 ²). That is, from the results of Tests 2 and 4, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the flooring material 1 of the present embodiment, if there are knots (through-holes in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness will not reach the value required for the flooring material 1 (11 N / mm 2 ²). However, it was found that even if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm, if there are no knots in the first and second layers 11a and 11b, even if there are knots in the third layer 11c, it will not have an adverse effect on the Brinell hardness on the surface.

[0105] [Tests 5 to 7] (Test 5) Test specimens 5-1 to 5-16 with a size of 900 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a lightweight floor impact sound test was conducted to measure the sound reduction amount of sounds from 125 Hz to 500 Hz.

[0106] Specimens 5-1 to 5-16 each have a different configuration of the base material 10. Specifically, Specimens 5-1 to 5-16 have different modes (presence or absence and depth) of the second groove 42 and different thicknesses of the surface strengthening layer 12, and other configurations are the same as those of the floor material 1. To fabricate Specimens 5-1 to 5-16, first, seven softwood thin plates with a thickness of 1.3 mm are laminated with an aqueous adhesive while alternating the fiber directions orthogonally, and then hot-pressed to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane-based adhesive, and then cut into small pieces of 900 mm × 150 mm. This actual processing is performed on the four sides of the cut plywood 11 to form female nuts 13 and male nuts 14. Also, only the first groove 41 or both the first groove 41 and the second groove 42 are formed on the back surface (the back surface of the seventh layer 11g) of the plywood 11, and then a cushioning material 30 made of a foamed cushioning material with a thickness of 3 mm is adhered to cover the entire back surface, thereby fabricating Specimens 5-1 to 5-16.

[0107] For Specimens 5-1 to 5-4, only the first groove 41 is formed on the back surface of the plywood 11, and the second groove 42 is not formed. For Specimens 5-5 to 5-16, both the first groove 41 and the second groove 42 are formed on the back surface of the plywood 11. The first groove 41 formed in Specimens 5-1 to 5-16 shall have the same groove width of 1.5 mm, groove interval of 10.2 mm, and depth with the groove bottom located within the second layer 11b (groove bottom thickness of 2.6 mm) as those of the floor material 1. The second groove 42 formed in Specimens 5-5 to 5-16 shall have the same groove width of 3.0 mm and groove interval of 47 mm as those of the floor material 1. Regarding the depth, for Specimens 5-5 to 5-8, the groove bottom is located within the third layer 11c (groove bottom thickness of 3.7 mm), for Specimens 5-9 to 5-12, the groove bottom is located within the fourth layer 11d (groove bottom thickness of 5.0 mm), and for Specimens 5-13 to 5-16, the groove bottom is located within the fifth layer 11e (groove bottom thickness of 6.3 mm).

[0108] Note that the test specimens 5-1 to 5-16 were made such that the first layer 11a had no knots after the parquet treatment, and the even-numbered layers 11b, 11d, and 11f had no knots after the log embedding treatment.

[0109] Also, for test specimens 5-1 to 5-4, the thickness of the surface strengthening layer 12 was made different. For test specimen 5-1, it was 1.0 mm; for test specimen 5-2, it was 1.3 mm; for test specimen 5-3, it was 1.5 mm; and for test specimen 5-4, it was 2.7 mm. Similarly, for test specimens 5-5 to 5-8, test specimens 5-9 to 5-12, and test specimens 5-13 to 5-16, the thickness of the surface strengthening layer 12 was also made different. For test specimens 5-5, 5-9, and 5-13, it was 1.0 mm; for test specimens 5-6, 5-10, and 5-14, it was 1.3 mm; for test specimens 5-7, 5-11, and 5-15, it was 1.5 mm; and for test specimens 5-8, 5-12, and 5-16, it was 2.7 mm.

[0110] The lightweight floor impact sound test was conducted in accordance with the test method described in "Method for Measuring the Reduction Amount of Floor Impact Sound Level of Floor Finishing Structures on Concrete Floors in Laboratories" in JIS A 1440-1 "Method for Measuring the Reduction Amount of Floor Impact Sound Level of Floor Finishing Structures on Concrete Floors in Laboratories" - "Method by Standard Lightweight Impact Source", and the reduction amounts of the lightweight floor impact sound levels of test specimens 5-1 to 5-16 were measured.

[0111] The results of Test 5 are shown in Fig. 10. When the reduction amount of the lightweight floor impact sound level from 125 Hz to 500 Hz is ΔLL-4 or more, it is indicated by "○"; when it is equivalent to ΔLL-3, it is indicated by "△"; and when it is less than ΔLL-3, it is indicated by "×". From the results of Test 5, it was found that if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) like the floor material 1 of the present embodiment and the second groove 42 is not formed, the flexibility of the floor material 1 is insufficient, making it difficult to absorb the impact force, and the floor material 1 lacks the required sound insulation performance. Also, it was found that if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm and the depth of the second groove 42 is such that the groove bottom is located within any of the third to fifth layers 11c to 11e, a floor material 1 with the required sound insulation performance and excellent sound insulation can be obtained. Although not shown in Fig. 10, it was found that the deeper the depth of the second groove 42, the better the sound insulation performance.

[0112] (Test 6) Test specimens 6-1 to 6-12 measuring 900 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a lightweight floor impact sound test was conducted to measure the sound reduction amount in the range of 125 Hz to 500 Hz. The test specimens 6-1 to 6-12 were obtained by changing the thickness of the softwood thin plates constituting the first layer 11a and the seventh layer 11g of the plywood 11 of the test specimens 5-1 to 5-12 to 1.7 mm, and the other configurations were the same as those of the test specimens 5-1 to 5-12.

[0113] The results of Test 6 are shown in FIG. 11. For all of the test specimens 6-1 to 6-12, the Brinell hardness of the surface was less than the value required for the floor material 1 (11 N / mm 2 ). That is, from the results of Tests 5 and 6, even if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the floor material 1 of the present embodiment, if the first layer 11a of the plywood 11 is thick, the rigidity in the longitudinal direction (the first direction) of the floor material 1 increases, resulting in a floor material 1 lacking in sound insulation performance having the required sound insulation performance.

[0114] [Tests 7, 8] (Test 7) Test specimens 7-1 to 7-8 measuring 900 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a wet-dry repeated test was conducted to visually observe the magnitude of the warp in the width direction (the second direction).

[0115] Specimens 7-1 to 7-8 have different configurations of the base material 10. Specifically, Specimens 7-1 to 7-8 have different aspects (depths) of the second groove 42 and different thicknesses of the surface strengthening layer 12, and other configurations are the same as those of the floor material 1. In the production of Specimens 7-1 to 7-8, first, seven coniferous thin plates with a thickness of 1.3 mm are laminated with an aqueous adhesive interposed so that the fiber directions are alternately orthogonal, and then hot-pressed to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane-based adhesive, and then cut into small pieces of 900 mm × 150 mm. This actual processing is performed on the four sides of the cut plywood 11 to form female nuts 13 and male nuts 14. Further, after forming the first and second grooves 41 and 42 on the back surface of the plywood 11 (the back surface of the seventh layer 11g), a cushioning material 30 made of a foamed cushioning material with a thickness of 3 mm is adhered so as to cover the entire back surface, thereby producing Specimens 7-1 to 7-8.

[0116] The first groove 41 formed in Specimens 7-1 to 7-8 shall have the same groove width of 1.5 mm, groove interval of 10.2 mm, and depth at which the groove bottom is located within the second layer 11b (groove bottom thickness of 2.6 mm) as those of the floor material 1. The second groove 42 formed in Specimens 7-1 to 7-8 shall have the same groove width of 3.0 mm and groove interval of 47 mm as those of the floor material 1. On the other hand, for the depth, in Specimens 7-1 and 7-2, the depth at which the groove bottom is located within the second layer 11b (groove bottom thickness of 1.6 mm); in Specimens 7-3 and 7-4, the depth at which the groove bottom is located within the third layer 11c (groove bottom thickness of 3.7 mm); in Specimens 7-5 and 7-6, the depth at which the groove bottom is located within the fourth layer 11d (groove bottom thickness of 5.0 mm); and in Specimens 7-7 and 7-8, the depth at which the groove bottom is located within the fifth layer 11e (groove bottom thickness of 6.3 mm).

[0117] Note that Specimens 7-1 to 7-8 are those in which the first layer 11a has no knots by putty treatment and the even-numbered layers 11b, 11d, and 11f have no knots by wood embedding treatment.

[0118] Also, for specimens 7-1 and 7-2, the thicknesses of the surface strengthening layers 12 were made different. For specimen 7-1, it was 1.0 mm, and for specimen 7-2, it was 1.3 mm. Similarly, for specimens 7-3 and 7-4, specimens 7-5 and 7-6, and specimens 7-7 and 7-8, the thicknesses of the surface strengthening layers 12 were also made different. For specimens 7-3, 7-5, and 7-7, it was 1.0 mm, and for specimens 7-4, 7-6, and 7-8, it was 1.3 mm.

[0119] The wet-dry repeated test was carried out by placing the specimens for 48 hours each under the moisture absorption condition of a temperature of 40 °C and a relative humidity of 90% and the moisture desorption condition of a temperature of 20 °C and a relative humidity of 40%, and performing 2 cycles of this, and then visually observing the magnitude of the warp in the width direction (the second direction) of specimens 7-1 to 7-8.

[0120] The results of Test 7 are shown in Fig. 12. Those with acceptable warping in the width direction (the second direction) are indicated by "○", and those with large unacceptable warping in the width direction (the second direction) are indicated by "×". From the results of Test 7, if the depth of the second groove 42 is such that the groove bottom is located within any of the third to fifth layers 11c to 11e (the thickness of the groove bottom is 3.7 mm or more), the warping in the width direction (the second direction) is acceptable. However, if the depth of the second groove 42 is such that the groove bottom is located within the second layer 11b (the thickness of the groove bottom is 1.6 mm), it was found that the warping in the width direction is large and unacceptable. In addition, there was no significant difference in the degree of warping in the width direction among specimens 7-3, 7-5, and 7-7, and there was also no significant difference in the degree of warping in the width direction among specimens 7-4, 7-6, and 7-8.

[0121] (Test 8) Specimens 8-1 to 8-8, each 900 mm × 150 mm and equipped with the base material 10, the decorative material 20, and the cushioning material 30, were prepared, and an 80 °C heat endurance test was carried out, and the magnitude of the warp in the width direction (the second direction) was visually observed. Note that specimens 8-1 to 8-8 were configured in the same way as specimens 7-1 to 7-8.

[0122] The 80°C heat durability test was conducted by drying test specimens 8-1 to 8-8 in a dryer at 80°C for 48 hours to bring them to a completely dry state, and then visually observing the amount of warping in the width direction (second direction).

[0123] The results of Test 8 are shown in Fig. 13, and the same results as in Test 7 were obtained. From the results of Test 8 as well, if the depth of the second groove 42 is such that the bottom of the groove is located within any of the third to fifth layers 11c to 11e (the thickness of the bottom of the groove is 3.7 mm or more), the warping in the width direction (second direction) is within an acceptable range. However, if the depth of the second groove 42 is such that the bottom of the groove is located within the second layer 11b (the thickness of the bottom of the groove is 1.6 mm), it was found that the warping in the width direction becomes unacceptably large. In Test 8, there was a slight difference in the warping in the width direction between test specimens 8-3, 8-5, 8-7 and between test specimens 8-4, 8-6, 8-8, and the deeper the depth of the second groove 42, the larger the warping in the width direction became. That is, it was found that the shallower the depth of the second groove 42 (the thicker the bottom of the groove), the less likely it is for warping in the width direction to occur due to heating and drying, and it is suitable for a floor material for floor heating.

[0124] -Effects of the Embodiment- In the base material 10 for floor materials of the present embodiment, the number of plies of the plywood 11 is set to 7 plies, and a plurality of first grooves 41 with a depth reaching from the back surface to the second layer 11b are formed on the back surface of the plywood 11. As the plywood for the base material of the floor material, those with 3 plies or 5 plies are often used. However, in the present embodiment, since the number of plies of the plywood 11 is set to 7 plies, the locations adhered with the adhesive (the interfaces between the layers made of softwood thin plates) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood 11 is set to 7 plies, the first grooves 41 reaching from the back surface to the second layer 11b become deeper compared to the case where the first grooves 41 are similarly formed in 3-ply plywood or 5-ply plywood. With such deep plurality of first grooves 41, the rigidity of the plywood 11 decreases and the flexibility increases, making it easier to absorb impact force. Further, in the present embodiment, not only the first grooves 41 but also a plurality of second grooves 42 extending in a direction (the first direction) orthogonal to the extending direction (the second direction) of the first grooves 41 are formed on the back surface of the plywood 11. By forming the second grooves 42 in this way, the rigidity of the plywood 11 decreases and the flexibility increases compared to the case where only the first grooves 41 are formed, making it easier to absorb impact force. That is, when the base material 10 for floor materials of the present embodiment is used, the floor material 1 has improved required sound insulation performance and excellent soundproofing properties.

[0125] Further, in the first embodiment, since the plurality of first grooves 41 extend in a direction (the second direction) orthogonal to the fiber direction (the first direction) of the first layer 11a of the plywood 11 and do not reach the first layer 11a, the fibers of the first layer 11a are not cut off. With such a configuration, in the first embodiment, even when the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 attempts to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer 11a extending in the first direction. As a result, it becomes difficult for the base material 10 for floor materials to expand and contract in the first direction due to moisture absorption or desorption, and warping in the first direction is suppressed.

[0126] Furthermore, in the present embodiment, a plurality of second grooves 42 extending in a direction (first direction) orthogonal to the fiber direction (second direction) of the second layer 11b have groove bottoms within any one of the third to fifth layers 11c to 11e and do not reach the second layer 11b. Therefore, the fibers of the second layer 11b extending in the second direction, which can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11, are not cut off. With such a configuration, in the first embodiment, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 expands or contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for flooring material becomes less likely to expand or contract in the second direction due to moisture absorption or desorption, and warping (width warping) in the second direction is suppressed. That is, according to the base material 10 for flooring material of the present embodiment, not only warping in the fiber direction (first direction) of the first layer 11a is suppressed, but also warping in the orthogonal direction (second direction) is suppressed.

[0127] Also, in FIG. 3 of the first embodiment, the second groove 42 is formed such that the groove bottom is located within the fourth layer 11d, and since the second groove 42 does not reach the third layer 11c, not only are the fibers of the second layer 11b extending in the second direction, which can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, not cut off, but also the second layer 11b is covered by the first layer 11a and the third layer 11c. Thus, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 expands or contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are more suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for flooring material becomes less likely to expand or contract in the second direction due to moisture absorption or desorption, and a flooring material 1 in which warping in the second direction is less likely to occur can be provided.

[0128] In addition, the inventors of the present application conducted verification tests (Tests 5, 7, and 8) on the correlation between the depth of the second groove 42, the sound insulation performance of the floor material 1, and warping. As a result of the verification tests, it was found that as the depth of the second groove 42 increases, the sound insulation performance improves, while warping in the second direction becomes more likely to occur. Also, when the groove bottom of the second groove 42 is located within the third to fifth layers 11c to 11e, it is possible to form the floor material 1 that has the required sound insulation performance and is less likely to warp in the second direction. In particular, from the viewpoints of sound insulation performance and warping, it was found that it is preferable that the groove bottom of the second groove 42 be located within the fourth layer 11d. Therefore, in the example of FIG. 3 of the first embodiment, the second groove 42 is formed to have a depth such that the groove bottom is located within the fourth layer 11d. Accordingly, according to the example of FIG. 3 of the first embodiment, it is possible to provide the floor material 1 that is excellent in sound insulation and suitable for a floor heating floor material and is less likely to warp.

[0129] In addition, in the present embodiment, the plywood 11 becomes thinner and has a higher density as it goes from the middle in the thickness direction toward the outermost layer. With such a configuration, the surface strength of the base material 10 for the floor material is improved.

[0130] As described above, according to the present embodiment, it is possible to provide the base material 10 for the floor material that is excellent in sound insulation and applicable to a floor heating floor material and is less likely to warp even when using softwood plywood.

[0131] In addition, in the present embodiment, each layer 11a to 11g of the plywood 11 is composed of softwood thin plates. Although softwood has more knots than hardwood, if the softwood thin plate constituting the second layer 11b has a knot hole whose size in the first direction is larger than the groove interval (the first groove interval) of the first groove 41, the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard will be cut off by the knot hole, so it cannot counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, and there is a risk of partial warping occurring in the second direction. However, according to the first embodiment, since the second layer 11b does not have a knot hole whose size in the first direction is larger than the first groove interval, an effect of suppressing warping in the second direction can be expected. Note that the second layer 11b is composed of softwood thin plates in which a plurality of (two in this embodiment) veneers are joined together in the first direction, and the veneers constituting the second layer 11b are smaller than the veneers constituting the first layer 11a. It is difficult to prepare a large veneer without large knot holes, but it is relatively easy to prepare a relatively small veneer used for the second layer 11b without large knot holes. Therefore, according to the present embodiment, a base material 10 for a floor material that can be expected to have an effect of suppressing warping in the second direction can be provided relatively easily.

[0132] In addition, the inventors of the present application conducted verification tests (Tests 2 to 4) on the correlation between the presence or absence of knots in the first to third layers 11a to 11c of the plywood 11 and the Brinell hardness of the surface of the flooring material 1. As a result of the verification tests, when there are knots in the first or second layer 11a, 11b constituting the surface layer portion of the plywood 11, the Brinell hardness of the surface of the flooring material 1 is lower than the desired hardness. On the other hand, even if there are knots in the third layer 11c, if there are no knots in the first and second layers 11a, 11b, it was found that the Brinell hardness of the surface of the flooring material 1 is equal to or higher than the desired hardness. That is, it was found that if the flooring material 1 is formed while there are knots in the first and second layers 11a, 11b of the plywood 11, the flooring material 1 may be easily damaged. In addition, if there are knots in the first and second layers 11a, 11b forming the surface layer portion of the plywood 11, the surface properties of the flooring material 1 may be deteriorated, leading to a decrease in the design quality of the flooring material 1. In particular, when a thin (e.g., about 1.5 mm) medium density fiberboard is used as the surface strengthening layer 12 in order to minimize the influence of warping as much as possible, if there are knots near the surface layer, the influence of the knots (such as unevenness) will appear up to the decorative material 20 through the surface strengthening layer 12 made of the thin medium density fiberboard, increasing the risk of deteriorating the design quality of the flooring material 1.

[0133] Therefore, in the first embodiment, the first and second layers 11a, 11b are configured to have no knots. Specifically, the first layer 11a is composed of a portion of the softwood without knots or, if composed of a portion with knots in the softwood, the knots are filled with putty and disappeared to make it knot-free. Further, the second layer 11b is composed of a portion of the softwood without knots or, if composed of a portion with knots in the softwood, the knots are made to disappear by inlaying wood treatment to make it knot-free. In the first embodiment, by configuring the first and second layers 11a, 11b to have no knots in this way, the flooring material produced using the flooring material base 10 is made difficult to be damaged and has good surface properties. The surface properties of the flooring material 1 are not deteriorated. Therefore, according to the first embodiment, it is possible to relatively easily provide the flooring material base 10 that does not deteriorate the surface properties of the flooring material 1.

[0134] In addition, in the first embodiment, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate than the xylem fibers of broad-leaved trees, a medium-density fiberboard made of the xylem fibers of broad-leaved trees (broad-leaved tree MDF) is used as the surface strengthening layer 12. By using the xylem fibers of broad-leaved trees as the medium-density fiberboard constituting the surface strengthening layer 12 in this way, the water absorption rate of the surface strengthening layer 12 can be kept low, and dimensional changes can be suppressed.

[0135] In addition, in this embodiment, this actual processing is performed on the peripheral side surface of the base material 10 for the flooring material. Also, the convex portions (front side convex portion 13b, back side convex portion 13c, rib portion 14a) protruding outside the female fruit 13 and the male fruit 14 are formed such that the female fruit 13 and the male fruit 14 always straddle a plurality of layers of the plywood 11. The convex portions 13b, 13c, 14a of the female fruit 13 and the male fruit 14 are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood 11 as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to this embodiment, it is possible to provide the base material 10 for the flooring material in which the convex portions 13b, 13c, 14a of the female fruit 13 and the male fruit 14 are less likely to chip.

[0136] In addition, in this embodiment, the female fruit 13 is formed such that the groove bottom corner x of the groove portion 13a of the female fruit 13 is located within one of the layers so as not to be located at the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the groove portion 13a of the female fruit 13 is located at the adhesive portion between the layers of the plywood 11, when the rib portion 14a of the male fruit 14 is inserted, the plywood 11 is likely to peel at a certain layer due to the groove bottom corner x. However, according to the above configuration, such peeling can be suppressed.

[0137] In addition, according to this embodiment, by providing the above-mentioned base material 10 for the flooring material, it is possible to provide a flooring material 1 with excellent sound insulation properties that is less likely to warp even when using coniferous plywood and is applicable to the flooring material for floor heating.

[0138] Also, in the manufacturing method of the floor material of the present embodiment, a plurality of first grooves 41 with a depth reaching from the back surface to the second layer 11b are formed on the back surface of the plywood 11 with 7 plies. As the plywood for the floor material base, those with 3 plies or 5 plies are often used. However, in the present embodiment, since the number of plies of the plywood 11 is 7 plies, the locations adhered with the aqueous adhesive (the interfaces between the layers made of softwood thin plates) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood 11 is 7 plies, the first grooves 41 reaching from the back surface to the second layer 11b become deeper compared to the case where the first grooves 41 are similarly formed in 3-ply plywood or 5-ply plywood. Due to such deep plurality of first grooves 41, the rigidity of the plywood 11 decreases and the flexibility increases, making it easier to absorb impact force. Further, in the present embodiment, on the back surface of the plywood 11, not only the first grooves 41 but also a plurality of second grooves 42 extending in a direction (the first direction) orthogonal to the extending direction (the second direction) of the first grooves 41 are formed. By forming the second grooves 42 in this way, the rigidity of the plywood 11 decreases and the flexibility increases compared to the case where only the first grooves 41 are formed, making it easier to absorb impact force. That is, according to the manufacturing method of the present embodiment, it is possible to provide the floor material 1 having the required sound insulation performance and excellent soundproofing performance.

[0139] Also, in the manufacturing method of the floor material of the present embodiment, a plurality of first grooves 41 extending in a direction (the second direction) orthogonal to the fiber direction (the first direction) of the first layer 11a of the plywood 11 are not made to reach the first layer 11a so that the fibers of the first layer 11a are not cut off by the first grooves 41. By forming the first grooves 41 in this way, even when the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 attempts to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer 11a extending in the first direction. Thereby, it is possible to manufacture the floor material 1 that is difficult to expand and contract in the first direction due to moisture absorption or desorption and is difficult to warp in the first direction.

[0140] Furthermore, in the present embodiment, a second groove 42 extending in a direction (first direction) orthogonal to the fiber direction (second direction) of the second layer 11b is not formed to reach the second groove 42, so that the fibers of the second layer 11b extending in the second direction, which can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, are not cut off. By forming the second groove 42 in this way, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 1 tries to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it is possible to manufacture the flooring material 1 that is difficult to expand and contract in the second direction due to moisture absorption or desorption and is less likely to warp in the second direction. That is, according to the manufacturing method of the flooring material of the present embodiment, it is possible to manufacture the flooring material 1 that is less likely to warp not only in the fiber direction (first direction) of the first layer 11a but also in the orthogonal direction (second direction).

[0141] Furthermore, in the manufacturing method for manufacturing the flooring material 1 shown in FIG. 3 of the present embodiment 1, since the bottom of the second groove 42 is located within the fourth layer 11d and the second groove 42 does not reach the third layer 11c, not only are the fibers of the second layer 11b extending in the second direction, which can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, not cut off, but also the second layer 11b is covered by the first layer 11a and the third layer 11c. Thus, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 1 tries to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it is possible to manufacture the flooring material 1 that is difficult to expand and contract in the second direction due to moisture absorption or desorption and is less likely to warp in the second direction.

[0142] Also, in the manufacturing method of the flooring material of the present embodiment 1, from the results of the verification tests (tests 5, 7, 8) on the correlation between the depth of the above-described second groove 42, the sound insulation performance of the flooring material 1, and the dimensional stability (warpage), if the second groove 42 is set to a depth such that the bottom of the groove is located within the fourth layer 11d, it is possible to provide a flooring material that is less likely to warp and has excellent sound insulation properties suitable for a floor heating flooring material.

[0143] In addition, in the method for manufacturing the flooring material of the present embodiment, while a plywood with a normal number of plies of 3 or 5 is often used for the base material for the flooring material, the number of plies of the plywood 11 is set to 7 plies and they are adhered with an aqueous adhesive. Therefore, in the present embodiment, compared with the case of forming a plywood with 3 or 5 plies, the laminate of softwood thin plates is hot-pressed in a state of having a higher moisture content, and the formed plywood becomes thinner and denser from the middle to the outermost layer in the thickness direction. According to the method for manufacturing the flooring material of the present embodiment, by using the plywood 11 having such a configuration, it is possible to provide the flooring material 1 having excellent surface strength.

[0144] As described above, according to the method for manufacturing the flooring material of the present embodiment, even when using a softwood plywood, it is possible to provide the flooring material 1 that is less likely to warp and has excellent sound insulation properties applicable to the flooring material for floor heating.

[0145] Also, in the method for manufacturing the flooring material of the present embodiment, 7 softwood thin plates are laminated and integrated to form the plywood 11. Although softwoods have more knots than hardwoods, if the softwood thin plate constituting the second layer 11b has a knot hole with a size in the first direction larger than the groove interval (the first groove interval) of the first groove 41, the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard will be cut off by the knot hole, so it cannot counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, and there is a risk that warping will partially occur in the second direction. However, according to the present embodiment, since the second layer 11b does not have a knot hole with a size in the first direction larger than the first groove interval, an effect of suppressing warping in the second direction can be expected.

[0146] In addition, in the method for manufacturing the floor material of the first embodiment, the first and second layers 11a and 11b are configured to have no knots. Specifically, the first layer 11a is composed of a part of a coniferous tree without knots, or when it is composed of a part with knots in the coniferous tree, the knots are filled with putty and disappeared to make it knot-free. Further, the second layer 11b is composed of a part of a coniferous tree without knots, or when it is composed of a part with knots in the coniferous tree, the knots are made to disappear by plugging treatment to make it knot-free. In the first embodiment, by configuring the first and second layers 11a and 11b in this way to have no knots, the floor material 1 is made difficult to be damaged and has good surface properties. Therefore, according to the method for manufacturing the floor material of the first embodiment, it is possible to provide a floor material 1 that is difficult to be damaged and has good surface properties.

[0147] In addition, in the method for manufacturing the floor material of the present embodiment, since the porosity of the tracheids of coniferous trees is significantly higher and the water absorption rate is higher than that of the xylem fibers of broad-leaved trees, medium-density fiberboard (broad-leaved tree MDF) mainly made of the xylem fibers of broad-leaved trees is used as the surface strengthening layer 12. By using the xylem fibers of broad-leaved trees as the medium-density fiberboard constituting the surface strengthening layer 12 in this way, the water absorption rate of the surface strengthening layer 12 can be kept low, and dimensional changes can be suppressed.

[0148] In addition, in the method for manufacturing the floor material of the present embodiment, the present processing is performed on the peripheral side surface of the base material 10 for the floor material. Also, the convex portions (front side convex portion 13b, back side convex portion 13c, rib portion 14a) protruding outside the female fruit 13 and the male fruit 14 are formed so as to necessarily straddle a plurality of layers of the plywood 11. The convex portions 13b, 13c, and 14a of the female fruit 13 and the male fruit 14 are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood 11 as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, and it becomes difficult to chip. Therefore, according to the method for manufacturing the floor material of the present embodiment, it is possible to provide a floor material 1 in which the convex portions 13b, 13c, and 14a of the female fruit 13 and the male fruit 14 are difficult to chip.

[0149] Also, in the method for manufacturing the floor material of the present embodiment, the female member 13 is processed so that the groove bottom corner x of the concave groove portion 13a of the female member 13 is located within one of the layers of the plywood 11, rather than at the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the concave groove portion 13a of the female member 13 is located at the adhesive portion between the layers of the plywood 11, when the protruding strip portion 14a of the male member 14 is inserted, the plywood 11 is likely to peel off at a certain layer due to the groove bottom corner x. However, by processing as described above, such peeling can be suppressed.

Industrial Applicability

[0150] The present invention is useful for a base material for a floor material, a floor material, and a method for manufacturing a floor material.

Explanation of Reference Numerals

[0151] 1 Floor material 10 Base material (base material for floor material) 10a Long side surface (peripheral side surface) 10b Short side surface (peripheral side surface) 11 Plywood 11a First layer 11b Second layer 11c Third layer 11d Fourth layer 11e Fifth layer 11f Sixth layer 11g Seventh layer 12 Surface strengthening layer 13 Female member 13a Concave groove portion 13b Front side convex portion (convex part) 13c Back side convex portion (convex part) 14 Male member 14a Protruding strip portion 15 Adhesive 20 Decorative material 30 Buffer material 41 First groove 42 Second groove

Claims

1. A flooring substrate in which a surface reinforcing layer made of medium density fiberboard is bonded to the surface of plywood, The plywood is a softwood plywood having first to seventh layers each made of seven softwood thin boards laminated and bonded together from the front side to the back side in order such that the fiber directions of adjacent two boards are perpendicular to each other, A plurality of first grooves extending in a second direction perpendicular to a first direction, which is a fiber direction of the first layer, are formed on the back surface of the plywood at a first groove interval, and a plurality of second grooves extending in the first direction are formed at a second groove interval, The first groove extends from one end to the other end of the plywood in the second direction, and a groove bottom is located within the second layer, The second groove extends from one end to the other end in the first direction of the plywood, and a groove bottom is located in any one of the third to fifth layers, The first to third layers have thicknesses decreasing while densities increasing in the order of the third layer, the second layer, and the first layer, The fifth to seventh layers have a thickness decreasing while a density increasing in the order of the fifth layer, the sixth layer, and the seventh layer, the first and seventh layers have a thickness equal to or less than the thickness of the surface reinforcing layer; The third and fifth layers are thicker than the surface reinforcing layer. A flooring base material characterized by:

2. The flooring substrate according to claim 1, the first, third, fifth and seventh layers of the softwood thin board are each made of a single veneer, while the second, fourth and sixth layers of the softwood thin board are each made of a plurality of veneers joined together in the first direction; The second layer has no knots whose size in the first direction is greater than the first groove interval. A flooring base material characterized by:

3. The flooring substrate according to claim 2, The first layer is made of a part of a coniferous tree that has no knots, or is made of a part of a coniferous tree that has knots and the knots are filled with putty, thereby making the first layer free of knots; The second layer is made of a part of a coniferous tree that has no knots, or is made of a part of a coniferous tree that has knots and the knots are filled with filler wood, so that there are no knots. A flooring base material characterized by:

4. The flooring substrate according to claim 1, The above medium density fiberboard is made primarily from hardwood wood fibers. A flooring base material characterized by:

5. The flooring substrate according to claim 1, One of the two opposing sides of the flooring base material has a concave groove portion that will become a female fruit in the middle of the thickness direction, and the other has a convex ridge portion that will become a male fruit in the middle of the thickness direction, In the above-mentioned flooring base material, the front-side convex portion adjacent to the front side of the concave groove portion, the back-side convex portion adjacent to the back side of the concave groove portion, and the convex strip portion are formed so as to span multiple layers of the plywood. A flooring base material characterized by:

6. The flooring substrate according to claim 5, The female is formed so that the groove bottom corner of the concave groove is located within one of the layers, not in the adhesive portion between the layers of the plywood. A flooring base material characterized by:

7. A flooring material comprising a flooring base material and a cushioning material adhered to the back surface of the flooring base material, The flooring base material is a flooring base material according to any one of claims 1 to 6. A flooring material characterized by:

8. A method for manufacturing a flooring material comprising a flooring base material having a surface reinforcing layer made of a medium density fiberboard adhered to a surface of a plywood, and a cushioning material adhered to a back surface of the flooring base material, comprising: a plywood forming step of stacking seven softwood thin boards of equal thickness in order with an aqueous adhesive interposed between each thin board and with the fiber directions of adjacent two softwood thin boards perpendicular to each other, and hot pressing the thin boards in the thickness direction to form the plywood having first to seventh layers made of the softwood thin boards stacked in order from the front side to the back side and bonded together; a surface reinforcing layer adhering step of adhering the surface of the plywood to the surface of the plywood to form the flooring base material; a groove processing step of forming a plurality of first grooves at a first groove interval on the back surface of the plywood, the first grooves extending in a second direction perpendicular to a first direction that is a fiber direction of the first layer, and forming a plurality of second grooves at a second groove interval that extend in the first direction; A cushioning material adhering step of adhering a cushioning material to the back surface of the plywood after the groove processing step, The first groove extends from one end to the other end of the plywood in the second direction, and a groove bottom is located within the second layer, The second groove extends from one end to the other end in the first direction of the plywood, and a groove bottom is located within any one of the third to fifth layers. A method for manufacturing a flooring material comprising the steps of:

9. The method for manufacturing a flooring material according to claim 8, the first, third, fifth and seventh layers of the softwood thin board are each made of a single veneer, while the second, fourth and sixth layers of the softwood thin board are each made of a plurality of veneers joined together in the first direction; The second layer is free of knots whose size in the first direction is greater than the first groove interval. A method for manufacturing a flooring material comprising the steps of:

10. The method for manufacturing a flooring material according to claim 9, The first layer is made of a part of coniferous wood that has no knots, or is made of a part of coniferous wood that has knots and the knots are filled with putty, thereby making the first layer free of knots; The second layer is made of a part of a coniferous tree that has no knots, or is made of a part of a coniferous tree that has knots and the knots are filled with filler wood, thereby making the second layer free of knots. A method for manufacturing a flooring material comprising the steps of:

11. The method for manufacturing a flooring material according to claim 8, The above medium density fiberboard is made primarily from hardwood wood fibers. A method for manufacturing a flooring material comprising the steps of:

12. The method for manufacturing a flooring material according to claim 8, The method further includes a processing step of forming a female berry in the middle of the thickness direction on one of the two opposing sides of the flooring base material, and forming a male berry in the middle of the thickness direction on the other side, In the above-mentioned main processing step, the female and male grains are formed so that the front side convex portion adjacent to the front side of the concave groove portion, the back side convex portion adjacent to the back side of the concave groove portion, and the convex strip portion each span multiple layers of the plywood. A method for manufacturing a flooring material comprising the steps of:

13. The method for manufacturing a flooring material according to claim 12, In the above-mentioned main processing step, the female part is formed so that the groove bottom corner of the concave groove part is located within one of the layers, not in the adhesive part between the layers of the plywood. A method for manufacturing a flooring material comprising the steps of:

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