Substrate for flooring, flooring material, and method for manufacturing 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] This invention relates to a base material for flooring, flooring material, and a method for manufacturing flooring material. [Background technology]

[0002] Conventionally, soundproof flooring materials for underfloor heating have been proposed that are installed on underfloor heating panels and comprise a base material having a decorative layer on the surface and a cushioning material on the back (see, for example, Patent Document 1 below). In Patent Document 1, the base material for the flooring material is made of plywood with a back groove processing, in which multiple grooves extending parallel to each other are formed on the back surface of the plywood. In the above flooring material, the multiple back grooves formed on the back surface of the base material for the flooring material make it easier for heat to be uniformly transferred to the surface of the flooring material, and also provide flexibility to the flooring material to improve sound insulation. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-145117 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, while tropical hardwood plywood such as lauan plywood was used as the base material for the above-mentioned flooring, in recent years, tropical hardwood plywood has become difficult to obtain due to the depletion of raw materials and concerns about preventing environmental damage, and efforts are being made to replace it with softwood plywood. Since softwood plywood is softer than hardwood plywood such as lauan plywood, replacing the base material of flooring with softwood plywood results in flooring that lacks surface strength and is easily scratched. Therefore, in some cases, medium-density fiberboard is bonded to the surface of softwood plywood to strengthen its surface strength.

[0005] However, because medium-density fiberboard is more susceptible to moisture absorption and expansion than plywood, a substrate in which medium-density fiberboard is bonded to the surface of plywood to strengthen its surface strength is more prone to warping than a substrate made solely of plywood. In particular, when the substrate is made of plywood with grooved backing, as in the soundproof flooring material for underfloor heating described in Patent Document 1, although the sound insulation performance can be improved by the multiple grooves, the fibers that can withstand the dimensional changes due to moisture absorption or release of the medium-density fiberboard are cut by the grooves, making the substrate more prone to warping. Furthermore, in the above-mentioned soundproof flooring material for underfloor heating, the substrate is more prone to warping because it is installed on underfloor heating panels and experiences large temperature changes, while the presence of a cushioning material prevents the flooring material from being pressed down and fixed to the underfloor heating panels, making it impossible to suppress the warping of the substrate. In addition, if the thickness of the plywood is increased to counteract the medium-density fiberboard in order to suppress warping, the overall rigidity of the substrate increases too much, resulting in a failure to achieve the desired sound insulation performance.

[0006] The present invention has been made in view of the above, and its purpose is to provide a soundproofing substrate for flooring that is less prone to warping even when using softwood plywood and is applicable to flooring for underfloor heating, a flooring material equipped therewith, and a method for manufacturing the flooring material. [Means for solving the problem]

[0007] To achieve the above objective, this invention uses a plywood with 7 layers, laminating 7 thin sheets of softwood so that the fiber directions of the 1st, 3rd, 5th, and 7th layers (first direction) and the fiber directions of the 2nd, 4th, and 6th layers (second direction) are perpendicular to each other, and forming a plurality of first grooves on the back surface of the plywood that extend in the second direction from the back surface to the 2nd layer, and a plurality of second grooves that extend in the first direction perpendicular to the second direction from the back surface to the 4th layer.

[0008] Specifically, the first invention is a flooring material base material in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of a plywood, wherein the plywood is a softwood plywood having 1 to 7 layers made of 7 softwood veneers that are sequentially laminated and bonded together from the surface side to the back side so that the fiber directions of adjacent sheets are perpendicular to each other, and on the back surface of the plywood, a plurality of first grooves extending in a second direction perpendicular to the 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, and the first grooves extend from one end to the other in the second direction of the plywood The groove extends, and its bottom is located within the second layer. The second groove extends from one end to the other in the first direction of the plywood, and its bottom is located within one of the third to fifth layers. The first to third layers decrease in thickness and increase in density in the order of the third, second, and first layers. The fifth to seventh layers decrease in thickness and increase in density in the order of the fifth, sixth, and seventh layers. The thickness of the first and seventh layers is less than or equal to the thickness of the surface reinforcement layer, and the thickness of the third and fifth layers is greater than the thickness of the surface reinforcement layer.

[0009] In the first invention, the number of layers of plywood is set to 7, and multiple first grooves are formed on the back surface of the plywood to a depth that extends from the back surface to the second layer. Plywood with 3 or 5 layers is often used as a base material for flooring, but in the first invention, the number of layers of plywood is set to 7, so the number of areas bonded with adhesive (between each layer made of softwood veneer) is increased compared to 3-ply or 5-ply plywood, thus improving its strength. In addition, because the number of layers of plywood is set to 7, the first grooves that extend from the back surface to the second layer are deeper than when the first grooves are similarly formed in 3-ply or 5-ply plywood. As a result of these deep, multiple first grooves, the rigidity of the plywood is reduced and its flexibility is increased, making it easier to absorb impact forces. Furthermore, in the first invention, multiple second grooves are formed on the back surface of the plywood, not only in the first groove but also in a direction perpendicular to the extension direction of the first groove (second direction) (first direction). By forming these second grooves, the rigidity of the plywood is reduced and its flexibility is increased compared to when only the first groove is formed, making it easier to absorb impact forces. In other words, when using the flooring material base material according to the first invention, the flooring material will have the required sound insulation performance and excellent soundproofing properties.

[0010] Furthermore, in the first invention, the multiple first grooves extending in a direction perpendicular to the fiber direction (first direction) of the first layer of the plywood (second direction) do not reach the first layer, so the fibers of the first layer are not cut. With this configuration, in the first invention, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the first direction due to moisture absorption or release, the expansion and contraction is suppressed by the fibers of the first layer extending in the first direction. As a result, the base material for the flooring material is less likely to expand or contract in the first direction due to moisture absorption or release, and warping in the first direction is suppressed.

[0011] Furthermore, in the first invention, the multiple second grooves extending in a direction perpendicular to the fiber direction (second direction) of the second layer (first direction) do not reach the second layer, so the fibers of the second layer extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the medium-density fiberboard bonded to the surface of the plywood, are not cut. With this configuration, in the first invention, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer extending in the second direction. As a result, the base material for the flooring becomes less likely to expand or contract in the second direction due to moisture absorption or release, and warping in the second direction is suppressed. In other words, according to the base material for the flooring of the first invention, not only is warping in the fiber direction (first direction) of the first layer suppressed, but warping in the direction perpendicular to it (second direction) is also suppressed.

[0012] Furthermore, in the first invention, the plywood becomes thinner and denser from the middle of the thickness direction towards the outermost layer. This configuration improves the surface strength of the base material for flooring.

[0013] As described above, according to the first invention, even when using softwood plywood, it is possible to provide a soundproofing base material for flooring that is less prone to warping and is applicable to flooring for underfloor heating.

[0014] The second invention is characterized in that, in the first invention, the softwood veneers constituting the first, third, fifth, and seventh layers are made from a single veneer, whereas the softwood veneers constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction, and the second layer does not have any knots that are larger in size in the first direction than the first groove spacing.

[0015] In the second invention, each layer of the plywood is made of softwood veneer. Softwood has more knots than hardwood, but if the softwood veneer making up the second layer has a knot that is larger in the first direction than the groove spacing of the first groove (first groove spacing), the fibers of the second layer that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the medium-density fiberboard, will be cut by the knot. As a result, it will not be able to counteract the dimensional changes due to moisture absorption or release of the medium-density fiberboard, and there is a risk that warping will occur partially in the second direction. However, according to the second invention, there are no knots in the second layer that are larger in the first direction than the groove spacing of the first groove, so it can be expected that warping in the second direction will be suppressed.

[0016] The third invention is characterized in that, in the second invention, the first layer is made up of parts of a conifer that are free of knots or parts of a conifer that are free of knots and the knots are filled with putty, and the second layer is made up of parts of a conifer that are free of knots or parts of a conifer that are free of knots and the knots are filled with wood filler, and the knots are also free of knots.

[0017] The inventors of this application conducted verification tests on the correlation between the presence or absence of knots in the first to third layers of plywood and the Brinell hardness of the flooring surface. The verification tests revealed that if there are knots in the first or second layer, which constitute the surface layer of the plywood, the Brinell hardness of the flooring surface falls below the desired hardness. However, even if there are knots in the third layer, if there are no knots in the first and second layers, the Brinell hardness of the flooring surface will be above the desired hardness. In other words, it was found that if flooring is formed with knots in the first and second layers of plywood, the flooring may become easily damaged. Furthermore, the presence of knots in the first and second layers, which constitute the surface layer of the plywood, may worsen the surface quality of the flooring and lead to a decrease in the aesthetic appeal of the flooring. In particular, when using a thin (e.g., 1.5 mm or less) medium-density fiberboard as a surface reinforcement layer to minimize the effects of warping, if there are knots near the surface of the plywood, the effects of the knots (such as unevenness) will be exposed through the thin medium-density fiberboard surface reinforcement layer to the decorative material, increasing the risk of degrading the aesthetic appeal of the flooring.

[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 made to disappear so that there are no knots. 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 so that there are no knots. Note that the burying wood treatment refers to a process 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 materials is made difficult to be damaged and has good surface properties. Therefore, by using the base material for floor materials 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 uses hardwood xylem fibers as the main raw material.

[0020] In the fourth invention, since the tracheary element fibers of coniferous trees have a significantly higher porosity and water absorption rate than the hardwood xylem fibers, a medium-density fiberboard (hardwood MDF) using hardwood xylem fibers as the main raw material 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 materials, a concave groove part serving as a female tenon is formed in the middle part in the thickness direction, and on the other, a convex rib part serving as a male tenon is formed in the middle part in the thickness direction. In the base material for floor materials, 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, the main 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 joints are formed so as to necessarily straddle a plurality of layers of the plywood. Although the convex portions of the female and male joints are brittle and easily chipped, 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 a flooring material in which the convex portions of the female and male joints are less likely to chip.

[0023] The sixth invention is characterized in that, in the fifth invention, the female joint 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 joint is formed such that the groove bottom corner of the concave groove portion of the female joint 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 joint 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 joint is inserted, but according to the above configuration, such peeling can be suppressed.

[0025] The seventh invention is a flooring material comprising a base material for a 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 a flooring material according to any one of the first to sixth inventions.

[0026] According to the seventh invention, by providing a base material for a 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 flooring comprising a base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, and a cushioning material bonded to the back surface of the base material for flooring, comprising a plywood forming step of sequentially laminating seven softwood slabs of equal thickness with a water-based adhesive interposed between each and with the fiber directions of each slab perpendicular to that of adjacent softwood slabs, and then hot-pressing in the thickness direction to form the plywood having the first to seventh layers made of the softwood slabs that are sequentially laminated and bonded together from the front side to the back side, and after sanding the surface of the plywood, bonding the surface reinforcement layer to the surface to form the flooring material The method comprises a surface reinforcement layer bonding step for a base material, a groove processing step for forming a plurality of first grooves on the back surface of the plywood at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer, and a plurality of second grooves extending in the first direction at a second groove interval, and a cushioning material bonding step for bonding a cushioning material to the back surface of the plywood after the groove processing step, wherein the first grooves extend from one end to the other in the second direction of the plywood, with the groove bottom located within the second layer, and the second grooves extend from one end to the other in the first direction of the plywood, with the groove bottom located within any of the third to fifth layers.

[0028] In the eighth invention, multiple first grooves are formed on the back surface of a 7-ply plywood, with a depth that extends from the back surface to the second layer. While 3-ply or 5-ply plywood is commonly used as a base material for flooring, the eighth invention uses 7-ply plywood, which increases the number of areas bonded with water-based adhesive (between layers of each layer made of softwood veneer) compared to 3-ply or 5-ply plywood, thus improving its strength. Also, because the plywood has 7 layers, the first grooves extending from the back surface to the second layer are deeper than when the same first grooves are formed in 3-ply or 5-ply plywood. These deep, multiple first grooves reduce the rigidity of the plywood, increase its flexibility, and make it easier to absorb impact forces. Furthermore, in the eighth invention, multiple second grooves are formed on the back surface of the plywood, not only in the first grooves but also in a direction (first direction) perpendicular to the extension direction (second direction) of the first grooves. By forming the second groove in this way, the rigidity of the plywood is reduced and its flexibility is increased compared to when only the first groove is formed, making it easier to absorb impact forces. In other words, according to the eighth invention, it is possible to provide a flooring material that has the required sound insulation performance and excellent soundproofing properties.

[0029] Furthermore, in the eighth invention, multiple first grooves extending in a direction perpendicular to the fiber direction (first direction) of the first layer of the plywood (second direction) do not reach the first layer, so that the fibers of the first layer are not cut by the first grooves. By forming the first grooves in this way, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the first direction due to moisture absorption or release, the expansion and contraction is suppressed by the fibers of the first layer extending in the first direction. As a result, it is possible to manufacture flooring material that is less likely to expand or contract in the first direction due to moisture absorption or release, and is less likely to warp in the first direction.

[0030] Furthermore, in the eighth invention, multiple second grooves extending in a direction perpendicular to the fiber direction of the second layer (second direction) (first direction) do not reach the second layer, so that the fibers of the second layer extending in the second direction, which can resist dimensional changes due to moisture absorption or release of the medium-density fiberboard, are not cut by the second grooves. By forming the second grooves in this way, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer extending in the second direction. As a result, it is possible to manufacture flooring that is less prone to expansion or contraction in the second direction due to moisture absorption or release, and is less prone to warping in the second direction. In other words, according to the eighth invention, it is possible to manufacture flooring that is less prone to warping not only in the fiber direction of the first layer (first direction) but also in the direction perpendicular to it (second direction).

[0031] Furthermore, in the eighth invention, while plywood with a typical 3-ply or 5-ply lamination count is often used as a base material for flooring, the plywood is made with 7 plies and bonded with a water-based adhesive. As a result, in the eighth invention, the laminated body of softwood veneers is hot-pressed with a higher moisture content compared to when forming 3-ply or 5-ply plywood, and the resulting plywood becomes thinner and denser from the middle of the thickness direction towards the outermost layer. According to the eighth invention, by using plywood with such a configuration, it is possible to provide flooring with excellent surface strength.

[0032] As described above, according to the eighth invention, even when using softwood plywood, it is possible to provide a flooring material that is less prone to warping and has excellent sound insulation properties, making it suitable for use as flooring for underfloor heating.

[0033] The ninth invention is characterized in that, in the eighth invention, the softwood veneers constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood veneers constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction, and the second layer is made without knots, with the size in the first direction being larger than the first groove spacing.

[0034] In the ninth invention, seven thin sheets of softwood are laminated together to form plywood. Although softwood has more knots than hardwood, if the softwood sheet constituting the second layer has a knot that is larger in the first direction than the groove spacing of the first groove (first groove spacing), the fibers of the second layer that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the medium-density fiberboard, will be cut by the knot. As a result, the dimensional changes due to moisture absorption or release of the medium-density fiberboard cannot be counteracted, and there is a risk that warping will occur partially in the second direction. However, according to the ninth invention, since there are no knots in the second layer that are larger in the first direction than the groove spacing, it is expected that warping in the second direction will be suppressed.

[0035] The tenth invention is characterized in that, in the ninth invention, the first layer is made of parts of coniferous trees that are free of knots or parts of coniferous trees that are free of knots and the knots are filled with putty, and the second layer is made of parts of coniferous trees that are free of knots or parts of coniferous trees that are free of knots and the knots are filled with wood filler, thereby ensuring that the knots are free.

[0036] In the tenth invention, the first and second layers are constructed so as to be free of knots. Specifically, the first layer is made from parts of the conifer that are free of knots, or if it is made from parts of the conifer that are free of knots, the knots are filled in with putty to make it knot-free. Similarly, the second layer is made from parts of the conifer that are free of knots, or if it is made from parts of the conifer that are free of knots, the knots are filled in with wood filler to make it knot-free. In the tenth invention, by constructing the first and second layers in this way so as to be free of knots, the flooring material made using the flooring material base material becomes scratch-resistant and has a good surface finish. Therefore, by using the flooring material base material according to the tenth invention, it is possible to provide flooring material that is scratch-resistant and has a good surface finish.

[0037] The eleventh invention is characterized in that, in the eighth invention, the medium-density fiberboard is made primarily from wood fibers of hardwoods.

[0038] In the 11th invention, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate compared to the wood fibers of hardwoods, a medium-density fiberboard (hardwood MDF) made primarily from the wood of hardwoods is used as the surface reinforcement layer. By using hardwood wood fibers as the medium-density fiberboard constituting the surface reinforcement layer in this way, the water absorption rate of the surface reinforcement layer can be kept low, and dimensional changes can be suppressed.

[0039] The twelfth invention further comprises a tongue-and-groove processing step in which, in the eighth invention, a recessed groove portion that will serve as a female tongue is formed in the middle of the thickness direction on one of two opposing sides of the base material for flooring, and a protruding ridge portion that will serve as a male tongue is formed in the middle of the thickness direction on the other side, wherein in the tongue-and-groove processing step, the female tongue and the male tongue are formed such that the front protrusion adjacent to the front side of the recessed groove portion, the back protrusion adjacent to the back side of the recessed groove portion, and the protruding ridge portion each span multiple layers of the plywood.

[0040] In the 12th invention, tongue and groove joints are applied to the surrounding sides of the base material for flooring, and the female and male tongues are formed so that the protruding portions (front protrusions, back protrusions, and ridges) that extend outward from the female and male tongues always span multiple layers of plywood. The protruding portions of the female and male tongues are brittle and prone to chipping, but by configuring them to span multiple layers of plywood as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to the 12th invention, it is possible to provide flooring in which the protruding portions of the female and male tongues are less prone to chipping.

[0041] The 13th invention is characterized in that, in the 12th invention, the tongue and groove joint process is performed such that the groove bottom corner of the recessed groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers.

[0042] In the 13th invention, the female tongue and groove is processed so that the bottom corner of the groove portion of the female tongue and groove does not occupy an adhesive portion between any of the layers of the plywood, but is instead located within one of the layers. If the bottom corner of the groove portion of the female tongue and groove is located in an adhesive portion between the layers of the plywood, the plywood is more likely to delaminate between the layers where the groove bottom corner is located when the protruding portion of the male tongue and groove is inserted, but such delamination can be suppressed by processing it as described above. [Effects of the Invention]

[0043] As described above, according to the present invention, the number of layers of plywood is set to 7 plies, and a plurality of first grooves extending in a second direction from the back surface to the second layer and a plurality of second grooves extending in a first direction perpendicular to the second direction from the back surface to the fourth layer are formed on the back surface of the plywood. As a result, even when using softwood plywood, warping is less likely to occur, and a sound-insulating substrate for flooring that can be applied to flooring for underfloor heating is provided, as well as flooring equipped therewith and a method for manufacturing the flooring. [Brief explanation of the drawing]

[0044] [Figure 1] Figure 1 is a perspective view of the flooring material according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view of the flooring material in Figure 1 in the first direction. [Figure 3] Figure 3 is a cross-sectional view of the flooring material in Figure 1 in the second direction. [Figure 4] Figure 4 is a cross-sectional view showing the female tongue and groove of the flooring material shown in Figure 1. [Figure 5] Figure 5 is a cross-sectional view showing the male tongue of the flooring material in Figure 1. [Figure 6] Figure 6 shows the plywood forming process of the flooring material manufacturing method according to Embodiment 1. [Figure 7] Figure 7 is a table showing the test results for Test 2. [Figure 8] Figure 8 is a table showing the test results for Test 3. [Figure 9] Figure 9 is a table showing the test results for Test 4. [Figure 10] Figure 10 is a table showing the test results for Test 5. [Figure 11] Figure 11 is a table showing the test results for Test 6. [Figure 12] Figure 12 is a table showing the test results for Test 7. [Figure 13] Figure 13 is a table showing the test results for Test 8. [Modes for carrying out the invention]

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

[0046] Embodiment 1 of the Invention -Flooring material composition- The flooring material 1 is installed, for example, on top of floor heating panels in a building such as a house. As shown in Figures 1 to 3, the flooring material 1 is formed in a rectangular shape and comprises a base material (base material for flooring 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 flooring material 1 is formed to have dimensions of 1850 mm x 303 mm and a thickness of 10 mm to 16 mm. The size of the flooring material 1 can be changed as appropriate.

[0047] The decorative material 20 is formed from a resin decorative sheet with a thickness of approximately 0.1 mm to 0.2 mm. As the resin decorative sheet, resin films that contain almost no moisture, such as olefin resin film, PET (polyethylene terephthalate) resin film, and polyvinyl chloride resin film, can be used. The decorative material 20 is printed with, for example, wood grain, stone pattern, or abstract pattern. In addition to resin decorative sheets, decorative paper such as coated paper or resin-impregnated paper, or thin sheet materials such as wood veneer can also be used as the decorative material 20. The thickness of the decorative material 20 should be approximately 0.1 mm to 0.8 mm.

[0048] Any cushioning material 30 can be used as long as it has cushioning properties, but in this embodiment, the cushioning material 30 is made of polyurethane foam with a thickness of about 1 mm to 3 mm.

[0049] [Composition of the base material] The base material 10 comprises a plywood 11 and a surface reinforcing layer 12 bonded to the surface of the plywood 11. The base material 10 is formed in a rectangular shape in plan view, and by applying tongue and groove jointing, female tongues 13 and male tongues 14 are formed on the surrounding side surfaces.

[0050] <Detailed composition of plywood> The plywood 11 is a seven-layer softwood plywood with a structure formed by laminating and bonding together seven softwood vases with an adhesive in between. The plywood 11 comprises the first to seventh layers 11a to 11g, which consist of softwood vases arranged sequentially from the front to the back. Each layer 11a to 11g of the plywood 11 is made up of one or more veneers cut from a softwood log using a rotary lathe. Examples of softwood vases that can be used include cypress, cedar, larch, spruce, Japanese red pine, radiata pine, and spruce. In this embodiment, cypress vases are used.

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

[0052] The seven softwood veneers constituting the first to seventh layers 11a to 11g of the plywood 11 are of equal thickness and size. The thickness of the softwood veneers used in the plywood 11 is preferably 1.0 mm to 1.5 mm. A thickness of less than 1.0 mm is undesirable because it is difficult to stably cut from the log, and the cut veneers cannot maintain their flatness during drying, making it impossible to ensure sufficient strength for uniform adhesive application to both sides. On the other hand, a thickness of more than 1.5 mm is undesirable because it increases the likelihood of cracking on the back during cutting, and after lamination, a larger portion is compressed by heat and pressure without being reinforced with water-based adhesive, while the uncompressed portion has poor thermal conductivity. The size of the softwood veneers can be designed in various ways depending on the size of the flooring material 1. In this embodiment, for example, to manufacture a flooring material 1 with dimensions of 1850 mm x 303 mm, a softwood veneer measuring 1900 mm x 345 mm and with a thickness of 1.3 mm is used.

[0053] The softwood vases constituting the first layer 11a, the third layer 11c, the fifth layer 11e, and the seventh layer 11g (odd-numbered layers) are made up of a single veneer cut so that the fibers extend in the longitudinal direction (first direction) of the plywood 11. On the other hand, the softwood vases constituting the second layer 11b, the fourth layer 11d, and the sixth layer 11f (even-numbered layers) are made up by joining together multiple veneers cut so that the fibers extend in the width direction (second direction) of the plywood 11 in a direction perpendicular to the fiber direction (see Figure 6). The number of veneers to be joined is not particularly limited, but in this embodiment 1, the softwood vases constituting the even-numbered layers are made up by joining together two veneers.

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

[0055] While plywood with 3 or 5 layers is commonly used as a base material for flooring, the plywood 11 in this embodiment has 7 layers, which is more than usual. As will be described in detail later, the plywood 11 is formed by laminating 7 thin sheets of softwood with a water-based adhesive interposed between them and then hot-pressing them. As a result, the plywood 11 in this embodiment is hot-pressed with a higher moisture content than the 3 or 5-ply plywood commonly used as a base material for flooring. Therefore, the moisture content increases from the middle of the thickness direction towards the outermost layer, resulting in a thinner and denser material from the middle of the thickness direction towards the outermost layer. Furthermore, in the second and third layers, water-based adhesive is applied and impregnated on both sides, so they are hot-pressed with a high moisture content, resulting in greater compression, and the compressed state is fixed by the impregnated adhesive.

[0056] Specifically, in the plywood 11 of this embodiment, which uses a 1.3 mm thick softwood veneer, 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 almost uncompressed, maintaining their original thickness of 1.3 mm. In other words, the first to third layers 11a to 11c decrease in thickness and increase in density in the order of third layer 11c, second layer 11b, and first layer 11a. Similarly, the fifth to seventh layers 11e to 11g decrease in thickness and increase in density in the order of fifth layer 11e, sixth layer 11f, and seventh layer 11g. Furthermore, the thickness of the first layer 11a and the seventh layer 11g is less than or equal to the thickness of the surface strengthening layer 12 (1.2 mm in this embodiment), which will be described later, while the thickness of the third layer 11c to the fifth layer 11e is greater than the thickness of the surface strengthening layer 12.

[0057] (1st groove, 2nd groove) Multiple first grooves 41 and multiple second grooves 42 are formed on the back surface of the plywood 11. Both the first grooves 41 and the second grooves 42 are formed to improve the sound insulation of the flooring material 1. In addition, if the flooring material 1 is installed on top of a floor heating panel, the first and second grooves 41 and 42 also have the effect of making it easier for heat to be transferred uniformly to the surface of the flooring material 1.

[0058] The first groove 41 is a groove that extends from one end to the other in the width direction of the plywood 11. In this embodiment, the first groove 41 is formed to have a rectangular cross-sectional shape. The first groove 41 is formed to have a groove width of 1.0 mm or more and 2.0 mm or less, and a groove spacing (length between adjacent first grooves 41, first groove spacing) of 10 mm or more and 50 mm or less. In this embodiment, the first groove 41 is formed to have a groove width of 1.5 mm and a groove spacing of 10.2 mm. Furthermore, 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 that extends from one end to the other in the longitudinal direction of the plywood 11. In this embodiment, the second groove 42 is formed to have a rectangular cross-sectional shape. The second groove 42 is formed to have a groove width of 2.0 mm or more and 4.0 mm or less, and a groove spacing (length between adjacent second grooves 42, second groove spacing) of 35 mm or more and 100 mm or less. In this embodiment, the second groove 42 is formed to have a groove width of 3.0 mm and a groove spacing of 47 mm. Furthermore, the second groove 42 is formed to a depth (5.0 mm in Figure 3) where the groove bottom is located within one of the third to fifth layers 11c to 11e (in Figure 3, the fourth layer 11d).

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

[0061] <Detailed composition of the 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 / cm³. 3 More than 0.9g / cm 3The following medium-density fiberboard (MDF) is used and bonded to the surface of the plywood 11 with an adhesive. In this embodiment 1, the surface reinforcement layer 12 is made of hardwood MDF, which mainly consists of hardwood wood fibers. In this embodiment 1, the surface reinforcement layer 12 uses hardwood MDF with dimensions of 1850 mm x 303 mm and a thickness of 1.2 mm, and the corners of the top and side surfaces of the hardwood MDF are chamfered. Any adhesive may be used to bond to the plywood 11, but a soft adhesive such as a water-based vinyl urethane type may be used and laminated and integrated by cold-pressing, or a soft adhesive such as a water-based vinyl urethane type may be used and laminated and integrated by cold-pressing followed by hot-pressing. Alternatively, an anhydrous soft adhesive such as PUR hot melt may be used and laminated and integrated by hot-pressing.

[0062] <Detailed composition of the female and male fruits> As shown in Figures 4 and 5, the surrounding sides of the base material 10 are fitted with tongue and groove joints. Specifically, on one of the two opposing sides of the base material 10 (long sides 10a, 10a and short sides 10b, 10b), a female tongue and groove 13 is formed, and on the other side, a male tongue and groove 14 that can be fitted into the female tongue and groove 13 is formed.

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

[0064] The male part 14 is formed by cutting out the base material 10 such that the intermediate portion in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 becomes a protruding ridge portion 14a. The protruding ridge portion 14a is a projection that extends from one end to the other in the length direction of each side surface 10a, 10b. In this embodiment, the cross-sectional shape of the protruding ridge portion 14a is formed to be rectangular, but the cross-sectional shape of the protruding ridge portion 14a is not limited to this, and any shape that fits into the recessed groove portion 13a may be used.

[0065] The female joint 13 and male joint 14 are formed so that their outwardly protruding convex portions (front convex portion 13b and back convex portion 13c for the female joint 13, and convex ridge portion 14a for the male joint 14) span multiple layers of the plywood 11. Specifically, in this embodiment, the front convex portion 13b of the female joint 13 is formed to span two layers of the plywood 11, the first layer 11a and the second layer 11b. The back convex portion 13c of the female joint 13 is formed to span three layers of the plywood 11, from the fifth layer 11e to the seventh layer 11g. The convex ridge portion 14a of the male joint 14 is formed to span four layers of the plywood 11, from the second layer 11b to the fifth layer 11e.

[0066] With this configuration, the protruding portions 13b, 13c, and 14a of the female and male fruits 13 and 14 are brittle and prone to chipping. However, by configuring them to span multiple layers of the plywood 11 as described above, they will always include fibers extending in the longitudinal direction (first direction) and fibers extending in the width direction (second direction) of the flooring material 1, making them less prone to chipping.

[0067] Furthermore, in this embodiment, by forming the female tongue and groove 13 as described above, the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located within the layers of the plywood 11 rather than in the adhesive portion between the layers (in this embodiment, the groove bottom corner x on the front side is located within the second layer 11b, and the groove bottom corner x on the back side is located within the fifth layer 11e). If the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue and groove 14 is inserted, but with the above configuration, such peeling can be suppressed.

[0068] -Flooring material manufacturing method- The manufacturing method for flooring material 1 will be described below.

[0069] 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 formation process] The base material formation process S1 comprises a plywood formation process S11, a surface reinforcement layer bonding process S12, and a cutting process (groove processing process) S13.

[0071] First, the plywood forming process S11 is performed. In the plywood forming process S11, first, softwood logs are cut using a rotary lathe to a thickness of 1.3 mm and a length in the grain direction of 1900 mm, preparing four first veneers with a length of 1900 mm in the grain direction and a length of 345 mm in the direction perpendicular to the grain, and six second veneers with a length of 345 mm in the grain direction and a length of 950 mm in the direction perpendicular to the grain. The four first veneers are used to make four softwood slabs for the odd-numbered layers 11a, 11c, 11e, and 11g. In addition, two second veneers are joined together in the direction perpendicular to the grain to form three softwood slabs for the even-numbered layers 11b, 11d, and 11f (see Figure 6).

[0072] Here, for the softwood veneer for the second layer 11b, a second veneer without knots is used, whose size in the first direction is larger than the groove spacing of the first groove 41 (first groove spacing). Two such second veneers without large knots may be selected and joined together in a direction perpendicular to the fibers to form the softwood veneer for the second layer 11b, or three softwood veneers without large knots may be selected from the three softwood veneers formed for the even-numbered layers 11b, 11d, and 11f to form the softwood veneer for the second layer 11b. Alternatively, in order to ensure that the softwood veneer for the second layer 11b is free of large knots, softwood veneers for the second layer 11b and sixth layer 11f may be prepared separately from softwood veneers for the fourth layer 11d, and those without large knots may be used as the softwood veneers for the second layer 11b and sixth layer 11f. Alternatively, by using softwood slabs without large knots for all of the even-numbered layers 11b, 11d, and 11f, the softwood slab for the second layer 11b may also be made free of large knots.

[0073] In this embodiment 1, the first layer 11a and the second layer 11b that constitute the surface layer of the plywood 11 are constructed without knots. Here, "without knots" includes not only those constructed from parts of a coniferous log that are free of knots, but also those constructed from parts of a coniferous log that have knots, but in which the knots have been removed by a predetermined treatment. In this embodiment 1, the treatment for removing knots differs between the first layer 11a and the second layer 11b. In the first layer 11a, the knots are removed by a putty treatment in which putty is used to fill the knots. On the other hand, in the second layer 11b, the knots are removed by a wood filler treatment in which a hole containing the knot is cut out, and the hole is filled without gaps with wood of the same shape as the cut-out hole (wood filler). Furthermore, putty treatment may be performed after the plywood is formed, and wood inlay treatment may be performed when preparing the second veneer, or after joining the second veneers in a direction perpendicular to the fibers to form a softwood veneer for the second layer 11b.

[0074] As mentioned above, in order to ensure that the first layer 11a and the second layer 11b are free of knots, it would be ideal to use only knot-free portions of softwood veneers for the first to seventh layers 11a to 11g. However, this is not practical because softwood has many knots. It is preferable to prepare separate softwood veneers for the odd-numbered layers 11a, 11c, 11e, and 11g, and for the even-numbered layers 11b, 11d, and 11f, and to ensure that the softwood veneers for the even-numbered layers 11b, 11d, and 11f are free of knots by wood-filling treatment before plywood molding. This plywood manufacturing method makes it easy to procure materials and offers excellent workability, as only two types of softwood veneers need to be prepared.

[0075] Alternatively, softwood slabs for 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 slabs for the second layer 11b and the sixth layer 11f may be treated with wood inlay before plywood molding to ensure they are free of knots. This plywood manufacturing method requires the preparation of three types of softwood slabs, but since wood inlay treatment is only required for the softwood slabs for the second layer 11b and the sixth layer 11f, processing costs can be reduced. Furthermore, after plywood molding, regardless of which side of the plywood 11 is the front (first layer 11a side), the second layer 11b will be free of knots, eliminating the need to distinguish between the front and back of the plywood 11 and simplifying the manufacturing process.

[0076] Furthermore, softwood slabs for even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b and for the fourth layer 11d and sixth layer 11f. Only the softwood slab for the second layer 11b may be treated with wood inlay before plywood forming to ensure there are no missing knots. This plywood manufacturing method requires the preparation of three types of softwood slabs, but since only the softwood slab for the second layer 11b is subject to wood inlay treatment, processing costs can be minimized.

[0077] Next, the seven thin sheets of softwood prepared for layers 11a to 7 (11g) are laminated in the following order, with a water-based adhesive in between: layer 7 (11g), layer 6 (11f), layer 5 (11e), layer 4 (11d), layer 3 (11c), layer 2 (11b), and layer 1 (11a).

[0078] Specifically, first, a softwood veneer for the 7th layer (11g), the bottommost layer, is placed on top of a softwood veneer (1st veneer) for the 6th layer (11f), with water-based adhesive applied to both sides of the entire surface. Then, a softwood veneer for the 5th layer (11e), the 1st veneer, is placed directly on top of the softwood veneer for the 6th layer (11f), and a softwood veneer for the 4th layer (11d), the 2nd veneer, is placed on top of that, with water-based adhesive applied to both sides of the entire surface. Then, a softwood veneer for the 3rd layer (11c), the 1st veneer, is placed directly on top of the softwood veneer for the 4th layer (11d), and a softwood veneer for the 2nd layer (11b), the 2nd veneer, is placed on top of that, with water-based adhesive applied to both sides of the entire surface. Finally, the softwood veneer for the first layer 11a (first veneer) is placed directly on top of the softwood veneer for the second layer 11b.

[0079] As described above, seven thin sheets of softwood veneer are laminated and then hot-pressed in the lamination direction to form a bonded and integrated plywood 11. In this embodiment, since the number of layers of plywood 11 is set to seven and bonded with a water-based adhesive, the laminated softwood veneer is hot-pressed with a higher moisture content compared to when forming a three-ply or five-ply plywood. As a result, the formed plywood 11 becomes thinner and denser from the middle of the thickness direction towards the outermost layer.

[0080] After the plywood forming process S11, the surface reinforcement layer bonding process S12 is performed. As mentioned above, if the first veneer constituting the softwood thin board for the first layer 11a is made of wood with knots, a putty treatment is performed before the surface reinforcement layer bonding process S12 to fill the knots in the first layer 11a with putty to eliminate the knots.

[0081] In the surface reinforcement layer bonding process S12, first, the surface of the plywood 11 is sanded to make it smooth. Then, a surface reinforcement layer 12 made of hardwood MDF is bonded to the surface of the plywood 11. Specifically, an adhesive (for example, a flexible adhesive such as water-based vinyl urethane or an anhydrous flexible adhesive such as PUR hot melt) is applied to the surface of the plywood 11, and the surface reinforcement layer 12 is placed on top of it. Then, the plywood 11 and the surface reinforcement layer 12 are bonded together by pressing them in the lamination direction (cold press in the case of a flexible adhesive such as water-based vinyl urethane, and hot press in the case of anhydrous flexible adhesive such as PUR hot melt).

[0082] After the surface reinforcement layer bonding process S12, a cutting process S13 is performed. The cutting process S13 includes a groove machining process S14 and a tongue and groove machining process S15.

[0083] In the grooving process S14, a first groove 41 and a second groove 42 are formed on the back surface of the plywood 11 by cutting. The first groove 41 is a groove with a predetermined width of 1.0 mm to 2.0 mm (1.5 mm in this embodiment 1), a depth from the back surface of the plywood 11 to the second layer 11b (6.9 mm in this embodiment 1), and a rectangular cross-sectional shape extending in the width direction (second direction). Multiple such first grooves 41 are formed at predetermined pitches of 10 mm to 50 mm (10.2 mm pitch in this embodiment 1). The second groove 42 is a groove with a predetermined width of 2.0 mm to 4.0 mm (3.0 mm in this embodiment 1), a depth of 5.0 mm from the back surface of the plywood 11 to one of the third to fifth layers 11c to 11e (fourth layer 11d in Figure 3), and a rectangular cross-sectional shape extending in the length direction (first direction). Multiple such second grooves 42 are formed at predetermined pitches of 35 mm to 100 mm (47 mm pitch in this embodiment 1).

[0084] In the tongue and groove jointing process S15, female tongues and grooves 13 and male tongues and grooves 14 are formed on the surrounding sides of the plywood 11 (two long sides 10a and two short sides 10b) by cutting (tongue and groove jointing).

[0085] Specifically, the female joint 13 is formed by cutting out the base material 10 so that the middle portion in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 becomes a recessed groove 13a. At this time, the female joint 13 is formed so that the front side protrusion 13b and the back side protrusion 13c of the recessed groove 13a span multiple layers of the plywood 11. Specifically, the female joint 13 is formed so that the front side protrusion 13b spans two layers, the first layer 11a and the second layer 11b, and the back side protrusion 13c spans three layers, the fifth layer 11e to the seventh layer 11g. In addition, the female joint 13 is formed so that the groove bottom corner x of the recessed groove 13a is located within the layers of the plywood 11, rather than in the adhesive portion between layers (in this embodiment, the front groove bottom corner x is within the second layer 11b, and the back groove bottom corner x is within the fifth layer 11e).

[0086] Furthermore, a male joint 14 is formed by cutting out the base material 10 such that the intermediate portion in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 becomes a protruding ridge 14a. At this time, the male joint 14 is formed so that the protruding ridge 14a spans multiple layers of the plywood 11. Specifically, a female joint 13 is formed so that the protruding ridge 14a spans four layers from the second layer 11b to the fifth layer 11e.

[0087] As described above, in the base material formation process S1, the plywood formation process S11, the surface reinforcement layer bonding process S12, and the cutting process (groove processing process) S13 are performed to form the base material 10.

[0088] In the decorative material bonding step S2, the decorative material 20 (in this embodiment, a resin decorative sheet) is bonded to the surface of the substrate 10 (the surface of the surface reinforcement layer 12) formed in the substrate forming step S1 using an adhesive.

[0089] In the cushioning material bonding step S3, the cushioning material 30 (nonwoven fabric in this embodiment) is bonded to the back surface (back surface of the plywood 11) of the base material 10 formed in the base material forming step S1 using an adhesive.

[0090] The flooring material 1 is manufactured by performing the above-described base material formation process S1, decorative material bonding process S2, and cushioning material bonding process S3.

[0091] -test- The flooring material 1 according to this embodiment, manufactured as described above, was subjected to the following tests 1 to 8. Test 1 was a test to confirm the sound insulation and dimensional stability of the flooring material 1; Tests 2 to 4 were Brinell hardness tests to confirm the effect of missing knots on the surface hardness of the flooring material 1; Tests 5 and 6 were lightweight floor impact sound tests to confirm the effect of grooves on the sound insulation (sound-insulating performance) of the flooring material 1; Tests 7 and 8 were tests to confirm the effect of the groove depth of the second groove 42 on the width curvature (curvature in the second direction) of the flooring material 1; Test 7 was a wet-dry cycle test; and Test 8 was an 80°C heat endurance test.

[0092] [Test 1] Similar to flooring material 1, test specimens 1-1 to 1-3 measuring 470 mm x 918.5 mm were prepared, each equipped with a base material 10, decorative material 20, and cushioning material 30. Sound insulation tests and water absorption length change rate tests were conducted, and the lightweight floor impact sound and water absorption length expansion rate were measured. Test specimens 1-1 to 1-3 differ in the configuration of the base material 10, as follows. Note that test specimen 1-1 has the same configuration as flooring material 1 of this embodiment. Test specimen 1-2 is a modified version of flooring material 1 of this embodiment, with the plywood 11 replaced by 5-ply softwood plywood (cypress plywood). Test specimen 1-3 is a modified version of flooring material 1 of this embodiment, with the plywood 11 replaced by 5-ply lauan plywood.

[0093] The soundproofing test results showed that test specimen 1-1 had the best reduction in lightweight floor impact sound with center frequencies of 250Hz and 500Hz, while test specimen 2 had the worst reduction. In other words, it can be seen that flooring material 1 of this embodiment has superior soundproofing performance compared to flooring materials using 5-ply softwood plywood (cypress plywood) and flooring materials using lauan plywood.

[0094] Furthermore, the water absorption length change rate test showed no significant difference in the water absorption length change rate among test specimens 1-1 to 1-3. However, the warping in the length direction was smallest in test specimen 1-1 and largest in test specimen 1-2. Similarly, the warping in the width direction was smallest in test specimen 1-1 and largest in test specimen 1-2. In other words, it can be seen that the flooring material 1 of this embodiment is less prone to warping than flooring materials using 5-ply softwood plywood (cypress plywood) and flooring materials using lauan plywood.

[0095] [Exams 2-4] (Exam 2) Test specimens 2-1 to 2-8, each measuring 150 mm x 150 mm and equipped with a base material 10 and a decorative material 20, were prepared, and a Brinell hardness test was performed to measure their Brinell hardness.

[0096] Test specimens 2-1 to 2-8 each have a different composition of the base material 10. Specifically, in all test specimens 2-1 to 2-8, seven 150mm x 150mm, 1.3mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive as interposition, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and a decorative material 20 made of an olefin decorative sheet with a thickness of 0.14mm are attached to each surface in that order using a water-based vinyl urethane adhesive.

[0097] In test specimens 2-1 to 2-4, an artificial through-hole (simulating a knot) with a diameter of 30 mm was formed in the center of the softwood veneer constituting the second layer 11b, and the first layer 11a was constructed to be free of knots by applying putty. On the other hand, in test specimens 2-5 to 2-8, both the first layer 11a and the second layer 11b were constructed to be free of knots.

[0098] Furthermore, the thickness of the surface strengthening layer 12 was varied for each of the test specimens 2-1 to 2-4: 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, the thickness of the surface strengthening layer 12 was varied for each of the test specimens 2-5 to 2-8: 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 was measured at the center 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).

[0100] The results of Test 2 are shown in Figure 7. The Brinell hardness was 11 N / mm². 2 In the above cases, mark with "○", 9.8 N / mm 2 More than 11N / mm 2 Less than 9.8 N / mm 2 Values ​​less than the given value are indicated by "×". Based on the results of Test 2, when the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less), as in flooring material 1 of this embodiment, if there are knots (through holes in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness will be the value required for flooring material 1 (11 N / mm²). 2 It was found that it would not reach ).

[0101] (Exam 3) Similar to flooring material 1, 150mm x 150mm test specimens 3-1 to 3-8 were prepared, each comprising a base material 10, a decorative material 20, and a cushioning material 30. A Brinell hardness test was then conducted, and the Brinell hardness was measured. Test specimens 3-1 to 3-8 are the same as those in test specimens 2-1 to 2-8, but with the thickness of the softwood veneers constituting the first layer 11a and the seventh layer 11g of the plywood 11 changed to 1.7mm. The other components are the same as those in test specimens 2-1 to 2-8.

[0102] The results of Test 3 are shown in Figure 8, and were the same as the results of Test 2 shown in Figure 7. In other words, from the results of Tests 2 and 3, when the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm to 1.3 mm), as in the flooring material 1 of this 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 flooring material 1 (11 N / mm²). 2 The result was not reached, and it was found that increasing the thickness of the first layer 11a of the plywood 11 did not have a significant effect on the Brinell hardness.

[0103] (Exam 4) Similar to the flooring material 1, test specimens 4-1 to 4-6 with dimensions of 150 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and Brinell hardness tests were 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 at 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 at the center of the softwood thin plate constituting the third layer 11c. The first layer 11a and the second layer 11b were both 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, similar to 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 (11 N / mm 2 ) required for the flooring material 1. 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 is a knot (through-hole in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness will not reach the value (11 N / mm 2 ) required for the flooring material 1. 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 is a knot in the third layer 11c, it will not have an adverse effect on the Brinell hardness of the surface.

[0105] [Tests 5 to 7] (Test 5) Test specimens 5-1 to 5-16 with dimensions 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. [[ID=1Test specimens 5-1 to 5-16 each have a different composition of the base material 10. Specifically, test specimens 5-1 to 5-16 differ in the configuration (presence or absence and depth) of the second groove 42 and the thickness of the surface reinforcement layer 12, while the other components are the same as those of flooring material 1. To prepare test specimens 5-1 to 5-16, first, seven 1.3 mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are attached to each surface in that order using a water-based vinyl urethane adhesive, and then the plywood is cut into 900 mm x 150 mm pieces. Tongue and groove joints are applied to the four sides of the cut plywood 11 to form female and male joints 13 and 14. Furthermore, test specimens 5-1 to 5-16 are prepared by forming the first and second grooves 41, 42 or only the first groove 41 on the back surface of the plywood 11 (the back surface of the seventh layer 11g), and then attaching a cushioning material 30 made of a 3 mm thick foamed cushioning material to cover the entire back surface.

[0107] Test specimens 5-1 to 5-4 have only the first groove 41 formed on the back surface of the plywood 11, and no second groove 42 formed. Test specimens 5-5 to 5-16 have both the first groove 41 and the second groove 42 formed on the back surface of the plywood 11. The first groove 41 formed in test specimens 5-1 to 5-16 has a groove width of 1.5 mm, a groove spacing of 10.2 mm, and a depth (groove bottom thickness of 2.6 mm) such that the groove bottom is located within the second layer 11b, similar to flooring material 1. The second grooves 42 formed in test specimens 5-5 to 5-16 shall have a groove width of 3.0 mm and a groove spacing of 47 mm, similar to flooring material 1. However, the depth shall be such that in test specimens 5-5 to 5-8 the groove bottom is located within the third layer 11c (groove bottom thickness 3.7 mm), in test specimens 5-9 to 5-12 the groove bottom is located within the fourth layer 11d (groove bottom thickness 5.0 mm), and in test specimens 5-13 to 5-16 the groove bottom is located within the fifth layer 11e (groove bottom thickness 6.3 mm).

[0108] In addition, for test specimens 5-1 to 5-16, the first layer 11a was treated with putty to ensure it was free of knots, and the even-numbered layers 11b, 11d, and 11f were treated with wood inlay to ensure they were free of knots.

[0109] Furthermore, the thickness of the surface reinforcement layer 12 was varied for test specimens 5-1 to 5-4, with 1.0 mm for test specimen 5-1, 1.3 mm for test specimen 5-2, 1.5 mm for test specimen 5-3, and 2.7 mm for test specimen 5-4. Similarly, the thickness of the surface reinforcement layer 12 was varied for test specimens 5-5 to 5-8, test specimens 5-9 to 5-12, and test specimens 5-13 to 5-16, with 1.0 mm for test specimens 5-5, 5-9, and 5-13, 1.3 mm for test specimens 5-6, 5-10, and 5-14, 1.5 mm for test specimens 5-7, 5-11, and 5-15, and 2.7 mm for test specimens 5-8, 5-12, and 5-16.

[0110] The lightweight floor impact sound test was conducted in accordance with the test method described in JIS A 1440-1 "Method for measuring the reduction in floor impact sound levels of floor finishing structures on concrete floors in laboratories," specifically the "Method using a standard lightweight impact source," and the reduction in lightweight floor impact sound levels for test specimens 5-1 to 5-16 was measured.

[0111] The results of Test 5 are shown in Figure 10. A reduction in the lightweight floor impact sound level of 125Hz to 500Hz of ΔLL-4 or more is indicated by "○", equivalent to ΔLL-3 is indicated by "△", and less than ΔLL-3 is indicated by "×". From the results of Test 5, it was found that even if the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm to 1.3 mm), as in the flooring material 1 of this embodiment, if the second groove 42 is not formed, the flexibility of the flooring material 1 will be insufficient, making it difficult to absorb impact force, resulting in a flooring material 1 that lacks sound insulation performance and does not have the required sound insulation performance. Furthermore, it was found that if the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm and the depth of the second groove 42 is set so that the bottom of the groove is located within one of the third to fifth layers 11c to 11e, a flooring material 1 with the required sound insulation performance and excellent sound insulation performance can be obtained. Although not shown in Figure 10, it was found that increasing the depth of the second groove 42 improved the sound insulation performance.

[0112] (Exam 6) Test specimens 6-1 to 6-12, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared, and lightweight floor impact sound tests were conducted to measure the reduction in sound from 125 Hz to 500 Hz. Test specimens 6-1 to 6-12 are the same as those in test specimens 5-1 to 5-12, but with the thickness of the softwood veneers constituting the first layer 11a and the seventh layer 11g of the plywood 11 changed to 1.7 mm. The other components are the same as those in test specimens 5-1 to 5-12.

[0113] The results of Test 6 are shown in Figure 11, and in all of the test specimens 6-1 to 6-12, the surface Brinell hardness was the value required for flooring material 1 (11 N / mm²). 2 ) became less than ). In other words, from the results of tests 5 and 6, it was found that even if the thickness of the surface reinforcement 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 this embodiment, if the first layer 11a of the plywood 11 is thick, the rigidity in the longitudinal direction (first direction) of the flooring material 1 increases, resulting in a flooring material 1 that does not have the required sound insulation performance and lacks soundproofing.

[0114] [Tests 7, 8] (Exam 7) Test specimens 7-1 to 7-8, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared. A wet-dry cycle test was performed, and the degree of warping in the width direction (second direction) was observed visually.

[0115] Test specimens 7-1 to 7-8 each have a different composition of the base material 10. Specifically, test specimens 7-1 to 7-8 differ in the configuration (depth) of the second groove 42 and the thickness of the surface reinforcement layer 12, while the other components are the same as those of flooring material 1. To prepare test specimens 7-1 to 7-8, first, seven 1.3 mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are attached to each surface in that order using a water-based vinyl urethane adhesive, and then the plywood is cut into 900 mm x 150 mm pieces. Tongue and groove joints are applied to the four sides of the cut plywood 11 to form female and male joints 13 and 14. Furthermore, test specimens 7-1 to 7-8 are prepared by forming first and second grooves 41 and 42 on the back surface of the plywood 11 (the back surface of the 7th layer 11g), and then attaching a cushioning material 30 made of a 3mm thick foamed cushioning material to cover the entire back surface.

[0116] The first grooves 41 formed in test specimens 7-1 to 7-8 shall have a groove width of 1.5 mm, a groove spacing of 10.2 mm, and a depth such that the groove bottom is located within the second layer 11b (groove bottom thickness of 2.6 mm), similar to flooring material 1. The second grooves 42 formed in test specimens 7-1 to 7-8 shall have a groove width of 3.0 mm and a groove spacing of 47 mm, similar to flooring material 1. However, the depth shall be such that in test specimens 7-1 and 7-2 the groove bottom is located within the second layer 11b (groove bottom thickness 1.6 mm), in test specimens 7-3 and 7-4 the groove bottom is located within the third layer 11c (groove bottom thickness 3.7 mm), in test specimens 7-5 and 7-6 the groove bottom is located within the fourth layer 11d (groove bottom thickness 5.0 mm), and in test specimens 7-7 and 7-8 the groove bottom is located within the fifth layer 11e (groove bottom thickness 6.3 mm).

[0117] In addition, for test specimens 7-1 to 7-8, the first layer 11a was treated with putty to ensure it was free of knots, and the even-numbered layers 11b, 11d, and 11f were treated with wood inlay to ensure they were free of knots.

[0118] Furthermore, the thickness of the surface reinforcing layer 12 was varied for test specimens 7-1 and 7-2, with 1.0 mm for test specimen 7-1 and 1.3 mm for test specimen 7-2. Similarly, the thickness of the surface reinforcing layer 12 was varied for test specimens 7-3, 7-4, 7-5, 7-6, and 7-7, 7-8, with 1.0 mm for test specimens 7-3, 7-5, and 7-7, and 1.3 mm for test specimens 7-4, 7-6, and 7-8.

[0119] The wet-dry cycle test involved placing the specimens under two conditions: 40°C and 90% relative humidity (moisture absorption) and 20°C and 40% relative humidity (moisture release) for 48 hours each. After two cycles of this process, the degree of warping in the width direction (second direction) of specimens 7-1 to 7-8 was observed visually.

[0120] The results of Test 7 are shown in Figure 12. A circle (○) indicates acceptable warping in the width direction (second direction), while a cross (×) indicates significant warping in the width direction (second direction) that is unacceptable. From the results of Test 7, it was found that if the depth of the second groove 42 is such that the groove bottom is located within one of the third to fifth layers 11c to 11e (groove bottom thickness of 3.7 mm or more), the warping in the width direction (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 (groove bottom thickness of 1.6 mm), the warping in the width direction becomes unacceptable. Furthermore, there was no significant difference in the degree of warping in the width direction between test specimens 7-3, 7-5, and 7-7, nor was there a significant difference in the degree of warping in the width direction between test specimens 7-4, 7-6, and 7-8.

[0121] (Exam 8) Test specimens 8-1 to 8-8, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared and subjected to an 80°C heat endurance test. The degree of warping in the width direction (second direction) was observed visually. Test specimens 8-1 to 8-8 were constructed in the same manner as test specimens 7-1 to 7-8.

[0122] The 80°C heat endurance test was conducted by drying test specimens 8-1 to 8-8 in an 80°C dryer for 48 hours until they were completely dry, and then visually observing the degree of warping in the width direction (second direction).

[0123] The results of Test 8 are shown in Figure 13, and were the same as those of Test 7. The results of Test 8 also showed that if the depth of the second groove 42 is set so that the groove bottom is located within one of the third to fifth layers 11c to 11e (groove bottom thickness of 3.7 mm or more), the curvature in the width direction (second direction) is acceptable. However, if the depth of the second groove 42 is set so that the groove bottom is located within the second layer 11b (groove bottom thickness of 1.6 mm), the curvature in the width direction becomes unacceptably large. In addition, in Test 8, the curvature in the width direction differed slightly between test specimens 8-3, 8-5, and 8-7, and between test specimens 8-4, 8-6, and 8-8, and the curvature in the width direction increased as the depth of the second groove 42 increased. In other words, it was found that the shallower the depth of the second groove 42 (the thicker the groove bottom), the less likely warping in the width direction due to heat drying is to occur, making it suitable for flooring materials used with underfloor heating.

[0124] -Effects of the embodiment- In the flooring material base material 10 of this embodiment, the number of layers of plywood 11 is set to 7 plies, and multiple first grooves 41 are formed on the back surface of the plywood 11 to a depth that extends from the back surface to the second layer 11b. Plywood with 3 or 5 layers is often used as a base material for flooring, but in this embodiment, the number of layers of plywood 11 is set to 7 plies, so the number of areas bonded with adhesive (between each layer made of softwood veneer) is increased compared to 3-ply plywood or 5-ply plywood, thus improving the strength compared to 3-ply plywood or 5-ply plywood. In addition, because the number of layers of plywood 11 is set to 7 plies, the first grooves 41 that extend from the back surface to the second layer 11b are deeper than when the first grooves 41 are similarly formed in 3-ply plywood or 5-ply plywood. Due to these multiple deep first grooves 41, the rigidity of the plywood 11 is reduced and its flexibility is increased, making it easier to absorb impact forces. Furthermore, in this embodiment, in addition to the first groove 41, a plurality of second grooves 42 are formed on the back surface of the plywood 11 in a direction perpendicular to the extension direction (second direction) of the first groove 41 (first direction). By forming the second grooves 42 in this way, the rigidity of the plywood 11 is reduced and its flexibility is increased compared to the case where only the first groove 41 is formed, making it easier to absorb impact forces. In other words, by using the flooring material base material 10 of this embodiment, the required sound insulation performance of the flooring material 1 is improved, resulting in superior soundproofing.

[0125] Furthermore, in this embodiment 1, the multiple first grooves 41 extend in a direction perpendicular to the fiber direction (first direction) of the first layer 11a of the plywood 11 (second direction), and these multiple first grooves 41 do not reach the first layer 11a, so the fibers of the first layer 11a are not cut. With this configuration, in this embodiment 1, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the first direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the first layer 11a extending in the first direction. As a result, the base material 10 for flooring becomes less likely to expand or contract in the first direction due to moisture absorption or release, and warping in the first direction is suppressed.

[0126] Furthermore, in this embodiment, the multiple second grooves 42 extending in a direction perpendicular to the fiber direction (second direction) of the second layer 11b (first direction) have their groove bottoms within 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 withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11, are not cut. With this configuration, in this embodiment 1, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for flooring becomes less likely to expand or contract in the second direction due to moisture absorption or release, and warping (width warping) in the second direction is suppressed. In other words, according to the flooring material base material 10 of this embodiment, not only is the warping of the first layer 11a in the fiber direction (first direction) suppressed, but the warping in the direction perpendicular to it (second direction) is also suppressed.

[0127] Furthermore, in Figure 3 of this embodiment 1, the second groove 42 is formed such that its bottom is located within the fourth layer 11d, and the second groove 42 does not reach the third layer 11c. As a result, the fibers of the second layer 11b extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, are not cut. Moreover, because the second layer 11b is covered by the first layer 11a and the third layer 11c, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion and contraction are further suppressed by the fibers of the second layer 11b extending in the second direction. This makes it possible to provide a flooring material 1 that is less prone to warping in the second direction, as the base material 10 for flooring material is less likely to expand or contract in the second direction due to moisture absorption or release.

[0128] Furthermore, the inventors of this application conducted verification tests (Tests 5, 7, and 8) on the correlation between the depth of the second groove 42 and the sound insulation performance and warping of the flooring material 1. The results of the verification tests showed that the deeper the second groove 42, the better the sound insulation performance, but the more likely warping in the second direction was to occur. It was also found that when the bottom of the second groove 42 is located within the third to fifth layers 11c to 11e, it is possible to form a flooring material 1 that has the required sound insulation performance while being less prone to warping in the second direction. In particular, from the viewpoint of sound insulation performance and warping, it is preferable that the bottom of the second groove 42 is located within the fourth layer 11d. Therefore, in the example shown in Figure 3 of this embodiment 1, the second groove 42 is formed to a depth where the bottom of the groove is located within the fourth layer 11d. Accordingly, according to the example shown in Figure 3 of this embodiment 1, it is possible to provide a flooring material 1 that is less prone to warping and has excellent sound insulation properties, making it suitable for floor heating.

[0129] Furthermore, in this embodiment, the plywood 11 becomes thinner and denser from the middle of the thickness direction towards the outermost layer. This configuration improves the surface strength of the flooring base material 10.

[0130] As described above, according to this embodiment, even when using softwood plywood, it is possible to provide a flooring base material 10 that is less prone to warping and has excellent sound insulation properties, making it suitable for use as flooring for underfloor heating.

[0131] Furthermore, in this embodiment, each layer 11a to 11g of the plywood 11 is made of softwood veneer. Although softwood has more knots than hardwood, if the softwood veneer constituting the second layer 11b has a knot in the first direction that is larger than the groove spacing of the first groove 41 (first groove spacing), the fibers of the second layer 11b that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, will be cut by the knot. As a result, it will not be able to counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, and there is a risk that warping will occur partially in the second direction. However, according to this embodiment 1, since the second layer 11b does not have a knot in the first direction that is larger than the first groove spacing, it is expected that warping in the second direction will be suppressed. The second layer 11b is made of thin softwood veneers formed by joining multiple veneers (two in this embodiment) 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 large veneers without large knots, but it is relatively easy to prepare relatively small veneers without large knots for use in the second layer 11b. Therefore, according to this embodiment, a base material 10 for flooring that can be expected to suppress warping in the second direction can be provided relatively easily.

[0132] Furthermore, the inventors of this application conducted verification tests (Tests 2-4) to examine the correlation between the presence or absence of knots in the first to third layers 11a-11c of the plywood 11 and the Brinell hardness of the surface of the flooring material 1. The results of the verification tests showed that if there are knots in the first or second layers 11a, 11b that constitute the surface layer of the plywood 11, the Brinell hardness of the surface of the flooring material 1 falls below 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, the Brinell hardness of the surface of the flooring material 1 is above the desired hardness. In other words, it was found that if the flooring material 1 is formed with knots in the first and second layers 11a, 11b of the plywood 11, the flooring material 1 may be prone to damage. Furthermore, if there are knots in the first and second layers 11a and 11b that form the surface of the plywood 11, it may worsen the surface quality of the flooring material 1 and lead to a decrease in the aesthetic appeal of the flooring material 1. In particular, when a thin (for example, about 1.5 mm) medium-density fiberboard is used as the surface reinforcement layer 12 in order to minimize the effect of warping, if there are knots near the surface, the effect of the knots (unevenness, etc.) will be expressed through the thin medium-density fiberboard surface reinforcement layer 12 to the decorative material 20, increasing the likelihood of a decrease in the aesthetic appeal of the flooring material 1.

[0133] Therefore, in this embodiment 1, the first and second layers 11a and 11b are constructed so as to be free of knots. Specifically, the first layer 11a is constructed from parts of the conifer that are free of knots, or if it is constructed from parts of the conifer that are free of knots, the knots are filled in with putty to make them disappear. Similarly, the second layer 11b is constructed from parts of the conifer that are free of knots, or if it is constructed from parts of the conifer that are free of knots, the knots are filled in with wood filler to make them disappear. In this embodiment 1, by constructing the first and second layers 11a and 11b so as to be free of knots, the flooring material produced using the flooring material base material 10 is made to be resistant to scratches and to have good surface properties. The surface properties of the flooring material 1 are not deteriorated. Therefore, according to this embodiment 1, a flooring material base material 10 that does not deteriorate the surface properties of the flooring material 1 can be provided relatively easily.

[0134] Furthermore, in this embodiment 1, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate compared to the wood fibers of hardwood trees, a medium-density fiberboard (hardwood MDF) made primarily from hardwood wood fibers is used as the surface reinforcement layer 12. By using hardwood wood fibers as the medium-density fiberboard constituting the surface reinforcement layer 12 in this way, the water absorption rate of the surface reinforcement layer 12 can be kept low, and dimensional changes can be suppressed.

[0135] Furthermore, in this embodiment, tongue and groove joints are applied to the surrounding sides of the flooring base material 10, and the female tongue and groove 13 and male tongue and groove 14 are formed such that the protruding portions (front side protrusion 13b, back side protrusion 13c, and protruding ridge portion 14a) that protrude outward from the female tongue and groove 13 and male tongue and groove 14 always span multiple layers of the plywood 11. The protruding portions 13b, 13c, and 14a of the female tongue and groove 13 and male tongue and groove 14 are brittle and prone to chipping, but by configuring them to span multiple layers of the plywood 11 as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to this embodiment, it is possible to provide a flooring base material 10 in which the protruding portions 13b, 13c, and 14a of the female tongue and groove 13 and male tongue and groove 14 are less prone to chipping.

[0136] Furthermore, in this embodiment, the female tongue 13 is formed so that the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located within one of the layers, so as not to be located in the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue 14 is inserted, but with the above configuration, such peeling can be suppressed.

[0137] Furthermore, according to this embodiment, by providing the above-mentioned base material 10 for flooring, it is possible to provide a flooring material 1 that is less prone to warping even when using softwood plywood and has excellent sound insulation properties that can be applied to flooring for underfloor heating.

[0138] Furthermore, in the manufacturing method of the flooring material of this embodiment, multiple first grooves 41 are formed on the back surface of the 7-ply plywood 11, with a depth that extends from the back surface to the second layer 11b. While 3-ply or 5-ply plywood is often used as a base material for flooring, in this embodiment, the plywood 11 has 7 layers, so the areas bonded with water-based adhesive (between layers of each layer made of softwood veneer) are increased compared to 3-ply or 5-ply plywood, resulting in improved strength. Also, because the plywood 11 has 7 layers, the first grooves 41 extending from the back surface to the second layer 11b are deeper than when the first grooves 41 are similarly formed in 3-ply or 5-ply plywood. As a result of these multiple deep first grooves 41, the rigidity of the plywood 11 is reduced, its flexibility is increased, and it becomes easier to absorb impact forces. Furthermore, in this embodiment, in addition to the first groove 41, a plurality of second grooves 42 are formed on the back surface of the plywood 11 in a direction perpendicular to the extension direction (second direction) of the first groove 41 (first direction). By forming the second grooves 42 in this way, the rigidity of the plywood 11 is reduced and its flexibility is increased compared to the case where only the first groove 41 is formed, making it easier to absorb impact forces. In other words, according to the manufacturing method of this embodiment, it is possible to provide a flooring material 1 that has the required sound insulation performance and excellent soundproofing properties.

[0139] Furthermore, in the manufacturing method of the flooring material of this embodiment, the multiple first grooves 41 extending in a direction perpendicular to the fiber direction (first direction) of the first layer 11a of the plywood 11 (second direction) do not reach the first layer 11a, so that the fibers of the first layer 11a are not cut by the first grooves 41. By forming the first grooves 41 in this way, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the first direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the first layer 11a extending in the first direction. As a result, it is possible to manufacture flooring material 1 that is less likely to expand or contract in the first direction due to moisture absorption or release, and is less likely to warp in the first direction.

[0140] Furthermore, in this embodiment, the second groove 42 extending in a direction perpendicular to the fiber direction (second direction) of the second layer 11b (first direction) is not made to reach the second groove 42, so as not to cut the fibers of the second layer 11b extending in the second direction, which can resist dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard. By forming the second groove 42 in this way, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it is possible to manufacture a flooring material 1 that is less likely to expand or contract in the second direction due to moisture absorption or release, and is less likely to warp in the second direction. In other words, according to the manufacturing method of the flooring material of this embodiment, it is possible to manufacture a 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 direction perpendicular to it (second direction).

[0141] Furthermore, in the manufacturing method for the flooring material 1 shown in Figure 3 of this embodiment 1, 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. As a result, the fibers of the second layer 11b extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, are not cut. Moreover, because the second layer 11b is covered by the first layer 11a and the third layer 11c, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. This makes it possible to manufacture flooring material 1 that is less prone to expansion or contraction in the second direction due to moisture absorption or release, and is less likely to warp in the second direction.

[0142] Furthermore, in the manufacturing method of the flooring material of this embodiment 1, verification tests (tests 5, 7, and 8) on the correlation between the depth of the second groove 42 and the sound insulation performance and dimensional stability (warping) of the flooring material 1 show that if the depth of the second groove 42 is set so that the groove bottom is located within the fourth layer 11d, warping is less likely to occur, and a flooring material with excellent sound insulation suitable for floor heating can be provided.

[0143] Furthermore, in the manufacturing method of the flooring material of this embodiment, while plywood with a typical number of layers (3 or 5) is often used as the base material for flooring materials, the number of layers of plywood 11 is set to 7, and it is bonded with a water-based adhesive. Therefore, in this embodiment, compared to the case of forming 3-ply or 5-ply plywood, the laminated body of softwood veneers is hot-pressed with a higher moisture content, and the resulting plywood becomes thinner and denser from the middle of the thickness direction towards the outermost layer. According to the manufacturing method of the flooring material of this embodiment, by using plywood 11 with such a configuration, it is possible to provide flooring material 1 with excellent surface strength.

[0144] As described above, the manufacturing method of the flooring material of this embodiment makes it possible to provide a flooring material 1 that is less prone to warping even when using softwood plywood and has excellent sound insulation properties that can be applied to flooring materials for underfloor heating.

[0145] Furthermore, in the manufacturing method of the flooring material of this embodiment, seven softwood veneers are laminated and integrated to form plywood 11. Although softwood has more knots than hardwood, if the softwood veneer constituting the second layer 11b has a knot in the first direction that is larger than the groove spacing of the first groove 41 (first groove spacing), the fibers of the second layer 11b that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, will be cut by the knot. As a result, it will not be able to counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, and there is a risk that warping will occur partially in the second direction. However, according to this embodiment, since the second layer 11b does not have a knot in the first direction that is larger than the first groove spacing, it is expected that warping in the second direction will be suppressed.

[0146] Furthermore, in the method for manufacturing the flooring material of this embodiment 1, the first and second layers 11a and 11b are constructed so as to be free of knots. Specifically, the first layer 11a is made from parts of the conifer that are free of knots, or if it is made from parts of the conifer that are free of knots, the knots are filled in with putty to make it knot-free. Similarly, the second layer 11b is made from parts of the conifer that are free of knots, or if it is made from parts of the conifer that are free of knots, the knots are filled in with wood filler to make it knot-free. In this embodiment 1, by constructing the first and second layers 11a and 11b so as to be free of knots, the flooring material 1 is made to be resistant to scratches and to have a good surface. Therefore, according to the method for manufacturing the flooring material of this embodiment 1, it is possible to provide a flooring material 1 that is resistant to scratches and to have a good surface.

[0147] Furthermore, in the manufacturing method of the flooring material of this embodiment, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate compared to the wood fibers of hardwoods, a medium-density fiberboard (hardwood MDF) made primarily from hardwood wood fibers is used as the surface reinforcement layer 12. By using hardwood wood fibers as the medium-density fiberboard constituting the surface reinforcement layer 12 in this way, the water absorption rate of the surface reinforcement layer 12 can be kept low, and dimensional changes can be suppressed.

[0148] Furthermore, in the manufacturing method of the flooring material of this embodiment, tongue and groove processing is applied to the surrounding side surface of the flooring material base material 10, and the female tongue and male tongue 13 and male tongue 14 are formed so that the protruding portions (front side protrusion 13b, back side protrusion 13c, and protruding ridge portion 14a) that protrude outward from the female tongue and male tongue 14 always span multiple layers of the plywood 11. The protruding portions 13b, 13c, and 14a of the female tongue and male tongue 13 and male tongue 14 are brittle and prone to chipping, but by configuring them to span multiple layers of the plywood 11 as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to the manufacturing method of the flooring material of this embodiment, it is possible to provide flooring material 1 in which the protruding portions 13b, 13c, and 14a of the female tongue and male tongue 13 and male tongue 14 are less prone to chipping.

[0149] Furthermore, in the manufacturing method of the flooring material of this embodiment, the female tongue 13 is processed so that the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located within one of the layers, rather than being located in the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue 14 is inserted, but such peeling can be suppressed by processing as described above. [Industrial applicability]

[0150] The present invention is useful for a base material for flooring, flooring material, and a method for manufacturing flooring material. [Explanation of Symbols]

[0151] 1. Flooring 10. Base material (base material for flooring) 10a Long side (surrounding side) 10b Short side (surrounding side) 11 Plywood 11a 1st layer 11b 2nd layer 11c 3rd layer 11d 4th layer 11e 5th layer 11f 6th floor 11g 7th layer 12 Surface reinforcement layer 13 Female fruit 13a Groove 13b Front side protrusion (protruding part) 13c Backside protrusion (protruding part) 14 Yumi 14a Convex part 15 Adhesives 20 Decorative materials 30 Cushioning material 41 First groove 42 2nd groove

Claims

1. A base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, The above plywood is a softwood plywood having seven layers, each consisting of seven thin softwood veneers, which are sequentially laminated and bonded together from the front side to the back side, with the fiber directions of each veneer perpendicular between two adjacent veneers. On the back surface of the above-mentioned plywood, a plurality of first grooves extending in a second direction perpendicular to the 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 groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. The second groove described above extends from one end to the other in the first direction of the plywood, and the bottom of the groove is located within one of the third to fifth layers. The first to third layers described above have progressively thinner thicknesses and higher density in the order of the third layer, second layer, and first layer. The fifth to seventh layers described above are arranged in such a way that the thickness decreases in the order of the fifth layer, the sixth layer, and the seventh layer, while the density increases. The thickness of the first and seventh layers is less than or equal to the thickness of the surface reinforcement layer. The thickness of the third and fifth layers described above is greater than the thickness of the surface reinforcement layer described above. A base material for flooring, characterized by the following features.

2. In the base material for flooring according to claim 1, The softwood slabs constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood slabs constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction. The second layer described above does not have any knots whose size in the first direction is larger than the spacing between the first grooves. A base material for flooring, characterized by the following features.

3. In the base material for flooring according to claim 2, The first layer described above is composed of parts of coniferous trees that do not have knots, or is composed of parts of coniferous trees that have knots, with the knots filled with putty, thereby ensuring that there are no knots. The second layer described above is composed of parts of coniferous trees that do not have knots, or is composed of parts of coniferous trees that have knots, with the knots filled with wood filler, thereby ensuring that there are no knots. A base material for flooring, characterized by the following features.

4. In the base material for flooring according to claim 1, The above-mentioned medium-density fiberboard is made primarily from wood fibers of hardwoods. A base material for flooring, characterized by the following features.

5. In the base material for flooring according to claim 1, On one of the two opposing sides of the above-mentioned flooring material base material, a recessed groove portion that will serve as a female joint is formed in the middle of the thickness direction, and on the other side, a protruding ridge portion that will serve as a male joint is formed in the middle of the thickness direction. In the above-mentioned base material for flooring, the front-side protrusions adjacent to the front side of the groove, the back-side protrusions adjacent to the back side of the groove, and the protruding ridges are formed to span multiple layers of the plywood. A base material for flooring, characterized by the following features.

6. In the base material for flooring according to claim 5, The above-mentioned female joint is formed such that the bottom corner of the groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers. A base material for flooring, characterized by the following features.

7. A flooring material comprising a base material for flooring and a cushioning material adhered to the back surface of the base material for flooring, The above-mentioned flooring material base material is the flooring material base material according to any one of claims 1 to 6. Flooring material characterized by the following features.

8. A method for manufacturing flooring comprising a base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, and a cushioning material bonded to the back surface of the base material for flooring, A plywood forming process is performed to form the above-mentioned plywood having first to seventh layers made of the above-mentioned softwood slabs, which are laminated in order from the front side to the back side and bonded together, by laminating seven softwood slabs of equal thickness in order with a water-based adhesive interposed between each of them and so that the fiber directions of the two adjacent softwood slabs are perpendicular to each other, and then hot-pressing them in the thickness direction, and thereby laminating and bonding the softwood slabs in order from the front side to the back side, After sanding the surface of the above-mentioned plywood, a surface reinforcement layer bonding step is performed to bond the above-mentioned surface reinforcement layer to the surface to form the base material for the flooring material. A grooving process is performed on the back surface of the above-mentioned plywood, in which a plurality of first grooves extending in a second direction perpendicular to the 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 process includes a cushioning material bonding step in which cushioning material is bonded to the back surface of the plywood after the groove processing step described above, The first groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. The second groove described above extends from one end to the other in the first direction of the plywood, and the bottom of the groove is located within one of the third to fifth layers. A method for manufacturing flooring materials characterized by the following:

9. In the method for manufacturing flooring material according to claim 8, The softwood slabs constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood slabs constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction. The second layer described above is made without knots, and the size in the first direction is larger than the spacing between the first grooves. A method for manufacturing flooring materials characterized by the following:

10. In the method for manufacturing flooring material according to claim 9, The above first layer is made up of parts of coniferous trees that do not have knots, or parts of coniferous trees that do have knots, and the knots are filled with putty, thereby making it knot-free. The second layer described above is made up of parts of coniferous trees that do not have knots, or it is made up of parts of coniferous trees that have knots, and the knots are filled with wood filler, thereby making it knot-free. A method for manufacturing flooring materials characterized by the following:

11. In the method for manufacturing flooring material according to claim 8, The above-mentioned medium-density fiberboard is made primarily from wood fibers of hardwoods. A method for manufacturing flooring materials characterized by the following:

12. In the method for manufacturing flooring material according to claim 8, The above-mentioned base material for flooring further comprises a tongue-and-groove processing step in which a recessed portion that will serve as a female tongue is formed in the middle of the thickness direction on one of the two opposing sides of the base material for flooring, and a protruding portion that will serve as a male tongue is formed in the middle of the thickness direction on the other side. In the above tongue and groove processing step, the front-side protrusion adjacent to the front side of the groove, the back-side protrusion adjacent to the back side of the groove, and the protruding ridge are formed such that they span multiple layers of the plywood, forming the female tongue and groove and the male tongue and groove. A method for manufacturing flooring materials characterized by the following:

13. In the method for manufacturing flooring material according to claim 12, In the above tongue and groove processing step, the female tongue and groove is formed such that the bottom corner of the groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers. A method for manufacturing flooring materials characterized by the following:

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