JP7792929B2 - Wood chipboards and flooring - Google Patents

Description

The present invention relates to shaved wood flake boards and flooring materials that use the shaved wood flake boards as a base material.

Oriented strand board (OSB, Japanese Industrial Standard JIS A 5908:2022) is a known type of wood board made by mixing small or thin pieces of wood with an adhesive, assembling them, and then bonding them together under heat and pressure. OSB is a type of structural panel specified in the Japanese Agricultural Standards (JAS). However, given the depletion of wood resources in recent years, there has been ongoing research into using OSB for purposes other than structural panels, such as as a base material for decorative panels.

Special Publication No. 2007-521163

[0003] Conventional OSB is generally produced by drying wood shavings (strands) about 0.65 to 1.20 mm thick, applying an adhesive, and piling the wood shavings with the grain direction set in a generally uniform direction, followed by pressure molding. Its physical properties include a density of 0.60 to 0.70 g/cm ³ , a bending strength of 25 to 35 N/mm ² , and a bending Young's modulus of about 3500 to 5000 N/mm ^{2 .} However, due to uneven distribution of the adhesive and uneven press load, some of the wood shavings often appear curled up on the surface, resulting in poor surface smoothness, making it practically difficult to directly apply decorative materials such as veneer or decorative sheet to the surface of OSB. Therefore, when using OSB as a substrate for decorative boards, a surface material with excellent surface smoothness, such as MDF, is applied to the surface, and then a decorative material such as veneer or decorative sheet is applied to that surface to form the decorative board. OSB has not previously been used alone as a base material for decorative boards.

Plywood has long been used as a base material for decorative boards, but in recent years, as high-quality veneers have become difficult to obtain, wood fiberboards such as MDF have become more widely used. Plywood has been recognized as a suitable material for use as a base material for decorative boards because it has excellent strength, little deflection, making it easy to install, and little deformation such as warping after installation. However, it lacks sufficient surface smoothness (as described below, the maximum height indicating surface roughness exceeds 200 μm). When a decorative material such as a thin veneer is directly applied to it, the unevenness of the plywood surface becomes visible on the surface of the veneer, resulting in poor surface quality and a poor walking feel when used as a floorboard. Therefore, when applying a decorative material to a plywood base material, it is necessary to fill in the unevenness of the plywood surface with putty to achieve a smooth surface finish. On the other hand, while MDF has excellent surface smoothness, it lacks bending strength, especially in the longitudinal direction.

Therefore, the problem that this invention aims to solve is to provide a wood board that has surface smoothness equivalent to that of MDF and bending strength superior to plywood, and that can be used as a base material for directly attaching decorative materials such as veneer or decorative sheeting to create a decorative panel.

To solve this problem, the inventors conducted tests to produce various types of shaved wood boards by varying the tree species of the wood shavings used as raw materials, which are obtained by mixing and aggregating wood shavings with adhesive and then thermo-compressing them together. They discovered that the density of the shaved wood board and the tree species density of the wood shavings are significantly related to the surface smoothness of the resulting shaved wood boards. Based on this discovery, they conducted further tests and studies, which led to the completion of this invention.

That is, the invention of claim 1 of the present application is a shaved wood board obtained by mixing and accumulating wood shavings and an adhesive, and then thermocompressing and integrating them, wherein the wood shavings have a tree species density a of 0.6 g/ ^cm3 or less, the density b of the shaved wood board is 0.5 g/ ^cm3 or more and 0.9 g/ ^cm3 or less, the density ratio b/a of the tree species density a of the wood shavings to the density b of the shaved wood board is 1.2 or more, and at least one of the wood shavings on the surface of the shaved wood board overlap each other in areas where the wood shavings are deformed or compressed so that the wood shavings are approximately flush with each other, and at least one of the surfaces has a maximum height of 200 μm or less, indicating the surface roughness defined in Japanese Industrial Standard JIS B 0601:2013 .

The invention of claim 2 of this application is characterized in that, in the wood shavings board described in claim 1, the thickness of the wood shavings is 0.1 mm or more and 0.6 mm or less.

The invention of claim 3 of the present application is characterized in that, in the wood shavings board described in claim 1, the width of the wood shavings is 1.0 mm or more and 50 mm or less, and the length of the wood shavings is 15 mm or more and 200 mm or less.

The invention according to claim 4 of the present application is a flooring material formed by laminating a decorative material on at least one surface of the wood chipboard according to any one of claims 1 to 3, characterized in that the bending strength is 30 to 80 N/mm ² and the bending Young's modulus is 3000 to 8500 N/mm ² .

The present invention provides a shaved wood flake board that has significantly improved surface smoothness over conventional OSB, a surface smoothness comparable to or better than that of MDF, which is known to have good surface smoothness, and excellent physical properties. Therefore, the shaved wood flake board of the present invention can be suitably used in place of conventionally used MDF, etc., as a substrate for making a decorative board by directly attaching a decorative material such as veneer or decorative sheet onto it.

Even when the wood shavings of the present invention are randomly stacked without any specific orientation, they can be made to have various physical properties, such as bending strength, suitable for use as a base material for decorative boards by adjusting the tree species density of the wood shavings and the board density. However, in a three-layer laminate structure, by giving the core layer an orientation that is approximately perpendicular to the longitudinal direction of the wood shavings and the two surface layers an orientation that is approximately parallel to the longitudinal direction of the wood shavings, bending strength can be further increased and dimensional stability can be improved by reducing the linear expansion rate.

Flooring materials made by laminating decorative materials such as veneer onto the smooth surface of this wood chipboard have good density and bending Young's modulus, and are excellent in strength, rigidity, scratch resistance, etc.

1 is a side view schematically showing a shaved wood board according to the present invention. FIG. 1 is a side view schematically showing a flooring material using the shaved wood flake board according to the present invention as a base material. FIG. 1 is a diagram showing measurement points for a surface roughness test in a test example. Schematic cross-sectional views of thick wood shavings with low tree species density (a), thin wood shavings with low tree species density (b), thick wood shavings with high tree species density (d), and thin wood shavings with high tree species density (e), as well as schematic cross-sectional views of thin wood shavings (b, e) compressed (c, f). Schematic cross-sectional views showing (a) a mat made of accumulated wood shavings with a low tree species density and (b) the state in which these mats have been compressed and both ends of the width direction cut vertically, and (c) a mat made of accumulated wood shavings with a high tree species density and (d) the state in which these mats have been compressed and both ends of the width direction cut vertically. Schematic cross-sectional views showing the surface condition (a) of a portion where wood shavings with a low tree species density overlap each other before compression and the surface condition (b) of the portion where wood shavings with a high tree species density overlap each other before compression and the surface condition (d) of the portion where wood shavings with a high tree species density overlap each other before compression and the surface condition (c) of the portion where wood shavings with a high tree species density overlap each other before compression and the surface condition (d ... This is a graph showing the correlation between the tree species density and the maximum height indicating the surface roughness of a shaved wood board when a shaved wood board having a substantially constant board density is manufactured from shaved wood boards of several tree species with different densities. 10 is a graph showing the correlation between board density and maximum height indicating the surface roughness of shaved wood boards when shaved wood boards having different board densities are manufactured from shaved wood boards of the same tree species. This is a graph showing the correlation between the density ratio (board density/tree species density) and the maximum height indicating the surface roughness of the shaved wood board when various shaved wood boards are produced from shaved wood boards of several tree species with different densities. This figure compares a shaved wood board and a solid wood board of the same wood species and volume, and explains how the density ratio is affected by whether or not the board has been crushed (compressed) or by the degree of compression.

The present invention relates to a shaved wood board obtained by mixing and aggregating wood shavings with an adhesive, and then thermocompressing and integrating them. Figure 1 is a cross-sectional view showing this shaved wood board 1 alone, with the reference numeral 2 indicating wood shavings. Figure 2 is a cross-sectional view showing a flooring material 4 (decorative board) in which this shaved wood board 1 is used as a base material and veneer 3 (decorative material) is laminated and adhered to its smooth surface.

Wood shavings are made by thinly cutting hardwood or softwood logs with a strander. Wood shavings can also be obtained from planted renewable hardwoods and softwoods.

The wood shavings used in the wood shavings board of the present invention preferably have a thickness of 0.1 mm to 0.6 mm, a width of 1 mm to 50 mm, and a length of 15 mm to 200 mm.

If the thickness of the wood shavings is less than 0.1 mm, the production capacity of wood shavings will decrease, and if it exceeds 0.6 mm, the surface smoothness of the resulting wood shavings board will decrease and the rigidity will tend to be uneven. If the thickness of the wood shavings is within the range of 0.1 mm to 0.6 mm, a wood shavings board with excellent surface smoothness and uniform rigidity can be obtained.

If the width of the wood shavings exceeds 50 mm, not only will they be difficult to handle and transport, but they will also be prone to curling, making them less adhesive-compatible. If the width of the wood shavings is less than 1 mm, the rigidity of the resulting wood shavings board will be reduced. If the width of the wood shavings is within the range of 1 mm to 50 mm, a wood shavings board with excellent surface smoothness and uniform rigidity can be obtained.

If the length of the wood shavings exceeds 200 mm, not only will handling and transport be impaired, but the wood shavings will also be more likely to curl, which will create localized cavities (core voids) when heated and pressed, reducing strength and causing punctures. If the length of the wood shavings is less than 15 mm, the rigidity of the resulting wood shavings board will be reduced. If the length of the wood shavings is within the range of 15 mm to 200 mm, the productivity of the wood shavings board will be excellent and the required rigidity will be easier to achieve.

The moisture content of the wood shavings is preferably 15% by weight or less, and they are dried until the moisture content reaches 15% by weight or less before entering the manufacturing process for the wood shavings board. If the moisture content exceeds 15% by weight, an extremely high-density layer is likely to form on the surface of the wood shavings board, which requires a long time for pressing during pressure molding and results in uneven rigidity of the resulting wood shavings board. From this perspective, it is more preferable that the moisture content of the wood shavings be 3% by weight or less. The moisture content MC of the wood shavings can be calculated using the formula MC = ( _m1 - _m0 ) x 100/ _m0 in accordance with Japanese Industrial Standard JIS A 5905:2022 7.5. Here, _m1 is the mass (g) of the wood shavings sample before drying, and _m0 is the mass (g) of the wood shavings sample when placed in an air dryer at 103°C and brought to constant weight.

The adhesive applied to the wood shavings can be thermosetting resins such as urea resin, melamine urea resin, phenolic resin, polyurethane resin, or epoxy resin, either alone or in appropriate mixtures. However, mixing these with polyisocyanates is particularly preferable, as it reduces formaldehyde emissions and improves physicochemical properties such as bending strength. Polyisocyanates are compounds containing two or more isocyanate groups per molecule, such as diisocyanate compounds like 4,4'-diphenylmethane diisocyanate (MDI) and compounds obtained by reacting an excess amount of a diisocyanate compound with a polyol. One example of a polyisocyanate is polymeric MDI (polymethylene polyphenyl polyisocyanate: a mixture of monomeric MDI and high-molecular-weight polyisocyanate, also known as crude MDI), which hardens or foams upon reaction with moisture.

The amount of adhesive used is preferably 4 to 30 parts by weight in solids per 100 parts by weight of bone-dry wood shavings. If the amount of adhesive solids per 100 parts by weight of bone-dry wood shavings is less than 4 parts by weight, the bending strength of the wood shavings board will decrease, and if it exceeds 30 parts by weight, it will be an excessive amount, causing excessive rigidity and being economically disadvantageous. If an isocyanate compound is used as the adhesive, the solids content should preferably be 4 to 12 parts by weight, and if a melamine urea resin is used, the solids content should preferably be 10 to 30 parts by weight.

Next, we will explain the method for manufacturing shaved wood boards according to the present invention. Generally speaking, shaved wood boards according to the present invention are manufactured by drying shaved wood, applying adhesive, randomly stacking the shaved wood boards without specifying the grain direction, and then pressure-molding this stack (mat). This will be explained in more detail below.

Renewable hardwood or softwood logs, waste wood, sawmill waste, recycled materials, etc. are prepared and cut using a strander (cutting machine) to produce wood shavings. As mentioned above, the wood shavings used in the wood shavings board of the present invention preferably have a thickness of 0.1 mm to 0.6 mm, a width of 1 mm to 50 mm, and a length of 15 mm to 200 mm, so the wood shavings should be cut to meet these dimensional requirements.

Next, the wood shavings are dried in a dryer to adjust the moisture content to 15% or less, preferably 3% or less, and then an adhesive is applied to their surface. One suitable method for applying the adhesive is to place the wood shavings inside a rotating drum rotating at a low speed (approximately 30 rpm), and then spray the adhesive onto the wood shavings as they fall naturally inside the drum.

The adhesive-coated wood shavings are then piled up and formed into a mat, which is then thermocompressed in a press. The heat from the thermocompression process hardens the thermosetting resin in the adhesive, firmly bonding the wood shavings together to produce a wood shavings board. The thermocompression temperature varies depending on the type of adhesive used, but is generally between 190 and 220°C.

When collecting and forming wood shavings into a mat, they may be formed into a single mat, or the wood shavings may be divided into multiple groups, for example three groups, and each group formed into a mat. These may then be stacked and thermo-compressed to produce a wood shavings board consisting of three layers: an upper layer, a core layer, and a lower layer. Wood shavings boards produced by thermo-compressing a single-layer mat may have unevenness in the wood shavings, but by forming them into multiple layers, the unevenness in the wood shavings can be dispersed or eliminated, resulting in uniform strength and rigidity.

The shaved wood flake board of the present invention is manufactured so that its density is 0.5 g/ ^cm3 or more and 0.9 g/ ^cm3 or less. If the density is less than 0.5 g/ ^cm3 , the strength of the shaved wood flake board will be insufficient, while if the density is greater than 0.9 g/ ^cm3 , the weight of the entire shaved wood flake board will increase, making it difficult to handle. If the density is within the range of 0.5 g/ ^cm3 or more and 0.9 g/ ^cm3 or less, various properties suitable for flooring and other indoor interior materials can be obtained.

Regarding the density distribution of the shaved wood board, by using shaved wood boards with a moisture content of 15% by weight or less, more preferably 3% by weight or less, it is possible to effectively prevent the formation of a high-density layer on the surface of the shaved wood board, and by adjusting the timing and pressure at which the hot platen is brought into contact with the shaved wood mat during hot pressing, it is possible to produce a shaved wood board with a uniform density distribution, with the density distribution being approximately uniform within the range of 0.5 g/ ^cm3 to 0.9 g/ ^cm3 . The density distribution (density profile) in the thickness direction can be measured using a density distribution measuring device (DAX5000, manufactured by Grecon GmbH, Germany).

Furthermore, the shaved wood flake board preferably has a bending strength of 25 to 90 N/mm ² and a bending Young's modulus of 3000 to 8500 N/mm ^2. If the bending strength is less than 25 N/mm ² and/or the bending Young's modulus is less than 3000 N/mm ² , the amount of deflection, particularly when used as a base material for flooring, will be greater than the deflection standard (3.5 mm or less; detailed description will be given later) set forth in the Japanese Agricultural Standards (JAS) wood flooring standard, making it unsuitable for use as a flooring material. On the other hand, if the bending strength exceeds 90 N/mm ² and/or the bending Young's modulus exceeds 8500 N/mm ² , the elasticity required for walking when used as a flooring material will be insufficient, resulting in an inferior walking feel. If the bending strength is within the range of 25 to 90 N/mm ² and the bending Young's modulus is within the range of 3000 to 8500 N/mm ² , the shaved wood flake board can be made suitable for use as a base material for flooring.

Furthermore, flooring can be produced by using the shaved wood flakes produced as described above as a substrate and laminating and adhering a decorative material such as veneer, decorative sheet, or decorative paper approximately 0.1 to 0.2 mm thick onto its surface using an F☆☆☆☆ grade adhesive in Table 3 of Japanese Industrial Standards JIS A 5536:2015 "Adhesives for Floor Finishing Materials." A coating layer of approximately 20 to 80 μm thick, such as a urethane coating, may also be formed on the surface of the decorative material. Because the surface of the shaved wood flakes is smooth, the flooring obtained by laminating and adhering a decorative material onto this smooth surface also has a smooth surface and is suitable for flooring with appropriate physical properties such as strength, elasticity, and flexure.

The following test examples are used to explain the examples and comparative examples of the present invention. In these test examples, a large number of wood shaving samples, each measuring 0.1 mm to 0.6 mm thick, 15 mm to 200 mm long, and 1 mm to 50 mm wide, were prepared by thinly shaving cypress logs using a strander (cutting machine). These were then weighed to a predetermined weight ratio and divided into three groups (upper layer samples Sa, core layer samples Sb, and lower layer samples Sc). In Example 1, the wood shavings were distributed so that, by bone-dry weight, upper layer samples Sa comprised 30%, core layer samples Sb comprised 40%, and lower layer samples Sc comprised 30%. In Example 2, the wood shavings were distributed so that, by bone-dry weight, upper layer samples Sa comprised 25%, core layer samples Sb comprised 50%, and lower layer samples Sc comprised 25%.

A resin adhesive containing polyisocyanate (Sumidur 44 (registered trademark) V20, a product of Sumika Covestro Urethane Co., Ltd.) was applied to the surface of each of the wood shavings for the upper layer sample Sa, the core layer sample Sb, and the lower layer sample Sc. The application was performed using a spray method, with the wood shavings for sample Sa placed inside a rotating drum rotating at a low speed (approximately 30 rpm), and the resin adhesive containing polyisocyanate sprayed onto the wood shavings as they naturally fell inside the rotating drum. The adhesive was sprayed onto samples Sb and Sc in the same manner.

The adhesive-coated upper layer sample Sa, core layer sample Sb, and lower layer sample Sc were each stacked in a mat shape to form an upper layer mat Ma, core layer mat Mb, and lower layer mat Mc, which were then stacked in order and hot-pressed for 2 to 4 minutes under hot-press conditions of a surface pressure of 3 to 10 N/mm ² and a temperature of 190 to 220°C to obtain a shaved wood flake board specimen (Examples 1 and 2) measuring 300 mm long, 300 mm wide, and 12 mm thick.

For comparison, plywood, which has traditionally been widely used as a base material for flooring, and commercially available OSB (made from thin wood chips with a thickness of 0.65 to 1.20 mm) were used as comparative examples. The dimensions of these comparative examples were the same as in Examples 1 and 2: length 300 mm x width 300 mm x thickness 12 mm.

For each of these examples and comparative examples (hereinafter collectively referred to as "test specimens"), the density, longitudinal bending strength, longitudinal bending Young's modulus, and maximum height were measured using a surface roughness measuring device (JIS B 0651:2001, Surftest SJ-310, manufactured by Mitutoyo Corporation). These measurement results are shown in Table 1. The measurement points for maximum height, which indicates surface roughness, were determined by dividing a test specimen with planar dimensions of 300 mm x 300 mm into nine 100 mm x 100 mm regions, as shown in Figure 3, with the centers of each region designated as measurement points 1 to 9. Specifically, a measuring device was placed on the surface of each test specimen, and a stylus set at each measurement point was automatically measured to measure the unevenness at 0.01 mm intervals as it moved along a 15 mm-long linear range. The uneven shape was measured by calculating the maximum height within the measurement range (JIS B 0601:2013, the distance from the bottom of the deepest recess to the apex of the highest protrusion, Rz = Rv + Rq), and the average maximum height measured at each measurement point is shown in Table 1.

Furthermore, each of these test specimens was used as a base material, and a 0.2 mm thick veneer was laminated and glued onto the surface to obtain flooring materials. The results of a visual evaluation of the surface condition are also shown in the rightmost column of Table 1. In this visual evaluation, a circle indicates that the veneer surface was in good condition, with no irregularities from the base material surface visible; a triangle indicates that the veneer surface was in a slightly poor condition, with only slight irregularities from the base material surface visible; and an cross indicates that the veneer surface was in a poor condition, with many irregularities from the base material surface visible.

As can be seen from the results shown in Table 1, the shaved wood flakes of Examples 1 and 2 of the present invention had maximum heights, indicating surface roughness, of 114 μm and 118 μm, respectively, and had surface smoothness far superior to that of the comparative plywood and OSB. Therefore, even when these were used as a base material and a thin veneer was attached to the surface to create flooring, it was confirmed that a good surface condition could be achieved without any visible irregularities on the veneer surface. Furthermore, the maximum height, indicating the surface roughness of MDF, was approximately 40 μm. While the shaved wood flakes of Examples 1 and 2 of the present invention are not as good as MDF, a good surface condition could be achieved with the veneer attached to the surface of the shaved wood flakes (marked with circles), with no visible irregularities on the veneer surface (marked with circles). These examples have sufficient surface smoothness in practice, and Tables 2 and 3 shown below include samples with surface smoothness comparable to or even better than that of MDF.

The shaved wood flakes of Examples 1 and 2 of the present invention also have excellent physical properties such as density, bending strength, and bending Young's modulus. Although not shown in the table, when tested against the bending deflection standard of the Japanese Agricultural Standards (JAS) wood flooring standard (a flooring sample measuring 300 mm wide x 1,800 mm long x 12 mm thick is supported at a span of 700 mm, and a load of 21 kg is applied to a load bar placed at the center of the span to measure the displacement D1, and similarly, when a load of 9 kg is applied, the displacement D2 must be 3.5 mm or less), the result was D1 - D2 = 1.9 mm, fully meeting the standard. These results confirm that the shaved wood flakes of Examples 1 and 2 of the present invention have physical properties suitable for use as a flooring base material.

It is speculated that the good surface smoothness achieved in the shaved wood boards of Examples 1 and 2 of the present invention is due to the fact that the cypress tree species used as the shaved wood boards has a low density and is therefore easily compressed, and that these are compressed to a certain degree to produce shaved wood boards with an appropriate density.

More specifically, we will first explain the compressive deformation of wood shavings with reference to Figure 4. As shown in Figures 4(a) to (c), when the tree species density is low, the proportion of woody parts 2a within the wood shavings is relatively small and the proportion of voids 2b is large, making the wood shavings more susceptible to compression. When wood shavings are cut thinly (Figure 4(b)), the presence of voids tends to create unevenness on the surface, but compression crushes the voids, reducing the surface unevenness (Figure 4(c)). On the other hand, as shown in Figures 4(d) to (f), when the tree species density is high, the proportion of voids 2b within the wood shavings is small, and woody parts 2a account for the majority of the wood shavings, increasing strength, so that the wood shavings are less likely to be compressed (Figure 4(f)) even when they are thin (Figure 4(e)).

Next, the deformation of the surface of a shaved wood board will be explained with reference to Figure 5. To create a shaved wood board with the same board density, if wood shavings 2c with a low tree species density are used, it is necessary to accumulate a large number of these shavings 2c to increase the mat volume (Figure 5(a)). However, a mat made of accumulated wood shavings 2c with a low tree species density is easily compressed, so when it is hot-pressed, its surface conforms to the smooth press surface, resulting in a shaved wood board with a smooth surface (Figure 5(b)). On the other hand, to create a shaved wood board with the same board density using wood shavings 2d with a high tree species density, it is necessary to reduce the amount of these shavings 2d used to reduce the mat volume (Figure 5(c)). However, a mat made of accumulated wood shavings 2d with a high tree species density is difficult to compress, so when it is hot-pressed, its surface conforms poorly to the smooth press surface, resulting in a shaved wood board with large irregularities and poor surface smoothness (Figure 5(d)).

Although it is inevitable that the surface of the shavings board will tend to become uneven where the shavings overlap, as shown in Figures 6(a) and 6(b), since the shavings 2c with a low tree species density are weak and easily compressed, it is assumed that both or at least one of the overlapping shavings 2c, 2c will deform or compress, becoming approximately flush, and the surface will maintain smoothness without large irregularities. To achieve this, it is preferable to use relatively thin shavings with a thickness of 0.1 to 0.6 mm, and when the mat containing these shavings is thermocompressed, it is preferable to compress the overlapping shavings with a compressive force sufficient to make them approximately flush, and form the shavings board into a board density of approximately 0.6 to 0.8 g/ ^cm3 . By doing so, the height of the step 5 formed at the overlapping portion of the wood shavings 2c, 2c on the surface of the wood shavings board obtained after compression is 0.2 mm or less, and it is easy to obtain a wood shavings board with a maximum height indicating surface roughness of 200 μm or less. On the other hand, when wood shavings 2d with a high tree species density overlap, as shown in Figures 6(c) and (d), the overlapping wood shavings 2d, 2d are almost undeformed and overlap as they are, leaving a step, and the height of the step 5 becomes larger than 0.2 mm, making it difficult to obtain a wood shavings board with a maximum height indicating surface roughness of 200 μm or less.

Based on these assumptions, it was thought that the surface smoothness of shaved wood boards would have a strong correlation with the tree species density of the shaved wood used as raw material and the board density. The inventors then investigated the effect or correlation of tree species density and board density on surface smoothness.

First, the following test was conducted to confirm the effect of the tree species density of the wood shavings on surface roughness. Specifically, six types of wood shavings board specimens of different tree species were prepared in the same manner as in Example 1, using wood shavings from six different tree species: sawtooth oak, zelkova, edulis, loblolly pine, cypress, and cedar. As mentioned above, it was assumed that surface roughness would also be related to board density, so each specimen was prepared so that the board density was approximately constant (approximately 0.7 g/cm ³ ). The results of measuring the surface roughness of each specimen in the same manner as above, as well as the results of visually evaluating the surface condition of flooring materials with 0.2 mm thick sliced veneer laminated and bonded to the surface of each specimen, are shown in Table 2. The correlation between tree species density and maximum height, which indicates surface roughness, is also shown in a graph in Figure 7.

The results shown in Table 2 and Figure 7 indicate a certain correlation between the density of the tree species used as the wood shavings and the maximum height, which indicates the surface roughness of the wood shavings boards made using them. The lower the tree species density, the smaller the maximum height, which indicates the surface roughness (better surface smoothness). Conversely, the higher the tree species density, the larger the maximum height, which indicates the surface roughness (decreasing surface smoothness).

More specifically, shaved wood boards made from shaved wood from tree species with a density of more than 0.6 g/ ^cm3 (oak, zelkova, and edulis) had a maximum height indicating surface roughness of more than 200 μm, and had surface smoothness equivalent to or inferior to that of plywood (see Table 1 for the maximum height indicating the surface roughness of plywood). As a result, the surface condition of the flooring material obtained by laminating and adhering veneer to the surface was also poor (×) or somewhat poor (△).

In contrast, shaved wood boards made from shaved wood from tree species (loblolly pine, cypress, cedar) with a density of 0.6 g/cm3 or ^less had a maximum height indicating surface roughness of 200 μm or less, providing superior surface smoothness to plywood, and the surface condition of flooring materials obtained by laminating and adhering sliced veneer to the surface was also good (◯).Furthermore, shaved wood boards made from shaved wood from tree species (cypress, cedar) with a density of 0.45 g/cm3 or ^less had a maximum height indicating surface roughness of 100 μm or less, providing significantly superior surface smoothness to plywood.

Next, the following test was conducted to confirm the effect of board density on surface roughness. As the above confirmed that surface roughness is related to the species density of the wood shavings, this test used cedar shavings, which have a low species density and are therefore soft and easily compressed. Nine specimens with different board densities were created in the same manner as in Example 1, except that the heat and pressure conditions on the mat were varied to achieve various board densities. The surface roughness of each specimen was measured in the same manner as above, and the results of visual evaluation of the surface condition of flooring materials with a 0.2 mm thick sliced veneer laminated and glued to the surface of each specimen are shown in Table 3. Figure 8 also shows a graph of the correlation between board density and maximum surface roughness height.

The results shown in Table 3 and Figure 8 indicate that there is a certain correlation between the board density of shaved wood flake boards and the maximum height indicating surface roughness, with a tendency for the higher the board density, the smaller the maximum height indicating surface roughness (better surface smoothness), and conversely, the lower the board density, the larger the maximum height indicating surface roughness (decreasing surface smoothness).

More specifically, the test specimens (cedar 1 and 2) with a board density of less than 0.5 g/ ^cm3 had a maximum height indicating surface roughness exceeding 200 μm, and had poor surface smoothness similar to that of plywood. Therefore, the surface condition of the flooring material obtained by laminating and adhering veneer to the surface was also poor (×).

In contrast, the test specimens (cedar 3 to 9) with a board density of 0.5 g/ ^cm3 or higher had a maximum height indicating surface roughness of 200 μm or less, which gave them a surface smoothness better than plywood, and the surface condition of the flooring material obtained by laminating and adhering sliced veneer to the surface was also good (◯). In this test, the upper limit of the board density of the test specimens was set at 0.86 g/ ^cm3 (cedar 9), but if the board density exceeds 0.9 g/ ^cm3 , the weight increases, making it difficult to handle and adversely affecting the walking feel when used as a flooring material, so it is preferable to set the upper limit of the board density at 0.9 g/ ^cm3 .

Furthermore, the inventors have found that the density ratio b/a, where a is the density a of the wood shavings used as raw material and b is the board density b of the shavings board obtained by thermocompression molding of the raw material, has a significant correlation with the surface smoothness of the shavings board. This is demonstrated by the fact that in Table 2, specimens with a density ratio of less than 1.2 (oak and zelkova) have poor surface smoothness, while specimens with a density ratio of 1.2 or more (Lithocarpus edulis, loblolly pine, cypress, and cedar) generally have good surface smoothness, and in Table 3, specimens with a density ratio of less than 1.2 (cedar 1) have poor surface smoothness, while specimens with a density ratio of 1.2 or more (cedars 3 to 9) have good surface smoothness, as well as by the graph in Figure 9 showing the results of Tables 2 and 3. In addition, although Cedar 2 in Table 3 satisfies the condition of a density ratio of 1.2 or more, the board density was 0.49 g/cm ³ , which was slightly below the lower limit (0.5 g/cm ³ ) of the board density range of the present invention, and therefore the desired surface smoothness was not obtained.

The density ratio will be further explained. As mentioned above, the results shown in Table 2 and Fig. 7 show that there is a certain correlation between the tree species density of the wood shavings and the surface smoothness of the wood shavings board, and that the lower the tree species density, the better the surface smoothness, and that the higher the tree species density, the lower the surface smoothness tends to be. However, this is a test result when the board density is kept approximately constant (about 0.7 g/cm ³ ). On the other hand, the results shown in Table 3 and Fig. 8 show that there is also a certain correlation between the board density and the surface smoothness of the wood shavings board, and that the higher the board density, the better the surface smoothness, and that the lower the board density, the lower the surface smoothness tends to be. However, this is a test result when wood shavings of the same tree species (= same tree species density) are used.

Therefore, if the correlation between tree species density and surface smoothness is tested using a lower board density, the correlation (a linear proportional relationship with a constant slope) will not be as pronounced as the results shown in Table 2 and Figure 7. It is estimated that the tendency for surface smoothness to improve with decreasing tree species density will slow (the slope will become gentler) and converge to a minimum value. Similarly, if the correlation between board density and surface smoothness is tested using wood shavings with a higher tree species density, the correlation (a linear proportional relationship with a constant slope) will not be as pronounced as the results shown in Table 3 and Figure 8. It is estimated that the tendency for surface smoothness to improve with increasing board density will slow (the slope will become gentler) and converge to a maximum value. In other words, tree species density and board density not only independently have a significant impact on surface smoothness, but also correlate with each other to affect surface smoothness. From these perspectives, the inventors focused on the density ratio (board density b/tree species density a).

The density ratio (board density b/species density a) is further explained. When a solid wood board with volume V is obtained from a specific tree species, its weight Wa is Wa = tree species density a x volume V. On the other hand, when shaved wood boards of the same tree species are thermocompressed to obtain shaved wood boards of the same volume V, their weight Wb is Wb = board density b x volume V, so board density b/species density a = weight ratio Wb/Wa. In other words, the density ratio indicates how many times the weight Wb of a shaved wood board is compared to the weight Wa of a solid wood board of the same volume obtained from the same tree species. In other words, the density ratio is a value that indicates the degree of compression of a shaved wood board relative to a solid wood board of the same volume and tree species.

Figure 10 shows a perspective view (upper left) of shaved wood board 1 and an enlarged cross-sectional view (lower left) of a portion thereof at a macroscopic level, as well as a perspective view (upper right) of solid wood board 7 of the same wood species and volume as this board (upper right) and an enlarged cross-sectional view (lower right) of a portion thereof at a macroscopic level. As already described with reference to Figure 4, in shaved wood board 1, the woody portions 2a and voids 2b of the shaved wood boards are crushed and compressed, and these compressed shaved wood boards are stacked in multiple layers to form shaved wood board 1. In contrast, in solid wood board 7, the woody portions 6a and voids 6b remain uncompressed. The presence or absence or degree of this crushing (compression) determines the board density b/tree species density a or the weight ratio Wb/Wa.

The present invention has been described in detail above using examples and test examples, but the present invention can be implemented with a wide variety of modifications and variations within the scope of the invention defined by the claims.

1 Wood cut thin plate (base material)
2 Wood shavings 2a Wood part 2b Void part 2c Wood shavings with low tree species density 2d Wood shavings with high tree species density 4 Veneer (decorative material)
5. Flooring (decorative panels)
6. Steps on the surface of the wood shavings board formed at the parts where the wood shavings overlap. 7. Solid board

Claims (4)

A shaved wood board obtained by mixing and aggregating wood shavings with an adhesive, and then thermocompressing and integrating the mixture, wherein the wood shavings have a tree species density a of 0.6 g/ ^cm3 or less, the wood shavings have a density b of 0.5 g/ ^cm3 or more and 0.9 g/ ^cm3 or less, the density ratio b/a of the tree species density a of the wood shavings to the density b of the wood shavings board is 1.2 or more, and where the wood shavings on the surface of the shaved wood board overlap each other, both or at least one of the wood shavings are deformed or compressed so that the wood shavings are approximately flush with each other, and at least one surface of the shaved wood board has a maximum height of 200 μm or less, which indicates the surface roughness as defined in Japanese Industrial Standard JIS B 0601:2013 . The wood shavings board of claim 1, characterized in that the thickness of the wood shavings is 0.1 mm or more and 0.6 mm or less. The wood shavings board of claim 1, characterized in that the width of the wood shavings is 1.0 mm or more and 50 mm or less, and the length of the wood shavings is 15 mm or more and 200 mm or less. A flooring material obtained by laminating a decorative material on at least one surface of the wood shavings according to any one of claims 1 to 3, wherein the bending strength is 30 to 80 N/mm ² and the bending Young's modulus is 3000 to 8500 N/mm ² .