JP7792894B2 - Wood chipboard and its manufacturing method - Google Patents

Description

The present invention relates to a shaved wood board and a method for manufacturing the same.

Oriented strand board (OSB) is a type of wood board made by mixing small or thin pieces of wood with adhesive, assembling them, and then thermocompressing them together. OSB is a type of structural panel defined by the Japanese Agricultural Standards (JAS), and is standardized as a type of particle board by the Japanese Industrial Standards (JIS). 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

Conventional OSB is generally produced by laminating numerous 0.7-1.2 mm thick wood shavings together in an overlapping state using a thermosetting resin adhesive, and then pressing this laminate at high temperature to form a board. However, uneven distribution of the adhesive and uneven pressing load often cause some of the wood shavings to appear curled up on the surface, and the surface has poor smoothness, making it practically difficult to directly apply decorative materials such as veneer or decorative sheeting 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 sheeting is applied to that surface to form the board. OSB has not previously been used alone as a base material for decorative boards.

Therefore, the problem that this invention aims to solve is to provide a wood board with improved surface smoothness that can be used as a base material for directly attaching decorative materials such as veneer or decorative sheets to create a decorative panel.

In order to solve this problem, the invention of claim 1 of the present application is a shaved wood board obtained by mixing and aggregating wood shavings obtained by cutting wood and having lengths of 10 to 200 mm, widths of 1 to 50 mm, and thicknesses of 0.6 mm or less, and wood shavings of 10 to 200 mm, widths of 1 to 50 mm, and thicknesses greater than 0.6 mm, with an adhesive, and then thermocompressing the mixture. The shaved wood board is characterized in that the shaved wood is stacked on top of each other, and the surface of the shaved wood board is formed by compressed shaved wood, and the average maximum height, which indicates the surface roughness defined in Japanese Industrial Standard JIS B 0601:2013, is 40 μm or less, and the maximum value is 50 μm or less.

The invention of claim 2 of this application is a method for producing a shaved wood board, which comprises preparing a first wood shavings group consisting of an aggregate of wood shavings having a thickness of 0.6 mm or less and a second wood shavings group consisting of an aggregate of wood shavings having a thickness of more than 0.6 mm, using 68% or more by weight of the first wood shavings group relative to the total blend amount, which is the sum of the first wood shavings group and the second wood shavings group, applying an adhesive to these raw wood shavings, mixing them, and accumulating them, followed by thermocompression.

The invention of claim 3 of the present application is characterized in that, in the method for manufacturing a wood shavings board described in claim 2, the first wood shavings group includes shavings generated when obtaining the wood shavings.

The invention of claim 4 of this application is a shaved wood board manufactured by the manufacturing method described in claim 2 or 3.

The present invention provides a shaved wood flake board that has significantly improved surface smoothness over conventional OSB, a surface smoothness comparable to or equivalent to 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 a board or decorative sheet onto it.

1 is a side view schematically showing a wood flake board according to the present invention. 1 is a side view schematically showing a decorative board using a wood flake board according to the present invention as a substrate. FIG. 1 is a diagram showing measurement points for a surface roughness test in a test example.

The present invention relates to a shaved wood board obtained by mixing and aggregating wood shavings with an adhesive, and then thermocompressing the mixture. Figure 1 is a cross-sectional view of this shaved wood board 1 alone, with reference numeral 2 indicating wood shavings with a thickness of 0.6 mm or less and reference numeral 3 indicating wood shavings with a thickness of more than 0.6 mm. Figure 2 is a cross-sectional view of a decorative board 5 obtained by using this shaved wood board 1 as a substrate and adhering a decorative material 4 onto it.

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

The moisture content of the wood shavings is preferably 15% by weight or less, and they are dried to this moisture content or less before entering the wood shavings board manufacturing process. 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, requiring a long time for pressing during pressure molding. The moisture content of wood shavings can be calculated using the formula (m ₁ -m ₀ ) x 100/m ₀ in accordance with Japanese Industrial Standard JIS A 5905-2003 6.4. Here, m ₁ is the mass (g) of the wood shavings sample before drying, and m ₀ is the mass (g) of the wood shavings sample when placed in an air dryer at 103°C and brought to constant weight.

The wood shavings used in the shaved wood board preferably have a length of 10 to 200 mm and a width of 1 to 50 mm . If the length of the wood shavings exceeds 200 mm, they will curl when dried, and if they are heated and pressed in this curled state, localized voids will form, causing poor adhesion and resulting in punctures and poor strength.

As mentioned above, conventional OSBs use wood shavings with a thickness of 0.7 to 1.2 mm. In this invention, however, a first wood shavings group consisting of an aggregate of wood shavings with a thickness of 0.6 mm or less and a second wood shavings group consisting of an aggregate of wood shavings with a thickness of more than 0.6 mm are prepared, and the first wood shavings group is mixed with an adhesive at a ratio of 68% by weight or more, preferably 70% by weight or more, and more preferably 80% by weight or more of the total weight of the first and second wood shavings groups. In other words, if the weight of the first wood shavings group is A and the weight of the second wood shavings group is B, the weights are mixed so that A/(A+B) ≥ 68%, preferably ≥ 70%, and more preferably ≥ 80%. This point will be explained in more detail later using test examples, but the reason for classifying the first and second wood shavings groups at a thickness of 0.6 mm is as follows.

As previously mentioned, conventional OSB was primarily intended for use as a structural panel, not as a substrate for attaching decorative materials such as veneer or decorative sheeting to its surface to create a decorative board. Therefore, wood shavings with a thickness of 0.6 mm or more, primarily 0.7 to 1.2 mm, which can be produced with relatively low cost and good productivity, were used as the raw material for OSB. While it is naturally predictable that reducing the thickness of the wood shavings used as raw material would improve surface smoothness for use as a substrate for decorative boards, the thinner the wood shavings, the more bulky they become, making management difficult and increasing costs, and therefore this approach was not generally adopted. Furthermore, when attempting to produce OSB using only thin wood shavings with a thickness of 0.6 mm or less, the mats would become unstable on the production line, often tilting, collapsing, or tipping over, causing line stoppages. Therefore, in this invention, we focused on the fact that by using wood shavings with a thickness of over 0.6 mm (0.7 to 1.2 mm), which have traditionally been commonly produced, and blending or mixing in a certain amount of thinner wood shavings, it is possible to efficiently produce wood shavings boards with a surface smoothness suitable for use as a base material for decorative boards at relatively low cost.

Furthermore, the wood shavings of 0.6 mm or less that make up the first wood shavings group are assumed to have an average thickness of approximately 0.35 mm, and if these are compressed to half their thickness by heat and pressure, or if the wood shavings bite into each other by half their thickness, the average depth of irregularities on the surface of the resulting wood shavings board is assumed to be approximately 0.175 mm. When this wood shavings board is used as the base material for a decorative board, the decorative material such as veneer or decorative sheet that is attached to the surface is generally 0.2 mm or thicker, so even if there are irregularities of approximately 0.175 mm on the surface of the wood shavings board, these can be absorbed by attaching a decorative material with a thickness that exceeds this unevenness depth, and irregularities are less likely to appear on the decorative surface. In contrast, if the upper limit of the thickness of the wood shavings making up the first wood shavings group is larger (for example, 0.7 mm), the unevenness that appears on the surface of the resulting wood shavings board will be approximately the same as or larger than the thickness of the decorative material, and even if the decorative material is applied, it will not be able to absorb the surface unevenness, resulting in unevenness appearing on the decorative surface, significantly reducing the commercial value of the decorative board. For this reason, when classifying the first wood shavings group and the second wood shavings group, a thickness of 0.6 mm is used as the standard, with wood shavings with a thickness of 0.6 mm or less being classified as the first wood shavings group, and wood shavings with a thickness of more than 0.6 mm being classified as the second wood shavings group.

The adhesive applied to the wood shavings can be thermosetting resins such as urea resin, melamine urea resin, phenolic resin, polyurethane resin, and epoxy resin, either alone or in appropriate mixtures. However, polyurethane resin or melamine urea resin is preferably used in order to shorten the pressing time during pressure molding and improve the water resistance of the molded product. As the polyurethane resin, an isocyanate compound with two or more isocyanate groups per molecule, such as crude diphenylmethane-4,4'-diisocyanate (Sumidur 44V20, a product of Sumika Covestro Urethane Co., Ltd.), can be used.

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, making it unsuitable as a base material for decorative laminates. If it exceeds 30 parts by weight, the amount will be excessive, resulting in more rigidity than necessary and being economically disadvantageous. More specifically, 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 15 to 25 parts by weight.

Next, we will explain the method for manufacturing wood shavings boards according to the present invention. As described above, a first wood shavings group consisting of an aggregate of wood shavings with a thickness of 0.6 mm or less and a second wood shavings group consisting of an aggregate of wood shavings with a thickness of more than 0.6 mm are mixed together so that the first wood shavings group accounts for 70% by weight or more, more preferably 80% by weight or more, of the total blend amount, which is the sum of the first wood shavings group and the second wood shavings group, to prepare raw wood shavings, and then the above-mentioned adhesive is applied to the surface and mixed. A spray method can be used as the application method; for example, the raw wood shavings are placed in a rotating drum rotating at a low speed, and the adhesive is sprayed onto the raw wood shavings as they naturally fall from the rotating drum.

The raw wood shavings coated with adhesive are then formed into a mat and thermo-compressed in a press. The heat from the thermo-compression process hardens the thermosetting adhesive, firmly bonding the raw wood shavings together to produce a wood shavings board. The thermo-compression temperature varies depending on the type of adhesive used, but is generally between 150 and 230°C.

As demonstrated by the following test examples, the shaved wood board produced in this manner has significantly improved surface smoothness compared to OSB produced by conventional technology, and has a density distribution of 0.3 to 0.95 g/cm ³ , a bending strength of 25 to 100 MPa, and a peel strength of 0.3 to 3.0 MPa, making it suitable for use as a substrate for directly attaching a decorative material such as sliced veneer or decorative sheet to produce a decorative board. Regarding the density distribution of the shaved wood board, using raw shaved wood boards with a moisture content of 15% by weight or less effectively prevents 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, the density distribution can be kept within the range of 0.3 to 0.95 g/m ³ , resulting in the production of a shaved wood board with a uniform density distribution.

The following test examples will explain the examples and comparative examples of the present invention. In these test examples, cypress logs were cut with a flaker to obtain Sample A (mainly wood shavings with a thickness of 0.1 to 0.6 mm, but also including wood powder and debris less than 0.1 mm thick that inevitably occurs when obtaining these thin wood shavings) with a thickness of 0.6 mm or less, and Sample B with a thickness of 0.7 to 1.2 mm. The wood shavings for Samples A and B were all the same in length and width, with a length of 10 to 200 mm and a width of 1 to 50 mm. Then, these samples A and B were used to prepare raw wood shavings by varying the weight blending ratio of sample A to the total weight (A+B) in nine ways: 80%, 70%, 68%, 66%, 64%, 62%, 60%, 50%, and 30%. An adhesive consisting of crude diphenylmethane-4,4'-diisocyanate was applied to these using the spray method described above, and after forming them into a mat, they were hot-pressed for 9 minutes at a temperature of 190°C and a surface pressure of 17 kg/cm2 to obtain test specimens 1 to ⁹ measuring 300 mm x 300 mm x 12 mm thick.

For comparison, MDF, known for its excellent surface smoothness, and OSB made using conventional technology (using only sample B as the raw wood shavings) were used as comparative examples A to D. Comparative examples A and B are MDF that is actually commercially available as a floor base material, while comparative examples C and D are OSB that is actually commercially available as a structural panel. The dimensions of comparative examples A to D were the same as those of the test specimens: 300 mm x 300 mm x 12 mm thick.

The surface profile of each of these specimens 1-9 and comparative examples A-D (hereinafter collectively referred to as "specimens") was measured using a surface roughness measuring device (JIS B 0651:2001, Surftest SJ-310, manufactured by Mitutoyo Corporation). As shown in Figure 3, the specimen, with planar dimensions of 300 mm x 300 mm, was divided into nine 100 mm x 100 mm regions, and the centers of each region were designated as measurement points 1-9. Specifically, the measuring device was placed on the surface of each specimen, and the stylus set at each measurement point was automatically measured to measure the uneven profile at 0.01 mm intervals as it moved within 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 and maximum values of the maximum heights measured at each measurement point are shown in Table 1.

Furthermore, the surface condition of each of these test specimens 1 to 9 and comparative examples A to D was visually evaluated when a decorative sheet was directly applied onto them, and the results are shown in Table 2. In this table, a circle indicates that the unevenness of the substrate surface was not visible on the decorative sheet surface, and a good surface condition was observed, while an X indicates that the unevenness of the substrate surface was visible on the decorative sheet surface, and a poor surface condition was observed.

As can be seen from the results in Table 1, there is a tendency for the average and maximum values of the maximum height Rz of surface irregularities to decrease as the weight blend ratio of Sample A increases. Specimens 1-9, which contain 30% or more Sample A, all have smaller average and maximum values of maximum height Rz than conventional OSB (Comparative Examples C and D: both have extremely large average and maximum values of maximum height Rz, indicating significant surface irregularities). While this improves surface smoothness, Specimens 4-9, which contain 66% or less Sample A by weight, do not achieve values comparable to MDF (Comparative Examples A and B). In contrast, Specimens 1-3, which contain 68% or more Sample A by weight, achieve surface smoothness close to that of MDF (Specimens A and B). In particular, it was confirmed that when the weight blend ratio of Sample A is 70% or more (Specimens 1 and 2), surface smoothness roughly equivalent to that of MDF (Comparative Examples A and B) is achieved.

Furthermore, as can be seen from the results shown in Table 2, all of specimens 1 to 3 had good surface conditions when a decorative sheet was applied directly onto them. These results demonstrate that shaved wood flake boards manufactured with a weight blend ratio of sample A of 68% or more, and more preferably 70% or more, are suitable for use as a base material for decorative boards in place of MDF.

In the above test example, the weight blending ratio of Sample A was set to a maximum of 80% (Specimen 1). Based on the results shown in Table 1, it is predicted that blending a larger amount of Sample A would result in smaller average and maximum values of the maximum surface height Rz, resulting in surface smoothness equal to or greater than that of MDF (Specimens A and B), and that blending 100% Sample A would produce the greatest effect. However, producing wood shavings with a thickness of 0.1 to 0.6 mm is less productive and more costly than producing wood shavings with a thickness of 0.7 mm or more, making it impractical to blend in excessive amounts. Furthermore, by blending a certain amount of Sample B, which is made up of relatively thick wood shavings, the weight of Sample B serves to sink the entire mat, stabilizing the mat on the production line and preventing line stoppages due to tilting, collapse, or tipping. From these perspectives, it is preferable to set the weight blending ratio of Sample A to 95% or less.

Furthermore, in the above test example, as mentioned above, Sample A was prepared by mixing not only 0.1-0.6 mm thick wood shavings, but also wood powder and chips less than 0.1 mm thick that are inevitably generated when obtaining these thin wood shavings. The shavings contained in Sample A can be obtained without the need for separation from the 0.1-0.6 mm thick wood shavings after obtaining them, which not only improves workability and cost benefits but also reduces raw material waste. Furthermore, by mixing the shavings into the raw wood shavings, the shavings penetrate into the gaps between the wood shavings during hot pressing and fill those gaps, thereby improving the surface smoothness of the resulting wood shavings board as well as improving various physical properties.

The present invention has been described in detail above using test examples, but the present invention can be implemented in 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 less than 0.6 mm thick 3 Wood shavings more than 0.6 mm thick 4 Decorative material 5 Decorative board

Claims (4)

A shaved wood board is obtained by mixing and aggregating wood shavings obtained by cutting wood and having lengths of 10 to 200 mm, widths of 1 to 50 mm, and thicknesses of 0.6 mm or less, and wood shavings of 10 to 200 mm, widths of 1 to 50 mm , and thicknesses greater than 0.6 mm, with an adhesive, and then thermocompressing the mixture. The shaved wood board is characterized in that the wood shavings are stacked one on top of the other, and the surface of the shaved wood board is formed by compressed wood shavings, and the average maximum height, which indicates the surface roughness defined in Japanese Industrial Standard JIS B 0601:2013, is 40 μm or less, and the maximum value is 50 μm or less. A method for producing a shaved wood board, comprising: preparing a first group of shaved wood flakes consisting of an aggregate of shaved wood flakes with a thickness of 0.6 mm or less; and preparing a second group of shaved wood flakes consisting of an aggregate of shaved wood flakes with a thickness of more than 0.6 mm; blending the first group of shaved wood flakes at 68% by weight or more of the total amount of the first and second groups of shaved wood flakes to form raw shaved wood flakes; applying an adhesive to the raw shaved wood flakes, mixing them, and accumulating them; and thermocompressing them together. The method for manufacturing a shavings board according to claim 2, wherein the first group of shavings includes shavings generated when obtaining the shavings. A shaved wood board manufactured by the manufacturing method described in claim 2 or 3.