JP4997067B2 - Wood fiber board and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a lightweight woody fiberboard having high hardness and high strength irrespective of superior heat resistance with good productivity by a wet sheet-forming method. <P>SOLUTION: The woody fiberboard is obtained by loading water with a bonding agent comprising of woody fibers as a main constituent and containing at least isocyanate groups and carrying out sheet forming of the resultant slurry into a wet mat, and thermally pressure-bonding the wet mat with a thermal press up to the state that the bonding agents on the front and rear layers turn semi-cured to keep the woody fiber on the front and rear layers from being sprung back. Then, the wet mat is pressure released to cause the woody fiber in the core layer of the wet mat to be sprung back, and then heated with hot air to completely cure the bonding agent. Thereby, a woody fiberboard is obtained of an entire density of 0.5 to 0.7 g/cm<SP>3</SP>, a density of the front and rear layers of 0.6 to 0.9 g/cm<SP>3</SP>and a density of the core layer of 0.4 to 0.65 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a wood fiber board having excellent strength despite being lightweight and having high heat insulation properties, and a method for producing the same.

Conventionally, a relatively low density wood fiber board of 0.45 g / cm ³ or less has been produced by wet papermaking. Normally, according to the method of manufacturing a wood fiber board by wet papermaking, the wet mat requires a very long heat drying because it contains a large amount of moisture. Springback due to the repulsive force is generated and cannot be formed in a high-density fiber layer, and therefore a high-strength wood fiberboard cannot be obtained. It is conceivable to increase the amount of binder added to the wood fiber in order to suppress the spring back of the wood fiber, which causes a decrease in density, but the productivity becomes worse and the surface of the wood fiber becomes the binder. There arises a problem that heat insulation and moisture absorption and desorption are reduced due to being covered with.

  Therefore, as a solution for increasing the strength of the wood fiberboard produced by wet papermaking, for example, as described in Patent Document 1, when producing a wood fiberboard by the wet papermaking method, As a fiber binder, a binder (adhesive) containing an isocyanate group that reacts with hydroxyl groups of water and wood fibers is used, and this binder is reacted with the hydroxyl groups of wood fibers to produce primary strength. Later, a method for producing a wood fiber board in which the binder is cured together with other binders to produce secondary strength has been developed.

JP 2007-13811 A.

  However, even in the wood fiberboard manufacturing method described above, there is a limit to the suppression of springback by the binder. Therefore, if the density is further increased and high strength is aimed at, it is possible to use hot press as in the hardboard manufacturing method. Although overall densification is conceivable, mere densification reduces heat insulation and moisture absorption and release. On the other hand, it is conceivable to aim for high strength by applying and impregnating a binder to the front and back surfaces of a wet mat or wood fiberboard and strengthening only the front and back surfaces of the wood fiberboard. Since the number of processes increases, problems such as an increase in cost and a decrease in productivity occur. In general, wet mats obtained by wet papermaking have the same fiber density between the front and back layers and the core, and the density distribution changes between the front and back layers and the core layer as in dry papermaking. It has been difficult to produce a wood fiber board that has a low density inclined from the back side toward the center.

  The present invention has been made in view of such problems, and the object of the present invention is to provide excellent heat insulation and moisture absorption and release properties using wood fibers and to reduce weight. It is in providing the wood fiber board provided with higher intensity | strength, and its manufacturing method.

In order to achieve the above object, the wood fiberboard of the present invention is a wood fiberboard manufactured by wet papermaking by adding a binder containing at least an isocyanate group to a wood fiber as described in claim 1. The front and back layers are formed in a fiber layer formed by bonding wood fibers without causing spring back, and the core layer is formed in a fiber layer formed by bonding wood fibers in a state where spring back is generated. It is characterized by.

In the wood fiber board configured as described above, the invention according to claim 2 is characterized in that the whole density of the wood fiber board is 0.5 to 0.7 g / cm ³ and the density of the front and back layers is 0.6 to 0.9 g / cm ^3. The dense fiber layer is formed into a coarse fiber layer having a core layer density of 0.4 to 0.65 g / cm ³ .

  The invention according to claim 3 is a method for producing the wood fiber board, wherein a wet mat is made from a slurry comprising wood fiber as a main component and at least an isocyanate group-containing binder added to water. After the primary dehydration of the mat, heat-pressing until the binder of the front and back layers of the wet mat is in a semi-cured state while performing secondary dehydration by a hot press, so that the wood fibers of the front and back layers cannot spring back, It is characterized in that after releasing the pressure and generating a spring back in the wood fiber of the core layer of the wet mat, the binder is cured by hot air drying.

In this wood fiberboard manufacturing method, the invention according to claim 4 has an overall density of 0.5 to 0.7 g / cm ³ , a front and back layer density of 0.6 to 0.9 g / cm ³ , and a core layer density of 0.4. It is characterized by obtaining a wood fiber board of ˜0.65 g / cm ³ .

According to the wood fiber board of the present invention, it is a wood fiber board obtained by wet papermaking, wherein the front and back layers are made of fiber fibers formed by joining wood fibers together without causing spring back, and the core layer is made of spring back. Is formed in a fiber layer in which wood fibers are bonded to each other in a state in which generation is generated, so that the front and back layers are formed in a high-density fiber layer having a density of 0.6 to 0.9 g / cm ^3. The core layer can be formed into a fiber layer of 0.4 to 0.65 g / cm ³ , which is coarser than the density of the front and back layers, and this low-density fiber layer can not only ensure weight reduction, but also has excellent heat insulation properties. In addition, since the density of the front and back layers is high, it is possible to achieve higher strength than the wood fiber board of the same density despite being light weight.

  Further, since this wood fiber board is manufactured by wet papermaking, it can provide a homogeneous wood fiber board with less variation in fiber density as a whole, and the wood fiber produced by wet papermaking has its wood fiber on the plate surface. Therefore, it is possible to exhibit even better heat insulation.

  Further, according to the above method for producing a wood fiber board, after making a wet mat from a slurry composed mainly of wood fibers and adding at least an isocyanate group-containing binder to water, the wet mat is subjected to primary dehydration. In addition, the water content is decreased by the primary dehydration because the binder of the front and back layers of the wet mat is hot-pressed to a semi-cured state where the wood fibers of the front and back layers cannot spring back while being subjected to secondary dehydration by hot press. The wet mat can be easily transported to the next process, and the thermal efficiency is increased, so that the heat energy during subsequent hot-pressing can be reduced, and moreover, the heat-pressure press is performed while performing secondary dehydration, so that the thermal efficiency is further improved. The heat energy in the subsequent hot air drying can be reduced and the productivity can be improved.

  Furthermore, at the time of hot-pressing, the density of the front and back layer portions of the wet mat can be increased by hot pressure, and the reaction between the binder containing isocyanate groups and the hydroxyl groups of water and wood fibers can be promoted to change the front and back layer portions. A semi-cured state that expresses primary strength in a short time (hereinafter, this semi-cured state is called a semi-cured state) can be advanced, and the density of the front and back layers can be kept high. As described above, since the binder containing the isocyanate group also reacts with the hydroxyl group contained in the wood fiber, the bonding force between the fibers can be increased even in a small amount, and a higher strength wood fiber board can be obtained. It can be produced efficiently.

  The semi-cured state is a state in which the binder is semi-cured, and at least the front and back layers are cured more than the semi-cured core layer of the wet mat, and the spring of the wood fiber is no longer present. A state where no back occurs. On the other hand, although the core layer is also in a semi-cured state, since the binder has not been cured, a fiber layer having a lower density than the front and back layers can be formed in a cured state in which a wood fiber springback occurs. it can.

In addition, as described above, by setting the front and back layers of the wet mat to a semi-cure state, the spring back of the wood fiber board when the hot press is released can be suppressed to a slight extent. With this hot air drying, the binder between the front and back layers and the core layer is finally cured, so that the density of the front and back fiber layers is cured without springback of the wood fibers. There the dense layer of 0.6 ~0.9 g / cm ^3, density than the front and back layer by the core layer is wood fiber to spring back crude 0.4 ~0.65g / cm ^3, preferably of 0.4 ~0.6 g / cm ³ A high-strength wood fiberboard can be obtained which can be formed in a low-density layer and has a light weight with an overall specific gravity of 0.5 to 0.7 g / cm ³ .

  At this time, the front and back layers of the wet mat are finally cured after the semi-cured state in which the wood fiber does not spring back even if the density is increased by hot pressing to release the pressure, so that the fiber density of the front and back layers is particularly high. It is possible to produce a wood fiberboard that exhibits excellent strength that is not obtained by conventional wet papermaking, although it is lightweight. Further, even when the semi-cure is in progress, since it is not finally cured, it does not prevent moisture remaining on the wet mat from evaporating from the front and back surfaces of the wet mat. Generation of puncture can be suppressed.

  On the other hand, since the core layer of the wet mat has a lower degree of semi-cure state than the front and back layers during hot-pressing, the wood fiber can be spring-backed when the pressure is released. Although the density can be lower than that of the front and back layers, the spring back of the wood fiber board of the core layer can be suppressed to the minimum necessary by the front and back layers of the semi-cured state. The fiber of the core layer part is slightly spring-backed to reduce the density, and the wood fiber board can be obtained that is lightweight and exhibits excellent heat insulation. Moreover, since a high strength can be realized at a low density without reducing the amount of wood fibers, the moisture absorption and release properties are not impaired.

The embodiment of the present invention will be described in detail. FIG. 1 is a simplified longitudinal sectional view of a part of a wood fiber board A. This wood fiber board is obtained by a wet papermaking method. The wood fibers are bonded to each other by a binder containing at least an isocyanate group as the main component, and the fiber layers 1 and 2 on the front and back sides of the fiber layers forming the respective layers at the time of production cause a springback. Without being formed in a dense fiber layer having a density of 0.6 to 0.9 g / cm ³ bonded with the binder, the core layer 3 as an intermediate layer is a woody material forming the core layer 3. density fiberboard is bonded at the bonding agent in the state that caused the springback 0.4 ~0.65g / cm ^3, preferably Yes it forms a coarse fiber layer 0.4 ~0.6 g / cm ^3, and The density of the whole wood fiber board is 0.5-0.7 g / cm ³ ing. FIG. 2 shows an example of the density distribution of the wood fiber board A having a thickness of 8.4 mm.

Thus, although the said wood fiber board A is a fiber board obtained by the wet papermaking method, the fiber density of the front and back layers 1 and 2 and the core layer 3 differs, and the density of front and back layers is 0.6- Since 0.9 g / cm ³ is high, high strength can be realized, while the density of the core layer is 0.4 to 0.65 g / cm ³ , which is formed in a fiber layer having a lower density than the front and back layers 1 and 2. The fiber layer can not only ensure weight reduction, but also can exhibit excellent heat insulation and moisture absorption and release properties. Furthermore, the wood fiber board A obtained by the wet papermaking method has little variation in fiber density as a whole, and the wood fibers are oriented in parallel to the board surface, so that more excellent heat insulation can be achieved.

  Next, the manufacturing method of the three-layered wood fiber board A having different densities in the front and back layers and the core layer as described above will be described with reference to FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a simple image figure of the wet mat from which a shape changes with each process, Comprising: First, the slurry formed by adding mainly the wood fiber and the binder containing an isocyanate group to water by the wet papermaking method is prepared. At this time, the type of wood fiber is not limited, and it is not limited to conifers and hardwoods, and it is also possible to use fibers derived from construction waste materials, pallet waste materials, etc., or plant fibers such as pulp, hemp, flax and the like.

As the binder containing the isocyanate group, monomeric MDI (4,4′-diphenylmethane diisocyanate), polymeric MDI, TDI (tolylene diisocyanate), XDI (xylylene diisocyanate), HDI (hexamethylene diisocyanate), H ₁₂ MDI (4,4′-methylenebis (cyclohexyl isocyanate)), IPDI (isophorone diisocyanate) and various polyols thereof (low molecular weight polyols, polyether polyols, polyester polyols, polycarbonate diols, acrylic polyols, silicon polyols) 2-hydroxyethyl acrylates), dibasic acids (eg azelaic acid, adipic acid, sebacic acid, isophthalic acid, terephthalic acid, etc.), various epoxy resins, Reactant with active hydrogen compounds such as bran oil, liquid polybutadiene, neoprene, etc., or those with improved dispersibility in water by adding various modifications and mixing with various surfactants, and extending pot life In order to achieve this, various modified products including those having blocked isocyanate groups are listed, and these can be used alone or in combination of two or more.

  Further, the binder added to the wood fiber together with water may be the above-mentioned binder containing an isocyanate group alone, but the addition of the binder containing the isocyanate group is essential, and other binders such as starch or It is also possible to use a thermosetting resin such as a urea resin, a urea-melamine resin, or a phenol resin in combination with a binder containing this isocyanate group.

  In this case, it is preferable that the addition amount of the binder containing the isocyanate group-containing binder is 10 to 30% by weight. If the added amount is less than 10% by weight, the wood fiber becomes 90% by weight or more, and the binding effect to the wood fiber becomes difficult to be expressed. If the added amount is more than 30% by weight, it flows out during the formation and dehydration of the wet mat. This is because only the amount of the binder increases, so that the binding effect is not improved and the productivity is lowered. In addition, the addition amount of the binder containing an isocyanate group is 1% by weight or more, more preferably 1 to 5% by weight. If the amount added is less than 1% by weight, the reaction effect (semi-cure state) cannot be expected in a heating state in which the core layer portion 3 ′ of the wet mat A ′ by the hot press described later does not fall below 100 ° C. Because.

  Furthermore, in order to enhance the reaction of the binder containing an isocyanate group and enable a strong bond with a short heating reaction, during the process of heating and drying the wet mat by adding an isocyanate group reactive substance other than water To produce urethane, urea, amide, burette, acylurea, allophanate, and the like.

  Examples of such isocyanate group-reactive substances include various polyols (low molecular weight polyols, polyether polyols, polyester polyols, polycarbonate diols, acrylic polyols, silicon polyols, etc.), and generally various polypropylene glycols (hereinafter referred to as PPG). (Ethylene oxide modified PPG, primary OOH-modified PPG, bisphenol A modified PPG, rosin modified PPG, etc.), various polyethylene glycols, various povals, polybutadiene polyols, hydrogenated polybutadiene polyols, polytetramethylene ether glycols, polyester polyols, castor oil-based Polyols, acrylic polyols, etc., and 2-hydroxyethyl acrylate and compounds having amino groups (acrylic amides, urine Compounds, various diamines, etc.), dibasic acids (eg azelaic acid, adipic acid, sebacic acid, isophthalic acid, terephthalic acid, etc.), compounds having a carboxyl group such as vinyl acetate, various epoxy resin compounds, castor oil, Examples thereof include active hydrogen compounds such as liquid polybutadiene and neoprene. Of course, these can be used alone or in combination of two or more.

  In addition, in order to perform wet papermaking from the slurry, papermaking additives such as a sizing agent, a flocculant, and an antifoaming agent may be added as necessary. Furthermore, you may use the heat sealing | fusion fiber which has the function as an adhesive agent as needed.

Next, the slurry formed by using the wood fiber and the binder as main raw materials as described above and adding other materials to water as necessary is wetted by a paper machine such as a long net type or a round net type. The wet mat A ′ is obtained by paper making, and the wet mat A ′ is primarily dehydrated. Primary dehydration is performed by using a dehydrator or a roll press alone or in combination. After the primary dehydration, the wet mat A ′ is fed into a hot press, and the binders of the front and back layers 1 ′ and 2 ′ of the wet mat A ′ are added while being hot depressurized from the front and back surfaces of the wet mat A ′. Semi-cure (semi-cured state) and then decompressed, and then wet mat A 'is dried with hot air to cure the binder of front and back layers 1', 2 'and core layer 3', resulting in a density of 0.5 to 0.7 g. / Cm ³ of wood fiberboard A is obtained.

  In the step of hot-pressing the wet mat A ′, the binder of the front and back layers 1 ′ and 2 ′ is semi-cured while secondary dehydrating the wet mat A ′, and may not be performed until final curing. It is important to make the binder of the front and back layers 1 ′, 2 ′ semi-cure, and then release the pressure to cause a slight springback in the fibers of the core layer portion 3 ′ of the wet mat A ′. The binder is finally completely reaction-cured in the heat-drying step according to 1. Note that when the front and back layers 1 'and 2' of the wet mat A 'are finally cured in the hot press process, the moisture contained in the wet mat A' is difficult to escape from the front and back surfaces, and puncture occurs in the subsequent heat drying process. It becomes easy and productivity will fall.

  The front and back layers 1 ′ and 2 ′ of the wet mat A ′ that has been hot-pressed are in a semi-cured state and in a semi-cured state, and in this state, the spring back of the fibers of the front and back layers 1 ′ and 2 ′ is On the other hand, since the binder does not harden in the core layer 3 ′, the fiber springs back due to the decompression, resulting in a lower density than the front and back layers 1 ′ and 2 ′. The spring mat prevents the wet mat A 'from expanding greatly in the thickness direction by the front and back layers 1' and 2 'in a semi-cured state, and promotes a slight spring back to increase the density of the core layer 3'. By suppressing, heat insulation is secured and weight reduction is achieved. In addition, the setting conditions of a hot press can be suitably set according to the quantity of wood fiber, reaction temperature, target density, etc.

By repeating this hot-pressing step and the primary dehydration step multiple times, or by repeating the hot-pressing step and depressurization multiple times, and also changing the hot-pressing temperature at that time, a density of the whole of the 0.5 ~0.7 g / cm ^3, and front and back layers is 0.6 ~0.9 g / cm ^3, the core layer is more accurately wood fiber board a formed to a density of 0.4 ~0.65g / cm ³ And it becomes possible to manufacture with high productivity.

  The temperature setting of the hot press may be set so that the temperature of the core layer 3 ′ of the wet mat A ′ does not exceed 100 ° C. When the core layer 3 ′ exceeds 100 ° C., the degree of semi-cure of the core layer 3 ′ is advanced, and it becomes impossible to cause fiber springback. Specifically, the temperature of the hot press is set to 60 to 120 ° C. If the set temperature is lower than 60 ° C, it takes time for the binder to harden and the productivity is lowered, and if it exceeds 120 ° C, the front and back layers 1 'and 2' of the wet mat A 'are hardened. Thus, as described above, moisture in the wet mat A ′ is difficult to escape from the front and back surfaces, and puncture is likely to occur during subsequent hot air drying. The heating and drying step is performed with a normal dryer, and the temperature is suitably 150 to 190 ° C. Next, examples of the present invention and comparative examples will be described.

[Example 1]
80% by weight of wood fiber, 5.75% by weight of powdered phenol as a binder, 5.75% by weight of polyvinyl alcohol (PVA), 7.0% by weight of tapioca starch, and 1.5% by weight of polymeric MDI as a binder containing isocyanate groups A slurry was prepared by stirring and mixing in water, and a flocculant and a sizing agent were added in appropriate amounts to the slurry, followed by paper making to obtain a wet mat. Furthermore, this wet mat was subjected to a pressure of 20 kgf / cm ² for 15 seconds, a pressure of 40 kgf / cm ² for 15 seconds, and a pressure of 20 kgf / cm ² for 60 seconds by a hot press maintained at a heating temperature of 90 ° C. This was hot-pressed to bring the front and back layers of the wet mat into a state where the semi-cure was advanced. At this time, the core layer was not in a semi-cured state.

After this hot-pressing process, the pressure is released to slightly spring back the fibers of the core layer of the wet mat, and then the product is transported to a dryer and dried with hot air at 170 ° C. for 90 minutes. Part of the binder was completely reaction-cured to obtain a thickness of 8.4 mm, an overall density of 0.62 g / cm ³ , a front and back layer density of 0.6 to 0.8 g / cm ³ , and a core layer density of 0.5 to 0.6 g / cm ³ . A three-layer wood fiberboard of cm ³ was obtained. This wood fiberboard is subjected to nail side resistance test and nail head penetration test according to ASTM D 1037, and racking test is performed according to the “Report on Test and Evaluation of Wooden Bearing Wall and Its Magnification” (Building Materials Testing Center). went. Moreover, the measurement result of the density distribution in the thickness direction is shown in FIG.

[Comparative Example 1]
80% by weight of wood fiber, 5.75% by weight of powdered phenol as a binder, 5.75% by weight of polyvinyl alcohol (PVA), 7.0% by weight of tapioca starch, and 1.5% by weight of polymeric MDI as a binder containing isocyanate groups A slurry was prepared by stirring and mixing in water, and a flocculant and a sizing agent were added in appropriate amounts to the slurry, followed by paper making to obtain a wet mat. The wet mat was dehydrated with a dehydrator and a roll press. The moisture content of the wet mat at this time was 200%. Next, this wet mat is transported to a dryer and dried with hot air at 170 ° C. for 90 minutes, and the binder of the front and back layers and the core layer is completely reacted and cured to have a thickness of 12 mm and a density of 0.43 g / cm. ^Three wood fiberboards were obtained. This wood fiber board was tested in the same manner as in Example 1 above. Table 1 shows the test results of Example 1 and Comparative Example 1.

  As is apparent from this table, Example 1 and Comparative Example 1 are different from each other in that the heat and pressure treatment conditions are different from Example 1 despite the fact that the wood fiber board is produced from a wet mat made of the same composition. Compared to Comparative Example 1, the density of the wood fiberboard increased and the strength increased. As is clear from FIG. 2, the wood fiberboard of Example 1 is formed such that the density of the front and back layers is higher than the density of the core layer, and the density changes between the front and back layers and the core layer. It can be seen that the density distribution is slanted from the front and back sides toward the center.

The simplified longitudinal cross-sectional view of a part of wood fiber board. The graph which shows the density distribution of a wood fiber board. (A) is a manufacturing process, (B) is a simplified image diagram of a wet mat whose shape changes depending on each process.

Explanation of symbols

A Wood fiberboard
A 'wet mat 1, 2 front and back layers 3 core layers

Claims (4)

A wood fiber board manufactured by a wet papermaking by adding a binder comprising at least an isocyanate group in wood fiber, front and back layers to the fibrous layer formed by binding the wood fibers to each other without causing springback core A wood fiberboard characterized in that the layer is formed into a fiber layer formed by joining wood fibers together in a state where a spring back is generated. Wood fiber board, a density of the total 0.5 ~0.7 g / cm ^3, and, in dense fibrous layer in the density of the front and back layer is 0.6 0.9 g / cm ^3, the density of the core layer is 0.4 ~0.65g / cm ^2. The wood fiber board according to claim 1, wherein the wood fiber board is formed into ^three coarse fiber layers.   A wet mat is made from a slurry composed mainly of wood fibers and containing at least an isocyanate group-containing binder in water. The wet mat is primarily dehydrated, and then the wet mat is subjected to secondary dehydration by a hot press. After the front and back layer binders are hot-pressed until they are in a semi-cured state, the wood fibers of the front and back layers are not allowed to spring back, and then the pressure is released to generate spring back on the wood fibers of the wet mat core layer. A method for producing a wood fiberboard, characterized in that the binder is cured by drying with hot air. In overall density is 0.5 ~0.7 g / cm ^3, and a feature that the density of the front and back layers is 0.6 ~0.9 g / cm ^3, the density of the core layer to obtain a wood fiber board of 0.4 ~0.65g / cm ³ The manufacturing method of the wood fiber board of Claim 3 to do.

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