JP2006289759A - Method for manufacturing wooden board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of improving the productivity of a wooden board such as a particle board (PB) and a medium density fiber board (MDF) and also producing a high quality product. <P>SOLUTION: In the wooden board manufacturing method comprising the forming process wherein a wooden material, such as chips and fibrillated fibers mixed with an adhesive, is evenly laid into a fixed thickness and the hot press process wherein the wooden material laid into the fixed thickness is hot-pressed into a predetermined thickness, the high-frequency preliminary heating process is arranged as a previous process of the hot press process. By providing the object to be worked with the high-frequency preliminary heating the inside of the worked object is heated, and by the synergistic effect with the subsequent hot press that is an external heating, the time of the hot press is shortened to improve the productivity, and the product having high quality is offered. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a wood board represented by particle board (PB), medium density fiber board (MDF) and the like.

  Wood boards are mainly used as building materials and construction materials. The quality of wood boards varies depending on the application. For example, particle boards and medium density fiber boards are widely used mainly for window frames, doors, flooring, cabinets and the like. In a general manufacturing method of particle board, a small piece of raw material made of various kinds of wood is cut into chips of a certain size by a flaker, and the chips dried by a dryer are sieved into large and small pieces by a screen. A thermosetting adhesive is mixed with the chip for the surface layer and the chip for the core layer, which are screened into large and small, respectively, and the chips mixed with the thermosetting adhesive are spread as much as the outer and inner layers of the product. A large thickness state is obtained, hot pressing is performed to a predetermined thickness using a hot press, and this is sanded and cut to complete the particle board.

  As the particle board manufacturing method, there are known a continuous type in which heat is continuously pressed and a multi-stage type in which heat is pressed by being stacked in multiple stages. In a continuous particle board manufacturing method, chips are spread on a conveyor that moves at a constant speed, and a preliminary press process is arranged to temporarily press the chips to a certain small thickness. Introduced in continuous hot pressing process. On the other hand, in the method of manufacturing a multistage particle board, a fixed-size coal plate is placed on a conveyor, a certain amount of chips are laid on the conveyor, and the chips are laid on the call plate. Workpieces (mats) are stacked in multiple stages, and in that state, hot pressing is performed in a multistage hot press process.

The general manufacturing method for medium density fiberboard (MDF) is to open a small amount of fiber after spreading a small piece of wood, mixing the dried fiber with a thermosetting adhesive and drying it. Thus, a thick state is obtained, which is temporarily pressed, hot pressed into a predetermined thickness using a hot press, and sanded or cut to complete a medium density fiber board.
That is, the medium density fiber board is completed by heat-pressing by a continuous hot pressing process which is external heating.
As disclosed in Patent Document 1, for example, it is known to use high-frequency dielectric heating as a method for producing a cellulose fiberboard.
JP-A-5-185524 JP-A-6-91611 JP2003-25309

In the manufacturing method of the wooden board, in order to realize the strength as the wooden board, the wooden material is sufficiently heated and bonded in the hot press process, and when the moisture contained in the material evaporates, the adhesive force is overcome ( In order not to cause a phenomenon (so-called puncture), it is necessary that the moisture contained in the wood material is completely removed below a certain value.
In the conventional method for producing a wooden board, it is necessary to heat and press for a relatively long time in order to satisfy the above conditions, which has been an obstacle to improving productivity.
That is, in the hot pressing process, which is external heating, the thermosetting adhesive mixed with the wood material such as chips and fibers is heated to a temperature that develops sufficient adhesive strength, and the moisture contained in the wood material is removed. In order to achieve this, it is necessary to heat-press for a long time, and it has been difficult to improve productivity (shortening the hot-pressing time).

Even if it is attempted to shorten the heating time by increasing the temperature of the hot pressing process, only the surface temperature of the workpiece becomes high because of external heating, and it is difficult to increase the temperature of the central portion in a short time. . In addition, a situation occurs in which the moisture inside cannot be completely removed, and the surface is overheated, and a puncture phenomenon occurs in which the steam expands after the pressure is released and the adhesive layer is damaged. Even in a situation where the puncture phenomenon does not occur, the board thickness does not reach the target after decompression due to insufficient adhesive force, and the strength as a plate material is insufficient, so that a high-quality product cannot be obtained. Thus, in the conventional manufacturing method, there is a limit to shortening the hot pressing time in the hot pressing process, and it has been difficult to improve productivity.
In view of the above-described drawbacks of the prior art, an object of the present invention is to realize a production method capable of efficiently producing a high-quality woody board.

  In order to achieve the above object, the present invention according to claim 1 includes a forming step of spreading a wood material such as a chip mixed with an adhesive or a defibrated fiber with a constant thickness, and a constant thickness. It consists of a high-frequency preheating process that heats the wood material by high-frequency dielectric heating and a hot press process that heats the wood material preheated by high-frequency dielectric heating to a certain high temperature and hot-presses it to a predetermined thickness. To do.

  The invention described in claim 2 is to continuously supply the wood material that has passed through the high-frequency preheating step to the hot press step, and in the hot press step, continuously press-mold the wood material.

The invention according to claim 3 intermittently supplies the wood material that has passed through the high-frequency preheating step to the hot press step, stacks the intermittently supplied wood material in several stages, and in the state of being stacked in the several stages, It is a hot press molding in a multi-stage type.
That is, the invention according to claim 2 relates to a continuous production method, and the invention according to claim 3 relates to a multistage production method.

  The invention according to claim 4 is that the heating in the high-frequency preheating step is a temperature at which the adhesive does not begin to harden in the center of the workpiece.

  According to the first aspect of the present invention, in the high-frequency preheating step, the temperature in the intermediate portion of the workpiece thickness is raised, and then hot pressing is performed from both sides of the workpiece in the hot pressing step. Therefore, the whole workpiece can be heated to a constant temperature in a short time as a whole, and productivity can be improved. In addition, since the entire workpiece is heated to a relatively uniform temperature, there is no partial excess heating, and the moisture content inside the workpiece is reduced in the high frequency preheating step, It is possible to manufacture a high-quality wooden board that is stable in strength and hardly generates puncture.

  The invention according to claim 2 relates to a specific configuration to which the present invention is applied in a continuous manufacturing method, and is provided with a high frequency preheating step for moving the workpiece at a constant speed. The feed rate can be increased and production efficiency can be increased.

  The invention according to claim 3 applies the present invention to a multi-stage manufacturing method, and shortens the press time by hot pressing and improves the production efficiency by preheating the work piece with high frequency. Can do.

  According to invention of Claim 4, a high quality product can be manufactured efficiently, without deteriorating an adhesive agent by high frequency preheating.

Hereinafter, a preferred embodiment of a method for producing a wooden board according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view of an entire apparatus showing an example of an apparatus for continuously performing a method for manufacturing a wooden board according to the present invention, and FIG. 2 is an apparatus for performing a method for manufacturing a wooden board according to the present invention in a multistage manner. FIG. 3 is a flow chart of a continuous particle board (PB) manufacturing process using the present invention, and FIG. 4 is a continuous medium density fiber board (MDF) manufacturing using the present invention. FIG. 5 is a flowchart of a multistage particle board (PB) manufacturing process using the present invention.

  In the production of particleboard, various wooden pieces such as building waste and plywood waste are used, and the wooden pieces carried by a truck or the like are stored in a silo. As shown in FIGS. 1 and 3, the small pieces of wood stored in the silo are cut to a certain size with a flaker to form chips, which are dried to some extent in the drying process, and the dried chips are temporarily stored. The dried chips are screened into a small particle size for the surface layer and the core layer in the screening process, and in the adhesive mixing process, the thermosetting adhesive is mixed into the surface layer chip and the core layer chip, respectively, in the forming process. Supply. The moisture content of the chip supplied to the forming process is different between the surface layer chip and the core layer chip, but is 25% or less for the surface layer chip and 15% or less for the core layer chip.

  In the forming process, the chips 3 mixed with the thermosetting adhesive are supplied on the conveyor 1 that is moved at a constant speed by the forming device 2 so as to have a constant thickness. That is, a necessary amount of chips 3 are arranged according to the product layer structure according to the thickness of the product. The thickness at this time varies depending on the air mixing state and the like, but is larger than the thickness of the final product. The chips 3 spread by the forming process are sent to the preliminary pressing process by the conveyor 1. That is, the chips 3 on the conveyor 1 are temporarily pressed by the press conveyor 4. In the preliminary pressing step, the spread chips are compressed to a thickness of about one half.

  A high-frequency preheating step is arranged following the prepressing step. The high-frequency heating device 5 disposed as a high-frequency preheating step is disposed above the lower electrode 5a disposed below the conveyor-side belt of the conveyor and the pre-compressed workpiece 7 on the conveyor. 7 and an upper electrode 5b arranged at a position where it passes without contacting. The workpiece 7 that has passed through the high-frequency preheating process is supplied to the hot press process. The continuous hot press apparatus 6 arranged in the hot press process moves forward while sandwiching the workpiece by the lower pressure belt 6a (steel belt) and the upper pressure belt 6b (steel belt) provided with heating means. In order to obtain a predetermined thickness, heat pressing is performed, and the adhesive is sufficiently cured to complete the molding.

  The workpiece 7 that has been molded by the hot press process is subjected to surface finishing by the sanding process, and is cut into product dimensions before shipment. Although the thickness of the spread in the forming process varies depending on the thickness of the final product, it is compressed to about 50% of the thickness spread in the preliminary press process, and the thickness reduction due to the sanding process in the hot press process. Is hot pressed to a predetermined thickness.

  Medium density fiberboard (MDF) is a thermosetting adhesive to the fiber obtained by the defibration process, which removes foreign substances such as sand by screening process and chip cleaning process, and removes the fiber by steaming. The fiber mixed with the thermosetting adhesive is dried to a moisture content of 20% or less. The fibers dried by the drying process are temporarily stored and supplied to the forming process as necessary, and are spread on the conveyor 1 in a certain thickness in the forming process. Thereafter, as in the case of the particle board, the molding is completed through a pre-pressing step, a high-frequency pre-heating step, and a hot pressing step, and then cut into product dimensions through a sanding step to complete a medium density fiber board.

As a manufacturing method of the wood board, there are not only the above-described continuous manufacturing method but also a multi-stage manufacturing method, and a schematic process thereof is shown in FIG.
Chips obtained by cutting various pieces of wood are supplied to a forming process through a drying process, a screening process, and an adhesive mixing process. Below the forming device 2, a transfer means 8 such as a chain conveyor is disposed, and a support plate having a certain size commonly called a call plate 9 is transferred by the transfer means 8. A fixed-size call board 9 has a fixed width crossbar 10 fixed at the top. The above-described call plate 9 is disposed without a gap, is sent forward at a constant speed by the transfer means 8, and the chip 3 is laid on the chip 3 in a required amount according to the thickness of the product. The state where the chips are spread is commonly called a mat.

  A high-frequency heating device 5 is disposed ahead of the forming process. The high-frequency heating device 5 is composed of a lower electrode 5a positioned below the call plate 9 and an upper electrode 5b positioned above the work piece (mat) laid out. The workpiece on the call plate 9 that passes through the space at a constant speed is preheated. The pre-heated workpiece is removed from the chips on the crossbar by the mat cutting device 11, and the workpiece (mat) having a certain size is placed on the call board, and the separation conveyor 12 Are taken out one by one and once accumulated in the loader 13.

Subsequently, the work pieces accumulated in the loader 13 are supplied to the multi-stage hot press device 14 and heat pressed to complete a wood board of a predetermined thickness. The finished wood board is discharged out of the machine by the discharge device 15. To do.
The multi-stage hot press apparatus 14 pressurizes the workpiece by hot pressing the cylinder 17 in a state where a plurality of workpieces (mats) are sandwiched between the hot platen 16 and the hot platen 16 and stacked. That is, a plurality of wood boards are completed at a time.

  Next, the high-frequency preheating process will be described in detail. In the forming process (including the pre-pressing process), the workpiece 7 formed with a constant thickness is formed between the lower electrode 5a and the upper electrode 5b of the high-frequency heating device 5 to which a high-frequency current (frequency of 40.46 MHz or less) is applied. When passing through, it is heated by high frequency dielectric. The high-frequency dielectric heating causes the workpiece 7 that is a dielectric to generate heat internally, and has a characteristic that the central portion is heated to a higher temperature. The heating temperature in the high-frequency preheating does not have to be particularly high. For example, a great effect is exhibited even by a temperature rise of about 1 to 5 degrees Celsius.

In the manufacturing method of the continuous and multi-stage wood board of the illustrated embodiment, the workpiece passes through the high-frequency preheating process at a constant speed, and is dielectrically heated during the process. As a result of shortening the hot pressing time in the hot press process, it is possible to increase the transfer rate of the workpiece and increase the production efficiency. According to the experiments by the present inventors, the hot pressing time of the workpiece can be shortened by 10 to 30% by performing high-frequency preheating in which the internal temperature of the workpiece is increased by about 1 to 5 degrees Celsius. It was.
In both the continuous and multi-stage methods in the illustrated example, the high-frequency preheating process is configured such that the work piece moves at a constant speed. In this case, preheating may be performed intermittently.

  FIG. 6 schematically shows the temperature distribution of the workpiece in the hot pressing process. As shown in (a-1), the whole work piece when the conventional preheating is not performed has a constant temperature. As shown in (a-2), the front and back surfaces of the workpiece are rapidly heated by the heating from the front and back surfaces by the hot press apparatus. By continuing heating from the front and back surfaces, the central portion is also gradually heated, and eventually the central portion is also heated to a high temperature necessary for heat bonding. That is, from (a-2) to (a-4) in FIG. 6, a certain amount of time is required because the thermal conductivity of the wood material is small.

  On the other hand, as shown in FIG. 6 (b-1), the workpiece subjected to the high-frequency preheating is heated at the central portion of the thickness, and is hot-pressed from the front and back surfaces by a hot press device. In addition, the front and back surfaces are heated as shown in (b-2), and heat is transferred to the central part of the thickness of the workpiece, and the whole shown in (b-3) is heated quickly to the heated state. can do. That is, the workpiece can be effectively heated in a short time by combining the internal heat generation of the high-frequency preheating device and the external heating of the hot press device. Thereby, the feed speed of the workpiece 7 can be increased and the production speed can be increased. Also, the amount of heat used as a whole can be reduced.

The effect of arranging the high-frequency preheating step is not only to raise the temperature of the workpiece in a short time but also to reduce the moisture of the workpiece.
FIG. 7 schematically shows moisture changes in the surface layer 18 and the core layer 19 of the workpiece 7 in the particle board manufacturing process. FIG. 7A shows a case where high-frequency preheating is not performed. FIG. 7B shows the moisture change in the workpiece when the high-frequency preheating is performed.

(A-1) of FIG. 7 shows the moisture state in the work piece 7 temporarily pressed in the preliminary pressing step, and the surface layer 18 and the core layer 19 each contain a relatively large amount of moisture. .
In the state of (a-1), when hot pressing is performed in the hot pressing step, the moisture in the surface layer 18 part becomes water vapor, transferring heat to the core layer 19 part, and heating the whole. At this time, since the surface layer portion is in close contact with the upper and lower pressure belts 6a and 6b, the water vapor moves in the direction of the mouth and is discharged, but is not effectively discharged. After a predetermined time during which the water vapor is discharged after being heated to a certain temperature, the product in a state where moisture is removed as shown in FIG. 5 (a-3) by releasing the pressurization by the hot press device, that is, The particle board is completed.

  If the hot pressing time is shortened in order to improve the productivity, even if the heating temperature is set high, the water vapor in the workpiece 7 cannot be completely removed, and as shown in FIG. A puncture phenomenon occurs in which the adhesive layer breaks due to the expansion of water vapor after decompression. Therefore, the hot pressing time in the hot press process cannot be shortened.

  (B-1) of FIG. 7 shows the moisture state in the work piece 7 temporarily pressed in the preliminary pressing step, and the surface layer 18 and the core layer 19 each contain a relatively large amount of moisture. This is the same as in the case of (a-1). When high-frequency preheating is performed on the workpiece 7 shown in (b-1) without being hot-pressed by a hot press, as shown in (b-2), mainly the central portion of the workpiece 7, that is, the core layer 19 The part is heated. As a result of heating the core layer 19 part, a part of the water is effectively evaporated from the surface of the surface layer 18 and the wood surface of the core layer 19, and the moisture content of the entire workpiece 7 is lowered.

  When the workpiece 7 that has undergone the high-frequency preheating step is hot-pressed in the hot press step, as shown in FIG. 7B-3, the moisture in the surface layer 18 becomes water vapor and moves to the core layer 19 portion. While transferring heat, the whole is heated. At this time, since the surface of the surface layer 18 is in close contact with the upper and lower pressure belts 6a and 6b, the movement of water vapor in the direction of the mouth is the same as in the case of (a-2) in FIG. However, in the case of (b-3) in FIG. 7, since the moisture has already been dispersed, it becomes as shown in (b-4) in FIG. 7 due to the short-time heat pressure. Therefore, by passing through the high-frequency preheating process, a high-quality product without puncture can be obtained even if the hot pressing time in the hot pressing process is shortened.

In general, particle board (PB) and medium density fiber board (MDF) are manufactured using thermosetting agents such as urea adhesives, urea-melamine co-condensation resins, amino adhesives, phenolic adhesives, and isocyanate adhesives. An adhesive is used.

  The present inventors verified the curing characteristics by high-frequency heating for the influence of high-frequency on the thermosetting adhesive itself. As a result, when the thermosetting adhesive was irradiated with a high frequency, the tendency of curing to be accelerated was remarkable. Accordingly, it has been found that the effect of improving the adhesive strength is greater even if the hot pressing time is shortened by performing high-frequency preheating in the manufacturing process of the wood board using at least a thermosetting adhesive.

For particle board (PB) and medium density fiber board (MDF), the bending strength is further improved compared with the conventional one even if the hot pressing time is shortened by the present invention that performs high frequency preheating. Is done. This is consistent with the physical property test results shown in FIGS. FIG. 8 shows the physical property test results of the particle board (PB), and FIG. 9 shows the physical property test results of the medium density fiber board (MDF).
From the test results shown in FIG. 8, in the particle board (PB), even when the press time by hot pressing is shortened by the present invention that performs high-frequency preheating, the bending strength and the peel strength are higher than those of the conventional one. It is proven to be excellent.

From the test results shown in FIG. 9, in the medium density fiber board (MDF), the press time by hot pressing can be shortened by performing high frequency preheating, and the medium density fiber board obtained by the method of the present invention is It is proved that it is superior in bending strength and peel strength as compared with a product produced by a conventional method.
From these results, in the present invention, not only productivity can be improved, but also a high quality product excellent in strength can be provided.

FIG. 1 is a schematic view of an entire apparatus showing an example of an apparatus for continuously performing the method of manufacturing a wooden board according to the present invention. FIG. 2 is a schematic view of the entire apparatus showing an example of an apparatus for carrying out the method for producing a wooden board according to the present invention in a multistage manner. FIG. 3 is a flow chart of a continuous particle board (PB) manufacturing process using the present invention. FIG. 4 is a flowchart of a medium density fiber board (MDF) manufacturing process using the present invention. FIG. 5 is a flowchart of a multistage particle board (PB) manufacturing process using the present invention. FIG. 6 is a schematic diagram showing a temperature distribution of a workpiece in a hot press process. FIG. 7 is a schematic diagram showing the moisture change of the workpiece. FIG. 8 shows the physical property test results of the particle board (PB). FIG. 9 shows physical property test results of medium density fiberboard (MDF).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conveyor, 2 ... Forming apparatus, 3 ... Chip, 4 ... Press conveyor, 5 ... High frequency heating apparatus, 5a ... Lower electrode, 5b ... Upper electrode, 6 ... Continuous hot press apparatus, 6a ... Lower pressure belt, 6b DESCRIPTION OF SYMBOLS ... Upper pressure belt, 7 ... Workpiece, 8 ... Transfer means, 9 ... Coal board, 10 ... Cross bar, 11 ... Mat cut device, 12 ... Separation conveyor, 13 ... Loader, 14 ... Multi-stage hot press device, 15 ... discharge device, 16 ... hot platen, 17 ... cylinder, 18 ... surface layer, 19 ... core layer.

Claims (4)

  A forming process for spreading wood materials such as chips mixed with adhesive and defibrated fibers to a certain thickness, a high-frequency preheating step for heating wood materials spread to a certain thickness by high-frequency dielectric heating, A method for producing a wood board, comprising: a hot press step of heating a wood material preheated by dielectric heating to a predetermined high temperature and hot pressing to a predetermined thickness.   2. The wood board according to claim 1, wherein the wood material that has passed through the high-frequency preheating step is continuously supplied to a hot press step, and the continuously supplied wood material is hot-pressed in the hot press step. Manufacturing method.   The wood material that has passed through the high-frequency preheating process is intermittently supplied to the hot press process, and in the hot press process, the intermittently supplied wood material is stacked in several stages, and the wooden materials are stacked in multiple stages in a multistage manner. 2. The method for producing a woody board according to claim 1, wherein hot pressing is performed. The method for producing a wood board according to any one of claims 1 to 3, wherein the heating in the high-frequency preheating step is a temperature at which the adhesive does not begin to harden in the center of the workpiece.