JPS5925655B2 - Manufacturing method of wood fiberboard using dry method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In manufacturing wood fiberboard using a dry method, the present invention provides improved mechanical strength and physical properties (hereinafter simply "
Regarding the method of obtaining fiberboard that has the same or better physical properties (called "physical properties") and also has excellent surface properties, I would like to further comment on how to significantly improve the physical properties of fiberboard, but it is extremely difficult to handle using the conventional dry method. While the main constituent material is highly entangled fibers, which have been considered to have a low bulk density, the binder for these fibers has low viscosity and low stickiness, and has a long gelation time. By applying a large amount of adhesive that hardens in a short time and rapidly pressing it with a high-temperature hot press, it has become possible to industrially produce fiberboard with an extremely dense surface layer and excellent physical properties. It is characterized by:

Fiberboard (hardboard,
(including semi-hard boards and insulation boards)
The adhesives used are urea, formaldehyde, de-resin, melamine-formaldehyde resin, etc., which are mainly used for plywood or particle board, so the adhesives used are 100 cps to 400 cps.
CPS, which has a high viscosity and high adhesiveness, has a fast gelling time of 5 to 10 minutes (60°C) when heated, and because it contains a curing agent, it has the disadvantage that it starts curing even at relatively low temperatures. Applying a large amount of this to fibers with low bulk density (and high entanglement) would cause process troubles such as undercoat, making it impossible to expect continuous operation of the production line.

In other words, since the above-mentioned conventional adhesive has a high viscosity, when it is turned into particles by the spray gun attached to the gluing machine, it is not made into fine particles and the number of particles is reduced, which causes the above-mentioned entanglement. When applied to fibers with a high surface area, i.e. fibers with a very large surface area, the presence of adhesive particles per unit surface area is quite low (not only is it a cause of uneven coating, but as a result, compaction is difficult). In addition to significantly deteriorating the physical properties of the fiberboard after boarding, areas to which excessive adhesive was applied formed stains, greatly deteriorating the surface quality of the board.

Furthermore, it is known that the high viscosity of the above adhesives can be reduced by adding a low viscosity solvent such as water; Since coating is required, the water content or solvent content of the fibers inevitably increases, resulting in board punctures during hot pressing, longer press times, or the amount of adhesive that permeates into the fibers after gluing. increases, and deterioration of the physical properties of the board cannot be avoided.

Furthermore, even if an adhesive whose viscosity has been temporarily lowered by adding a low-viscosity solvent as mentioned above is used, the adhesive will disperse and adhere to the fiber surface during the air blowing process after applying the adhesive. When the surface layer of the microparticles dries and a mat is formed using a forming machine to increase the adhesiveness again, a uniform mat cannot be obtained, and the physical properties of the board made by hot-pressing this board are affected by the dispersibility of the adhesive. Although the method was good, it did not yield good results and was not a fundamental solution.

Furthermore, fibers coated with high-tack adhesive can be used in blenders, air ducts and fans after the blender, etc.
It easily adheres to the board and gradually accumulates and builds up, clogging the process, or the fibers with a high resin content that have accumulated during the blending process can be peeled off and mixed in, causing resin spots on the board surface after board formation. This had significantly reduced the product value of the product.

On the other hand, with conventional adhesives, it was customary to add an acidic curing agent to shorten the heat pressing time during board formation and to completely cure the adhesive. Due to the presence of the adhesive, the adhesive begins to harden gradually at 40°C to 80°C, so if the fiber is exposed to residual heat from a dryer, some of the adhesive applied to it will cause precure due to the residual heat. In addition, even if the fiber does not have the residual heat of the dryer, the surface layer of the mat will be damaged just by contacting the hot plate of the hot press during heat compaction. In any case, the adhesive did not contribute to the efficient bonding of the fibers by the specified heat pressing, as some parts of the fibers hardened.

Therefore, the traditional method of manufacturing dry fiberboard is
By reducing the adhesive application rate to reduce the causes of the above-mentioned troubles, and at the same time increasing the specific gravity to increase the contact area between fibers and improving physical properties, the formed board is In addition to being heavy and lacking stability against moisture, conventional board manufacturing requires lower hot plate temperatures and longer press cycles, which reduces production efficiency and reduces board production. It was not possible to form a high specific gravity layer near the surface layer of the board, which resulted in deterioration of the physical properties and surface properties of the board.

In order to eliminate the above drawbacks, melamine or urea alone is blended with formalin, water, and a relatively large amount of hardening agent to create a low-viscosity, low-tack adhesive, which can be applied to ordinary fibers to improve the process. Some measures have been taken to prevent clogging and improve the physical properties of the formed board, but this method has extremely low adhesion, so the finished mat is Weak (there is a risk that it will break during transportation or the mat surface will be blown off during closing of the hot press, and a major drawback is that the formalin that is a component of this adhesive is easily scattered by heat) Therefore, the coating efficiency deteriorates and the physical properties of the board deteriorate.

Furthermore, since a large amount of hardening agent is added, the water resistance of the board is poor, and the moisture in the center layer increases, slowing down the curing of the adhesive (
Therefore, it is necessary to use dangerous high-frequency heating in combination, and if it is not used in combination, there are problems such as an extension of the hot pressing time and a significant drop in productivity.

In view of these circumstances, the method of the present invention eliminates various drawbacks in fiberboard manufacturing in the conventional method described above, and
The method of the present invention enables the industrial production of fiberboard that has excellent physical properties and surface performance despite its low specific gravity. Highly entangled wood fibers that have been defibrated to ~25 kg/m are dried to a moisture content of 3 to 10, and then processed using urea formaldehyde resin, melamine formaldehyde resin, or melamine formaldehyde resin whose main component is a methylol compound. A formalin-based thermosetting resin such as a modified resin is used as an adhesive under the following conditions.

(1) Viscosity 20 cps ~ 50 cps (
(25°C) (2) Gelation time 5 minutes to 60 minutes (60
°C) (10% NH4Cl solution was added to resin 10 with a resin ratio of 55%)
(3) pH 7 to 12 (4) Methanol content in formalin during resin synthesis In the case of urea formaldehyde resin (including modified resin) 1
, 0 to 6,0 In the case of melamine formaldehyde resin (including modified resins), apply the above adhesive to the wood fiber in an amount of 8,0 to 25 by solid weight. After coating at a certain rate, it is made into a mat shape using a known dry papermaking method, and this mat is heat pressed. The sheet is hot-pressed for a certain period of time from 15 seconds to 30 seconds.

A feature of the method of the present invention is that the mechanical strength of the board made of fibers with good entanglement, which is the main constituent material, is greatly improved. This is because a large number of fluff-like fine fibers are branched from the fiber, and the good entanglement of such fibers is generally indicated by a low bulk density. Bulk density 8kV7
7+3-25 kg/m".

Such fibers with low bulk density can be obtained, for example, by steaming wood chips in high-temperature, high-pressure steam for 1 to 10 minutes and defibrating them with a pressurized double disc refiner. is extracted, which adheres to or is absorbed by the fiber surface during the next drying process, and acts as a hardening agent by interacting with the moisture in the fiber that evaporates during the heat-pressing process, as described below.

Next, the viscosity of the adhesive used in the present invention was set to 2.
The range was 0 cps to 50 cps (25°C).
For example, when the resin percentage is 55%, the lower limit of the viscosity is 20%.
cps, and dispersibility decreases when it exceeds 50 cps.

In addition, the gelation time was set at 5 to 60 minutes because if it is less than 5 minutes, the adhesive may cause precure before hot pressing, and if it is longer than 60 minutes, the gelation time is 170°C to 240°C.
This is because hot pressing at a high temperature of °C also causes undercuring.

In addition, the methanol content in formalin, which is a component of adhesives, is generally considered to be an important factor for shortening the curing time of adhesives at high temperatures. In the case of urea formaldehyde resin (including modified ones), 1 to 6,0%
is preferable, but the reason for this is that when the modulus is 6.0 or higher, a large number of ether bonds are generated by reaction with methanol during hot pressing, and polymerization due to the formation of methylene bonds between formaldehyde and urea, etc. This is because curing is inhibited, and if the ratio is less than 1, the quality of the adhesive is severely deteriorated and the pot life is shortened, making it difficult to use.

Further, in the case of melamine formaldehyde resin (including modified ones), the methanol content is preferably 3 to 20.0.

The former is about 1 factor lower than the methanol content of normal formalin, and the latter is more than 6 factors lower.

In synthesizing this adhesive, we tried to suppress the production of urea with a developed molecular chain that underwent a methylene reaction with formaldehyde, or addition condensates of melamine and formaldehyde, as in the case of conventional adhesives, but rather to synthesize monodi- or trimethylol compounds. In addition to increasing the abundance as much as possible,
Single substances such as urea and melamine are also present.

The adhesive having the composition described above has a resin percentage of 45 to 55%.
Despite its high viscosity, it has a low viscosity (because the particles can be made fine with the spray gun of the gluing machine without excess water, it has excellent dispersibility into the fibers, which greatly contributes to improving the strength of the board. In addition, by using a high resin ratio, a small amount of moisture is required to obtain the same amount of coating, which reduces the heat energy and press time required to release moisture during hot pressing, and prevents board punctures. It has various effects such as prevention.

On the other hand, this low viscosity also means low adhesion, so the adhesion of fibers to blenders, fans, and ducts is drastically reduced compared to conventional adhesives, which greatly reduces clogging in the process. At the same time, there is almost no occurrence of fiber balls, which greatly contributes to improving the physical properties of the board as described above.

Furthermore, in the present invention, the application rate of the adhesive is set to 8 to 25 parts, which is the range necessary to obtain a board with a specific gravity 10 to 40 parts lower than conventional fiberboards and having the same physical properties. This coating rate, along with the aforementioned fiber shape and adhesive dispersibility, is an important factor in determining the physical properties of the board.

Furthermore, because the adhesive has the above-mentioned characteristics, it is possible to industrially produce boards at a high coating rate within this range.

By the way, thermosetting resins such as urea and melamine harden when made acidic and heated, but the fibers of the present invention are defibrated using a pressurized disc refiner and then immediately dried in a flash dryer. In order to be
As mentioned above, the acidic substances present in wood fibers dry and adhere to the surface of the wood fibers, and this is dissolved by the steam generated from the fibers during heating with a hot press, causing the applied adhesive to harden. Although the pH of the adhesive is maintained on the alkaline side (7 to 12) to prevent precure before hot pressing, combined with the low methanol content mentioned above, hot It quickly hardens during pressing and exhibits the special effect of bonding the fibers together.

Next, the closing time, which is the time it takes to close the hot plate loaded with the mat and press it to the specified thickness, was set at 15 to 30 seconds to ensure the mechanical strength of the board, especially its rigidity and surface properties. The purpose is to generate a high specific gravity layer in an extremely low part of the surface layer of the board, which is necessary for increasing the specific gravity of the mat. It is necessary to keep the above-mentioned closing time to 8 to 15 well and shorten the closing time.

Based on this idea, in the present invention, the distance from the surface layer is 0.5 m /
It has succeeded in forming a high specific gravity layer between m and 3.0 m/m, and unlike fiberboard in the conventional dry process, this closing time has been reduced to 40 to 5 m/m.
Wait for more than 0 seconds to remove the high specific gravity layer from 2.0 to 4. On/
The smoothness of the board surface is significantly improved compared to the case where the board is made to harden, and the amount of sanding required to obtain hardness and its energy can be greatly reduced, resulting in an economical and excellent surface finish. This made it possible to obtain a fiberboard with

Incidentally, when compressed at such high temperatures, conventional adhesives actually weaken the bond between fibers due to thermal decomposition due to the high temperatures, making it impossible to form a strong high specific gravity layer.

Examples of the present invention detailed above are shown below.

Example 1 Lauan log chips were steamed in a digester,
Defibrated by double disc refiner to bulk density 10
A fiber of ~12 kg/m' is obtained and dried in a tube flash dryer to a moisture content of about 6 parts.

For this dry fiber, the methanol content in formalin during resin synthesis was 5.0, and the pH was 9.0.6.
Gel time at 17 minutes at °C, viscosity at 25 °C 28 cp
s, Apply a urea formaldehyde resin adhesive with a resin ratio of 55 parts to a coating ratio of 19 parts with a spray gun attached to a pasting machine, and then blow it into a Forminog machine to form a matte shape. After further pre-pressing, the hot plate temperature was 230℃ and the pressure was 50ky using a multi-stage hot press.
/cyrt, a press time of 6 minutes, and a closing time of about 20 seconds to obtain a fiberboard with a board thickness of 15 m/m.

Example 2 Melamine formaldehyde resin was used as an adhesive, and the methanol content in formalin during resin synthesis was reduced to 7.
PH9.0, gelation time 17 minutes (at 60℃)
The conditions were the same as in Example 1 above, except that the viscosity was 24 cps (at 25° C.) and the resin ratio was 55%.

□Example 3 Using coniferous log chips, the heat pressing pressure was approximately 20 kg.
/CrIL1 All conditions were the same as in Example 1 except that the press time was 3 minutes, and the thickness was 12. Om /
m insulation board was obtained.

The physical properties of the boards obtained from each of the above examples are shown in the table below.

In addition, as a comparative example, Material A shown in the table below is a commercially available medium-density fiberboard made by dry-forming method (the amount of urea formaldehyde resin applied is thought to be about 8 parts), and Material B is a commercially available insulation board. Do (seeding board)
Material C was formed under the same conditions as Example 1, except that a curing agent (NH4CI) was added to the adhesive of Example 71 to make the pH 5,0 to 4,5. be.

The effects of the present invention will be described with reference to the above Examples and Comparative Examples.

First, when comparing Example 2 and Material A, which are similar in specific gravity, the fiberboard produced by the method of the present invention has a bending strength and a bending Young's modulus of approximately 30, although the specific gravity is somewhat low.
In addition, the expansion coefficient due to water absorption, which is a physical property, is about half that in the thickness direction, and the water resistance is remarkable.

Next, when comparing Example 3, which is an insulation board with a specific gravity of about 0.3 to 0.32, and Material B, it can be seen that the board produced by the method of the present invention has more than twice the strength.

Further, when comparing Example 1 and Document C, it is clear that when a curing agent is added to the adhesive of the present invention to lower the pH, the strength is considerably reduced.

Note that actually manufacturing a board with a specific gravity of around 0.6 using the dry method under the conditions shown in Document C will result in many problems during the process, or problems such as punctures may occur during hot pressing, resulting in poor product yield. was very bad.

From the above, it is clear that the fiberboard manufactured by the method of the present invention has higher mechanical strength and physical properties (strength) than any of the conventional ones, and moreover, its surface is extremely dense. Moreover, it has a beautiful finish without stains, unevenness, etc., and has significantly improved the value of this type of fiberboard.

Claims (1)

[Claims] 1. A process for producing dry fiberboard in which wood fibers are coated with an adhesive containing a methylol compound as a main component and cured under heat, with a bulk density of 81 y/m'.
Formalin-based thermosetting resin adhesive with low methanol content was applied to ~25 kg/m' of wood fiber.
Adjust to pH 7-12, 8%-25% (solid weight)
A method for manufacturing wood fiberboard by a dry method, which comprises applying the coating, forming a mat by dry paper forming, and rapidly pressing the mat to form a board. 2. A method for producing wood fiberboard by a dry method according to claim 1, wherein the main component of the adhesive is a methylol compound, and the adhesive contains urea, melamine, or a modified version thereof. 3 Adhesive with a resin ratio of 55 has a viscosity of 20 cps-50c
ps (25℃), gelation time 5 minutes to 60 minutes (60℃)
A method for producing a wood fiberboard by a dry method according to claim 1 or 2, having the following characteristics. 4. A method for producing wood fiberboard by a dry method according to any one of claims 1 to 3, wherein the mat hot press has a closing time of 15 seconds to 30 seconds.