JP2001522735A - Steam pretreatment in the production of oriented strand board - Google Patents

Abstract

(57) Abstract: An oriented strand board (10) is manufactured using a continuous belt press (22). SOLUTION: This manufacturing method uses an isocyanate binder, and exposes a mat (18) of a wood material to steam before entering a press. It provides moisture by exposure to steam, softens wood fibers and enhances lignin flow on mats. In addition, moisture reacts with the isocyanate binder to generate polyurea from the isocyanate binder (eg, the preferred binder is pMDI). This lowers the curing conditions (ie, temperature, pressure, and time) required to press and fuse the mat and binder together. The isocyanate binder further forms both chemical and physical bonds with the wood material by reacting with the hydroxyl groups of the cellulose and hemicellulose of the wood material. The oriented strand board leaving the press has a high water content and a high resistance to thickness swelling in the wet state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

This application is related to U.S. patent application Ser. No. 08/968, filed Nov. 12, 1997.
No. 946 is a continuation-in-part application.

[0002] The present invention relates generally to oriented strand boards, and more particularly, to improving production efficiency and product quality in producing oriented strand boards.

[0003]

[Prior art]

Oriented strand board is described in M. Hoover, Georgia Pacific,
It is commercially available from many companies, including Louisiana-Pacific, and other sources. This material has multiple layers of wood "flakes" or "strands" bonded together by a binder such as a phenol formaldehyde resin or an isocyanate resin containing a sizing agent such as a paraffinic wax. Flakes are made by cutting thin slices with a knife edge parallel to the length of the peeled log. Flake thickness is typically between 0.254 mm and 12
. 7 mm (0.01 inches to 0.5 inches), but thinner or thicker flakes can be used in some applications, typically 2.54 cm (1 inch) in length.
Inches) to several inches and a width of one inch to several inches. Flakes are typically longer than wide. In the manufacture of oriented strand boards, the flakes are first driven off moisture and then coated with a thin layer of binder and sizing agent. The coated flakes are then spread on a conveyor belt in a series of alternating layers. In this case, the flakes of one layer are generally oriented in the direction of the conveyor belt, and the subsequent flake layers are:
The alternating layers of flakes are oriented generally perpendicular to the conveyor belt such that the flakes are oriented substantially perpendicular to one another. The term "strand" is used to mean the cellulosic fibers that form wood, and because the wood grain extends the length of the wood flakes, the "strands" of the oriented strand board are composed of alternating layers. They are oriented substantially perpendicular to each other. Ultimately, heat and pressure are applied to the layer of oriented "strands" or "flakes" to fuse the strands and binder together. Thereafter, the resulting product is cut into a predetermined size and transported. Typically, the resin and sizing agent are one of the oriented strand board products.
0% by weight or less. The manufacture of oriented strand board is described in U.S. Patent No. 5,524,394 to Clark et al. By reference to this patent, the disclosure of that patent is incorporated herein. Oriented strand board is strong and light under various moisture conditions, easy to nail,
Dimensional stability has been used in the most important attributes, cladding subwalls, wood I-beam structural supports, and roofs and floors. Oriented strand board
It is sold considerably cheaper than soft plywood of structural grade.

[0004] Several other patents describe the manufacture of oriented strand boards. U.S. Patent No. 5,635,248 to Huss et al. Describes a process for providing a smooth, hard finish to products such as oriented strand board. In the Hus patent, a foamed polymerized latex emulsion is applied to the surface and dried. After drying, the emulsion is crushed and then cured to form a coating. It has been found that applying post-cure heat treatment improves the hardness of the coating. U.S. Pat. No. 5,554,429 to Iwata et al. Discloses an oriented strand board flooring material which is designated as having a high water resistance. In the Iwata patent, an oriented strand board is produced in which the average length and width of the strands in the surface layer is greater than the centrally located layer. The Iwata patent uses a combination of a foamed urethane resin and a non-foamed aqueous emulsion phenolic resin to join wood strips together. In the Iwata patent, a decorative material sheet (eg, an oak sheet) is attached to an oriented strand board surface using an aqueous polymer isocyanate adhesive, and then the decorative sheet is coated with polyurethane, thus providing a shiny decoration with an oak appearance. It is also envisaged to produce traditional wood flooring materials.
By reference to the patents listed above, the disclosure of those patents is incorporated herein.

In recent years, efforts have been made to produce oriented strand boards continuously.
In conventional manufacturing systems, batch press operations have been used to fuse flake mats together. These systems required the use of a saw-separation process to separate the individual lengths of the mat-like flakes. Advances in the press subsystem and the shuttling subsystem allow multiple lengths of mat-like flakes to be pressed and fused simultaneously. However, despite these developments, it has been considered advantageous to use a continuous press in the manufacture of oriented strand board. This is because the use of a continuous press eliminates the step of cutting and separating the press mat, thereby increasing the production capacity. Examples of continuous belt presses for producing oriented strand board are described in US Pat. No. 5,520,530 to Gene Percamp and US Pat. No. 5,596,924 to Gerhard. An example of a continuous manufacturing process for forming particleboard or fiberboard is described in U.S. Pat. No. 5,538,676 to Bifeld, and by touching the patents cited above, The contents disclosed in these patents are incorporated herein.

[0006]

[Problems to be solved by the invention]

In an oriented strand board manufacturing process that uses a continuous belt to move material through a pressing step, a conveyor moves a mat through two adjacent belts that press the flakes together. A heated pair of plates or heated movable rams and an opposing table are placed behind an adjacent opposing belt to apply heat and provide additional pressing force. Thus, as the mat is moved through two adjacent belts in close proximity, the wood fibers are pressed together by the belt and by the plates and rams, and the individual wood flakes or "strands" are fused together to form a continuous flake board or sheet. Heat the binder and filler to the point where they form a "strand" board product.

[0007]

[Means for Solving the Problems]

According to the present invention, isocyanate-based binder materials such as methylene diphenyl diisocyanate (MDI) and polymeric methylene diphenyl diisocyanate (pMDI) are used in a continuous production system for oriented strand board or "flake board". Produce mats made of wood flakes or "strands". The mat includes alternating strand layers oriented generally perpendicular to each other. The strands are coated with an isocyanate binder, preferably pMDI, and a filler. Typical fillers are waxes based on paraffin, but may include wood flour, dyes, fine fibers, and the like. Matt is
It is transported to a continuous press on a conveyor. Immediately before entering the continuous press, steam treatment is applied to the mat to raise the temperature of the mat and increase the water content. The wood fiber is softened by the steam treatment, the glass transition temperature Tg of lignin decreases, and the lignin starts to flow. Because of the use of the isocyanate binder material, the moisture provided by the steam as well as the moisture coming from the wood material itself reacts with the isocyanate to generate polyurea. In addition, the isocyanate binder material reacts chemically with the hydroxyl moieties of the cellulose and hemicellulose components of the wood material, producing urethane bonds.

Heretofore, isocyanates, and specifically pMDI, have not been used as a resin or binder material in a method of making oriented strand board that includes the step of preheating wood material to obtain a desired moisture level. This is because the presence of pMDI during the preheating step was thought to cause a condition known as premature curing, thereby solidifying the resin prior to compression of the wood material. However, the process disclosed herein does not cause such premature curing. Furthermore, the reactivity of isocyanates with water and hydroxyl moieties allows for the curing of the binder and fusing with the wood material under relatively mild press operating conditions (eg, temperature, pressure, and exposure time) and at high production rates. It can be carried out. Thereby, the generated volatile organic compound (V
OC) The amount of emissions is reduced. Furthermore, the oriented strand board coming out of the continuous press has a relatively high water content, so that it can withstand thickness swelling under wet conditions.

[0009] These and other objects, features, and advantages will be better understood by reading the following detailed description of a preferred embodiment of the invention with reference to the accompanying drawings.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, the oriented strand board 10 is a "flake" or "flake" of wood.
It can be seen that it includes a number of layers 12, 14, and 16 made of "strands". These layers are typically adjacent layers and oriented perpendicular to each other. However, these strand layers may be oriented parallel to each other,
It should be noted that they may be oriented in various other ways. Strand sizes can be varied to meet various design requirements,
The number of layers of the oriented strand board can be varied. Further, the size of the strands in the different layers can be varied. As discussed above, the strands are held together by a binder, and the oriented strand board typically includes a sizing wax material. The oriented strand board 10 can be manufactured by various techniques, but common to all manufacturing processes is the layer 12,
Applying high temperature and high pressure to 14 and 16 to fuse and bond the layers together using a binder.

In practicing the present invention, the binder is an isocyanate, most preferably a polyisocyanate such as pMDI. FIG. 2 compares the curing reaction of pMDI to the PF resin system described in U.S. Pat. No. 5,538,676 to Beefeld. In pMDI, urethane bonds are formed between hydroxyl moieties on the wood surface, as occurs along the cellulose and hemicellulose chains. In addition, urea bonds are formed between pMDI monomers in the presence of moisture. In sharp contrast, in phenol formaldehyde resins, the monomer subunits react in a condensation reaction, releasing water as a reaction by-product. Thus, the presence of excess moisture prevents the curing of the PF resin. FIG. 3a shows that pMDI chemically and mechanically binds to wood materials, whereas the PF resin system binds mainly to wood materials in the manufacture of oriented strand boards. . During the production of oriented strand board,
A large amount of energy is used to drive out water molecules before and during curing of the resin. pMD
When an isocyanate resin such as I is used, a chemical reaction proceeds with a water molecule and a hydroxy moiety. This is because they are thermodynamically desirable. p
The net result is that isocyanate resin systems such as MDI fuse with wood materials at lower temperatures and shorter exposure times compared to PF resin systems.

FIG. 4 illustrates a process for continuously forming an oriented strand board according to the present invention. A mat 18 of wood flakes is advanced from left to right on a conveyor 20 through a continuous press 22 to produce a continuous sheet of oriented strand board 24. The conveyor is preferably coated with a release agent that allows the board to be easily removed from the press without delamination or blistering. A typical release agent is
A wax-based release agent such as EX-24 from Blackhawk Specialty Chemicals or a soap-based release agent such as # 8315 from Houghton International.

As discussed in connection with FIG. 1, wood flakes or “strands” are placed on the conveyor 20 in alternating layers. In this case, the "strands" of adjacent layers are oriented substantially perpendicular to each other. The number of layers depends on the application of the oriented strand board to be produced and the desired thickness. Typically, the thickness of the mat 18 is 2.54 c
m to 50.8 cm (1 inch to 20 inches). The individual strands of the mat have been coated with other materials such as isocyanate binders, sizing agents such as paraffin wax, and / or dyes using conventional processes.
A preferred isocyanate binder is pMDI, an IC from New Jersey.
Commercially available from the I Polyurethane Group (as rubinate pMDI) and from other commercial sources. Preferably, the isocyanate binder comprises about 1.5% to about 8% by weight of the mat and the sizing agent comprises about 0.5% to about 4% by weight of the mat. The wood flakes are dried before being placed on the conveyor. The water content of the mat 18 is preferably between 2% and 20% by weight. Since pMDI and other isocyanates advantageously react with water, the water content does not need to be tightly controlled and is not as low as the water content used when using a PF binder resin.

Before entering the continuous press, the mat 18 of wood material is exposed to steam treatment by a steam source 26. The steam sources may be located on both sides of the mat 18. In a preferred embodiment, the conveyor 20 is made of a porous wire material so that steam can pass through to the underside of the mat 18. The steam serves to soften the wood fibers. In addition, the steam lowers the glass transition temperature (Tg) of the lignin, thereby increasing the flow of the lignin through the wood material of the mat 18. As described above in connection with FIGS. 2 and 3, water enhances the isocyanate curing reaction,
This allows the use of relatively lower temperatures and lower press times than when using a phenol formaldehyde resin system. Further, the oriented strand board product 24 having a high moisture content has improved resistance to thickness swelling caused by exposure to moisture. The amount of steam can be varied depending on the thickness of the mat or the desired properties of the final product. In many applications, it is expected that the steam will increase the temperature of the mat 18 from about 50 ° C. to about 95 ° C. and increase the water content from about 6% to about 24%.

[0015] Because isocyanates such as pMDI react with water molecules and hydroxyl moieties at relatively low temperatures, the temperature and pressure and the number of exposure conditions in the continuous press 22 may differ from those using PF resin for curing. Can be reduced in comparison.

Thus, as in US Pat. No. 5,538,676 to Bifeld, no additional preheating station is required prior to pressing. However,
This is also due to the reaction, but the mat 1 is used to allow the binder to fuse with the wood material.
It is important to advance 8 directly into press 26. Prior art systems have used pMDI as a binder for oriented strand board products, but have not used it in combination with steam pretreatment. These prior art systems used a batch / shuttle mechanism in combination with a multi-port press so that multiple oriented strand boards could be produced simultaneously in a single press, but stacking separate strand board sections before pressing. It was necessary to send it to a predetermined position. If steam pretreatment was used in these systems, the reaction between pMDI and water would go too far before pressing, thus limiting the chemical reaction with the wood material,
Probably hinders the mechanical bonding of the isocyanate to the wood (as shown in FIG. 3). Thus, prior to the present invention, it was believed by those skilled in the art that steam pre-treatment could not be used in the manufacture of oriented strandboard using isocyanates such as pMDI. However, because the continuous press 22 can continuously receive and process the steamed mat 18, the advantages in curing / pressing conditions and in the physical properties of the oriented strand board 24 produced in the oriented strand board manufacturing can be obtained. It has been found that isocyanates can be used as binders to obtain and that steam pretreatment can be used advantageously.

The continuous press 22 is disclosed in US Pat. No. 5,520,530, US Pat.
, 676, and U.S. Pat. No. 5,596,924, but various continuous presses can be used in practicing the present invention. The main requirement for the continuous press 22 is that the mat
8 can be pressed and heated so that the isocyanate binder can be fused to the wood material and the oriented strand board 24 can be output continuously. Continuous press 22
Typically has a pair of closely opposed conveyors 28 and an internal heated press plate 30. These plates can move gradually and repeatedly towards each other. Instead of the heated press plate 30, one movable plate or "ram" and one stationary plate can be used. The heated press plate plays a role in exerting pressure on the mat material at a predetermined temperature at which both curing of the resin binder and fusion of the wood and the binder occur. The press plates 30 are typically closer together than the gap between the opposed conveyors 28, and the distance between the press plates 30 can be varied to produce oriented strand boards 24 of various thicknesses.

The temperature used in the press 22 can be varied depending on the application and properties of the oriented strand board to be produced and the transit time of the press 22. In many applications using an isocyanate resin binder, the temperature of the belt of the press 22 will be in the range of about 120 ° C to about 260 ° C. If pMDI is used as the binder, the preferred temperature for the belt of press 22 is from about 175 ° C to about 227 ° C. It will be apparent to those skilled in the art that the temperature can be varied to obtain the same end product by varying the pressure and residence time of the press 22.

The pressure exerted by the press plate 30 can be varied in a manner similar to temperature. For many applications embodying the present invention, the maximum pressure is about 2068.
41 kPa to about 6205.23 kPa (about 300 psi to about 900 psi)
Within the range. Similarly, the dwell time in the press 22 can be varied and depends on the length of the press 22, the speed of the conveyor 20, and the thickness of the panel. For many applications embodying the invention, the dwell time ranges from 30 seconds to 10 minutes.
Press residence time and product properties can also be changed by adding a catalyst or polyol to the isocyanate or pMDI binder or wood strand.

The temperature, pressure, and time in the press 22 are preferably selected so that the isocyanate resin is completely cured and can be fused to the wood material. These operational specifications for the press as well as the moisture content of the mat 18 regulated by the steam generator 26 can be varied to continuously produce oriented strand boards 24 of the desired moisture content. Experiments have shown that the higher the water content, the greater the resistance of the oriented strand board 24 to thickness expansion and linear expansion caused by exposure to moisture. In a preferred embodiment, the oriented strand board 24 having a moisture content of about 4% to 12% by weight is produced depending on the parameters used in the press and steam generator.

While the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. By way of example, and not limitation, the steam pretreatment process described above can be used in the manufacture of other engineered wood products such as wood composite room, rimboard, webstock, particleboard, and fiberboard. .

[Brief description of the drawings]

FIG. 1 is a partially cut perspective view of an oriented strand board showing the general orientation of wood flakes in a pressed composite product.

FIG. 2 is a schematic diagram showing chemical reactions of a pMDI resin system and a phenol formaldehyde (PF) resin system.

FIG. 3a is a schematic diagram showing the chemical and mechanical binding of pMDI resin to wood material on oriented strand board, and b shows the mechanical binding of PF resin to wood material on oriented strand board. It is a schematic diagram.

FIG. 4 is a schematic side view of a system and method for continuous production of an oriented strand board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Oriented strand board 12, 14, 16 layers 18 Mat 20 Conveyor 22 Continuous press 24 Oriented strand board 26 Steam source 28 Conveyor 30 Internal heating press plate

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] August 11, 1999 (August 11, 1999)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

23. In an engineered wood product having a water content of about 4% to about 12% by weight, providing a predetermined amount of wood material in the form of strands, said wood material being treated with an isocyanate-based binder. Coating, forming the layered mat of the wood material from the wood material, exposing the wood material mat to steam to preheat the wood material mat, and exposing the wood material mat to the steam. After the above step, without additional preheating steps, the mat of wood material is pressed in a continuous belt press at a temperature of about 120 ° C to about 260 ° C for about 2068.
41 kPa to about 6205.23 kPa (about 300 psi to about 900 psi)
And pressing the isocyanate-based binder and the wood material to form an engineered wood product.

[Procedure amendment]

[Submission date] February 13, 2001 (2001.1.23)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

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Claims (23)

[Claims] 1. A method of manufacturing an oriented strand board, comprising: providing a predetermined amount of wood material in a strand form; coating the wood material with an isocyanate-based binder; Forming a mat from the wood material that is layered in layers and the strands of adjacent layers are oriented substantially perpendicular to each other; exposing steam to the mat of wood material; Pressing the mat of wood material with a continuous belt press, fusing the isocyanate-based binder and the wood material together to form an oriented strand board. 2. The exposing step, wherein the temperature of the mat is from about 50 ° C. to about 95 ° C.
The method of claim 1, wherein the method comprises: 3. The exposing step comprises: adjusting the water content of the mat from about 6% by weight to about 2%.
2. The method of claim 1, wherein the method increases to 4% by weight. 4. The method of claim 2, wherein the pressing is performed at a temperature of about 120 ° C. to about 260 ° C. and a pressure of about 300 psi to about 905.23 kPa.
The method of claim 1, wherein the method is performed at a pressure of 0 psi) for a period of about 30 seconds to about 10 minutes. 5. The method according to claim 1, wherein the isocyanate-based binder is pMDI. 6. The method of claim 5, wherein said binder comprises an agent selected from the group consisting of a catalyst and a polyol. 7. The water content of the oriented strand board is from about 4% by weight to about 12% by weight.
5. The method of claim 4, wherein the method is weight percent. 8. The method of claim 1, wherein the isocyanate binder is pMDI and the pMD
The method of claim 1, wherein I comprises from about 1.5% to about 8% by weight of the wood material mat. 9. The method of claim 1, wherein the pressing step is performed within about 30 seconds to about 10 minutes after the exposing step. 10. A method of manufacturing an engineered wood product, comprising: providing a predetermined amount of wood material in the form of strands; coating the wood material with an isocyanate-based binder; Forming the mat from the wood material; and exposing the wood material mat to steam; pressing the wood material mat by a continuous belt press to form a binder based on the isocyanate; Fusing the wood materials together to form an engineered wood product. 11. The method of claim 10, wherein the wood material is layered in alternating layers in which the strands are oriented substantially perpendicular to each other. 12. The step of exposing the mat to a temperature of about 50 ° C. to about 95 ° C.
The method according to claim 10, wherein the temperature is raised to ° C. 13. The method of claim 10, wherein the exposing step increases the moisture content of the mat from about 6% to about 24% by weight. 14. The method according to claim 14, wherein the pressing is performed at a temperature of about 120 ° C. to about 260 ° C.
About 2068.41 kPa to about 6205.23 kPa (about 300 psi to about 9
11. The method of claim 10, wherein the method is performed at a pressure of 00 psi) for a period ranging from about 30 seconds to about 10 minutes. 15. The method of claim 10, wherein the isocyanate-based binder is pMDI. 16. The method of claim 15, wherein the water content of the engineered wood product ranges from about 4% to about 12% by weight. 17. The method of claim 10, wherein the isocyanate-based binder is pMDI, wherein the pMDI comprises about 1.5% to about 8% by weight of the wood material mat. 18. The method of claim 10, wherein the pressing step is performed within about 30 seconds to about 10 minutes after the exposing step. 19. A method for manufacturing an oriented strand board, comprising: forming a layered mat of strand-form wood material coated with an isocyanate-based binder; and exposing steam to the wood material mat. And pressing the mat of wood material with a continuous belt press to fuse the isocyanate-based binder and the wood material together. 20. The method of claim 19, wherein the exposing step increases the moisture content of the mat from about 6% to about 24% by weight. 21. The method of claim 19, wherein the isocyanate-based binder is pMDI. 22. The method of claim 21, wherein said binder comprises an agent selected from the group consisting of a catalyst and a polyol. 23. In an engineered wood product having a moisture content of about 4% to about 12%, providing a predetermined amount of wood material in the form of strands, and coating the wood material with an isocyanate-based binder. Forming a layered mat of the wood material from the wood material, exposing steam to the wood material mat, and subjecting the wood material mat to about 120 ° C. by a continuous belt press. From about 2068.41 kPa to about 6205.2 at a temperature of from about
A wood product, produced by pressing at a pressure of 3 kPa (about 300 psi to about 900 psi) to fuse the isocyanate-based binder and the wood material to form an engineered wood product.