CA1213707A - Method of making dimensionally stable composite board and composite board produced by such method - Google Patents
Method of making dimensionally stable composite board and composite board produced by such methodInfo
- Publication number
- CA1213707A CA1213707A CA000471094A CA471094A CA1213707A CA 1213707 A CA1213707 A CA 1213707A CA 000471094 A CA000471094 A CA 000471094A CA 471094 A CA471094 A CA 471094A CA 1213707 A CA1213707 A CA 1213707A
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- Prior art keywords
- board
- heat treatment
- wood
- secondary heat
- composite board
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
- B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
- B27N7/00—After-treatment, e.g. reducing swelling or shrinkage, surfacing; Protecting the edges of boards against access of humidity
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Wood Science & Technology (AREA)
- Forests & Forestry (AREA)
- Dry Formation Of Fiberboard And The Like (AREA)
- Chemical And Physical Treatments For Wood And The Like (AREA)
Abstract
ABSTRACT
This invention relates to a novel composite board made from a mixture of particles of a cellulose material and binder and a method of making same whereby the composite board so produced displays improved dimensional stability (resistance to thickness swellling) when the board is subjected to high humidity or moisture conditions. As a result, the novel method and composite board produced thereby can be employed as a construction material in locations hitherto regarded as unacceptable or questionable due to the undesired thickness swelling characteristic of conventional composite panels such as particlehoard or waferboard. The method and composite board displaying the attribute of improved dimensional stability involves subjecting a composite board that is conventionally formed by heat and pressure treatment to a secondary heat treatment for a predetermined period of time and at preselected temperature range. When compared to conventional composite board that has not been subjected to secondary heat treatment, the difference in thickness swelling is significant. The board surfaces and board edges are preferably subjected to the secondary heat treatment. Admixtures of regular resins and a slower curing binder such as spent sulphite liquor, hitherto regarded as unsuitable in the production of composite board, can now also be employed.
This invention relates to a novel composite board made from a mixture of particles of a cellulose material and binder and a method of making same whereby the composite board so produced displays improved dimensional stability (resistance to thickness swellling) when the board is subjected to high humidity or moisture conditions. As a result, the novel method and composite board produced thereby can be employed as a construction material in locations hitherto regarded as unacceptable or questionable due to the undesired thickness swelling characteristic of conventional composite panels such as particlehoard or waferboard. The method and composite board displaying the attribute of improved dimensional stability involves subjecting a composite board that is conventionally formed by heat and pressure treatment to a secondary heat treatment for a predetermined period of time and at preselected temperature range. When compared to conventional composite board that has not been subjected to secondary heat treatment, the difference in thickness swelling is significant. The board surfaces and board edges are preferably subjected to the secondary heat treatment. Admixtures of regular resins and a slower curing binder such as spent sulphite liquor, hitherto regarded as unsuitable in the production of composite board, can now also be employed.
Description
3~
TITLE OF INVENTION
-Improved method of making dimensionally stable composite board and composite board produced by such method.
BACKGROUND OF INVENTION
This invention relates to a novel method of producing composite board made from a mi~ture of particles of cellulosic material and a binder such as wood~based particle board or wafer board and which exhibits improved dimensional stability over conventional composite board when exposed to high humidity or moisture conditionsO Additionally, ~he invention is directed towards a novel composite board which exhibits resistance to moisture swelling when produced or manufactured in accordance with the methology of this invention.
The dimensional stability of a composite board or panel is normally determined by measuring the thickness swelling the of panel following controlled exposure to moisture. Conventional wood-based composite boards or panels can experience a thickness swelling ranging from 10 to 25 percent of the panel's thickness following a ~4 hour cold water soak and which can range from 2 to 40 percent iE subjected to a vertical 2~ hour cold water soak. When sub~ecting a conventional panel to a 2 hour boiling period followed by a l hour cold water soak, thickness swelling in the range of 50 to 60 percent can be anticipated. As a result, the use of conventional composite boards and panels as a construction material is limited to installations and environments where the moisture conditions are controlled or anticipated in advance. Consequently, wood-based composites are regarded as undesirable for exterior applications and particularly ground contact applications because of differential dimensional changes between the wet and dry portions of the material below and above the ground.
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~2~3~
The moisture and moisture cycling effect experienced by composite panels subjected to variations in humidity or exposure to water also contribute to the breakdown or degradation of the panel rendering it unfit as a construction material for the purpose intended. Indeed, building contractors are reluctant to use wood-based composite panels as a flooring or sub-flooring since the marginal edges of a panel can exhibit greater thickness swelling over its central portion which detracts from a substantially planer abutment joint with neighboring panels.
Where used as a flooring, it is not uncommon for composite board installers to plane or shave down to swollen panels adjacent their side edges.
The novel composite panel of this invention displays improved dimensional stability and hence improved bond durability of the cellulosic particles which, together with a binder, make up the composite panel. As a consequence, composite panels produced in accordance with this invention, can be employed in areas hitherto regarded as not recommened or open to question and, additionally, can be further treated with preservatives, fire retardants or other chemicals without causing significant deleterious damage to the panel from the standpoint of excessive thickness swelling or loss of strength as heretofore encountered.
Although not employed commercially, it is known that composite products such as boards will display improved dimensional stability if subjected to high temperature ranges in the order of 450 degrees fahrenheit or higher. There is, however, a very real risk of fire when operating at this temperature due to the accumulation of wax, dust and loose wood particles around the hot press. It has, hitherto, also been recognized that dimensional changes can be reduced by placing wood composites in a heating chamber or oven for a relatively long period of time in order to obtain improved dimensional stability. This procedure, however, results in deterioration of -- 3 ~
the panel strength and again constitutes a fire hazzard.
Furthermore, it contrlbutes significantly to a slow-down in a line production run and is not regarded as being commercially or economically viable.
SUMMARY OF INVENTION
In accordance with this invention, I have surprisingly and unexpectedly found that a composite board made Erom mixture oE
particles of cellulosic material and a binder which is conventionally formed by heat and pressure treatment will display significantly improved dimensional stability through the simple expedient of subjecting the conventionally formed composite board to a secondary heat treatment for a predetermined period of time and at a preselected temperature.
Preferably, the composite board subjected ~o the secondary heat treatment step is first trimmed to a predetermined size. By doing so, the entire board, the board faces or the board edges, can be subjected to the secondary heat treatment, as desired.
Trimming of the composite board prior to the secondary heat treatment is desired as it removes the loose particles and thus prevents fire hazard and additionally renders these exposed edges of the final board available for secondary treatment.
The preferred predetermined period of time and preselected temperature when practicing the method and producing the final composite board embodied by my invention is from about 2 to 15 minutes and a temperature range from 230C to about 270C.
From a production run standpoint, the secondary heat treatment step can be carried out by, say, a heating chamber, a hot press or a set of hot plates downstream in the production line oE the equipment: used in initially heat-pressing the mat.
In this type of arrangement, the exposure time to the secondary heat treatment can be made to correspond with the initial press period of the mat in order to render the sequential steps 3';~C3~
harmonious Additionally, following initial heat pressing of the mat to form the composite board or panel, the residual heat following the initial mat pressing can be advantageously carried over to reduce the temperature differen~ial and hence the energy required during the second heat treatment in order to bring the panel during this secondary heat treatment step up to its preselected temperature. Where only edge treatment is desired, the panels can be merely piled up and the edges treated with hot plantens for a predetermined time and temperature.
While any suitable heating means in order to carry out the secondary heat ~reatment step can be employed such as, say, a heating chamber, a hot press or at least one set oE hot platens, physical contact of the board surface or edge to be treated is preferred in order to reduce the oxygen environment during this step as it has been recognized that when the panel is heated in the presence of oxygen, thermal degradation can take place affecting a loss in board or panel strengthc As is used in the production of conventional composite panels, the preEerred binder is a heat resistant or thermosetting one such as phenol formaldehyde resins or isocyanate binders. I`he particles oE
cellulosic material employed in the composite panel and as is known can be any one or a combination of fibers, flakes, chips, wafers and strands.
As the preferred operating temperature used in the secondary treatment step is from 230~C to about 270C, I have also found that admixture of regular resin such as phenol formaldehyde (PF) resin, and a slower curing binder, such as spent sulphite liquor (SSL) hitherto regarded as unpractical and unfeasable is now a viable alternative and thus can contribute to a significant reduction in resin costs.
Exactly why the secondary heat treatment emparts to conventional composite board improved dimensional stability and thus its bond durability in high humidity or wet environments is ~3~
-- 5 ~
yet unknown. ~owever, in attempting to explain this unexpected phenonomen, it is believed that high wood temperatures as previously practiced in an attempt to achieve dimensional stability, by analogy, can be applied to the secondary heat treatment step of this invention operating at a significantly lower temperature range which preferably is Erom 230C to about 270C. In this regard, high wood temperature is believed to cause a plastic Elow of lignen "in situ' and thus reduces internal (pent up) stresses in the wood compared to wood compressed at a lower temperature~ Further, high wood -temperature causes thermal degradation of hemicelluloses which is the most hygroscopic component of wood, to furfural and various sugars~ These tend to react with each other to form insoluable polymers, and thus the hygroscopicity of the wood tends to decrease. Additionally, high wood temperatures in the absence of oxygen can cause a small loss of constitution water which leads to a reduction of hygroscopicity of cellulose and perhaps provides a lignin-rich fused surface that is analagous to a hot-melt adhesive.
In a companion patent application being filed concurrently with this application, I disclose an alternative improved method of making dimensionally stable composite board and composite board produced by such method and which essentially comprises subjecting the wood particles IEurnish) to a steam-pressure step prior to the mat or composite board forming. It will be recognized, therefor, that this alternative method can usefully and advantageously be combined with my secondary heat treatment technique of the subject invention in order to further enhance the dimensional stability of composite board.
The following e~amples illustrate the marked improvement imparted to conventional composite boards or panels when same have been subjected to the secondary heat treatment step of this inven-tion and as compared to panels which have not undergone secondary treatment. It should also be recognized that the secondary heat treatment technique can be practiced on composite panels that have been produced and stored for some significant period of time without appreciable differences in resul-ts.
___ Conventional waferboards measuring l" x 24" x 24" were fabricated with the following parameters.
1. Wafers: commercial disk-cut wafers
TITLE OF INVENTION
-Improved method of making dimensionally stable composite board and composite board produced by such method.
BACKGROUND OF INVENTION
This invention relates to a novel method of producing composite board made from a mi~ture of particles of cellulosic material and a binder such as wood~based particle board or wafer board and which exhibits improved dimensional stability over conventional composite board when exposed to high humidity or moisture conditionsO Additionally, ~he invention is directed towards a novel composite board which exhibits resistance to moisture swelling when produced or manufactured in accordance with the methology of this invention.
The dimensional stability of a composite board or panel is normally determined by measuring the thickness swelling the of panel following controlled exposure to moisture. Conventional wood-based composite boards or panels can experience a thickness swelling ranging from 10 to 25 percent of the panel's thickness following a ~4 hour cold water soak and which can range from 2 to 40 percent iE subjected to a vertical 2~ hour cold water soak. When sub~ecting a conventional panel to a 2 hour boiling period followed by a l hour cold water soak, thickness swelling in the range of 50 to 60 percent can be anticipated. As a result, the use of conventional composite boards and panels as a construction material is limited to installations and environments where the moisture conditions are controlled or anticipated in advance. Consequently, wood-based composites are regarded as undesirable for exterior applications and particularly ground contact applications because of differential dimensional changes between the wet and dry portions of the material below and above the ground.
~r~
~2~3~
The moisture and moisture cycling effect experienced by composite panels subjected to variations in humidity or exposure to water also contribute to the breakdown or degradation of the panel rendering it unfit as a construction material for the purpose intended. Indeed, building contractors are reluctant to use wood-based composite panels as a flooring or sub-flooring since the marginal edges of a panel can exhibit greater thickness swelling over its central portion which detracts from a substantially planer abutment joint with neighboring panels.
Where used as a flooring, it is not uncommon for composite board installers to plane or shave down to swollen panels adjacent their side edges.
The novel composite panel of this invention displays improved dimensional stability and hence improved bond durability of the cellulosic particles which, together with a binder, make up the composite panel. As a consequence, composite panels produced in accordance with this invention, can be employed in areas hitherto regarded as not recommened or open to question and, additionally, can be further treated with preservatives, fire retardants or other chemicals without causing significant deleterious damage to the panel from the standpoint of excessive thickness swelling or loss of strength as heretofore encountered.
Although not employed commercially, it is known that composite products such as boards will display improved dimensional stability if subjected to high temperature ranges in the order of 450 degrees fahrenheit or higher. There is, however, a very real risk of fire when operating at this temperature due to the accumulation of wax, dust and loose wood particles around the hot press. It has, hitherto, also been recognized that dimensional changes can be reduced by placing wood composites in a heating chamber or oven for a relatively long period of time in order to obtain improved dimensional stability. This procedure, however, results in deterioration of -- 3 ~
the panel strength and again constitutes a fire hazzard.
Furthermore, it contrlbutes significantly to a slow-down in a line production run and is not regarded as being commercially or economically viable.
SUMMARY OF INVENTION
In accordance with this invention, I have surprisingly and unexpectedly found that a composite board made Erom mixture oE
particles of cellulosic material and a binder which is conventionally formed by heat and pressure treatment will display significantly improved dimensional stability through the simple expedient of subjecting the conventionally formed composite board to a secondary heat treatment for a predetermined period of time and at a preselected temperature.
Preferably, the composite board subjected ~o the secondary heat treatment step is first trimmed to a predetermined size. By doing so, the entire board, the board faces or the board edges, can be subjected to the secondary heat treatment, as desired.
Trimming of the composite board prior to the secondary heat treatment is desired as it removes the loose particles and thus prevents fire hazard and additionally renders these exposed edges of the final board available for secondary treatment.
The preferred predetermined period of time and preselected temperature when practicing the method and producing the final composite board embodied by my invention is from about 2 to 15 minutes and a temperature range from 230C to about 270C.
From a production run standpoint, the secondary heat treatment step can be carried out by, say, a heating chamber, a hot press or a set of hot plates downstream in the production line oE the equipment: used in initially heat-pressing the mat.
In this type of arrangement, the exposure time to the secondary heat treatment can be made to correspond with the initial press period of the mat in order to render the sequential steps 3';~C3~
harmonious Additionally, following initial heat pressing of the mat to form the composite board or panel, the residual heat following the initial mat pressing can be advantageously carried over to reduce the temperature differen~ial and hence the energy required during the second heat treatment in order to bring the panel during this secondary heat treatment step up to its preselected temperature. Where only edge treatment is desired, the panels can be merely piled up and the edges treated with hot plantens for a predetermined time and temperature.
While any suitable heating means in order to carry out the secondary heat ~reatment step can be employed such as, say, a heating chamber, a hot press or at least one set oE hot platens, physical contact of the board surface or edge to be treated is preferred in order to reduce the oxygen environment during this step as it has been recognized that when the panel is heated in the presence of oxygen, thermal degradation can take place affecting a loss in board or panel strengthc As is used in the production of conventional composite panels, the preEerred binder is a heat resistant or thermosetting one such as phenol formaldehyde resins or isocyanate binders. I`he particles oE
cellulosic material employed in the composite panel and as is known can be any one or a combination of fibers, flakes, chips, wafers and strands.
As the preferred operating temperature used in the secondary treatment step is from 230~C to about 270C, I have also found that admixture of regular resin such as phenol formaldehyde (PF) resin, and a slower curing binder, such as spent sulphite liquor (SSL) hitherto regarded as unpractical and unfeasable is now a viable alternative and thus can contribute to a significant reduction in resin costs.
Exactly why the secondary heat treatment emparts to conventional composite board improved dimensional stability and thus its bond durability in high humidity or wet environments is ~3~
-- 5 ~
yet unknown. ~owever, in attempting to explain this unexpected phenonomen, it is believed that high wood temperatures as previously practiced in an attempt to achieve dimensional stability, by analogy, can be applied to the secondary heat treatment step of this invention operating at a significantly lower temperature range which preferably is Erom 230C to about 270C. In this regard, high wood temperature is believed to cause a plastic Elow of lignen "in situ' and thus reduces internal (pent up) stresses in the wood compared to wood compressed at a lower temperature~ Further, high wood -temperature causes thermal degradation of hemicelluloses which is the most hygroscopic component of wood, to furfural and various sugars~ These tend to react with each other to form insoluable polymers, and thus the hygroscopicity of the wood tends to decrease. Additionally, high wood temperatures in the absence of oxygen can cause a small loss of constitution water which leads to a reduction of hygroscopicity of cellulose and perhaps provides a lignin-rich fused surface that is analagous to a hot-melt adhesive.
In a companion patent application being filed concurrently with this application, I disclose an alternative improved method of making dimensionally stable composite board and composite board produced by such method and which essentially comprises subjecting the wood particles IEurnish) to a steam-pressure step prior to the mat or composite board forming. It will be recognized, therefor, that this alternative method can usefully and advantageously be combined with my secondary heat treatment technique of the subject invention in order to further enhance the dimensional stability of composite board.
The following e~amples illustrate the marked improvement imparted to conventional composite boards or panels when same have been subjected to the secondary heat treatment step of this inven-tion and as compared to panels which have not undergone secondary treatment. It should also be recognized that the secondary heat treatment technique can be practiced on composite panels that have been produced and stored for some significant period of time without appreciable differences in resul-ts.
___ Conventional waferboards measuring l" x 24" x 24" were fabricated with the following parameters.
1. Wafers: commercial disk-cut wafers
2. Resin type and content: powdered phenol-formaldehyde
3. Wax type and content: slack wax 1.5~
4. Mat moisture content: 6~ in face, 3~ in core
5. Press time and panel thickness: 2 min. 40 sec., 4 min.
10 sec., 5 min. and 10 min. 30 sec. for 5/16 in., 7/16 in., 1/2 in. and 3/4 in. thick boards respectively
10 sec., 5 min. and 10 min. 30 sec. for 5/16 in., 7/16 in., 1/2 in. and 3/4 in. thick boards respectively
6. Press temperature: 410F (210C) After the boards were made, their edges were trimmed and the trimmed boards were divided into three groups. The first group was used as control; the panels of second and third groups were subjected to secondary heat treatment, being treated at 464~F
(240~C) forthe times stiplulated. The treatments were done by placing each panel between two hot platens. The boards were not hot-stacked. the result of this e~periment is shown in Table 1.
Thickness Swelling after 24-hour Water Immersion of Untreated and Treated WaferboardS
_ _ _ . _ _ Location Percent Increase in Test of Heat ~oard Thickness Method* Measure- Treat-ment** ment 5/16" 7/16" 1/2" 3/4"
Horizontal 1" in from No(control)16.7 11.5 10.6 6.7 adjacent edge Yes6.3 3.9 4.0 2.3 Vertical 1" down from No(control~1504 9.3 7.4 5.7 top edge Yes 7.14.0 4.0 1.4 Vertical 1" in up from No(control)27.5 18.0 18.1 12.6 bottom edge Yes9.1 5.3 5.S 2.8 Vertical Average No(control)21.513~6 12.7 9.2 Yes 8.14.7 4.8 2.1 * specimen size 4" x 4"
** for vertical test 3 points 1" from top edge and 3 points 1' from bottom edge Boards were made in a similar manner described in Example 1 but they were conditioned at 20 ~/- 3C and 65 ~/- 1% relative humidity to reach equilibrium moisture content (about 7~). They were heated at 244C between hot p]atens or various lengths in time. The results are shown in Table 20 3.f~7~
__ Effect of Heat Treatment on Board Properties Treatment Time~ ~5~n~ 5 Properties 0 2.5 3.
(Untreated) Density lb/ft2 43.0 41.4 41~1 40.5 Thickness swelling (TS) after 24 hour soak 13.0(T)b 9.5(T)b 7.7(T)b 6.7(T)b Vertically 33.6(B)C 29.0(B)C 23.5(B)C 21.0(B)C
23 3(A)d 19.3(A)d 15.6(A)d 13.9(A)d MOE, 103 psi 739 723 762 719 MOE, psi 4426 4153 4258 3996 Wet MORe, psi 2207 2236 2305 2201 _ MOE - modulus of elasticity; MOR - modulus oE rupture b TS at the points 1 in. from the top edge and 2 in. below water surface c TS at the points 1 in. from teh bottom edge and 6 in. below water surEace d Average of (b) and (c) e MOR after 2 hour boil and 1 hour cold water soak ~37~3Y~
g Boards were made in a similar manner as described in Example 1.
They were cut into 7 in. x 10 in. strips and piled up. Fi~e minutes after hot pressingt the pile of 7 in. x 10 in. strips was heated at 240C on edges for 5 minutes. Commercial (i.e, third party manufactured) waEerboard were also used and treated as mentioned prevously except the boards were heated up from room temperature at 240C for 10 and 15 minutes. The results are summarized in Table 3.
Thickness Swelling of edged treated Waferboard after 5 days Cold Water Soak and then Re-Dry Conditions Duration of Speci- of Heat mens before Treat- Thickness Swelling % Ratio of Heat Treat- ment Treated Untreated 1" in Thickness ment min. Edges(A) Edges(B) from Swelling Edges(C) C/A C/B
_ Coola 10 23.1 30.2 21.3 .922 .705 Coola 15 15.4 20.6 15.9 1.032 .772 Hotb 5 19.3 37.7 24.5 1027 .650 _ a Room temperatue at 5% moisture content (commercial waferboard) b 5 minutes after hot pressing Boards were made in a similar manner as described in Example 1, except that the binder used an admixture of 40%
phenol-formaldehyde (PF) resin and 60% powdered spent sulphite liquor (SSL).
~2~L3'71D~
~ 10 -% Thickness Swelling after 24 hr~ Water Immersi.on of 7/16" thick Waferboards Bonded with an Admixture of Phenol Formaldehyde (PF) Resin and 5pent Sulfite Liquor (SSL) _ _ _ _ =
Location Test of Measure- Resin Type and Content Method ment 2.25% PF* core 1% ~ +
2O25%PF* 1% PF* + 1.5~ 1.5~
SSL*** in faces SSL***
Horizontal 1" from every 3.9% 4.4% 4.8%
two adjacen-t edge Vertical 1" down from 4~0% 4.0% 3.7 top edge Vertical 1" up from 5.3~ 7.6% 7.4%
bottom edge Vertical Average 4.7% 5.8% 5.6 _ _ * PF: phenol formaldehyde resin ** SSL: powdered spent sulfite liquor An examination of Table 1 clearly indicates that improved dimensional stability (resistance to thickness swelling) is achieved employing the secondary heat step and or a 464F
(240C) heat application, an exposure time of 5 minutes is preferred. Table 2 confirms secondary heat treatment can also be applied to the cool panels, but a prolonged treatment time is preferredO Table 2 also suggests that it is more effective to treat boards containing residual heat (Table 1) than conditioned boards (Table 2) which may be due to the existing board heat and reduced moisture content of the board itself.
~ 3~ 37 Table 2 also indicates that the mechanical properties of the boards were not impaired by the secondary heat treatment as contemplated by this invention.
Table 3 indicates that thickness swelling of board edges that have no~ undergone secondary heat treatment is significantly greater than comparable panel edges that have undergone this secondary step. Moreover, the thickness swelling measured 1" in from the board edges when compared to the thickness swelling at the treated edges is significantly less than that tabulated when comparing the thicXness swelliny 1" in from the edges to the swelling occasioned at the untreated edges; the result being that the edges oE composite boards or panels when viewed in cross-section are less likely to be Elared at the edges if the edges have undergone the secondary heating step.
Table 4 indicates that waferboard can be made from an inexpensive admixture of phenol formaldehyde resin (40%) and spent sulphite liquor (SSL) with significantly improved dimensionally improved stability when compared with the control specimens of Table I.
While specified embodiments of this invention have been disclosed herein, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the concept and scope of this invention as defined in the appended claims.
(240~C) forthe times stiplulated. The treatments were done by placing each panel between two hot platens. The boards were not hot-stacked. the result of this e~periment is shown in Table 1.
Thickness Swelling after 24-hour Water Immersion of Untreated and Treated WaferboardS
_ _ _ . _ _ Location Percent Increase in Test of Heat ~oard Thickness Method* Measure- Treat-ment** ment 5/16" 7/16" 1/2" 3/4"
Horizontal 1" in from No(control)16.7 11.5 10.6 6.7 adjacent edge Yes6.3 3.9 4.0 2.3 Vertical 1" down from No(control~1504 9.3 7.4 5.7 top edge Yes 7.14.0 4.0 1.4 Vertical 1" in up from No(control)27.5 18.0 18.1 12.6 bottom edge Yes9.1 5.3 5.S 2.8 Vertical Average No(control)21.513~6 12.7 9.2 Yes 8.14.7 4.8 2.1 * specimen size 4" x 4"
** for vertical test 3 points 1" from top edge and 3 points 1' from bottom edge Boards were made in a similar manner described in Example 1 but they were conditioned at 20 ~/- 3C and 65 ~/- 1% relative humidity to reach equilibrium moisture content (about 7~). They were heated at 244C between hot p]atens or various lengths in time. The results are shown in Table 20 3.f~7~
__ Effect of Heat Treatment on Board Properties Treatment Time~ ~5~n~ 5 Properties 0 2.5 3.
(Untreated) Density lb/ft2 43.0 41.4 41~1 40.5 Thickness swelling (TS) after 24 hour soak 13.0(T)b 9.5(T)b 7.7(T)b 6.7(T)b Vertically 33.6(B)C 29.0(B)C 23.5(B)C 21.0(B)C
23 3(A)d 19.3(A)d 15.6(A)d 13.9(A)d MOE, 103 psi 739 723 762 719 MOE, psi 4426 4153 4258 3996 Wet MORe, psi 2207 2236 2305 2201 _ MOE - modulus of elasticity; MOR - modulus oE rupture b TS at the points 1 in. from the top edge and 2 in. below water surface c TS at the points 1 in. from teh bottom edge and 6 in. below water surEace d Average of (b) and (c) e MOR after 2 hour boil and 1 hour cold water soak ~37~3Y~
g Boards were made in a similar manner as described in Example 1.
They were cut into 7 in. x 10 in. strips and piled up. Fi~e minutes after hot pressingt the pile of 7 in. x 10 in. strips was heated at 240C on edges for 5 minutes. Commercial (i.e, third party manufactured) waEerboard were also used and treated as mentioned prevously except the boards were heated up from room temperature at 240C for 10 and 15 minutes. The results are summarized in Table 3.
Thickness Swelling of edged treated Waferboard after 5 days Cold Water Soak and then Re-Dry Conditions Duration of Speci- of Heat mens before Treat- Thickness Swelling % Ratio of Heat Treat- ment Treated Untreated 1" in Thickness ment min. Edges(A) Edges(B) from Swelling Edges(C) C/A C/B
_ Coola 10 23.1 30.2 21.3 .922 .705 Coola 15 15.4 20.6 15.9 1.032 .772 Hotb 5 19.3 37.7 24.5 1027 .650 _ a Room temperatue at 5% moisture content (commercial waferboard) b 5 minutes after hot pressing Boards were made in a similar manner as described in Example 1, except that the binder used an admixture of 40%
phenol-formaldehyde (PF) resin and 60% powdered spent sulphite liquor (SSL).
~2~L3'71D~
~ 10 -% Thickness Swelling after 24 hr~ Water Immersi.on of 7/16" thick Waferboards Bonded with an Admixture of Phenol Formaldehyde (PF) Resin and 5pent Sulfite Liquor (SSL) _ _ _ _ =
Location Test of Measure- Resin Type and Content Method ment 2.25% PF* core 1% ~ +
2O25%PF* 1% PF* + 1.5~ 1.5~
SSL*** in faces SSL***
Horizontal 1" from every 3.9% 4.4% 4.8%
two adjacen-t edge Vertical 1" down from 4~0% 4.0% 3.7 top edge Vertical 1" up from 5.3~ 7.6% 7.4%
bottom edge Vertical Average 4.7% 5.8% 5.6 _ _ * PF: phenol formaldehyde resin ** SSL: powdered spent sulfite liquor An examination of Table 1 clearly indicates that improved dimensional stability (resistance to thickness swelling) is achieved employing the secondary heat step and or a 464F
(240C) heat application, an exposure time of 5 minutes is preferred. Table 2 confirms secondary heat treatment can also be applied to the cool panels, but a prolonged treatment time is preferredO Table 2 also suggests that it is more effective to treat boards containing residual heat (Table 1) than conditioned boards (Table 2) which may be due to the existing board heat and reduced moisture content of the board itself.
~ 3~ 37 Table 2 also indicates that the mechanical properties of the boards were not impaired by the secondary heat treatment as contemplated by this invention.
Table 3 indicates that thickness swelling of board edges that have no~ undergone secondary heat treatment is significantly greater than comparable panel edges that have undergone this secondary step. Moreover, the thickness swelling measured 1" in from the board edges when compared to the thickness swelling at the treated edges is significantly less than that tabulated when comparing the thicXness swelliny 1" in from the edges to the swelling occasioned at the untreated edges; the result being that the edges oE composite boards or panels when viewed in cross-section are less likely to be Elared at the edges if the edges have undergone the secondary heating step.
Table 4 indicates that waferboard can be made from an inexpensive admixture of phenol formaldehyde resin (40%) and spent sulphite liquor (SSL) with significantly improved dimensionally improved stability when compared with the control specimens of Table I.
While specified embodiments of this invention have been disclosed herein, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the concept and scope of this invention as defined in the appended claims.
Claims (29)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing an improved composite board made from a mixture of particles of a cellulosic material and a binder, wherein the composite board is conventionally formed by heat and pressure treatment, said method comprising subjecting the formed composite board to a secondary heat treatment for a predetermined period of time and at a preselected temperature range, said secondary heat treatment resulting in a board having improved dimensional stability when subjected to an environment of high humidity or moisture.
2. The method as claimed in Claim 1 wherein the said composite board is trimmed to a predetermined size prior to said secondary heat treatment.
3. The method as claimed in Claim 1, wherein said secondary heat treatment is applied to at least one of the panel surfaces and the edges of said board.
4. The method as claimed in Claim 3, wherein said secondary heat treatment is applied only to the side edges of said board.
5. The method as claimed in Claim 3, wherein said secondary heat treatment is applied to the opposite panel surfaces of said board.
6. The method as claimed in Claim 1, 2 or 3, wherein the secondary heat treatment comprises directly contacting the board with an element having a termperature higher than the temperature of said board.
7. The method as claimed in claim 1, 2 or 3 wherein said predetermined period is from about 2 to 15 minutes and said preselected temprature ranges from about 230°C to about 270°C.
8. The method as claimed in Claim 1, 2 or 3 wherein the secondary heat treatment is carried out while said board still contains residual heat from originally being formed.
9. the method as claimed in Claim 1, 2 or 3 wherein said secondary heat treatment is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
10. The method as claimed in Claim 1, 2 or 3, wherein the period of said secondary heat treatment is no greater than the time required to conventionally form said board.
11. The method as claimed in Claim 1, 2 or 3, wherein said particles of cellulosic material comprise at least one of fibers, particles, flakes, chips, wafers and strands of wood.
12. The method as claimed in Claim 1, 2 or 3 wherein said binder is a thermo-setting resin.
13. The method as claimed in Claim 1, 2 or 3, wherein said binder is at least one of phenol formaldehyde, esocyanate and spend sulphite liquor.
14. The method as claimed in Claim 1, 2 or 3, wherein said secondary heat treatment is carried out in an oxygen reduced environment.
15. A method of producing bond-durable wood-based composite boards having improved resistance to swelling when subjected to high humidity comprising the steps of:
(a) forming a mat which primarily consists of wood particles and a binder;
(b) heat-pressing said mat to form a composite panel; and (c) subjecting said composite panel to secodary heating at a temperature in a range from about 230°C to about 270° for a period of time from about 2 to about 15 minutes.
(a) forming a mat which primarily consists of wood particles and a binder;
(b) heat-pressing said mat to form a composite panel; and (c) subjecting said composite panel to secodary heating at a temperature in a range from about 230°C to about 270° for a period of time from about 2 to about 15 minutes.
16. The method as claimed in Claim is wherein the edges of said composite panel are trimmed to provide a panel of a predetermined size prior to said secondary heating.
17. The method as claimed in claim 16 wherein said secondary heating is applied to at least one of the panel faces and applied to the trimmed edges of said composite panel.
18. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out while said composite panel still contains residual heat from the heat-pressing of said mat.
19. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
20. The method as claimed in Claim 15; 16 or 17, wherein the time of said secondary heating is no greater than the time required for heat-pressing said mat and said wood particles are wafers and said binder is a phenol formaldehyde resin.
21. The method as claimed in Claim 15, 16 or 17, wherein said wood particles include at least one of fibers, chips, flakes, wafers and strands and said binder is at least one of phenol-formaldehyde, isocyanate and spent sulphite liquor.
22. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out in an oxygen reduced environment.
23. An improved bond-durable wood-based composite board which has improved resistance to moisture swelling and which is primarily composed of a cured mixture of a thermosetting resin and wood particles, said board being characterized by first being formed into a hot-pressed substantially thermally cured wood-based composite panel and thereafter subjected to a secondary heat treatment.
24. A board as claimed in Claim 23, wherein said secondary heat treatment is in a temperature range from about 230°C to about 270°C for a period of time from about 2 minutes to about 15 minutes.
25. The wood-based composite board as claimed in Claim 23, wherein said thermosetting resin is at least one of phenol formaldehyde, isocyanate and spent sulphite liquor and said wood particles comprises at least one of fibers, flakes, chips, wafers and strands.
26. The wood-based composite board as claimed in Claim 23, 24 or 25, wherein said secondary heating of said wood-based composite panel is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
27. A method as claimed in Claim 1, 2 or 3, wherein the cellulosic material comprises particles of wood subjected to a steam-pressure treatment prior to being formed into the composite board.
28. A method as claimed in claim 15, 16 or 17, wherein said wood particles prior to said mat forming are subjected to a steam-pressure treatment.
29. The composite board as claimed in Claim 23, 24 or 25, wherein said wood particles are characterized by being subjected to a steam-pressure treatment prior to being formed into said panel.
ABSTRACT
This invention relates to a novel composite board made from a mixture of particles of a cellulose material and binder and a method of making same whereby the composite board so produced displays improved dimensional stability (resistance to thickness swellling) when the board is subjected to high humidity or moisture conditions. As a result, the novel method and composite board produced thereby can be employed as a construction material in locations hitherto regarded as unacceptable or questionable due to the undesired thickness swelling characteristic of conventional composite panels such as particleboard or waferboard. The method and composite board displaying the attribute of improved dimensional stability involves subjecting a composite board that is conventionally formed by heat and pressure treatment to a secondary heat treatment for a predetermined period of time and at preselected temperature range. When compared to conventional composite board that has not been subjected to secondary heat treatment, the difference in thickness swelling is significant. The board surfaces and board edges are preferably subjected to the secondary heat treatment. Admixtures of regular resins and a slower curing binder such as spent sulphite liquor, hitherto regarded as unsuitable in the production of composite board, can now also be employed.
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing an improved composite board made from a mixture of particles of a cellulosic material and a binder, wherein the composite board is conventionally formed by heat and pressure treatment, said method comprising subjecting the formed composite board to a secondary heat treatment for a predetermined period of time and at a preselected temperature range, said secondary heat treatment resulting in a board having improved dimensional stability when subjected to an environment of high humidity or moisture.
2. The method as claimed in Claim 1 wherein the said composite board is trimmed to a predetermined size prior to said secondary heat treatment.
3. The method as claimed in Claim 1, wherein said secondary heat treatment is applied to at least one of the panel surfaces and the edges of said board.
4. The method as claimed in Claim 3, wherein said secondary heat treatment is applied only to the side edges of said board.
5. The method as claimed in Claim 3, wherein said secondary heat treatment is applied to the opposite panel surfaces of said board.
6. The method as claimed in Claim 1, 2 or 3, wherein the secondary heat treatment comprises directly contacting the board with an element having a termperature higher than the temperature of said board.
7. The method as claimed in claim 1, 2 or 3 wherein said predetermined period is from about 2 to 15 minutes and said preselected temprature ranges from about 230°C to about 270°C.
8. The method as claimed in Claim 1, 2 or 3 wherein the secondary heat treatment is carried out while said board still contains residual heat from originally being formed.
9. the method as claimed in Claim 1, 2 or 3 wherein said secondary heat treatment is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
10. The method as claimed in Claim 1, 2 or 3, wherein the period of said secondary heat treatment is no greater than the time required to conventionally form said board.
11. The method as claimed in Claim 1, 2 or 3, wherein said particles of cellulosic material comprise at least one of fibers, particles, flakes, chips, wafers and strands of wood.
12. The method as claimed in Claim 1, 2 or 3 wherein said binder is a thermo-setting resin 13. The method as claimed in Claim 1, 2 or 3, wherein said binder is at least one of phenol formaldehyde, esocyanate and spend sulphite liquor.
14. The method as claimed in Claim 1, 2 or 3, wherein said secondary heat treatment is carried out in an oxygen reduced environment.
15. A method of producing bond-durable wood-based composite boards having improved resistance to swelling when subjected to high humidity comprising the steps of:
(a) forming a mat which primarily consists of wood particles and a binder;
(b) heat-pressing said mat to form a composite panel; and (c) subjecting said composite panel to secodary heating at a temperature in a range from about 230°C to about 270° for a period of time from about 2 to about 15 minutes.
16. The method as claimed in Claim 15 wherein the edges of said composite panel are trimmed to provide a panel of a predetermined size prior to said secondary heating.
17. The method as claimed in claim 16 wherein said secondary heating is applied to at least one of the panel faces and applied to the trimmed edges of said composite panel.
18. The method as claimed in Claim 15, 16 or 17 I wherein said secondary heating is carried out while said composite panel still contains residual heat from the heat-pressing of said mat.
10. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
20. The method as claimed in Claim 15; 16 or 17, wherein the time of said secondary heating is no greater than the time required for heat-pressing said mat and said wood particles are wafers and said binder is a phenol formaldehyde resin.
21. The method as claimed in Claim 15, 16 or 17, wherein said wood particles include at least one of fibers, chips, flakes, wafers and strands and said binder is at least one of phenol-formaldehyde, isocyanate and spent sulphite liquor.
22. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out in an oxygen reduced environment.
23. An improved bond-durable wood-based composite board which has improved resistance to moisture swelling and which is primarily composed of a cured mixture of a thermosetting resin and wood particles, said board being characterized by first being formed into a hot-pressed substantially thermally cured wood-based composite panel and thereafter subjected to a secondary heat treatment.
24. A board as claimed in Claim 23, wherein said secondary heat treatment is in a temperature range from about 230°C to about 270°C for a period of time from about 2 minutes to about 15 minutes.
25. The wood-based composite board as claimed in Claim 23, wherein said thermosetting resin is at least one of phenol formaldehyde, isocyanate and spent sulphite liquor and said wood particles comprises at least one of fibers, flakes, chips, wafers and strands.
26. The wood-based composite board as claimed in Claim 23, 24 or 25, wherein said secondary heating of said wood-based composite panel is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
27. A method as claimed in Claim 1, 2 or 3, wherein the cellulosic material comprises particles of wood subjected to a steam-pressure treatment prior to being formed into the composite board.
28. A method as claimed in claim 15, 16 or 17, wherein said wood particles prior to said mat forming are subjected to a steam-pressure treatment.
29. The composite board as claimed in Claim 23, 24 or 25, wherein said wood particles are characterized by being subjected to a steam-pressure treatment prior to being formed into said panel.
ABSTRACT
This invention relates to a novel composite board made from a mixture of particles of a cellulose material and binder and a method of making same whereby the composite board so produced displays improved dimensional stability (resistance to thickness swellling) when the board is subjected to high humidity or moisture conditions. As a result, the novel method and composite board produced thereby can be employed as a construction material in locations hitherto regarded as unacceptable or questionable due to the undesired thickness swelling characteristic of conventional composite panels such as particleboard or waferboard. The method and composite board displaying the attribute of improved dimensional stability involves subjecting a composite board that is conventionally formed by heat and pressure treatment to a secondary heat treatment for a predetermined period of time and at preselected temperature range. When compared to conventional composite board that has not been subjected to secondary heat treatment, the difference in thickness swelling is significant. The board surfaces and board edges are preferably subjected to the secondary heat treatment. Admixtures of regular resins and a slower curing binder such as spent sulphite liquor, hitherto regarded as unsuitable in the production of composite board, can now also be employed.
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing an improved composite board made from a mixture of particles of a cellulosic material and a binder, wherein the composite board is conventionally formed by heat and pressure treatment, said method comprising subjecting the formed composite board to a secondary heat treatment for a predetermined period of time and at a preselected temperature range, said secondary heat treatment resulting in a board having improved dimensional stability when subjected to an environment of high humidity or moisture.
2. The method as claimed in Claim 1 wherein the said composite board is trimmed to a predetermined size prior to said secondary heat treatment.
3. The method as claimed in Claim 1, wherein said secondary heat treatment is applied to at least one of the panel surfaces and the edges of said board.
4. The method as claimed in Claim 3, wherein said secondary heat treatment is applied only to the side edges of said board.
5. The method as claimed in Claim 3, wherein said secondary heat treatment is applied to the opposite panel surfaces of said board.
6. The method as claimed in Claim 1, 2 or 3, wherein the secondary heat treatment comprises directly contacting the board with an element having a termperature higher than the temperature of said board.
7. The method as claimed in claim 1, 2 or 3 wherein said predetermined period is from about 2 to 15 minutes and said preselected temprature ranges from about 230°C to about 270°C.
8. The method as claimed in Claim 1, 2 or 3 wherein the secondary heat treatment is carried out while said board still contains residual heat from originally being formed.
9. the method as claimed in Claim 1, 2 or 3 wherein said secondary heat treatment is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
10. The method as claimed in Claim 1, 2 or 3, wherein the period of said secondary heat treatment is no greater than the time required to conventionally form said board.
11. The method as claimed in Claim 1, 2 or 3, wherein said particles of cellulosic material comprise at least one of fibers, particles, flakes, chips, wafers and strands of wood.
12. The method as claimed in Claim 1, 2 or 3 wherein said binder is a thermo-setting resin 13. The method as claimed in Claim 1, 2 or 3, wherein said binder is at least one of phenol formaldehyde, esocyanate and spend sulphite liquor.
14. The method as claimed in Claim 1, 2 or 3, wherein said secondary heat treatment is carried out in an oxygen reduced environment.
15. A method of producing bond-durable wood-based composite boards having improved resistance to swelling when subjected to high humidity comprising the steps of:
(a) forming a mat which primarily consists of wood particles and a binder;
(b) heat-pressing said mat to form a composite panel; and (c) subjecting said composite panel to secodary heating at a temperature in a range from about 230°C to about 270° for a period of time from about 2 to about 15 minutes.
16. The method as claimed in Claim 15 wherein the edges of said composite panel are trimmed to provide a panel of a predetermined size prior to said secondary heating.
17. The method as claimed in claim 16 wherein said secondary heating is applied to at least one of the panel faces and applied to the trimmed edges of said composite panel.
18. The method as claimed in Claim 15, 16 or 17 I wherein said secondary heating is carried out while said composite panel still contains residual heat from the heat-pressing of said mat.
10. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out by means of one of a heating chamber, a hot press and a set of hot platens.
20. The method as claimed in Claim 15, 16 or 17, wherein the time of said secondary heating is no greater than the time required for heat-pressing said mat and said wood particles are wafers and said binder is a phenol formaldehyde resin.
21. The method as claimed in Claim 15, 16 or 17, wherein said wood particles include at least one of fibers, chips, flakes, wafers and strands and said binder is at least one of phenol-formaldehyde, isocyanate and spent sulphite liquor.
22. The method as claimed in Claim 15, 16 or 17, wherein said secondary heating is carried out in an oxygen reduced environment.
23. An improved bond-durable wood based composite board which has improved resistance to moisture swelling and which is primarily composed of a cured mixture of a thermosetting resin and wood particles, said board being characterized by first being formed into a hot-pressed substantially thermally cured wood-based composite panel and thereafter subjected to a secondary heat treatment.
24. A board as claimed in Claim 23, wherein said secondary heat treatment is in a temperature range from about 230°C to about 270°C for a period of time from about 2 minutes to about 15 minutes.
25. The wood-based composite board as claimed in Claim 23, wherein said thermosetting resin is at least one of phenol formaldehyde, isocyanate and spent sulphite liquor and said wood particles comprises at least one of fibers, flakes, chips, wafers and strands.
26. The wood-based composite board as claimed in Claim 23, 24 or 25, wherein said secondary heating of said wood-based composite panel is carried out by means of one of a heating chamber, a hot press and a set of hot platens
27. A method as claimed in Claim 1, 2 or 3, wherein the cellulosic material comprises particles of wood subjected to a steam-pressure treatment prior to being formed into the composite board.
28. A method as claimed in claim 15, 16 or 17, wherein said wood particles prior to said mat forming are subjected to a steam-pressure treatment.
29. The composite board as claimed in Claim 23, 24 or 25, wherein said wood particles are characterized by being subjectd to a steam-pressure treatment prior to being formed into said panel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000471094A CA1213707A (en) | 1984-12-28 | 1984-12-28 | Method of making dimensionally stable composite board and composite board produced by such method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000471094A CA1213707A (en) | 1984-12-28 | 1984-12-28 | Method of making dimensionally stable composite board and composite board produced by such method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213707A true CA1213707A (en) | 1986-11-12 |
Family
ID=4129474
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000471094A Expired CA1213707A (en) | 1984-12-28 | 1984-12-28 | Method of making dimensionally stable composite board and composite board produced by such method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1213707A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4879160A (en) * | 1988-07-15 | 1989-11-07 | Macmillan Bloedel Limited | Edge stabilized wood composite panel |
| US5049334A (en) * | 1989-09-25 | 1991-09-17 | Alberta Research Council | Post-press heat treatment process for improving the dimensional stability of a waferboard panel |
| EP1688230A1 (en) * | 2001-12-20 | 2006-08-09 | Dieffenbacher GmbH & Co. KG | Method and apparatus for continuous manufacturing of fiberboards from wood |
-
1984
- 1984-12-28 CA CA000471094A patent/CA1213707A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4879160A (en) * | 1988-07-15 | 1989-11-07 | Macmillan Bloedel Limited | Edge stabilized wood composite panel |
| US5049334A (en) * | 1989-09-25 | 1991-09-17 | Alberta Research Council | Post-press heat treatment process for improving the dimensional stability of a waferboard panel |
| EP1688230A1 (en) * | 2001-12-20 | 2006-08-09 | Dieffenbacher GmbH & Co. KG | Method and apparatus for continuous manufacturing of fiberboards from wood |
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