Process for producing molded wooden products without gas retention

Abstract

 A process is provided for producing a molded wooden product from a fibrous wood mixture made of wood fibers, binder, water-repelling agent, and other additives. The fibrous mixture is placed in a heated compression mold directly or after forming into a mass of predetermined shape and then placing the mass into the compression mold. The wood fiber (fibrous mixture) are then hot-compression molded to form the molded wooden product. During the compression step, air and gases are evacuated and vented from the mold cavity through various air passages formed in the mold.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a process and apparatus for producing molded wooden products and, more specifically, to a process and apparatus for producing a molded wooden product by feeding a fibrous mixture comprising wood fibers, a binder, a water-repelling agent, etc., into a compression mold and subjecting it to heat-compression molding while evacuating gas from the mold cavity.

Description of the Related Art

[0002] Molded wooden products, e.g. hardboard, are lighter than plywood and superior in heat resistance, water resistance, and moisture resistance. Furthermore, they are strong relative to their mass and thickness. Because of these favorable properties, molded wooden products are widely used for such applications as building interiors, automobile interiors, furniture, and television and stereo cabinets.

[0003] Processes for producing molded wooden products typically involve the following steps, explained with reference to Fig. 1. First, wood chips C are fed to the hopper 2 of a wood splitting apparatus (defibrator). The wood chips are then fed to a steaming tank 4 by a first feeding means such as a screw feeder : installed at the bottom of the hopper 2. The steaming tank 4 is supplied from above with steam S which swells the wood chips C s< that they are easily split or defibrated. The steamed chips are then fed to a splitting disk 6 from the bottom of the steaming tank 4 by a second feeding means such as screw feeder 5. The wood chips are defibrated into wood fiber Wl by the splitting disk 6, which is driven by a motor 7. The defibrated wood fiber _Wl is fed to a dryer 10 (Fig. 2) through a feed pipe 8 by the pressure feeder 7'. The wetted wood fiber Wl, together with hot air H supplied from the blower 11, passes through a meandering drying tube 12. The dried wood fiber enter a cyclone 13 in which hot air A containing moisture and fine dust is removed. Thus, dried wood fibers W2 about 5 to 40 mm long are obtained.

[0004] The dried wood fiber W2 is then fed to the charge port 16 of the mixer 15 as shown in Fig. 3. In the mixer 15, the wood fiber is generally combined with a binder, a water-repelling agent, and other optional additives. The binder may be any material which enhances the binding properties of the wood fibers to themselves. Examples of binder materials include thermosetting resins (e.g., phenolic resin) and thermoplastic resins. The water-repelling agent may be, for example, a paraffin. The binder and water-repelling agent are supplied to the mixer 15 through a plurality of spray nozzles 17. The wood fiber W2 is further combined with about 17% of hemp fiber (which facilitates deep drawing) and about 7% of polypropylene fiber or the like (e.g. thermoplastic resin) necessary for mat construction. These components are uniformly mixed by the mixing blades 18. The resulting product is a wood-based raw material or fibrous mixture

[0005] which undergoes subsequent steps as described herein. The binder typically comprises 5 to 10% by weight of the mixture and the water-repelling agent typically comprises 1 to 5% of the mixture.

[0006] The fibrous mixture W3 is fed to a mat making machine (not shown) to be made into a molding mat, generally 10 to 40 mm thick and of standard size. The mat, in which the wood fiber, hemp fiber, and polypropylene fiber are intertwined and pressed against one another, is easily storable and transportable. Thus, it is stored as such and transferred as required.

[0007] The mat is cut to a size slightly larger than the finished molded wooden product. The mat thus cut is subjected to heat-compression molding. If the mat contains a large amount of wood fiber and is to undergo deep drawing, it must be softened, for example, by steaming and pre-molding using a mold similar to a compression mold. Deep drawing is necessary to form projections or protrusions such as an armrest or the like projecting from one side or both sides of an automobile door trim.

[0008] The above-mentioned conventional process for producing molded wooden products has the following disadvantages. The wood fiber must be formed into the mat as an intermediate material to facilitate storage and transportation. The mat must be cut to a predetermined shape prior to molding. These steps make the production process complex, and result in lowered productivity. The molded wooden product must be finished by cutting away excess portions. The cutting required before and after molding wastes the material, which leads to poor yields. In addition, the mat-making process requires an extra amount of binder, long fiber (such as expensive hemp fiber), and thermoplastic resin net if the mat is to undergo deep drawing. Where hemp fiber is used, it is necessary to add a large amount of binder (thermosetting resin). This also leads to increased production costs.

[0009] Where the mat contains a large amount of wood fiber, it is necessary to soften if, for example, by steaming, and to pre-for it into the approximate shape of the molded product desired before it can undergo deep drawing. Not only does the pre-forming add to the production steps and correspondingly to the costs, but it also presents a problem with regard to the finished product. The deep-drawn, pre-formed mat has thinned corners which, upon compression molding, result in a molded product with low-density corners having poor strength. In the case of a mat containing, for example, 85% wood fiber, the deep-drawn corner is generally reinforced with a patch of the same material as the mat prior to compression molding to address this problem.

[0010] Recently, the present inventors proposed a new process to remedy the above-mentioned drawbacks. According to the new process, the fibrous mixture is formed into a low-density, pre-shaped, wood fiber mass which is fed directly to the mold for heat-compression molding, without being formed into an intermediate mat. According to this process, the pre-shaped mass is formed using a mass forming apparatus 20 as shown in Fig. 4.

[0011] The mass forming apparatus 20 comprises a spreading case 21 and a collecting vessel 22 positioned under the spreading vessel 21. An opening 21a is located the stop of the spreading vessel 21. Above the opening 21a is a spreading under 23 to spread the fibrous mixture W3 fed through a pressurized feed pipe (not shown). Air blowers 24 having air nozzles (not shown) on the inside thereof are provided on each side of the opening 21a. The air nozzles control the spreading direction in two dimensions. The air blowers 24 are supplied with air through the air supply lines 25 and the switch valve 26. A vacuum duct 22a is connected to the bottom of collecting vessel 22 to apply vacuum to the collecting vessel 22. A perforated member 27 such as a wire net or punched metal plate is provided in the collecting vessel 22 above the vacuum duct 22a to form the bottom surface of the mass.

[0012] The mass forming apparatus operates in the following manner. With the switch valve 26 open, air is supplied to the air blowers 24 through the air supply lines 25 so that an air flow is created across the spreading vessel 21 and the collecting vessel 22. The fibrous mixture W3 is then released from the spreading unit 23 and fed into the air flow. The mixture W3 is carried or falls from the opening 21a of the spreading vessel 21 into the collecting vessel 22, and it accumulates on the perforated member 27. The mixture W3 can be accumulated on the desired part or locations of the perforated member 27 by controlling the air flow from the air blowers 24 with the switch valve 26.

[0013] Unlike the conventional mat mentioned above, the wood fiber mass W thus obtained has a low density and a specific gravity of 0.008 to 0.05

[0014] and can be as thick as 50 to 300 mm. Wood fibers in the mass are lightly bonded and loosely interlaced with one another.

[0015] Alternatively, the fibrous mixture W3 may be supplied directly to the compression mold by allowing it to fall under the force of gravity or carrying it in an air stream directly into the mold, i.e., without forming the mass W. The mixture W3 which has accumulated in the mold then undergoes heat-compression molding.

[0016] The pre-formed mass method and the direct molding method have drawbacks attributable to the loose interlacing of the wood fibers. The wood fibers of the mass in the mold are moved, or thickened portions of the mass are dislocated, when the upper and lower molds comprising the compression mold are closed. The latter case leads to a nonuniform density distribution in the molded product and thinning of the deep-drawn portion.

SUMMARY OF THE INVENTION

[0017] It is an object of the invention to provide a process for producing molded wooden products having improved properties and improved quality by overcoming the problems of movement or dislocation of the wood fibers noted above.

[0018] Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part ; will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the insertion may be realized and attained by means of the processes and combinations particularly pointed out in the appended claims. To achieve the objects and in accordance with the purpose the invention as embodied and broadly described herein, the manufacturing method of this invention comprises a first step oi placing a fibrous mixture comprising wood fiber into a cavity of a compression mold, the compression mold including an upper mold and a corresponding lower mold which are movable relative to one another, the lower mold including a frame and the lower mold and the upper mold forming the cavity; and a second step of compression molding the fibrous mixture under heat and simultaneously evacuating gases from the fibrous mass. This inventive process limits or prevents movement or deformation and uneven density distribution of the wood fibers during the molding process, including during processing of deep-drawn portions, thus providing a molded wooden product having substantially unform density throughout. The strength problems noted above are also thus avoided.

[0019] The wood fiber used in this invention is obtained, for example, by splitting or defibrating wood. The wood used is not limited to a specific type and may be, for example, Japanses cypress, Japanese red pine, Japanese cedar, Japanese beech, and lauan. In addition, rice straws, flax husks and bagasse may be used. Similarly, the process of defibration is not limited to a specific method and may be accomplished, for example, by steaming wood chips and mechanically disintegrating them.

[0020] The binder to be added to the wood fiber is not limited to a specific type provided it can supplement the interfiber bonding properties inherent in the wood fibers. Examples of the binder include thermoplastic resins such as coumarche resin and thermosetting resins such as phenolic resin and urea resin. A water-repelling agent may also be incorporated with the wood chips (in addition to the binding) to improve water resistance and promote mold release.

[0021] According to the process of this invention, the wood fiber (with additives if desired) may be placed into the mold in a variety of ways. For example, the wood fiber may be allowed to fall under the force of gravity, or it may be fed by means of an air stream into a cavity between the upper and lower molds comprising an opened compression mold. Alternatively, the wood fibers may be pre-formed into a mass of predetermined shape and the mass then placed into the mold. In the latter case, the mass may be formed using the mass-forming apparatus 20 shown Fig. 4. The mass is subsequently transferred to a holder equipped with a vacuum mechanism and brought to a position directly over the mold where vacuum is terminated, allowing the mass to drop into the mold.

[0022] According to the process of this invention, the wood fiber placed in the mold is integrally bonded and formed into a molded wooden product. The molding conditions are selected based on and in accordance with the materials (wood fiber, binder and other additives) used, the thickness and shape of molded product, and the strength of molded product desired, and are not limited to specific values. For example, the molding temperature may range from 100 to 200°C, the molding pressure may range from 20 to _kg/m², and the molding cycle may range from 20 seconds to 10 minutes.

[0023] The air passages formed in the mold are not limited in shape and position. For example, they may be formed such that they open on the molding surface of the upper mold or lower mold or both. Alternatively, they may be formed through a frame surrounding the mold cavity. The air passage may be a groove tapered surface in combination with a hole, groove, etc. formed on the inner wall of the frame.

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiment of the invention and together with the description serve to explain the principles of the invention.

BRIEF DESCRIPTION. OF THE DRAWINGS

[0025] 

Figs. 1 through 3 are schematic representations of an apparatus which may be used to produce wooden fibers which can bi used in the process of the present invention.

Fig. 1 is a schematic representation of a defibrator or wood splitting apparatus;

Fig. 2 is a schematic representation of a dryer; and

Fig. 3 is a schematic representation of a mixer.

Fig. 4 is a schematic representation of a mass forming apparatus used to form the wood fiber mass;

Figs. 5 through 10 are sectional views showing various type: of compression molds used to practice the process of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Preferred embodiments of the invention are now described with reference to the accompanying drawings. The process of the present invention is directed to producing a molded wooden product by forming a mass of predetermined shape from wood fibers or similar fibrous material and then placing the mass in a compression mold, where the mass is heat-compression molded. The processes of producing the wood fibers and of subsequently forming the wood fibers into a mass are essentially the same as described above with reference to Figs. 1 through 4 and, therefore, the description of these processes will not be repeated here. The detailed description of the present invention is thus limited to the process of heat-compression molding.

[0027] Figs. 5 and 6 show an example of a compression mold used to practice the present invention. The mold 40a is designed for the molding of, for example, an automobile door trim. It is comprised of a lower mold 41 and an upper mold 42. The lower mold 41 has a recess Cl to form the armrest core by deep drawing. (The armrest core is later finished by covering with a cushioning material and surfacing material.) The upper mold 42 has a protrusion C2 which corresponds to and mates with the recess Cl. The lower mold 41 is provided with a hot plate 43 on the lower side thereof, and the upper mold 42 is also provided with a hot plate 44 on the upper side thereof. The hot plates are heated by a beater (not shown) and temperature-controlled by a controller (not shown), and the upper and lower molds in turn are heated by shown), and the upper and lower molds in turn are heated by the hot plates. I

[0028] The lower mold 41 is provided with a frame 45 at the periphery thereof. The upper mold 42 has gas vent ducts 46 through which gases in the mold cavity C are evacuated as the upper and lower molds come together. The gas vent ducts 46 communicate with a vacuum pump (not shown) through the passage 47 formed between the upper mold 42 and the hot plate 44 and the vacuum duct 48. The vacuum duct is provided with a valve 49 to initiate and terminate evacuation of the mold cavity C.

[0029] Before initiation of compression molding, the lower mold 41 and upper mold 42 are heated by means of the hot plaes 43 and 44, respectively. The fibrous mass W obtained in the previous step (shown in Fig. 4) is placed in the mold cavity C. The upper ram (not shown) of the mold is forced downward so that the mass W of wood fibers is compressed between the upper mold 42 and the lower mold 41 as the upper mold 42 moves downward. As the result of compression, the individual wood fibers become interlaced more densely. During the compression process, the valve 49 is opened to evacuate the cavity through the gas vent ducts 46. This evacuation step which occurs simultaneously with compression prevents turbulent air flow which may occur as the upper mold 42 comes down. As a result, it is possible to prevent the scattering of wood fiber and the dislocation of the mass W. The evacuation removes a large amount of air, gas, and moisture which are released from the mass W as the compression proceeds. The removal of gases from the cavity prevents the formation of defects such as blisters. In this way, a high-quality molded wooden product M is obtained as shown in Fig. 6. The molded wooden product M has a deep-drawn portion Ml formed by the recess Cl of the lower mold 41 and the protrusion C2 on the upper mold 42.

[0030] _Fig. 7 shows a second embodiment of the mold. (The reference characters used in Fig. 5 are also used for corresponding parts in Figs. 7 through 10, and their explanation is omitted.) The mold 40b includes vent holes 51 formed through the supporting frame 45 in the lower mold 41. The vent holes 51 are preferably positioned adjacent the surface of the lower mold 41, and are in the form of elongated perforations at spaced intervals around the entire circumference of the frame 45. In addition, the vent holes 51 have a wire net 52 attached therein which prevents wood fibers from escaping through the vent holes 51 as air and gas are vented through these holes.

[0031] In this example, the vent holes 51 effectively prevent the turbulent air flow which typically occurs at the initial stage of molding as the upper mold 42 comes down. The effect of the vent holes 51 is enhanced if the mold cavity is evacuated through the gas vent ducts 46.

[0032] Fig. 8 shows a third embodiment of the mold. The mold 40c is characterized by outward tapering 53 on the inside of the frame 45 of the lower mold 41. The tapered surface 53 forms a clearance G with the vertical when the upper mold comes downwich permits air to escape from the mold cavity, thereby limiting or preventing the occurrence of turbulent air flow. Fig. 9 illustrates a fourth embodiment of the mold. The mold 40d is characterized by a plurality of grooves 54 formed vertically on the inside of the frame 45. The grooves 54 permit air to escape from the mold cavity C when the upper mold is move downwardly, thereby limiting or preventing the occurrence of turbulent air flow. The grooves 54 may also be formed in a fifth embodiment of the mold such that the lower end of each groove is connected to a hole formed through the frame 45 as shown in Fig. 10.

[0033] It will be apparent to those skilled in the art that various modifications and variations can be made in the process for producing molded wooden products of the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A method of manufacturing a molded wooden product, comprising:

a first step of placing a fibrous mixture comprising wood fiber into a cavity of a compression mold, said compression mold including an upper mold and a corresponding lower mold whic are movable relative to one another, said lower mold including a frame, said lower mold and said upper mold forming said cavity; and

a second step of compression molding said fibrous mixture under heat and simultaneously evacuating gases from said fibrous mass.

2. A method as set forth in claim 1, wherein said second step includes a first substep of evacuating gases from said mass during compression molding using at least one gas vent duct incorporated into said upper mold of said compression mold.

3. A method as set forth in claim 1, wherein said second step includes a second substep of venting gases from said mass during compression molding using at least one vent hole comprising an elongated perforation formed in the frame adjacent the surface of said lower mold.

4. A method as set forth in claim 1, wherein said second step includes a third substep of venting gases from said mass during compression molding using an outward tapered surface on the inside of said frame of said lower mold.

5. A method as set forth in claim 1, wherein said second step includes a fourth substep of venting gases from said mass during compression molding using a plurality of vertical grooves formed in the interior surface of said frame of said lower mold.

6. A method as set forth in claim 1, wherein said first step comprises a first substep of collecting the fibrous mixture to form a mass of predetermined shape prior to placing said mixture into the compression mold.

7. A method as set forth in claim 6, wherein said second step includes a first substep of venting gases from said mass during compression molding using at least one gas vent duct incorporated into said upper mold of said compression mold.

8. A method as set forth in claim 6, wherein said second step includes a second substep of venting gases from said mass during compression molding using at least one vent hole comprising an elongated perforation formed in the frame adjacent the surface of said lower mold.

9. A method as set forth in claim 6, wherein said second step includes a third substep of venting gases from said mass during compression molding using an outward tapered surface on the inside of said frame of said lower mold.

10. A method as set forth in claim 6, wherein said second step includes a fourth substep of venting gases from said mass during compression molding using a plurality of vertical grooves formed in the interior surface of said frame of said lower mold. I

11. A method as set forth in claim 1, wherein said first step comprises a second substep of placing the fibrous mixture directly into the compression mold without pre-forming said mixture prior to compression molding.

12. A method as set forth in claim 11, wherein said second step includes a first substep of venting gases from said mass during compression molding using at least one gas vent duct incorporated into said upper mold of said compression mold.

13. A method as set forth in claim 11, wherein said second step includes a second substep of venting gases from said mass during compression molding using at least one vent hole comprising an elongated perforation formed in the frame adjacent the surface of said lower mold.

14. A method as set forth in claim 11, wherein said second step includes a third substep of venting gases from said mass during compression molding using an outward tapered surface on the inside of said frame of said lower mold.

15. A method as set forth in claim 11, wherein said second step includes a fourth substep of venting gases from said mass during compression molding using a plurality of vertical grooves formed in the interior surface of said frame of said lower mold.

Drawing