EP0226163A2

EP0226163A2 - Process for producing molded wooden products having a hole therein

Info

Publication number: EP0226163A2
Application number: EP86117081A
Authority: EP
Inventors: Sadao Ikeda; Yoshio Taguchi
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1985-12-07
Filing date: 1986-12-08
Publication date: 1987-06-24
Also published as: EP0226163A3; AU6616186A; AU590368B2; JPS62134208A

Abstract

A process is provided for producing a molded wooden product having at least one hole therein by placing a fibrous mixture composed of wood fiber, a binder, a water-repelling agent, and mold release agent, etc., in the compression mold and compressing molding the mixture. The fibrous mixture is placed in the mold either directly or in the form of a preformed mass of predetermined shape. Each hole is provided by a mandrel in the mold or in both the mass-forming apparatus and the mold.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a process for producing molded wooden products and, more specifically, to a process for producing a molded wooden product by placing a fibrous mixture comprising wood fiber, a binder, water-repelling agent, etc., into a compression mold and subjecting it to heat-compression molding.

Description of Related Art

Molded wood 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 used for such applications as building | interiors, automobile interiors, furniture, and television and stereo cabinets.
Processes for producing molded wooden products typically involve the following steps. First, wood chips are steamed at 160 to 180°C in the steaming tank of a defibrator (wood splitting machine) until they are soft enough for disintegration. The steamed wood chips are then defibrated by a splitting or defibrating disk. The defibrated wood fiber is dried by hot air, and the dried wood fiber is incorporated with long fibers (e.g., hemp fiber or polypropylene fiber) to improve the deep drawing properties, a binder (e.g., phenolic resin), and a water-repelling agent (e.g., rosin and paraffin). The resulting fibrous mixture is accumulated to form a mat with a predetermined thickness, followed by slight compression with heating. The resulting product is a mat 10 to 40 mm thick, which is easy to store and transport. The mat is cut to a proper size and the trimmed mat is placed in a compression mold for heat compression molding at 180 to 220°C. The molded wooden product is finished by trimming away excess portions.
The above-mentioned process for producing molded wooden products has the following disadvantages. The wood fiber must be formed into the mat, and the mat must be cut to a predetermined shape. These steps make the production process complex, and result in lowered productivity. The mat must be cut to a size slightly larger than the finished product. This cutting or trimming required before and after molding wastes the material, which leads to poor yields and increased production costs. In addition, if a single mat is to be made into a molded wooden product by deep drawing, expensive hemp fiber (for example as much as 17%) generally must be incorporated into the mat. Where hemp fiber is used, it is necessary to add an extra amount of binder, e.g., synthetic resin. This also leads to increased production costs.
The molded wooden product as described above is typically finished by forming a hole into which an object is later installed. This requires a special apparatus and adds to the manufacturing steps. This again leads to increased production costs. The hole is usually formed by punching, which makes the periphery of the punched hole weak and gives it a poor appearance, for example, from burrs.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a process for producing molded wooden products having improved properties and improved quality, and into which one or more holes are formed.
By following the process of the invention, it is possible t omit the mat-construction step and to make the hole or holes in the molded wooden product during the molding process. Thus, an advantage of the present invention is that it simplifies the production steps and improves yield.
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 invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, a process is provided for producing a molded wooden product from a fibrous mixture comprising wood fibers, a binder, a water-repelling agent, and other optional additives,. The fibrous mixture is placed into a compression mold and heat-compression molding is performed. The fibrous mixture may be placed directly in the mold or may be formed into a mass of predetermined shape in such a manner that a first mandrel formed in the mold displaces the mixture, and a hole is thereby formed in the molde wooden product.
The wood fiber used in this invention is obtained, for example, by defibrating or splitting wood chips. The wood used is not limited to a specific type and may, for example, include Japanese cypress, Japanese red pine, Japanese cedar, Japanese beech, and luaun. In addition, rice staws, flax husks, and bagasse may be used. Similarly, the process of defibration or splitting is not limited to a specific method. For example, splitting may be accomplished by steaming wood chips and mechanically disintegrating them.
The binder to be added to the wood fiber is not limited to specific type provided it can supplement the interfiber bonding properties inherent in the wood fibers. Examples of the binder include thermoplastic resins such as coumarone resin and thermosetting resins such as phenolic resin and urea resin. A water-repelling agent may also be incorporated with the wood fibers (in addition to the binder) to improve water resistance and promote mold release. An example of a water-repelling agent is paraffin, but any agent which provides enhanced water-repelling properties may be used.
The fibrous mixture may be introduced into a cavity formed by the upper mold and the lower mold of an opened compression mold by means of an air flow. Alternatively, the mixture may be formed into a mass of predetermined shape prior to placing it in the mold. A hole may be formed in the mass at the position corresponding to a first mandrel incorporated into the mold, and the mass may be placed in the mold such that the first mandrel fits into the hole.
According to the process of this invention, the mixture placed in the mold is integrally bonded and formed. The molding conditions may be properly established depending on the materials (e.g., wood fiber and binder) used, and the desired shape and strength of the resulting molded wooden product. They are not generally limited to specific values. For example, the molding temperature may range from 100 to 200°C, the molding pressure may range from 20 to 80 kg/cm², and the molding cycle may range from 20 seconds to 10 minutes.
According to the process of this invention, the mixture may be placed directly into the mold or it may be formed into a mass of predetermined shape. Therefore, the process of the invention allows the omission of the mat-construction step and consequently simplifies the manufacturing steps. Upon demolding, the molded wooden product has a hole formed in situ by the first mandrel. Thus, the step of forming a hole after molding may be omitted. A fibrous mixture of extremely low density may be used, which improves moldability. The density of the mixture is increased in the vicinity of the first mandrel, which results in high quality products.
The improved moldability makes it possible to use less binder and reduces the need to add expensive fibers such as hemp fibers, both of which contribute to reducing production costs.
The accompanying drawings which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1 to 8 are schematic representations of an apparatus used to practice the process of this invention for producing molded wooden products.
Figs. 1 and 2 are sectional views in elevation of a compression mold for heat-compression molding according to the process of the present invention;
Figs. 3 and 4 are schematic diagrams of a mass forming apparatus for forming the mass to be placed into the mold;
Figs. 5 and 6 are schematic diagrams of a holding vessel for transporting the mass; and
Figs. 7 and 8 show apparatus in elevation for feeding the fibrous mixture directly into the compression mold (Fig. 7 is a sectional view of the feeding and molding apparatus, and Fig. 8 is an elevational view of a door used in the mold of Fig. 7.)

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Figs. 1 and 2 show the structure of a compression mold used to practice the process of this invention for producing the molded wooden products. The compression mold comprises an upper mold 1 and a lower mold 2, which are provided with the hot plates 3 and 4, respectively. The upper and lower molds also have gas vent ducts (not shown) for evacuating gases from a cavity formed by the upper and lower molds during the molding process. The lower mold 2 is surrounded by a frame 5 which extends beyond the top o the lower mold 2 so that a cavity is formed on the lower mold 2 to contain the fibrous mass W. The upper mold 1 can slide along the inner periphery of the frame 5. The lower mold 2 is provide with a first mandrel 6. The upper mold 1 has a receptacle 7 intd which the mandrel 6 is inserted. The first mandrel 6 is provided at a location corresponding to the position of the hole in the molded wooden product P (Fig. 2). The mandrel 6 has a diameter approximately equal to that of the hole.
Before the compression-molding step is initiated, the upper mold 1 and lower mold 2 are preheated by hot plates 3 and 4. The mass W is placed into the preheated lower mold 2. The mass W used in this example is one which has an extremely low density. It is produced from a fibrous mixture M comprising wood fiber (e.g., defibrated wood chips), a binder (e.g., phenolic resin) and a water-repelling agent (e.g., paraffin). The fibrous mixture M may be fed to a mass forming apparatus (shown in Figs. 3 and 4 and discussed below) in which a mass W of predetermined shape is formed. The mass W has a hole Wl into which the mandrel 6 is inserted.
After the mass W is placed in the mold, the upper ram of the mold (not shown) is forced downward so that the mass W is compressed. As a result of this compression, the wood fibers become more densely interlaced and the molding pressure increases. In the initial stage of compression, the wood fibers are not well interlaced and are highly fluid. Therefore, they can undergo deep drawing without the occurrence of molding defects such as thinning and cracking. When the upper mold 1 reaches its lower limit and the compression mold is in fully compressed state, a molded wooden product P having a high density and a predetermined thickness (e.g., 2 to 6 mm) is obtained as shown in Fig. 2. Upon demolding, a hole of desired size and shape is formed at the place where the first mandrel 6 was positioned. The portion of the mass W which surrounds the first mandrel 6 becomes denser than the remaining portions of the mass. Therefore, the periphery of the hole in the molded wooden product P has a correspondingly higher density and is stronger than the other parts of the product.
The mass forming apparatus used to obtain the mass W is shown in Figs. 3 and 4. The mass forming apparatus 11 is comprised of a spreading vessel 12 and a collecting vessel 13 positioned beneath the spreading vessel. The spreading vessel is comprised of, for example, iron sheet, and forms a pyramidal or conical roof over the collecting vessel. The collecting vessel 13 is designed to permit the fibrous mixture M to accumulate therein. At the top of the spreading vessel 12 is an opening 12a. Above the opening 12a is a spreading unit 14 to spread the fibrous mixture M fed through a pressure feed pipe (not shown). At both sides of the opening 12a are air blowers 15 having air nozzles (not shown) on the inside thereof. The air nozzles control the spreading direction for the mixture in two dimensions. The air blowers 15 are supplied with air through th air supply lines 19 and the switch valve 20.
The bottom of the collecting vessel 13 is connected a vacu duct 13a to apply a vacuum to the vessel 13. A first preforated member 16 such as wire net or a punched metal plate is provided to shape the bottom surface of the mass W. The collecting vessel 13 is also provided with the height sensors 17, which are arranged on the wall of the collecting vessel and above the first perforated member 16. The height sensors 17 are used to control the upper profile of the mass as required. A second mandrel 18 extends from the bottom of the collecting vessel through the perforated member 16. The second mandrel 18 has an outside diameter equal to or slightly less than that of the mandrel 6 attached to the lower mold 2. The second mandrel 18 is positioned at a place corresponding to that of the first mandrel 6.
The mass forming apparatus 11 constructed as described above operates in the following manner to form the mass W. With the switch valve 26 open, air is supplied to the air blowers 15 through the air supply lines 19, so that an air flow is created across the spreading vessel 12 and the collecting vessel 13. Then, the fibrous mixture M is released from the opening 12a of the spreading vessel 12 and fed into the air flow. The mixture descends to the collecting vessel 13 and accumulates on the firs perforated member 16. The mixture M can be accumulated at desired positions of the perforated member 16 by controlling the air flow from the air blowers 15. This control is generally accomplished by switch valve 20. The accumulation of the mixture M is promoted by applying a vacuum to the bottom of the collecting vessel 13 through the vacuum duct 13a.
The accumulation of the mixture M continues until one of th height sensors 17 on the wall of the collecting vessel 13 detect the predetermined amount of accumulation. The switch valve 20 i controlled so that the mixture M accumulates at different places until the other height sensors detect a predetermined amount of accumulation. This procedure is repeated until all the height sensors 17 detect predetermined amounts of accumulation. The supply of the mixture M and the supply of air through the air supply lines 19 are terminated. A mass W with the desired shape is thus obtained. Being a mere accumulation, the mass W has an extremely low density, and it has a thickness 20 to 120 times that of the final molded wooden product.
The mass W prepared as described above is then transferred to the mold for heat-compression molding according to the following procedure. The collecting vessel 13 is disengaged from the spreading vessel 12. In the example shown in Fig. 5, the holding vessel 21 is fitted to the collecting vessel 21. The holding vessel 21 has a second perforated member 22 (also made of wire net or the like) which matches the upper profile of the mass W. The top of the holding vessel 21 is connected to an exit port 23. When vacuum is applied to the holding vessel 21 throug the exit port 23 by means of a vacuum pump (not shown), the ligh mass W is lifted upward until it comes into close contact with the second perforated member 22 in the holding vessel 21. With vacuum applied, the holding vessel 21 is lifted. The hole Wl is formed at a place where the second mandrel 18 was positioned as shown in Fig. 6. The holding vessel 21 is brought to a position directly over the compression mold by a transfer means (not shown). At the correct position, the vacuum is terminated, allowing the mass W to fall into the lower mold 2.
In the embodiment described above, the fibrous mixture M is formed into a low-density mass W. In an alternative embodiment of this invention, it is possible to use the mixture M (which is the raw material of the mass W) by directly placing the mixture into the compression mold.
_Fig. 7 shows an embodiment of the apparatus used to feed the mixture M directly into the mold. The feeding apparatus 30 comprises a feeding container 31 and a pressure container 32. The former communicates with the latter through the opening 33 which is opened and closed by a masking plate 35 actuated by cylinder 34. The feeding container 31 has an inlet 36 at the top for receiving the mixture M. A pair of rotatable bush wheels 37 are mounted above the opening 33. The pressure container 32 is connected at one end thereof to an air supply means (not shown) and the other end thereof to the heat-compression mold (as shown in Figs. 1 and 2). A weighing plate 38 connected to a load cell (not shown) is mounted under the opening 33.
The frame 5 of the mold has two opposing openings 39 and 40. The first opening 39 is connected to the pressure container 32, and the other opening 40 is open to the atmosphere. The height of the openings 39 and 40 corresponds to the cavity 41 of the I partially closed mold, and the openings have a width adequate to fit the molded wooden product. In addition, the frame 5 has side plates 42 and 43 which open and close the openings 39 and 40, respectively. Fig. 8 is a front view of the side plate 42. It has a feeding port 44 which is about the same size as the opening 39. The window 42 of the sliding door 43 for the second opening 40 is provided with the wire net 45. Each of the side plates 42 and 43 is provided at the lower end thereof with a rack 46. A motor 48 is fixedly mounted on a bracket 47 projecting from the frame 5. The output shaft of the motor 48 is provided with the pinion 49 which engages with the rack 46. In other words, the doors 42 and 43 are horizontally movable by the driving force of the motor 48, so that the openings 39 and 40 are opened and closed as required.
The mixture M fed into the feeding container 31 through the inlet 36 is discharged through the opening 33 by the aid of the rotating brush wheels 37. The discharged mixture accumulates on the weighing plate 38 in the pressure container 32. When the accumulated mixture reaches a predetermined level or weight, the cylinder 34 is actuated and the opening 33 is closed by the masking plate 35. At the same time, air is supplied in the direction of the arrow A by the air supply means. The mixture M which has accumulated on the weighing plate 38 is forced into the cavity 41 by the air flow.
The mixture M introduced into the mold cavity is contained by the wire net 45. Air passes in the direction of arrow B through the wire net 45. The cavity 41 is thus filled with the mixture M. Then, the motor 48 moves the doors 42 and 43 which close the first and second openings 39 and 40, respectively. Subsequently, compression molding is carried out in the same manner as explained with reference to Figs. 1 and 2. Thus, the high-quality molded wooden product P having a hole as in the above-mentioned examples is obtained.
It will be apparent to those skilled in the art that various modifications and variations can be made in the process of the present invention without departing from the scope or spirit of the invention. For example, rather than using a single first mandrel to form a single hole in the molded wooden product, a plurality of mandrels may be used to form a corresponding plurality of holes in the product. 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 havin a hole therein, 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 first mandrel, said upper mold including a receptacle for receiving said first mandrel, and said lower mold and said upper mold forming said cavity; and

a second step of compression molding said fibrous mixture under heat to form a molded wooden product having a hole in a position corresponding to said first mandrel.

2. 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.

3. A method as set forth in claim 2, wherein said first substep comprises forming said mass in a mass forming apparatus, said mass forming apparatus including a spreading vessel and a collecting vessel, said collecting vessel including a first perforated member and a second mandrel extending through said first perforated member, and said first substep further comprises forming a hole in said mass at said second mandrel corresponding to the position of said first mandrel in said mold and the hole in the molded wooden product.

4. 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.