WO2009020379A1

WO2009020379A1 - Short grain plywood and method of manufacturing thereof

Info

Publication number: WO2009020379A1
Application number: PCT/MY2007/000086
Authority: WO
Inventors: Ah Tee Ong; Yong Khang Ong; Ah Ching Chiam; Wah Yak Lim
Original assignee: Ah Tee Ong; Yong Khang Ong; Ah Ching Chiam; Wah Yak Lim
Priority date: 2007-08-09
Filing date: 2007-11-28
Publication date: 2009-02-12
Also published as: MY166028A

Abstract

This invention relates to a plywood comprising surface veneers laminated on a core structure in a cross-banding way; wherein the surface veneers are of short grain (54) or of long grain (51) formed by joining a plurality of short grain veneers with an adhesive. Another embodiment of the present invention is a method of manufacturing plywood comprising: a) joining a plurality of short grain veneers to form surface veneers (51, 54); b) laminating the surface veneers (51, 54) on at least one surface of a core structure with an adhesive to form a veneer stack; and c) pressing the veneer stack to form the plywood.

Description

SHORT GRAIN PLYWOOD .4ND METHOD OF MANUFACTURING

THEREOF

FIELD OF LNVENTION

The present invention relates to a plywood and a method of manufacturing thereof. In more particular, the present invention relates to an innovative plywood and the technique of manufacturing thereof whereby the short grain veneers are joined together by overlapping in building up of long grain veneers to form the surface veneers of a plywood.

BACKGROUND OF THE INVENTION

Plywood is a type of engineered wood that made of wood veneer which is generally called veneers or plies. The plies of wood veneer are stacked together by cross- banding with the direction of each ply's grain differing from its neighbours^" by 90°.

Plywood is manufactured from an odd number of wood veneers to provide stability. The most common varieties of plywood come in three, five or seven plies. Odd number of wood veneers that bonded face to face with the grain running in alternate direction will ensure the balance of the tensions in between the wood veneers and prevent the plywood from distortion or warping.

Plywood is manufactured in standard sizes such as 4 feet x 8 feet, 3 feet x 7 feet, 4 feet x 4 feet, 3 feet x 6 feet and others. The most favourable type of plywood among contractors and furniture makers is that with the most common size, which is of a metric dimension of 4 feet x 8 feet. The thickness of the plies varies depending on the panel thickness. Plywood is one of the versatile wood products that can be applied in many applications. Because of woods and logs from natural forest are becoming scarce and costly, many of the plywood plants had to- terminate their production. Since the surface veneers (face veneers and back veneers) of a plywood are traditionally constructed by veneers with longitudinal grains, a timber log with a length greater than 8 feet is usually required in the manufacturing of plywood. However, as more and more rainforest is destroyed to meet the demands of the developed world's wood industry, long timber log with large diameter is more difficult to obtain. Therefore, a solution to this problem is a necessary.

There are some plywood manufacturing techniques described in the prior arts designing to join the small pieces of wood veneers together to a standard size to be used in the manufacture of plywood.

Of interest in connection with an improved method in joining together the veneers to form larger veneers is U. K. Patent No. GB541945 to Henry Kremer. This patent discloses a method of joining small pieces of veneers edge to edge by placing over the joint a binding strip that is impregnated with an adhesive. The binding strip may , have a paper base and may be cut from the binding sheets as used for binding together the superimposed veneers in making plywood. The binding strip is assembled at an intermediate position in the thickness of the stack and secured together with the veneers by heating.

Of interest with respect to another method of joining pieces of veneer and wood of any thickness is U. K. Patent No. GB291794 to Leo Michael Conn Wegner. The patent discloses a method of joining pieces and wood such that the articles under construction are lengthened in the direction of the grain wherein the articles to be made are provided at the ends to be joined with milled out teeth such that the joints run parallel and at an acute angle to the direction of the grain.

There is also a U. S. Patent No. US4640857 to Vlenan Machinery Works, relating to a plywood which comprises two standard sections consisting of multiple plies joined together wherein two contiguous ends of two adjacent veneer sheets forming the external opposite faces of the plywood and are glued together lapping one on the other. The invention utilizes veneers that are too short for a desired length of plywood panel.

The joining methods as described by the prior arts are generally more complicated and the joining process usually involves small veneer pieces that are too short for any desired lengths of plywood product. Long timber tog with a length greater than 8 feet is still required as the raw material in plywood manufacture and large rotary lathe with the width greater than 8 feet is still required to peel veneers to obtain a sufficient width for producing plywood of standard sizes.

SUMMARY OF INVENTION

The primary object of the invention is to innovate a new structure of plywood where small pieces of short grain veneer obtained from timber logs less than 5 feet can be utilized to form plywood of standard sizes by overlapped joints.

Another object of the invention is to develop a method of manufacturing plywood which is more cost-saving and requires lower management intensity since only timber logs less than 5 feet is utilized in the plywood manufacture.

Still another object of the present invention is to cope with the shortage of rainforest timber logs as the raw materials for woodworking industry since the present invention mainly employ the short timber logs obtained from the plantation woods.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention describes a plywood comprising surface veneers laminated on a core structure in a cross-banding way; wherein the surface veneers are of short grain (54) or of long grain (51) formed by joining a plurality of short grain veneers with an adhesive. Anotner embodimeni of the invention is a method oi manuracτuring plywood comprising: a) joining a plurality of short grain veneers to form surface veneers (51 , 54); b) laminating the surface veneers (51, 54) on at least one surface of a core structure with an adhesive to form a veneer stack; and c) pressing the veneer stack to form the plywood.

The present invention provides a plywood which is mainly made from short timber logs of plantation woods wherein the wood veneers are joined together to form surface veneers of a plywood without sacrificing its strength, stability and durability. The manufacturing method of plywood is lower in production cost, requires lower management intensity, and helps conserving the rainforest.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

Figure 1 is the perspective view of a 3-ply plywood with long grain surface veneers (51). Figure 2 is the perspective view of a 3-ply plywood with short grain surface veneers (53. 54).

Figure 3 is the perspective view of a 5-ply plywood with long grain surface veneers (51).

Figure 4 is the perspective view of a 5-ply plywood with short grain surface veneers (53, 54).

Figure 5 is the cross-sectional view of a 3-ply plywood shown in Figure 1.

Figure 6 is the cross-sectional view of a 3-ply plywood shown in Figure 2.

Figure 7 is the cross-sectional view of a 5-ply plywood shown in Figure 3.

Figure 8 is the cross-sectional view of a 5-ply plywood shown in Figure 4.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of ■the present invention and it is envisioned that those skilled in the art may devise

-various modifications wiihoui departing from the scope of the appended claim.

The present invention discloses a plywood comprising surface veneers laminated on a core structure in a cross-banding way; wherein the surface veneers are of short grain (54) or of long grain (51) formed by joining a plurality of short grain veneers with an adhesive.

According to the preferred embodiment of the present invention, the plywood consists of two different types of veneers. The first type is thin veneers with a thickness ranged from 0.30mm to 1.50mm. The second type is thick veneers with a thickness ranged from 1.00mm to 4.00mm. Generally, the thin veneers are used as surface veneers (51, 53. 54) whereas the thick veneers are used as core veneers (52).

As illustrated by Figure 1 and 3, long grain veneers (51) are traditionally used as the surface veneers of a plywood especially when plywood is applied in the manufacturing process of furniture. In the present invention, only short grain veneers that obtained from timber logs shorter than 5 feet in length are used as the raw materials. Therefore, the surface veneers with long grain (51) are obtained from joining a plurality of short grain veneers with an adhesive. The plurality of short grain veneers are joined by overlapping one veneer sheet on another. The overlapping zone is in a length range from lmm to 100mm. According to the preferred embodiment, the overlapping zone is preferably to be 3mm. On the other hand, short grain surface veneers (54), as illustrated by Figure 2 and 4, can also be produced as this innovative type of plywood may be useful in other applications.

Figure 2 shows one of the preferred embodiments of the present invention, whereby the surface veneers are devided into face veneers (53) which serve as the external surface and back veneers (54) which serve as internal surface when plywood is used for construction. Therefore, veneers with grains of finer texture, better appearance and minimum defect are usually selected as face veneers (53). The surface veneers are laminated on a core structure in cross-banding way in which the grain of each ply of veneers differs from its neighbours' by 90°. According to the preferred embodiment of the present invention, the core structure of the plywood comprises 1 to 13 plies of core veneers (52). The core veneers (52) are full sheets or one-piece short grain veneers, as shown in Figure 1 , or joined short grain veneers, as shown in Figure 2. In one of the preferred embodiments as shown in Figure 6, 7 and 8, the short grain core veneers (52) are joined by bevel joints, edge joints or any combination thereof.

The joints between the pieces of veneers are secured by the application of an adhesive. The adhesive is preferably to be urea-formaldehyde resins (UF), melamine- formaldehyde resins (MF), phenol-formaldehyde resins (PF) or methylene diphenyl diisocyanate (MDI). According to the most preferred embodiment of the present invention, the adhesive used is urea-formaldehyde resins (UF). The core veneers (52) and surface veneers (51, 53, 54) are also adhered together by using the same types of adhesive.

The plywood is manufactured in odd number of plies. According to the preferred embodiment, it is usually manufactured in 3-ply, 5-ply, 7-ply, 9-ply, 1 1 -ply, 13-ply or 15-ply. The most preferred types are 3-ply and 5-ply. as illustrated in any one of the Figures 1 to 8.

The timber logs are preferably obtained from the plantation softwoods such as Paraserianτhes falcataria. Gmelina arborea, Hevea brasiliensis or Anthocephalus cadamba. In the most preferred embodiment of the present invention, the timber logs are obtained from the wood of Paraserianthes falcataria. This species is preferably selected for the present invention because it requires a short period of growth. It can give a timber log with a diameter of approximately 250mm in 5 years. Another embodiment of the invention is a method of manufacturing plywood comprising: a) joining a plurality of short grain veneers to form surface veneers (51 , 54); b) laminating the surface veneers (51. 54) on at least one surface of a core structure with an adhesive to form a veneer stack; and c) pressing the veneer stack to form the plywood.

The timber logs for the making of wood veneers are selected from the plantation softwood based on the trunk straightness and uniformity of diameter between its bottom and its top end. Since this invention employs veneers of short grain, the short timber logs less than 5 feet in length can be utilized. According to the preferred embodiment of the present invention, the short grain veneers are obtained by longitudinally peeling veneer logs by using a 5-feet rotary lathe. The veneers are then dried in a dryer at a temperature range from 100°C to 150°C until its moisture content is below 14%.

According to the preferred embodiment of the present invention, the manufacturing method of plywood of the present invention is initiated by joining a plurality of short grain veneers to form surface veneers (51, 54). As set forth in the foregoing description, the plurality of short grain veneers can be joined .to form either short grain surface veneers (54) or long grain surface veneer (51). As illustrated in Figure 2, to form a joined short grain surface veneers (54), the plurality of short grain veneers are joined together by overlapping one short grain veneer on another with the grain aligned in parallel. Figure 1 shows a method of forming a joined long grain surface veneers (51), whereby the plurality of short grain veneers are joined together by overlapping one short grain veneer on another with the grain aligned end to end. The overlapping zone is in a length range from lmm to 100mm. According to the preferred embodiment the overlapping zone is preferably to be 3mm.

According to the preferred embodiment, the joint of a joined face veneer should be located at a different position from the joint of the joined back veneer of a plywood, as shown m Figure 5 and 7. The position of the joints of these surface veneers should differ in a range of at least 10mm, preferably more than 20mm. This design is essential to produce a plywood that is structurally stronger and having a smoother surface after sanding since this design balance up the tensions between the surface veneers.

By using a one-piece (53) or joined short grain surface (54), an innovative plywood with short grain surface veneers is obtained; whereas the conventional plywood with long grain surface veneers (51) can be produced by using the joined short grain surface veneers.

The surface veneers are laminated on at least one surface of a core structure with an adhesive to form a veneer stack. Adhesive materials are applied on the dried veneers before. the laminating step. The adhesive is preferably to be melamine-formaldehyde resins (MF), urea-formaldehyde resins (UF), phenol-formaldehyde resins (PF) or methylene diphenyl diisocyanate (MDI). According to the most preferred embodiment of the present invention, the adhesive used is urea-formaldehyde resins (UF).

The core structure can comprise 1 to 13 plies of core veneers (52) according to the applications of the plywood. Therefore, the method of the present invention further comprises a step of adhering and pressing 1 to 13 plies of veneer by cross-banding to form the core structure before the laminating step. Cross-banding is the common technique used in plywood manufacture wherein the plies of veneer are bonded face to face with the grain running in alternate directions such that each ply's grain differs from its neighbours' by 90°.

The glued veneer stack is subjected- to a pressing step to form a plywood with longitudinal grain. The pressing step preferably includes a cold pressing process and followed by a hot pressing process. The cold pressing process is carried out at room temperature and by mechanical (screw type) or hydraulic presses. The purposes of cold pressing process are to make the adhesive evenly spread on the surface of the veneers and penetrate into the veneers as well as to hold the veneer together to form pre-bonded panel for easing the handling of hot pressing process. Hot pressing process cures the adhesive and holds the veneer permanently. The temperature applied for the hot pressing process is between 100°C to 120°C with the pressure ransed from 7kε/cπr to 1 Oka' cm².

The plywood manufactured is subjected to a sizing process after the pressing processes. The plywood is cut into standard sizes according to demands. According to the preferred embodiment of the present invention, /the plywood is further sent for a sanding process to obtain a final product. The edges of the final product can be sealed i' / to prevent any damage or alteration of its moisture content by humidity. The plywood manutfactured can be sent for refinishing process depending ΌΠ the market for which if i& intended.

The present disclosure includes as contained in the'appended claims, as well as that of tie foregoing description. Although this invention has been described m its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.

Claims

1. A plywood comprises surface veneers laminated on a core structure in a cross- banding way; wherein the surface veneers are of short grain (54) or of long grain (51) formed by joining a plurality of short grain veneers with an adhesive.

2. A plywood as claimed in claim 1. wherein the surface veneers (51, 54) are joined by overlapping one veneer sheet on another.

3. A plywood as claimed in claim 1 or 2, wherein the core structure comprises 1 to 13 plies of core veneers (52).

4. A plywood as claimed in any one of claims 1 to 3, wherein the core veneers (52) are one-piece short grain veneers or joined short grain veneers.

5. A plywood as claimed in any one of claims 1 to 4. wherein the adhesive is a melamine-formaldehyde resin (MF), a urea-formaldehyde resin (UF), a phenol- formaldehyde resin (PF) or a methylene diphenyl diisocyanate (MDI).

6. A method of manufacturing plywood comprising: a) joining a plurality of short grain veneers to form surface veneers (51, 54); b) laminating the surface veneers (51, 54) on at least one surface of a core structure with an adhesive to form a veneer stack: and c) pressing the veneer stack to form the plywood.

7. A method as claimed in claim 6, wherein the plurality of short grain veneers are obtained by longitudinally peeling veneer logs of less than 5 feet in length.

8. A method as claimed in any one of claims 6 to 7, wherein the plurality of short grain veneers is joined to form short grain surface veneers (54) or long grain surface veneers (51).

9. A method as claimed in any one of claims 6 to 8. wherein the short grain surface veneers (54) are formed by overlapping one short grain veneer on another with the grain aligned in parallel.

10. A method as claimed in any one of claims 6 to 9, wherein the long grain surface veneers (51) are formed by overlapping one short grain veneer on another with the grain aligned end to end.

1 1. A method as claimed in any one of claims 6 to 10, wherein the overlapping zone is in a length range from lmm to 100mm.

12. A method as claimed in any one of claims 6 to 1 1 , wherein the core structure comprises 1 to 13 plies of core veneers (52).

13. A method as claimed in any one of claims 6 to 12, wherein the pressing step comprises a cold pressing process and followed by a hot pressing process.

14. A method as claimed in any one of claims 6 to 13, further comprises a sanding step after the pressing step.

15. A method as claimed in any one of claims 6 to 14, wherein the adhesive is a melamine-formaldehyde resin (MF), a urea- formaldehyde resin (UF), a phenol- formaldehyde resin (PF) or a methylene diphenyl diisocyanate (MDI).