METHOD OF FUSING A HOLLOW BOARD OF SYNTHETIC RESIN

Abstract: Portions of a thermoplastic synthetic resin panel (B) formed by extrusion and integrally having a first sheet (2a), a second sheet (2b) parallel to the first sheet (2a), and a plurality of ribs (3) integrally joining the first and second sheets (2a, 2b) are welded together by ultrasonic welding by applying an ultrasonic welding head (6) and a work support block (7) of an ultrasonic welding machine to the first sheet (2a) and the second sheet (2b), respectively, and compressing the portions of the thermoplastic synthetic resin panel (B) between the ultrasonic welding head (6) and the work support block (7). When welding together two thermoplastic synthetic resin panels (B1, B2), at least portions of the panels (B1, B2) are put one on top of the other to form an overlapping section, an head (6C) and a work support block (7C) are applied to the opposite surfaces of the overlapping section, respectively, and the head (6C) is driven to generate ultrasonic waves, compressing the overlapping section between the ultrasonic welding head (6C) and the work support block (7C). The overlapping section vibrates, generates frictional heat therein, and is welded under compression.

Description: The present invention relates to a method of welding a hollow thermoplastic synthetic resin panel. Such a method is known from US 4 265 842 and WO91/04849, according to which a seam along an edge of the panel is formed by electrically heating the edges of the two panels and pressing these heated edges together to fuse them. It is known e. g. from JP 59-071817 to weld panels of the kind mentioned above by using ultrasonic vibrations. Hollow thermoplastic synthetic resin panels having two parallel sheets and a plurality of ribs integrally connecting together the two sheets are used for forming packages, such as boxes, architectural materials, such as partition members and walls, and the like. The hollow thermoplastic synthetic resin panel for such purposes are produced by extruding a material in the direction of extension of the ribs. Generally, the material is a thermoplastic resin such as a polypropylene rein or a polyethylene resin. The hollow thermoplastic synthetic resin panel has become prevalently used owing to its excellent strength and durability as compared with those of corrugated cardboards, Since the side edges parallel to the ribs of the conventional hollow panel of this kind, and the end edges of the same hollow panel perpendicular to the ribs are open 'to the outside, the interior of the spaces of the hollow panel are liable to be contaminated with foreign matters including dust and unwanted bacteria, and the cleaning of the interiors of the hollows is practically impossible. Accordingly, the conventional hollow panel could not have been used for forming boxes for containing food, medical and pharmaceutical products, cosmetics, etc. which must meet severe sanitary standards. When using hollow panels of this kind as a packaging material, the hollow panels need to be subjected to processes to form grooves and/or recesses in the surface thereof, and to form folding grooves and openings in the hollow panels. Such processes use press working including hot-plate press working. However, since folding grooves formed by press working are shallow and portions of the hollow panels corresponding to the folding grooves are excessively resilient, various troubles arises during and after assembling the hollow panels to form boxes. If an opening is formed in the hollow panel by press working, the interior of the hollows are opened on the edge of the opening and hence the interior of the hollows are contaminated with foreign matters including dust. When a hot plate is used for press working, the surface of the hot plate melts portions on the opposite sides of a pressed part of the opposite sheets of the hollow panel and many pores are formed in the hollow panel. Hollow panels are joined together or a hollow panel is joined to another part, such as a frame, by methods respectively using staples, rivets, an adhesive tape and an adhesive. These methods have been employed in joining together corrugated cardboards made of paper and, in some cases, these methods are applicable to joining together hollow synthetic resin panels without entailing any problem. Hollow thermoplastic synthetic resin panels are used for forming a package for containing a heavy article that applies a large load that cannot be born by a corrugated cardboard or fiberboard to the package or a highly air-tight or liquid-tight package. Therefore, a package formed by welding together hollow thermoplastic synthetic resin panels with adhesive tapes or an adhesive is not perfectly reliable when used for such purposes. Stapling and riveting have difficulty in carrying out air-tight or liquid-tight welding. A method of welding together hollow thermoplastic synthetic resin panels with a hot plate, similarly to the method of forming grooves and/or recesses in hollow thermoplastic synthetic resin panels and forming folding grooves and openings in the hollow thermoplastic synthetic resin panel, has problems in that many holes and impressions are formed in the surface of the hollow thermoplastic synthetic resin panel, and in that two hollow thermoplastic synthetic resin panels, or a hollow thermoplastic synthetic resin panel and a thermoplastic synthetic resin part are not welded firmly together with satisfactory appearance and, in a worst case, the welded portions of the hollow thermoplastic synthetic resin panel are burnt off. The present invention has been made to solve those problems in the prior art and it is therefore an object of the present invention to provide a hollow thermoplastic synthetic resin panel welding method capable of firmly welding together the opposite sheets of a hollow thermoplastic synthetic resin panel, two hollow thermoplastic synthetic resin panels or a hollow thermoplastic synthetic resin panel and another part with satisfactory appearance. Another object of the present invention is to provide a thermoplastic synthetic resin panel welding method capable of surely closing the edges or the line of a hollow thermoplastic synthetic resin panel by fusion to seal the interior of the hollow thermoplastic synthetic resin panel panel. Still another object of the present invention is to provide a thermoplastic synthetic resin panel welding method capable of surely forming grooves, recesses, folding grooves, openings and such in a hollow thermoplastic synthetic resin panel without inducing resilience in portions of the hollow thermoplastic synthetic resin panel corresponding to the grooves, the recesses, the folding grooves, the openings and such. These objects are solved by the method of claim 1. Further advantageous features of the invention are described in the subclaims. The present invention employs an ultrasonic welding process instead of a heat bonding process which applies heat to portions of components to be welded together. An ultrasonic welding process employed in the present invention makes the material forming the hollow thermoplastic synthetic resin panel vibrate to generate heat in the hollow thermoplastic synthetic resin panel instead of applying heat to the hollow thermoplastic synthetic resin panel. Frictional heat is easily generated in portions of the sheets of hollow thermoplastic synthetic resin panels pressed against each other and hence those portions are easily fused. Accordingly, welding starts from the interior of those portions and the external surfaces of the sheets are hardly affected by welding and are kept clean. Since the internal portions of the components of the hollow thermoplastic synthetic resin panel are welded, the junctions has a high weld strength. Since the range of welding can easily be controlled, the components can be welded together accurately, for example, along a line. Ultrasonic waves can effectively propagate through the ribs of the hollow thermoplastic synthetic resin panel, and the sheets of the hollow thermoplastic synthetic resin panels can effectively be welded together owing to the agency of the ribs. The heat bonding process heats portions of components to be welded together by applying heat to those positions from the outside. Therefore, the surfaces of the hollow thermoplastic synthetic resin panel are liable to be affected adversely by the heat, the inner portion of the components of the hollow thermoplastic synthetic resin panel are not necessarily be welded with reliability, portions of the components around the welded portions are liable to be affected by heat and, in most cases, it is difficult to weld the components exactly as designed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a hollow thermoplastic synthetic resin panel to which the present invention is applied; Fig. 2 is a partly cutaway perspective view of the hollow thermoplastic synthetic resin panel of Fig. 1; Fig. 3 is a side view of the hollow thermoplastic synthetic resin panel in an initial stage of a method of closing openings in an end edge of the hollow thermoplastic synthetic resin panel; Fig. 4 is a side view of the hollow thermoplastic synthetic resin panel in a final stage of the method of closing openings in an end edge of the hollow thermoplastic synthetic resin panel; Fig. 5 is a partly cutaway perspective view of a hollow thermoplastic synthetic resin panel having end edges closed as shown in Fig. 4; Fig. 6 is a sectional view of the hollow thermoplastic synthetic resin panel of Fig. 4; Fig. 7 is sectional view of a hollow thermoplastic synthetic resin panel, explaining a method of welding portions of the hollow thermoplastic synthetic resin panel along lines; Fig. 8 is a sectional view of a hollow thermoplastic synthetic resin panel, explaining a method of two-dimensionally welding together portions of the first and the second sheets of the hollow thermoplastic synthetic resin panel; Fig. 9 is sectional view of a hollow thermoplastic synthetic resin panel having welded portions formed by the methods illustrated in Figs. 7 and 8; Fig. 10 is a perspective view of a hollow thermoplastic synthetic resin panel having a linearly welded portion; Fig. 11 is a plan view of a hollow thermoplastic synthetic resin panel provided with an opening and a recess demarcated by welded portions; Fig. 12 is a sectional view taken on line. XII-XII in Fig. 11. BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. Referring to Figs. 1 and 2 showing a hollow thermoplastic synthetic resin panel B relevant to the present invention in a sectional view and a partly cutaway perspective view, respectively, the hollow thermoplastic synthetic resin panel has a first sheet 2a, a second sheet 2b extended opposite to and in parallel to the first sheet 2a, and a plurality of parallel ribs 3 integrally joining the sheets 2a and 2b. A plurality of hollow spaces 4 are formed between adjacent ribs 3. The sheets 2a and 2b and the ribs 3 are formed in an integral structure by extruding a thermoplastic resin, such as a polypropylene resin or a polyethylene resin, through an extrusion die. In the hollow thermoplastic synthetic resin panel B thus formed, the side edges 5 parallel to the ribs 3 are open to the outside as shown in Fig. 1, and the spaces 4 are open in the longitudinal end edges as shown in Fig. 2. Therefore, the interior of the hollow thermoplastic synthetic resin panel B is liable to be contaminated with foreign matters including dust and unwanted bacteria and, once contaminated, it is practically impossible to wash the interior of the hollow thermoplastic synthetic resin panel B. A thermoplastic synthetic resin panel welding method in a preferred embodiment according to the present invention solves such a problem. For example, the open ends of the spaces 4 opening in the longitudinal end edges of the hollow thermoplastic synthetic resin panel B are closed by welding together the longitudinal end portions of the first sheet 2a and the second sheet 2b as shown in Figs. 3 and 4. The present invention employs an ultrasonic welding machine, the principle of which is generally known, for welding together the longitudinal end portions of the first sheet 2a and the second sheet 2b. The ultrasonic welding machine is provided with a transducer which uses a unidirectional piezoelectric effect for converting electric power into ultrasonic vibration, and an amplifier. Ultrasonic vibration is exerted through an ultrasonic horn on a workpiece to generate heat in the workpiece by stimulating atomic movement in molecules of the material forming the workpiece. Fig. 3 shows an ultrasonic welding machine which carries out a thermoplastic synthetic resin panel welding method in accordance with the present- invention. The ultrasonic welding machine has an ultrasonic welding head 6, i.e., an ultrasonic horn, and a work support block 7 having a flat support surface. The ultrasonic welding head 6 is extended along an end edge of the outer surface of the first sheet 2a of the hollow thermoplastic synthetic resin panel B (perpendicularly to the sheet of Fig. 3), and the work support block 7 is disposed with its support surface extended along an end edge of the outer surface of the second sheet 2b of the hollow thermoplastic synthetic resin panel B so as to correspond to the ultrasonic welding head 6. The end edge of the hollow thermoplastic synthetic resin panel B is placed on the work support block 7, the ultrasonic welding head 6 is actuated to generate ultrasonic waves, and the ultrasonic welding head 6 is moved in the direction of the arrow A (Fig. 3) toward the work support block 7 to compress the end edge portion of the hollow thermoplastic synthetic resin panel B between the ultrasonic welding head 6 and the work support block 7. The ultrasonic waves generated by the ultrasonic welding head 6 are transmitted through the first sheet 2a and the ribs 4 to the second sheet 2b. Then, heat is generated in the first sheet 2a, the second sheet 2b and the ribs 3 by intramolecular vibration and the first sheet 2a, the second sheet 2b and the ribs 3 are fused and welded together. Since those fused portions of the first sheet 2a, the second sheet 2b and the ribs 3 are compressed between the ultrasonic welding head 6 and the work support block 7, the first sheet 2a is pressed toward the second sheet 2b as the ribs 3 are softened and, finally, the end edge of the first sheet 2a is joined to the end edge of the second sheet 2b as shown in Fig. 4. The end edge portion of the first sheet 2a is bent toward the end edge portion of the second sheet 2b and the respective end edges of the first sheet 2a and the second sheet 2b are welded together. The ultrasonic welding head 6 has a concave, curved shape with the outer edge portion protruding to the largest extent as shown in Fig. 4, and the end edge portion of the first sheet 2a is bent in a curve conforming to the concave, curved shape of the ultrasonic welding head 6. The end portions of the ribs 4 are melted into a shape conforming the curved shape of the end edge portion of the first sheet 2a. Since the ultrasonic waves are effective only in a region between the ultrasonic welding head 6 and the work support block 7, only portions of the hollow thermoplastic synthetic resin panel B in this region are melted and the rest of the same are not melted. The other end edge of the hollow thermoplastic synthetic resin panel B is closed also by welding to form closed end edges or seams 8 in the hollow thermoplastic synthetic resin panel B as shown in Figs. 5 and 6. The closed end seams 8 can be formed in a desired shape by properly determining the shapes of the ultrasonic welding head 6 and the work support block 7. When the end seams 8 are thus formed, the space 4 of the hollow thermoplastic synthetic resin panel B are not contaminated with foreign matters including dust, and air is sealed in the spaces 4. Consequently, the heat insulating performance and the rigidity of the hollow thermoplastic synthetic resin panel B are enhanced. If necessary, the side edges of the hollow thermoplastic synthetic resin panel B parallel to the ribs 3 may be closed by welding. Welding work similar to that mentioned above can be practiced for portions of the hollow thermoplastic synthetic resin panel B other than the edge portions. When forming a hollow panel structure shown in Fig. 7, an ultrasonic welding head 6A is formed in a tapered cross section and has a middle nose 9. and a work support block 7A is basically the same as the foregoing work support block 7 and has a flat support surface. A desired portion of the hollow thermoplastic synthetic resin panel B is placed on the work support block 7A, the ultrasonic welding head 6A is driven to generate ultrasonic waves and the ultrasonic welding head 6A is moved toward the work support block 7A. Consequently, the desired portion of the hollow thermoplastic synthetic resin panel B is softened and partly melted and the first sheet 2a is curved and welded to the second sheet 2b to form a linear grove 10 having a substantially V-shaped cross section as indicated by alternate long and two short dashes lines in Fig. 7. Thus, a weld line 11 is formed in the bottom of the V-shaped linear groove 10 in the hollow thermoplastic synthetic resin panel B. The shape of the linear groove 10 is dependent on the shape of the ultrasonic welding head 6A. A member may be attached to the panel B by fitting the member in the linear groove 10 or the groove 10 may be formed in characters, patterns or marks. A thermoplastic synthetic resin panel welding method shown in Fig. 8 forms a recess 12 having a flat bottom surface instead of the linear groove 10. An ultrasonic welding head 6B having a flat end surface and a work support block 7B having a flat support surface corresponding to the flat end surface of the ultrasonic welding head 6B are employed. The ultrasonic welding head 6B is driven to generate ultrasonic waves and is moved toward the work support block 7B. Consequently, a portion of the hollow thermoplastic synthetic resin panel B corresponding to the flat end surface of the ultrasonic welding head 6B is softened, portions of the ribs 3 corresponding to the ultrasonic welding head 6B are melted, and a portion of the first sheet 2a corresponding to the ultrasonic welding head 6B is welded to the second sheet 2b to form the recess 12 as shown in Fig. 9. The recess 12 may be a gripping recess, pattern or marks. Fig. 10 shows a hollow panel structure obtained by forming a folding line 14 perpendicular to ribs 3 in a hollow thermoplastic synthetic resin panel B. This folding line 14 can be formed by compressing a portion of the hollow thermoplastic synthetic resin panel B between an ultrasonic welding head similar to the ultrasonic-welding head 6A shown in Fig. 7, and a work support block of a shape similar to that of the ultrasonic welding head. In this hollow panel structure, corresponding portions of the' first sheet 2a and the second sheet 2b are curved in linear grooves similar to the linear groove 10 of Fig. 9 and the bottoms of the linear grooves are joined to each other to form the folding line 14. The hollow thermoplastic synthetic resin panel B can be folded along the folding line 14. The folding line 14 can be formed in parallel to or at an inclination to the ribs 3. Since corresponding portions of the sheets 2a and 2b on the folding line 14 are directly welded together, the resilience of the hollow thermoplastic synthetic resin panel B against bending along the folding line 14 is low and, when used as a hinge, the folding line 14 has an increased fatigue strength. Although the linear groove 10 having a V-shaped cross section as shown in Fig. 7 may be used as a folding line, it is desirable that the folding line be formed by forming linear grooves having a common bottom in the opposite surfaces of the hollow thermoplastic synthetic resin panel B. The first sheet 2a and the second sheet 2b can be welded together in a manner as shown in Figs. 11 and 12. An opening 16 or a recess 17 is formed in the hollow thermoplastic synthetic resin panel B as shown in Fig. 11, the edges of the opening 16 or the recess 17 are held between an ultrasonic welding head and a work support block having the shape of the opening 16 or the recess 17, and then ultrasonic waves are generated by the ultrasonic welding head. Consequently, portions of the sheets 2a and 2b corresponding to the edges of the opening 16 or the recess 17 are welded together. Thus, the edges 18 of the opening 16 are closed or seamed as shown in Fig. 12.

Claims: A method of welding a hollow thermoplastic synthetic resin panel (B) having a first sheet (2a), a second sheet (2b) parallel to the first sheet, and parallel ribs (4) interposed between and integrally joining the first and second sheets, wherein opposite portions of the first and second sheets (2a, 2b) are welded together to close the interior space of the panel (B), comprising the steps of: providing an ultrasonic welding machine with an ultrasonic welding head (6, 6A) and a work support block (7, 7A), said welding head (6, 6A) having an end surface and said work support block (7, 7A) having a flat work support surface cooperable with said end surface of the welding head (6, 6A), said end surface of the welding head having a protruding tip portion and a sloping surface portion contiguously provided adjacent to said tip portion; placing said ultrasonic welding head (6, 6a) with said tip portion thereof positioned in opposition to and along a first elongated region, extending in a direction transverse to said ribs (4), of the first sheet (2a); placing said work support block (7, 7A) with said flat work support surface thereof positioned in a face-to-face relation to a second elongated region of the second sheet (2b) located in opposition to and along said first elongated region of the first sheet (2a); moving said welding head (6, 6A) and said work support block (7, 7A) toward each other to bring the welding head and the work support block into contact with the first and second elongated regions, respectively; generating ultrasonic waves from the welding head (6, 6A) to the work support block (7, 7A) through the first sheet (2a), the ribs (4) and the second sheet (2b) to the work support block (7, 7A) to generate internal frictional' heat by ultrasonic vibrations so as to melt the first sheet (2a), the ribs (4) and the second sheet (2b) in portions thereof in which ultrasonic waves are generated; compressing the first and second elongated regions of the first and second sheets (2a, 2b) between the end surface of the welding head (6, 6A) and the flat work support surface of the work support block (7, 7A) with said protruding tip portion of the welding head (6, 6A) abutting against said first elongated region of the first sheet (2a); causing said protruding tip portion of the welding head (6, 6A) to move the first elongated region of the first sheet (2a) toward and against the second elongated region of the second sheet (2b); causing said sloping surface portion of the welding head (6, 6A) to move the first elongated region of the first sheet (2a), to thereby shape said first elongated region of the first sheet (2a) to conform in shape to the sloping surface portion of the welding head (6, 6A); and concurrently causing said sloping surface portion of the welding head (6, 6A) to shape portions of the ribs (4) adjacent to the first elongated region of the first sheet to conform in shape to the sloping surface portion, thereby joining the first and second elongated regions along said protruding tip portion of the welding head (6, 6A) to form a closed end seam (8) of a converging cross-sectional shape along the first and second regions. The method according to claim 1, characterised in that said sloping surface portion of the welding head (6) has a concave curved shape so that said closed seam (8) is given a convex curved shape on the side of the first sheet (2a). The method according to claim 1 or 2, characterised in that said elongated region of the first sheet (2a) and said elongated region of the second sheet (2b) are an end edge of the first sheet (2a) and an end edge of the second sheet (2b), respectively. The method according to one of claim 1 to 3, characterised in that a welding head (6A) is used which has a shape corresponding to an integral combination of two of said welding head (6) in a back-to-back arrangement in which the protruding tip portions of the two of said welding head (6) are combined to form a single middle nose (9), and said elongated region of the first sheet (2a) and said elongated region of the second sheet (2b) are opposing intermediate regions of the first and second sheets (2a, 2b). The method according to one of claim 1 to 4, characterised in that said elongated regions of the first and second sheets (2a, 2b) form a folding line (14) of said first and second sheets (2a, 2b). The method according to one of claim 1 to 4, characterised in that said elongated regions of the first and second sheets (2a, 2b) are. edges of an opening (16) formed through said first and second sheets (2a, 2b). and 12) The method according to one of claim 1 to 4, characterised in that said elongated regions of the first and second sheets (2a, 2b) are edges of a cutout recess (17) formed through said first and second sheets (2a, 2b). The method according to one of claim 1 to 4, characterised in that it further comprises the steps of: compressing said first and second sheets (2a, 2b) between an ultrasonic welding head (6B) having a flat end surface and a work support block (7B) having a flat work support surface; generating ultrasonic waves from the welding head (6B) to the work support block (7B) through the first sheet (2a), the ribs (4) and the second sheet (2b) to the work support block (7B) to generate internal frictional heat by ultrasonic vibrations so as to melt the first sheet (2a), the ribs (4) and the second sheet (2b) in portions thereof in which ultrasonic waves are generated; and joining the first and second sheets (2a, 2b) in a two-dimensional region corresponding to the welding head (6B) and the work support block (7B).

Inventors: HAGIWARA KENJIRO, SAITOH TSUYOSHI, SASAKI HISASHI, HAGIWARA, KENJIRO, SAITOH, TSUYOSHI, SASAKI, HISASHI
Applicants: KISHIMOTO SANGYO CO, UNITEK CO LTD, KISHIMOTO SANGYO CO., LTD., UNITEK CO., LTD.
Application year: 1996
Main classification: B29C65
IPC codes: B29C53, B29C65, B29C63, B32B3, E04C2, B29C67