NO872564L - PROCEDURE FOR THE MANUFACTURE OF RHEADED THERMOPLASTIC REQUIREMENTS WITH END CLOSED PARTS. - Google Patents

Description

The invention relates to a method for forming thermoplastic tubular containers and more particularly a method for forming a head on a tubular sleeve to provide a neck part on a thermoplastic tubular container.

Tubular thermoplastic containers, particularly collapsible or compressible containers, are taking over an increasingly large share of the container market for metallic tubular containers. Such tubular thermoplastic containers are used to a large extent for the packaging of cosmetics, medical preparations, hair shampoos and other products. With the constant development of multi-layer tubes or laminated tubes which have oxygen barrier properties, and which resist oxygen penetration, there will be a further increase in the use for packaging of pharmaceutical products and foodstuffs in such thermoplastic tubes.

An advantageous method of forming such containers involves extruding a hollow tube and then cutting the tube to desired lengths and forming a head or neck portion to close one end of the resulting tube. The other end is held open for filling the container with the product to be packaged, followed by sealing of the open end to provide a uniform sealed tubular container.

A known method for forming collapsible plastic tubes with neck parts, known as the "Downs" process, is described in US-PS 3,047,910, the content of which is referred to here. As described in this US patent, tubular thermoplastic containers are made by placing a thermoplastic tubular member or hollow tube in a forming collar and forcing a cut, molten disc into an open end of the tubular member. The latent heat from the molten disk is sufficient to weld the peripheral edge of the disk to the inner wall of the tubular part and thus form an end closure for the tubular container. As described in the US patent, pressure is applied through the interior of the tubular container to the sealed end closure to shape the latter into a desired contour shape. The preferred means of applying pressure to the sealed end closure is the use of a mandrel which is inserted through the open end of the tubular member. Air pressure, or negative pressure, is not suggested for forming the contour or outline of the sealed end closure, although it is suggested that air under suitable pressure or a reciprocating flat end mandrel may be placed inside the tube to ensure that a flat end closure is not destroyed by cooling and remains flat as desired.

While the above-mentioned process has been suitable for forming the head or neck of collapsible tubular containers, complicated tooling is required to force the plastic disc to fit a mold cavity, necessitating high tooling costs and subsequent maintenance. Also when using compression molding of the head-supplied part, it will be necessary to use powerful hydraulic equipment, which increases capital costs and maintenance costs. In addition, relatively thick discs are required where compression molding is used with increased costs and larger portions of scrap. Not only are cost considerations predominant when using such a process, but the process is also limited with respect to the type or shape of the head produced by such a compression molding system. Such a process is e.g. not easily adaptable to the formation of heads on pipes where the heads have multiple openings or complex head designs.

A modification of the above-mentioned process for use in forming multi-layer or laminated collapsible thermoplastic containers with a tubular shape is described in US patent no. 3,962,006. In this process, a laminated film is used to form a thermoplastic sleeve with an impermeable layer, and a molten disc also formed with an impermeable or impermeable layer is welded to an inner wall of the laminated thermoplastic sleeve. A press operation is used for the formation of a head part for the pipe, the press operation using a female mold part and a core which internally supports the laminated thermoplastic sleeve.

It is an aim of the present invention to provide an improved method for forming tubular thermoplastic containers where a head can be easily formed even with a

predetermined, complex head design.

It is also a purpose of the invention to provide a method for shaping a tubular thermoplastic container where a melted disc is used to seal the end of a tubular sleeve, but where powerful hydraulic equipment is not required, as is used today when compression forming the head of a pipe.

It is a further object of the invention to provide a method for forming a tubular thermoplastic container where a fused disk is used to seal the end of the tubular sleeve and where it enables the use of a thinner shoulder compared to compression molded heads, so that the manufacturing speed can is increased, material costs are lowered and the proportion of scrap is reduced.

These purposes are achieved by a method which is characterized by what appears in the requirements.

A method of forming a tubular thermoplastic container wherein a molten plastic disc is attached within the confines of an open end of a hollow tubular member, with the latent heat of the molten disc utilized to weld the disc to the inner wall of the hollow tubular member for sealing thereto thus involves the use of an inner sealing mandrel to seal only one shoulder thereof and then forming the thermoplastic disc, while still in a malleable state, into a molded design. The inner sealing mandrel, having a sealing head on the end, is inserted into the upper open end of the hollow tubular part, the sealing head having a first shoulder which encloses the circumference of the disc between the first shoulder and a second shoulder around the circumference of a mold cavity. Pressure on the sealing mandrel is exerted only for the formation of a seal of the thermoplastic material between the first and the second shoulder, and the actual shaping of the thermoplastic disk, while in a formable state and while only the sealing of the thermoplastic is in contact with the sealing head, is carried out either by the exercise of a fluid pressure against the surface of the thermoplastic disk facing the sealing head, or by the application of a negative pressure on the surface of the thermoplastic disk opposite to the surface facing the sealing head, or both. Such shaping of the disc while in a formable state causes the disc to conform to the predetermined shape of a mold cavity for the formation of a closed end wall of the tubular container, having the predetermined shape.

In the following, the invention will be explained in more detail by means of exemplary embodiments which are shown in the drawing, which shows: Fig. 1, including figures 1A to 1F, where the usual method for the formation of a head on a tubular element by means of a inner forming mandrel, as described in US patent 3,047,910,

fig. 2, a sealing mandrel useful in the invention in a hollow tubular member with one end closed with a washer, located at a mold cavity,

fig. 3, the application of pressure to the sealing mandrel with the insertion of the lower part of the hollow tubular member and the moldable disk into the mold cavity and the application of a fluid pressure therein to form a head,

fig. 4, a sealing mandrel in a hollow tubular member having one end closed with a disk, located at a mold cavity for use in applying a negative pressure to form a head;

fig. 5, the application of a pressure on the sealing mandrel with the insertion of the lower part of a hollow tubular element and the moldable disk with the mold cavity and the application of a negative pressure for the formation of a head,

fig. 6, a sealing mandrel useful in the method of the invention in a hollow, tubular member, one end closed with a disk, placed over a mold cavity prior to the application of both fluid pressure and negative pressure to form a head,

fig. 7, the application of pressure to the sealing mandrel with the insertion of the lower portion of the hollow tubular member and the moldable disk into the mold cavity and the application of both fluid pressure and negative pressure thereon to form a head,

fig. 8, a tubular member and disc located adjacent to a mold cavity for the formation of a "bulb" shaped head,

fig. 9, the application of fluid pressure for the formation of a "bulb" shaped head,

fig. 10, a container with a "bulb" shaped head, moldable by means of the invention,

fig. 11, the application of fluid pressure for the formation of an application type head, in accordance with the present invention,

fig. 12, a container with an application head that can be shaped by the invention,

fig. 13, the application of fluid pressure for the formation of a new head in the form of a clown head in accordance with the present invention,

fig. 14, a container with a new head, such as a clown head, which can be shaped according to the invention,

fig. 15, the application of fluid pressure for the formation of a detachable head according to the invention, and

fig. 16, a container with a detachable head which can be shaped by means of the invention.

The method according to the invention is an improvement over the previously known, common methods for the formation of a head or a tubular container with a closed end, and enables the formation of unconventional heads with different shapes. As is known, conventional methods, such as the "Downs" process described in US patent 3,047,910, employ the use of latent heat from a molten thermoplastic disc to seal the circumference of the disc to the inner circumferential wall of a pipe to close the end thereof . Fig. 1A-1F illustrate such a previously known, common process. As illustrated there, a hollow, tubular element 1 or a sleeve is formed from a thermoplastic material, e.g. by extruding a tube of thermoplastic material and cutting the desired lengths, as illustrated in fig. 1A. The hollow tubular element 1 is then transported to a punching station (Fig. 1B) with punches 3, while it is supported on a forming mandrel 5 which has a support part 7, head part 9 and an extension 11. The supported hollow tubular element is placed over a melted strip or film 13 of thermoplastic material which is carried on a base 15. When the punching station is activated, the punching stamp 3, e.g. by lowering this as indicated by the arrow in fig. 1C, mechanically brought to cut through the molten thermoplastic strip 13, forming and receiving a circular portion or disc 17. The molten thermoplastic disc 17 is then in contact with the bottom edge of the hollow tubular member 1, the latent head formed by the disc 17 will partially melt the fitted edge of the hollow tubular member 1 and form a natural weld 19 between the peripheral edge 21 and the disc 17 and the inner peripheral wall 23 of the tubular member 1 to seal these parts to each other (Fig. 1D) , so that a first mold part 25 is formed for subsequent further shaping. This first mold or preform 25 (Fig. 1D) is then transported to a forming station, where hydraulic pressure is applied to the forming mandrel in a mold. As illustrated in fig. 1E, the preform 25 is carried by the forming mandrel 5 and placed over a mold 27 with a cavity 29 with surrounding walls 31. The mandrel 5 will facilitate the application of the pressure on this, as indicated by the arrow (fig. 1F), pressing the molten disk 17 against the walls 31 of the cavity 29 of the mold 27 and force the thermoplastic to assume the shape of a head 33 with the shape of the mold cavity between the forming mandrel head 9 and the projection 11 and the walls 31 of the mold cavity 29. The outer tool is kept constantly cooled, so that when the shaped disc 17 is pressed to the desired shape, the thermoplastic will "harden", and thus permanently retain the shape desired for the thermoplastic pipe head. This previously known process, as illustrated in fig. 1, has been very successful in the formation of tubular thermoplastic containers, but has certain disadvantages. The forming mandrel must be able to force the thermoplastic disc into the required shape and thus limits the shapes that can be produced. In addition, the costs and subsequent maintenance costs are high, while the manufacturing speed is not as high as desired. Powerful hydraulic systems are also required to provide the compression forces necessary for molding the head. In addition, strangely shaped heads or newly shaped heads cannot be easily formed using such a compression-type forming mandrel.

By using the present new method, these disadvantages are avoided. The present method uses either fluid pressure, negative pressure or a combination of fluid pressure and negative pressure for the formation of heads on pipes where an internal sealing mandrel is used only to provide a seal around the circumference of the head being formed.

Reference should now be made to fig. 2 and 3, where an embodiment of the method according to the invention is illustrated where only fluid pressure is used for the formation of a head. A hollow tubular element or sleeve 1 is formed with a fused disk 17 with the peripheral edge 21 of this welded to the inner peripheral wall 23 of the hollow tubular part and an inner sealing mandrel 35 is inserted therein, the inner sealing mandrel 35 having a sealing head 37 at the end, which sealing head has a first shoulder 39 at the surface in contact with the disc. A conduit 41 in the mandrel communicates with a channel 43 extending through the sealing head 37. The hollow, tubular element 1 with the disc 17 still in a formable state is placed adjacent to a mold 27, which can be a unitary part or formed from mutually compatible sections 27a and 27b, have internally a cavity 29 with walls 31 around the cavity, with a section 45 of the wall 31 formed with a second shoulder 47 which is complementary to the first shoulder 39 of the sealing head 37 of the sealing mandrel 39. A pressure fluid source, such as air 49 , is in connection with the line 41 in the sealing mandrel over a line 51. In the shaping or formation of a head 53, as illustrated in fig. 3, the hollow tubular member 1 with the disc 17 in a formable condition is placed in the mold cavity 29 of the mold 27, and pressure is applied as indicated by the dashed arrow, on the sealing head 35 only to form a seal of the thermoplastic material, indicated at 55, between the first shoulder 39 on the sealing head and the complementary second shoulder 47 on the mold cavity wall. After the formation of the seal of the thermoplastic material 55, air from the source 49 is introduced through the conduit 41 into the sealing mandrel 35 and forces the part of the thermoplastic disk surrounded by the sealed part 55, while still in a formable state, into contact with the exposed wall 31 of the mold , e.g. with the thread form illustrated, for the formation of the head or neck of the pipe being produced. The injection or introduction of air against the thermoplastic disc thus causes the part of the disc which is not between the complementary first and second sealing shoulders 39 and 47 to adapt in shape to the predetermined shape, e.g. the cylindrical, thread-like shape illustrated, for the formation of a closed end wall on the thermoplastic tubular container of predetermined shape.

Another embodiment of the present method is illustrated in fig. 4 and 5, where a negative pressure or vacuum is applied to the disk while it is in a formable state instead of fluid pressure being used, as shown in fig. 2 and 3. As shown in fig. 4 and 5, a sealing mandrel 57 corresponding to a sealing mandrel 35 is used, but differs from that in fig. 2 and 3 in that the rod, wire or extension can be a fixed, rod-like element 59 with a sealing head 61 on its end. The sealing head 61 has a first shoulder 63, the surface of which corresponds to that of the disk 17. The hollow, tubular element 1 with the disk 17 still in a formable state is placed opposite a mold 65, which can be a unitary unit or formed from one another mating sections 65a and 65b, which define a cavity 67 with walls 69 around the cavity, and a section 71 of the wall 69 is formed with a second shoulder 73 complementary to the first shoulder 63 on the sealing head 61 of the sealing mandrel 57. The mold 65 is in the area surrounded by the second shoulder 73 formed with a number of openings 75 which extend from the wall 69 of the cavity 67 towards an inner surface 77 of the mold 65. This source of negative pressure 79 is connected to the openings 75 via a line 81 and branch lines 83. In the formation of the head 53 using vacuum or negative pressure, as illustrated in fig. 5, the hollow tubular member with the malleable disk 17 is placed in the mold cavity 67 and pressure is applied as indicated by dashed arrow, on the seal head 61 only to form a seal of the thermoplastic material, indicated at 85, between the first shoulder 63 of the seal head and the complementary second shoulder 73 on the mold cavity wall. After the formation of the seal of the thermoplastic material 85, a negative pressure is exerted from the source 79, through the line 81, the branch lines 33 and the opening 75, which negative pressure draws the parts of the moldable thermoplastic disk, which are surrounded by the sealed part 85 into contact with the exposed wall 69 of the mold, e.g. with the thread pattern illustrated, to form the head of the tube to be produced. The application of negative pressure causes the portion of the disc not between the complementary first and second sealing shoulders 67 and 73 to conform to the predetermined shape and form a closed end wall of the tubular thermoplastic container.

In carrying out the present invention which is illustrated in fig. 6 and 7, the application of fluid pressure is used, e.g. from air in combination with the application of a negative pressure, to the formation of a head. A hollow, tubular element 1 with the disc 17 welded to the inner peripheral wall has inserted an inner sealing mandrel 35, which sealing mandrel has a sealing head 37 at the end. The sealing mandrel has a first shoulder 39 around the surface facing the disk, and a line 41 therein which communicates with the channel 43 extending through the sealing head 3. A source of air 49 communicates through the line 51 with the line 41.

The hollow, tubular element on the sealing mandrel 35 is placed against a mold 65 with a cavity 67 with walls 69 around the cavity. The sealing head 37 has a first shoulder 39 around the surface which stands above the disc, while the wall 69 of cavity 67 in the mold 65 has a second shoulder 73 which is complementary to the first shoulder 39. The surface of the mold 65 which is surrounded by the second shoulder 73 has a number of openings 75 which extend from wall 69 to the outer surface 77 and a source of negative pressure 79 is in connection with these openings 75 through line 81 and branch lines 83.

Fig. 7 illustrates the formation of a threaded head using both fluid pressure and vacuum or negative pressure. The hollow tubular member 1 with the disk 17 still in a formable state is placed in the mold cavity 67 and pressure is applied as indicated by the dashed arrow on the sealing line 37 only to form a thermoplastic seal 87 between the first shoulder 39 of the sealing head 37 and the complementary second shoulder 73 in the mold 65. After the seal 87 has been formed, negative pressure is exerted through line 81, the branch lines 83 and openings 73 on the surface 89 of the disc facing the mold cavity wall 69, while at the same time air from the source 49 is introduced through the line 41 on the sealing mandrel 35 against the surface 91 of the disc facing the sealing head 37. The application of both vacuum on one side of the disc surrounded by the shoulder 73 and fluid pressure on the other side of the disc surrounded by the shoulder 39 forces the free area of the disc to conform to the shape, e.g. the illustrated threaded head shape.

As described above, the application of a fluid pressure, the application of a negative pressure or both will be carried out while the thermoplastic disk is still in a formable state. The thermoplastic material in the disc is no longer in a pure molten state or above its melting point after the latent heat of the disc has melted it to the tubular element wall, but must still be above the glass transition temperature of the thermoplastic so that the disc is soft and flexible and malleable to the desired shape .

When the application of pressure is used for the formation of the head, pressure between 0.35 and 9.8 kg/cm^ is used. When a negative pressure is applied for the formation of the head, a negative pressure of approx. 254-762 mm. The tubular thermoplastic container formed according to the present method will usually have a pipe wall thickness between approx. 0.254 and 1.02 mm wall thickness, while the head part which is then formed will have a thickness of between approx. 0.254 and 2.03 mm wall thickness.

The present method can also be used for the formation of thermoplastic containers from laminated or layered thermoplastic material. Such laminates comprise layers of a thermoplastic material and a barrier layer such as aluminum foil or the like, or layers of different plastic materials which can be co-extruded in layers to form a multi-layer thermoplastic material. In the formation of such laminated tubular thermoplastic containers, the pipe wall portion and the plastic disc are formed from laminated plastic material and then sealed to each other and shaped as if it were a tubular thermoplastic container of a single thermoplastic material. Such a laminate of three layers in the disc and the hollow tubular element will e.g. could have inner and outer layers of a material such as polyethylene or another thermoplastic, while an intermediate layer, such as an oxygen impermeable layer, could be of a polyamide, such as nylon or ethylene polyvinyl alcohol, or the like. Optionally, a five-layer composition can be used with successively following layers consisting of an outer thermoplastic resin, adhesive, an intermediate, impermeable layer, adhesive, and an inner thermoplastic resin. The thermoplastic resin may comprise polyethylene, polypropylene, a polyester such as polyethylene terephthalate or the like, while the intermediate impermeable layer may comprise an oxygen impermeable material such as nylon, ethylene polyvinyl alcohol, polyvinylidene chloride or the like, with the two adhesive layers added to bond the intermediate layer to each of the respective inner and outer layers.

The production of various designs of complex heads which can be formed according to the present invention and which cannot be easily formed by means of the original "Down's" process, is illustrated in fig. 8-16.

Figures 8-10 illustrate the formation of a bulb-like head on a hollow tubular member. Fig. 8 illustrates a hollow, tubular element 1 with a welded-on disk 17 and with the sealing mandrel removed, which element is placed adjacent to a mold 27 which is formed by matching mold parts 27a and 27b. The mold cavity 29 has the shape of a spherical cavity. Fig. 9 illustrates the application of a fluid pressure from the sealing mandrel 35 through the line 41 which is in communication with the channel 43 in the sealing head 37 for the formation of the disk, while in a formable state, in accordance with the walls 31 of the mold cavity 29 for the formation of the "bulb "-shaped head 93 on the end of the hollow tubular member, as illustrated in FIG. 10. Such a "bulb"-shaped head could not be easily formed by the use of a forming mandrel, as this would not be able to pass the narrowed portion 95 between the tubular member 1 and the bulb-shaped head 93.

Figs 11 and 12 illustrate the formation of another complex head by means of the method according to the invention, and here is shown the shape of an application head for the application of ointments or the like over a larger area than that provided by a single pipe outlet. The application head 97 has a number of projections 99, through which openings will be shaped so that the contents of the finished and packed tube will be emitted through the number of openings over a large surface area. Fig. 13 and 14 illustrate the formation of a new type of heads 1 e.g. in the shape of a clown's head, with a narrowed part 103 forming a neck for the clown and with a hat 105 which is applied later and which covers the opening (not shown) for discharging the product, which hat is in the shape of a clown's hat. Figures 15 and 16 illustrate the formation of a twisting head or ampoule-like head 107 for a hollow, tubular element, where a very narrow constriction 109 is placed between the body with tubular circumference 111 and a grippable head part 113. By gripping the grippable head part 113 and turn this, there will be a rupture of the narrowed part 109 with access to the contents of the body 111 of the tubular container.

It should be noted that in fig. 8-16 illustrates the application of a fluid pressure, while the application of a negative pressure through a mold could be used just as effectively, as described above, as well as the application of both fluid pressure and negative pressure, as was also previously described in connection with the illustration of the method according to the invention.

The present method enables the production of complicated head designs which cannot easily be produced using compression molding, as is carried out by the known technique, and will enable the use of a thinner disc when forming heads on tubular elements and will provide an efficient and economical possibility for the formation of heads on thermoplastic pipes.

Claims (11)

1. Method of manufacturing a tubular thermoplastic container wherein a molten plastic disc is attached within the boundary of an open end of a hollow tubular element, and wherein the latent heat of the molten plastic disc is allowed to fuse the circumferential edge of the disc firmly to the inner circumferential wall of the tubular element for sealing these parts to each other, characterized in that an inner sealing mandrel is inserted into the other end of the hollow, tubular part, which inner sealing mandrel has a sealing head at its end, which sealing head has a first circumferentially extending shoulder, that hollow tubular member and the disk is placed in a mold cavity defining a predetermined shape, with a second shoulder around the circumference of the mold cavity complementary to the first shoulder, that pressure is exerted on the sealing head only for the formation of a seal of the thermoplastic material between the first and second shoulders , and that the thermoplastic disc is shaped while it is in a malleable state d and while only the seal of the thermoplastic material is in contact with the seal head so that it conforms in shape to the predetermined shape of the mold cavity for the formation of a closed end wall of the tubular thermoplastic container, which closed end wall has the predetermined shape. 2. Method according to claim 1, characterized in that the inner sealing mandrel has devices for introducing a fluid therethrough, and that the shaping of the thermoplastic disc is carried out by introducing a fluid through the fluid introduction device towards the surface of the disc opposite the inner sealing mandrel. 3. Method according to claim 2, characterized in that the device for introducing fluid through the inner sealing mandrel comprises an inner sealing mandrel with a sealing head with an axial channel through it, and devices which are in connection with the channel for introducing fluid therethrough. 4. Method according to claim 3, characterized in that the fluid is compressed air. 5. Method according to claim 3, characterized in that the shaping of the thermoplastic disc is carried out by introducing a fluid through the inner sealing mandrel, and that a negative pressure or vacuum is exerted on the surface of the disc opposite to the surface facing the inner sealing mandrel. 6. Method according to claim 1, characterized in that the shaping of the thermoplastic disk is carried out by applying a vacuum or negative pressure on the surface of the disk which is opposite to the surface facing the inner sealing mandrel. 7. Method according to claim 1, characterized in that the hollow, tubular element and the disk consist of a laminate of a number of layers of material. 8. Method according to claim 7, characterized in that at least one of the layers is a barrier material, preferably an oxygen impermeable material. 9. Method of forming a tubular thermoplastic container, wherein a molten plastic disc is attached to and defines an open end of a hollow tubular member and wherein the latent heat of the molten plastic disc permits welding of the circumferential edge of the disc to the inner circumferential wall of the tubular member for to seal these parts to each other, characterized in that an inner sealing mandrel is inserted into the other end of the hollow, tubular part, which inner sealing mandrel has a sealing head at its end, which sealing head has a first round continuous shoulder, that the hollow, tubular element and disc are placed in a mold cavity defining a predetermined shape, with a second shoulder around the circumference of the mold cavity, which is complementary to the first shoulder, that pressure is exerted on the sealing head only for the formation of a seal of the thermoplastic material between the first and the second shoulder, and that a fluid pressure is exerted against the surface of the disc that is opposite or the inner sealing mandrel, while at the same time a negative pressure is exerted on the surface of the washer opposite to the surface facing the inner sealing mandrel, while the washer is in a formable state, and while only the sealing of the thermoplastic material is in contact with the sealing head, in order to causing the thermoplastic material to assume the shape of the predetermined shape of the mold cavity for the formation of a closed end wall of the tubular thermoplastic container, having the predetermined shape. 10. Method according to claim 9, characterized in that the hollow, tubular element and the disc consist of a laminate of a number of material layers. 11. Method according to claim 10, characterized in that at least one of the layers is a barrier material, preferably an oxygen impermeable material.