Method of forming a headed thermoplastic tube

Abstract: A headed thermoplastic tube (29) is formed solely from a thermoplastic extruded, stretched, cylinder (3) by positioning the cylinder over a forming mandrel (5) with an exposed portion (13). The inner surface (15) of the exposed portion is heated above the glass transition temperature of the thermoplastic material to render the inner surface molten while the outer surface provides support for the exposed portion of the cylinder. The heated exposed portion is then shaped into a conical shape (25), such as by heating the outer surface, thereby releasing internal stresses, and pressure is applied to the conical shaped exposed portion to form a headed thermoplastic tube. The headed tubes produced have a body portion (30), shoulder portion (31) and neck portion (33), without any seams, all of which are formed from the starting thermoplastic extruded, stretched cylinder.

Description: THE PRESENT INVENTION relates to a method of forming headed thermoplastic tubes solely from an extruded thermoplastic sleeve without use of any additional thermoplastic material. Thermoplastic tubes that are formed as squeeze tubes are extensively used in packaging of cosmetics, toothpaste, shampoos, and the like. These tubes are formed as tubular members having an open end at a first end and a threaded or other closure-acceptable head at the second end, with a closure used to seal the second end of the tube while the contents of the tube are charged to the tube through the first end. After filling, the first end of the tube is closed, such as by heat sealing, to complete the filled tube for sale. A problem has existed in the formation of such tubes in that the closure-acceptable head is usually formed separately from the tubular member and the provision of a complete seal between the head and tubular member must be assured. One well-known commercial method for producing such headed tubes is that disclosed in US-A-3,047,910. In this process, a tubular member is placed in a forming collar and a separate molten disc of thermoplastic material is forced into an open end of the tubular member while retained by the forming collar. The latent heat of the molten disc welds the peripheral edge of the disc to the inner circumferential wall of the tubular member, and forms an end closure for the tubular member. Pressure is applied to the hot sealed end closure to shape the head into the desired shape and an orifice is then formed through the end of the closure. The head is then fitted with a threaded cap or other closure to provide a closed end tube ready for filling with the desired contents for the tube. In methods such as that disclosed by US-A-3,047,910, some difficulties remain, such as controlling the thickness and weight of the head and exact colour matching of the tubular member and the head. The prior art process also can not be used to commercially prepare tubes from polycarbonates and polyvinyl chloride material. Also, any time two separate units such as a tubular member and head are combined, a possible source of weakness exists at the juncture of the two units. In addition, with such a juncture, a joint between the tubular member and head, a problem of providing a continuous barrier is present where the tube is formed of a barrier material, such as from an oxygen-barrier containing composite thermoplastic material. There have been attempts in the past to produce thermoplastic squeeze tubes by extruding a thermoplastic tubing, cutting the tubing into sleeves or tubular members, heating one end of the sleeve to a molten mass and forming it into a head to make the thermoplastic tube. These methods have not been successful because the heat transfer is slow and the molten plastic difficult to control. In such attempts, a sufficient amount of molten thermoplastic cannot be accumulated on the end of the tube to form the desired head. Another known method for producing such headed tubes is that disclosed in US-A-3,347,970. In this process, a portion of a circumferentially orientated plastic tubular member is supported internally by a suitably shaped mandrel. Said circumferentially orientated plastic tubular member is then subjected to heat, whereby the internally unsupported portion thereof shrinks about a suitably shaped portion of the mandrel, to provide the tubular member with a headed portion. Whilst this method succeeds in producing a headed thermoplastic tube solely from a tubular member, with no joint between the tubular portion of the tube and the head portion, it does not provide any degree of control over the thickness and weight of the head portion. It is an object of the present invention to provide a method for forming a headed thermoplastic tube solely from a sleeve or tubular member. It is another object of the present invention to provide a thermoplastic squeeze tube having a head portion that does not have any joint or juncture between the tubular portion of the tube and the head portion thereof. According to this invention there is provided a method of forming a headed thermoplastic tube from an extruded cylinder of thermoplastic material having a continuous wall with inner and outer wall surfaces, the method comprising the steps of positioning a thermoplastic extruded, longitudinally stretched, cylinder over a forming mandrel having a head forming end, with an exposed portion of said thermoplastic cylinder extending beyond said head forming end; heating the inner wall surface of the exposed portion of the thermoplastic extruded, longitudinally stretched, cylinder to a temperature above the glass transition temperature of said thermoplastic material, while maintaining the outer surface thereof below said temperature so as to provide support for said exposed portion, such that the exposed portion retains its cylindrical shape; shaping said heated exposed portion of said thermoplastic extruded, longitudinally stretched, cylinder into a conical shape; and applying pressure to the conical shaped exposed portion of said thermoplastic cylinder to form a headed thermoplastic tube. Preferably heating is effected by a hot fluid directed against the inner wall surface of the exposed portion of the thermoplastic extruded, longitudinally stretched, cylinder. Advantageously the hot fluid is directed against said inner wall surface and away from the head forming end of said forming mandrel. Conveniently the hot fluid is air. Advantageously the shaping of the heated exposed end to a conical shape is by heating of the outer surface of said exposed portion. Advantageously pressure is applied to the conical shaped exposed portion of said thermoplastic extruded cylinder by forcing the same, by the head forming end of said forming mandrel, into an abutting die. Preferably the extruded cylinder of thermoplastic material comprises a laminate of a plurality of layers of material. Advantageously at least one of said layers is comprised of an oxygen -impermeable layer. Thus the invention provides a method of forming a headed thermoplastic tube from an extruded cylinder of thermoplastic material have a continuous wall with inner and outer wall surfaces, comprising positioning a thermoplastic extruded, longitudinally stretched, cylinder over a forming mandrel having a head forming end, with an exposed portion of said thermoplastic cylinder extending beyond said head forming end; directing a hot fluid against the inner wall surface of the exposed portion of the thermoplastic extruded, longitudinally stretched, cylinder and away from the head forming end of said forming mandrel to heat said inner wall surface to a temperature above the glass transition temperature of said thermoplastic material, while maintaining the outer surface thereof below said temperature so as to provide support for said exposed portion, such that the exposed portion retains its cylindrical shape; then heating the outer surface of said heated exposed end to shape said heated exposed portion of said thermoplastic extruded, longitudinally stretched, cylinder into a conical shape; and applying pressure to the conical shaped exposed portion of said thermoplastic cylinder to form a headed thermoplastic tube. Preferably hot air is directed against said outer surface of said heated exposed end to heat the same and preferably said fluid directed against said inner wall surface is hot air. Advantageously pressure is applied to the conical shaped exposed portion of said thermoplastic extruded cylinder by forcing the same, by the head forming end of said forming mandrel, into an abutting die. The invention also relates to a headed thermoplastic tube formed solely from a thermoplastic extruded, longitudinally stretched, cylinder, said tube having a body portion, shoulder portion and neck portion, all of which are comprised of the thermoplastic material from which said thermoplastic extruded, longitudinally stretched, cylinder was formed, with no seams or joints present throughout said body portion, shoulder portion and neck portion. The thermoplastic material may be selected from the group comprising high density polyethylene, low density polyethylene, polypropylene and polyethylene terephthalate. Preferably the thermoplastic material comprises a laminate of a plurality of layers of thermoplastic materials, one of said layers consisting of an oxygen-impermeable material. The oxygen-impermeable layer may be selected from the group comprising nylon, ethylene polyvinyl alcohol and polyvinylidene chloride. As will be described, the invention provides a method of forming a headed thermoplastic tube from an thermoplastic extruded, longitudinally stretched cylinder is provided by positioning the cylinder over a forming mandrel with an exposed portion of the cylinder extending beyond a head forming end of the mandrel. The inner wall surface of the exposed portion of the thermoplastic cylinder is heated to a temperature above the glass transition temperature of the thermoplastic material to render the inner surface area molten, such as by use of a blast of hot air directed against the inner wall surface, while maintaining the outer surface of the cylinder below the glass transition temperature so as to provide support for the exposed portion of the cylinder and retain the cylindrical shape thereof. The heated exposed portion is then shaped into a conical shape, such as by directing hot air against the outer surface thereof. Pressure is then applied to the conical shaped exposed portion of the thermoplastic extruded cylinder to form a headed thermoplastic tube. The pressure is applied to the conical shaped exposed end portion preferably by forcing the same into an abutting die by use of the head forming end on the mandrel. The extruded thermoplastic cylinder may be formed from a single thermoplastic material or the cylinder may be formed from a laminate or composite of a plurality of layers of materials, one layer of which may be an oxygen-impermeable material. The tubes of the present invention are formed solely from a thermoplastic extruded, longitudinally stretched, cylinder and have a tube body, shoulder and neck, all of which are comprised of the thermoplastic material from which the cylinder was formed, the tubes having no seams or joints present throughout the tube. The present method will now be described by way of example, with reference to the accompanying drawings, wherein like numerals indicate like parts throughout, and wherein: FIGURE 1 illustrates, in cross-section, a thermoplastic extruded, stretched, cylinder from which the method of the present invention forms a headed thermoplastic tube, FIGURE 2 illustrates the thermoplastic extruded, stretched, cylinder of Figure 1 supported on a forming mandrel having a head forming end, FIGURE 3 illustrates heating of the exposed inner wall surface of the exposed portion of the thermoplastic extruded, stretched, cylinder by a hot fluid, FIGURE 4 illustrates the shaping of the heated exposed portion of the thermoplastic extruded cylinder into a conical shape, FIGURE 5 illustrates pressure being applied to the conical shaped exposed portion of the thermoplastic extruded cylinder into an abutting die to form a head, FIGURE 6 illustrates a finished headed thermoplastic tube on the forming mandrel prior to release therefrom, FIGURE 7 illustrates the finished headed thermoplastic tube released from the forming mandrel; FIGURE 8 illustrates a finished headed thermoplastic tube formed by the present method from a multilayer thermoplastic extruded, stretched, cylinder having three layers, and FIGURE 9 illustrates a finished headed thermoplastic tube formed by the present method from a multilayer thermoplastic extruded, stretched, cylinder having five layers. The headed thermoplastic tubes produced by the present method can be formed from various thermoplastic materials. Such thermoplastic materials include, but are not limited to, high density polyethylene, low density polyethylene, polypropylene, a polyester such as polyethylene terephthalate, polycarbonates, polyvinyl chloride, and the like. The headed thermoplastic tubes may also be formed from multi layers or laminates of various plastic materials, such as a layer of an oxygen-impermeable material comprising a polyamide such as nylon, or ethylene polyvinyl alcohol, a polyvinylidene chloride or the like sandwiched between two polyethylene outer layers. Also, five layer composites, comprising outer layers of a thermoplastic such as polyethylene, polypropylene, a polyester such as polyethylene terephthalate, an inner layer of an oxygen-impermeable material, and adhesive layers between the oxygen-impermeable material and each outer layer of thermoplastic to bond the same, can be used to form thermoplastic headed tubes according to the present method. The thermoplastic headed tubes are formed from a flexible material and, when filled, are readily squeezable and collapsible to force the contents of the tube out of an orifice formed in the end of the tube at the head portion. They are generally of a size having a wall thickness of the cylindrical portion of between about 0.25 mm to 1 mm (0.010 to 0.040 inch) in thickness, while a shoulder of the neck portion of the tube will be thicker than the wall of the cylinder, generally between 0.90 mm to 1.14 mm (0.035 to 0.045 inch) thick. Since the tube is formed from an extruded cylinder, the wall thickness of the cylindrical portion will be very uniform, with a variance in wall thickness of the cylindrical portion being only about + or - 10 percent. The extruded cylinder from which the headed thermoplastic tube is formed is a cylinder cut from a tubular extrusion which has a wall thickness in the molten state preferably two to three times the wall thickness of the final cooled extruded thickness. Such a tubular extrusion, as is known, is formed by extruding thermoplastic material from an extrusion annulus in a molten state and stretching the hot tubular form, in the direction of the longitudinal axis, into a tube or cylinder having a wall thickness one-half (½), one-third ( 1 / 3), or less, than the extrusion annulus. Such a stretch oriented extruded cylinder, when heated above the glass transition temperature of the thermoplastic material, due to the plastic memory of the thermoplastic material, will increase in thickness to the thickness of the molten material exiting the extrusion annulus, and shrink in length, thus providing sufficient molten plastic mass to form a head on the cylinder according to the present method. When using high density polyethylene or low density polyethylene, for example, the annulus would extrude a tubular form of about 38 mm (1.5 inch) in diameter having a wall thickness between 1 to 1.17 mm (0.040-0.046 inch), which would be stretched into a stretch oriented extruded cylinder of about 25 mm (1.0 inch) in diameter having a wall thickness between about 0.38 to 0.46 mm (0.015-0.018 inch). Referring now to the drawings, Figure 1 shows a thermoplastic extruded, stretched extrusion 1 from which a thermoplastic extruded, stretched, cylinder 3 is cut. The thermoplastic extruded, stretched, cylinder 3 is disposed on a forming mandrel 5 that has a head forming end 7 formed of a shoulder 9 and a reduced diameter portion 11, with an exposed portion 13 of the thermoplastic extruded, stretched, cylinder 3 extending beyond the head forming end 7 of the forming mandrel 5 (Figure 2). The thermoplastic extruded, stretched, cylinder 3 is frictionally held on the forming mandrel 5, with only a small clearance, such as about a 0.13 mm (0.005 inch) clearance, which maintains the cylinder in place, while preventing subsequent flow of hot fluid between the forming mandrel 5 and the inner wall surface 15 of the thermoplastic extruded, stretched, cylinder 3. With the thermoplastic extruded, stretched, cylinder 3 disposed on the forming mandrel, the inner wall surface 15 of the exposed portion 13 is heated, such as by impingement thereon of a hot fluid illustrated by the arrows in Figure 3, such as air, from a hot air nozzle 17 which is sized so as to permit insertion thereof into the open end 19 of the exposed portion 13. The hot air is directed outwardly towards the inner wall surface and flows away from the head forming end 7 of the unheated forming mandrel 5. The hot air nozzle 17 and forming mandrel 5 are reciprocally movable, indicated by the dashed arrow in Figure 3, while alternately the same can be fixed and the forming mandrel can be reciprocally movable. The hot fluid heats the inner wall surface 15 of the exposed portion 13 to a temperature above the glass transition temperature of the thermoplastic material and melts the inner wall surface, while the outer surface 21 of the exposed portion 13 provides sufficient support to maintain the exposed portion 13 as a substantially cylindrical shape. When sufficient heat has been applied to the inner wall surface 15 of the exposed portion 13 to melt the same, the hot air nozzle 17 is removed from the exposed portion and the heated exposed portion 13 is shaped into a conical or fluted cone shape 25, such as by the application of additional heat of further hot fluid, indicated by arrows in Figure 4, such as hot air, from external hot air nozzles 23, which heats the outer surface 21 of the exposed portion 13 of the thermoplastic extruded, stretched, cylinder 3 to a temperature above the glass transition temperature of the thermoplastic material and melts the same and renders it in a mouldable state. While heating of the outer surface 21 by a hot fluid may be used to form the conical shape, it is also possible to continue the heating of the inner wall surface 15 of the exposed portion 13 until the outer surface no longer maintains the substantially cylindrical shape, such that a conical shape results in the exposed portion. Because the thermoplastic extruded cylinder 3 is a stretched material, when the exposed portion 13 is heated above the glass transition temperature, the plastic memory responds and the exposed portion 13 swells to the thickness of (or substantially to the thickness of) the original tubular extrusion, generally about two to three times the wall thickness of the thermoplastic extruded, stretched, cylinder. The hot exposed portion, when above the glass transition temperature in addition to swelling in wall thickness, shrinks in the direction of the axis of the cylinder and provides a mass of mouldable thermoplastic material 27 for forming of a head. After shaping of the heated exposed portion 13 of the thermoplastic extruded, stretched, cylinder 3 into the conical shape 25 of mouldable thermoplastic material 27, pressure is applied through the head forming end 7 of the forming mandrel 5 to form a headed thermoplastic tube 29 which comprises a body portion 30, shoulder portion 31 and neck portion 33 having a closed end 35 to close the end of the cylinder 3. The forming is carried out by applying pressure to the conical shaped portion 13, and, as illustrated schematically in Figure 5, by the application of pressure by use of the head forming end 7 of the forming mandrel 5 and an abutting die 37. As illustrated, the die 37 may have a shoulder forming portion 39, neck forming section 41, and a closed end forming section 43 which are retained in separable mould sections 45 and 47. While the forming mandrel 5 is illustrated as being reciprocable to form the conical shaped portion 13 on the forming mandrel 5 into the abutting die 37, the forming mandrel could be fixed and the abutting die 37 reciprocated to cause application of pressure and formation of the headed thermoplastic tube. Figure 6 illustrates the formed headed thermoplastic tube 29 after removal of the head from the die 37, still retained on the forming mandrel 5, while Figure 7 shows the stripping or unloading of the finished headed thermoplastic tube 29 from forming mandrel 5 for finishing or use. As is conventional, the closed end 35 of the thermoplastic headed tube is subsequently punctured to form an orifice 49 therethrough. The thermoplastic headed tubes formed by the present method are tubes which have no seams or joints between the various portions. As shown in Figure 7, the thermoplastic headed tube 29 has a body portion 30, shoulder portion 31 and neck portion 33, all of which are comprised of the thermoplastic material that the thermoplastic extruded, stretched, cylinder 3 was formed, and there are no seams or joints present throughout the entire tube. The thermoplastic headed tube, as hereinbefore described, may be formed from a single thermoplastic material or a laminate comprised of multilayers of thermoplastic materials, at least one of which may be an oxygen-impermeable material. Figure 8, for example, illustrates a multilayer thermoplastic headed tube 29a as would be produced according to the present method, having three layers, an outer layer 51, intermediate layer 53 and inner layer 55, where the outer and inner layers 51 and 55 are formed of a different thermoplastic material than the intermediate layer 53. For example, the outer and inner layers can comprise polyethylene while the intermediate layer would be an oxygen-impermeable layer, such as a polyamide such as nylon, or ethylene polyvinyl alcohol, a polyvinylidene chloride, or the like. Figure 9 illustrates a multilayer thermoplastic headed tube 29b as would be prepared using the present method, having five layers, an outer layer 57 inner layer 59, intermediate impermeable layer 61, and two adhesive layers 63 and 65, one of the layers of adhesive provided between the intermediate layer 61 and each of the outer and inner layers 57 and 59. Such a tube could, for example, use polyethylene, polypropylene, or a polyester such as polyethylene terephthalate as the outer and inner layers, an oxygen-impermeable material such as nylon, ethylene polyvinyl alcohol, polyvinylidene chloride, as the intermediate layer, and adhesive layers to bond the outer and inner layers to the intermediate layer. EXAMPLE As an example of the present method, an extrusion of a thermoplastic material, a low density polyethylene, was made through an orifice size 1 mm (0.040 inch) and stretched into a cylindrical form having a 19 mm ( 1 / 3 inch) inner diameter with a wall thickness of 0.38 mm (0.015 inch). A thermoplastic extruded, stretched cylinder about 124 mm (4 ⅞ inches) long was cut from the cylindrical form and was fitted over a forming mandrel with an exposed portion of about 22.35 mm (⅞ inch) extending beyond a head forming end of the mandrel. The inner wall surface of the exposed portion was heated with hot air (about 704°C) (1300°F), above the glass transition temperature of the thermoplastic material while maintaining the outer surface thereof below said temperature. The heated exposed portion was then shaped into a conical shape by heating the outer surface of the heated exposed portion with hot air (704°C (1300°F)), and the conical shaped exposed portion pressed into an abutting die to form a neck and shoulder on the cylindrical body. The resultant low density polyethylene tube had a body portion having a 0.38 mm (0.015 inch) wall thickness and inner diameter of 19mm (¾ inch), a neck portion of about 6.4 mm (¼ inch) in length and 7.9 mm ( 5 / 16 inch) in diameter, with a wall thickness of about 1 mm (0.040 inch) and a shoulder portion of about 3.2 mm (⅛ inch) in length, having a wall thickness of about 1 mm (0.040 inch). The resultant tube thus had a total length of about 111.13 mm (4 ⅜ inches) and had no seams or joints between the body portion, shoulder portion and neck portion. The described method thus provides for the formation of a headed thermoplastic tube from an extruded plastic sleeve without the need for welding or fusing together of any separate components. The resultant headed tube has no seams, welds or joints. With thermoplastic laminates containing a barrier layer, the absence of such seams or joints is especially useful since there is a continuous barrier layer throughout the body portion, shoulder portion and neck portion. Complete control of the thickness and weight of the head portion of the tube can be achieved. Also, the colour of the head portion and body portion will be exactly the same, and the decorative features of the body portion, such as stripes or windows can be carried through and incorporated in the head portion of the resultant tube.

Claims: A method of forming a headed thermoplastic tube from an extruded cylinder(3) of thermoplastic material having a continuous wall with inner and outer wall surfaces, the method comprising the steps of positioning a thermoplastic extruded, longitudinally stretched, cylinder(3) over a forming mandrel(5) having a head forming end(7), with an exposed portion(13) of said thermoplastic cylinder extending beyond said head forming end; heating(19) the inner wall surface of the exposed portion of the thermoplastic extruded, longitudinally stretched, cylinder to a temperature above the glass transition temperature of said thermoplastic material, while maintaining the outer surface thereof below said temperature so as to provide support for said exposed portion, such that the exposed portion retains its cylindrical shape; shaping said heated exposed portion of said thermoplastic extruded, longitudinally stretched, cylinder into a conical shape(25), and applying pressure to the conical shaped exposed portion of said thermoplastic cylinder to form a headed thermoplastic tube. A method of forming a headed thermoplastic tube as defined in Claim 1, wherein said heating is effected by a hot fluid directed against the inner wall surface(15) of the exposed portion(13) of the thermoplastic extruded, longitudinally stretched, cylinder(3). A method of forming a headed thermoplastic tube as defined in Claim 2, wherein said hot fluid is directed against said inner wall surface(15) and away from the head forming end(7) of said forming mandrel(5). A method of forming a headed thermoplastic tube as defined in Claim 2 or 3, wherein said hot fluid is air. A method of forming a headed thermoplastic tube as defined in any one of the preceding Claims wherein the shaping of the heated exposed end(13) to a conical shape(25) is by heating of the outer surface of said heated exposed portion. A method of forming a headed thermoplastic tube as defined in any one of the preceding Claims wherein pressure is applied to the conical shaped(25) exposed portion(13) of said thermoplastic extruded cylinder by forcing the same, by the head forming end(7) of said forming mandrel(5), into an abutting die(37). A method of forming a headed thermoplastic tube as defined in any one of the preceding Claims wherein said extruded cylinder(3) of thermoplastic material comprises a laminate of a plurality of layers(51,53,55) of material. A method of forming a headed thermoplastic tube as defined in Claim 7, wherein at least one of said layers is comprised of an oxygen-impermeable material. A headed thermoplastic tube(29) formed solely from a thermoplastic extruded, longitudinally stretched, cylinder, said tube having a body portion(30), shoulder portion(31) and neck portion(33), all of which are comprised of the thermoplastic material from which said thermoplastic extruded, longitudinally stretched, cylinder was formed, with no seams or joints present throughout said body portion, shoulder portion and neck portion. A headed thermoplastic tube as defined in Claim 9 wherein said thermoplastic material comprises a laminate of a plurality of layers(51,53,55) of thermoplastic materials, one of said layers(53) consisting of an oxygen-impermeable material.

Inventors: HOLOUBEK GEORGE HENRY, RHOADES JOHN JOSEPH, HOLOUBEK, GEORGE HENRY, RHOADES, JOHN JOSEPH
Applicants: COURTAULDS PACKAGING INC, COURTAULDS PACKAGING INC.
Application year: 1991
Main classification: B29C57
IPC codes: B29D23, B29C47, B29C35, B65D35, B29B13, B29C57, B29C61, B29K23, B29K67