GB2156265A

GB2156265A - Manufacturing thermoplastic tubular containers

Info

Publication number: GB2156265A
Application number: GB08506478A
Authority: GB
Inventors: Vincent E Fortuna; Donald N Maclaughlin
Original assignee: Vercon Inc
Current assignee: Vercon Inc
Priority date: 1984-03-26
Filing date: 1985-03-13
Publication date: 1985-10-09
Also published as: SE8501423D0; AU3866985A; JPS60224533A; SE8501423L; GB8506472D0

Abstract

A tubular container is formed by extruding, coextruding, and/or laminating a sheet of thermoplastic polymer having one or more discrete layers of polymer, trimming the sheet into one or more continuous strips, heating and rolling the or each strip on a mandrel into a continuous tube, and joining the adjacent edges of the rolled strip together to form the completed tube. Sections of the tube are cut to length and closed with end closures to form containers. The sheet may comprise a barrier layer of polymer or metallic foil and adhesive layers interior of the outer layer. The end closures are attached by spin or friction welding.

Description

SPECIFICATION Methods for Manufacturing Barriered Thermoplastic Tubular Containers The present invention generally relates to manufacturing thermoplastic containers and more particularly involves methods for manufacturing plastic containers from multiple components.

Conventional containers generally involve metals, glass, or composite paper materials formed into container shapes. Other conventional containers involve the forming of plastics into container shapes. The present invention is directed towards the area of technology relating to plastics and more particularly to polymers such as polyesters and polyolefins. The containers made by the processes herein disclosed replace those manufactured by conventional plastic forming techniques as well as those of glass, metal, and paper.

In conventional plastic bottle manufacturing, a bottle may be formed by one of several methods.

One such method is to make a pre-form or "parison" by injection molding a molten plastic material into a parison mold and allowing itto solidify. This parison is then placed in a blow molding apparatus which utilizes a combination of heat, air pressure and mechanical stretching means to expand the parison into a finished bottle.

Generallythistwoorthreestep process is very lengthy and expensive due to the time and equipment required in its manufacture as well as the large amount of energy input into the polymer. The melting of the polymer to injection-moldthe parison, with a subsequent cooling down, and then a required reheating to blow-mold requires a large amount of heat input.

An alternative method of manufacturing plastic containers is in the straight injection molding technique where the finished bottle design is formed in a single mold and liquid molten polymer is injected straight into the mold to form a finished bottle. This design, while eliminating the dual heat input of the parison process, suffers from the disadvantage that no orientation of the polymer is obtained and the resulting bottle is structurally weak. Also, because of the lack of orientation in the polymer there is a low barrier to the ingress of oxygen and the egress of CO2.

A third means of forming thermoplastic containers is to extrude a tubular parison and, while the tubular parison is still in a melted state, enclosing the parison in a mold and blow molding it into a final bottle. This suffers from the disadvantages that very little orientation is achieved in the bottle and the bottle also hus weakened areas in the bottom section where the seam is formed during the blow molding process.

On the other hand, the manufacture of cans by conventional techniques is considerably different than the conventional manufacture of bottles.

Composite cans are primarily made of paperboard with either metal or plastic ends crimped on or glued on. The paperboard cylindrical bodies of cans are usually "spiral-wound" using a helically wound strip of paperboard, and then the metal or plastic bottoms and tops are placed on the bodies before and after filling, respectively.

One improved method of manufacturing cans is disclosed in the following copending applications to Vincent Fortuna et al.: S. N. 405,642, filed 5th August 1982, for "Thermoplastic Container End and Method and Apparatus for Inertial Spinwelding of Thermoplastic Container Ends"; and S. N. 415,126, filed 17th September, 1982, for "Inertial Spinwelding of Thermoplastic and Thermoplastic Coated Container Parts". In these copending applications, can bottoms are spin-welded onto spiral-wound paperboard bodies. One means for attaching thermoplastic ends to tubular container bodies is that disclosed in Reissue Patent No.

RE 29448 to Brown, et al, the drawings and specification of which are hereby incorporated by reference herein. A second method of affixing thermoplastic end closures to all shapes of tubes involves oscillatory bonding as disclosed in a copending U.S. Patent Application, S. N. 371,363, filed by Donald MacLaughlin and Vincent Fortuna on 23rd April, 1982, titled "Method of Oscillatory Bonding", the drawings and specification of which are hereby incorporated by reference herein.

The disadvantages of the prior art methods of can manufacturing is that the can bodies, whether they are seamed metal tubes or spiral-wound paperboard tubes, are made by a process that is long and expensive. Also both the crimped metal tube and the spiral-wound paperboard tube are subject to leaking. In addition, the paperboard can usually must be coated interiorly to prevent seepage through the wall of liquid material. Even coated paperboard cans suffer a further disadvantage of "wicking" where the canned fluid enters the paperboard at the edge around the bottom and syphons up into the wall of the can, eventually leaking out through the label.

Another type of conventional can is the drawn aluminum beverage can made of soft aluminum.

Although this type of can is seamless at the bottom and sides, the top must be crimped to the body.

Also, the use of aluminum is becoming prohibitively expensive, as the use of aluminum requires large expenditures of energy to refine the metal, to form the aluminum into sheets, and to draw the can from the sheet. The tops must be of relatively thick material which has to be scored and have a pull-tab mechanically fused thereto by welding or other means. This too is very expensive.

An improved method of forming bottles and cans is that disclosed in copending application, S. N.

492,928, filed 9th May, 1983, by Granville Hahn, et al, wherein a container is formed by thermoforming a top closure having a peripheral friction-welding flange, thermoforming a bottom closure also having a friction-welding flange, and extruding a cylindrical body portion to which the upper and lower closures are friction-welded.

The Hahn et al container process relies upon the formation of a continuous tubular body portion having a single-layer or multiple-layer thermoplastic wall structure, which tubular body portion is formed by tubular extrusion or tubular coextrusion.

Although the Hahn et al process is a quantum improvement over prior techniques of container manufacture, the present invention provides even further significant advantages of over the Hahn at al process and conventional container manufacturing techniques. For example, in the Hahn process, each extruder is limited to making a single tube which is a restriction on the output of the extruder. The present invention allows an extruderto be operated at maximum output by extruding through a wide sheet die and splitting the extruded sheet into as many strips as necessary to utilize the entire output of the sheet die. Each strip thereafter is formed into a continuous tube, a process that can be five to ten times faster than the Hahn process.The present invention can also be used for making noncylindrical tubes such as square tube, rectangular tube, triangular tube, etc., using different rollers and mandrels. Also different tube shapes can be manufactured simultaneously when the sheet is split into multiple strips, by using different rollers and mandrels on each adjacent strip coming from the wide sheet.

The present invention provides a method and apparatus for forming thermoplastic containers wherein almost no scrap material is produced, excellent polymer orientation is achievable, and good adhesion in barriered, multi-layered wall sections can be obtained. These advantages are realized by extruding or coextruding a barriered multi-layered sheet of thermopolymer, orienting the sheet by stretching it axially or biaxially, and then rolling the sheet into one or more continuous tubular sections which are cut to length and closed by bottoms and tops which are attached by means such as friction welding, into the tube sections.

Accordingly the present invention provides a process for manufacturing thermoplastic articles having tubular bodies, which process comprises forming a sheet of thermoplastic material in a predetermined desirable thickness; trimming the said sheet into at least one continuous strip of predetermined desired width; heating the strip to a temperature at which the thermoplastic material may be shaped; rolling the heated strip into a continuous tube; sealing the two edges of the rolled strip together to form the tube; cutting sections of predetermined length from the tube; and, securing at least one end closure in each tube section to form a tubular article therefrom.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:~ Figures 1 and 2 are isometric representations of sheet coextrusion lines; Figure 3 is a schematic cross-sectional view of a coextruded sheet being formed; Figure 4 is a side view of a coextrusion line and sheet orienter; Figure 5 is a side view of an extrusion/co-laminate line; Figue 6 is a top view of a container forming line to be connected to the lines of Figures 4 and 5; Figures 7-13 represent a tube-forming line to be used with Figure 6; Figures 14~16 represent a thermoplastic bottle type container which can be manufactured by the present invention; Figure 17 represents a thermoplastic can made by the present invention;; Figures 18~21 illustrate different shaped tube roller assemblies; and Figure 22 illustrates an axial view of an alternate type of butt-welder.

Referring to the drawings, Figure 1 is an isometric representation of a coextrusion line 110 in which a main screw type extruder 112 is operably connected by feed tube 114 to a coextrusion feed block 120.

Extruder 112 may be of the conventional crew type thermoplastic extruder. A second extruder 116 often called a coextruder, having an outlet feed tube 118 is also operably connected to feed block 120.

Extruders 112 and 116 are selected for their ability to plasticize thermoplastic polymers such as polypropylene, polystryene, polyethylene, polyvinyl chloride, polyethylene terephthalate, ethylene vinyl alcohol and other similar container plastics. The plasticized thermopolymer entering feed block 120 from feed tubes 114 and 118 is distributed within the feed block in a strictly pre-determined distribution into sheet die 122. The sheet die 122 spreads the thermopolymer from a generally tubular molten flow into a relatively wide flat sheet through die exit slit 124.The purpose of feed block 120 isto separate and recombine various combinations of the two thermoplastic flow streams from extruders 112 and 116 so that sheet 126 extruded from die 122 comprises the desired combination of thermoplastic layers coextruded into a single integral sheet. The coextruded sheet 126 then passes over chill rolls 128, 130 and 132 to solidify the sheet and allow it to be physically handled after the coextrusion process.

Figure 2 represents a coextrusion line having a main extruder 112 and two coextruders 116 and 134.

Whereas the coextrusion line of Figure 1 is capable of producing from two to four layers in a coextruded sheet by dividing and recombining the output streams of the two coextruders, the coextrusion line of Figure 2 is capable of extruding multi-layered sheets having from two up to six layers therein. The addition of each additional coextruder to the coextrusion line thus adds an additional two layers of capacity in the multi-layered sheet being formed.

Each additional coextruder requires additional channels and distribution means within the coextrusion block 120. In one particular embodiment, the coextrusion line of Figure 2 is utilized to manufacture a five-layered sheet wherein the main coextruder 112 produces the base layer of the sheet which is split into two streams to provide the outermost layers of polymer. A second polymer may be coextruded through the second coextruder 116 and generally comprises a barrier-layer material such as ethylene vinyl alcohol (EVOH), and the third coextruder 134 may be utilized to provide a tie-layer of an adhesive for adhering the base layers to the barrier layer.A sheet die 122, similar to that of Figure 1 is connected to the output of feed block 120 and receives the multi-layered molten polymer in a tubular flow stream and spreads it out into a thin flat sheet 126 which is then cooled on chill rolls 12#132.

Figure 3 is schematic cross-sectional illustration of the sheet die 122 of Figures 1 and 2 coextruding a multiple layer sheet 126 which is cooled between chill rolls 12#132. The thickness of the coextruded sheet 126 is greatly exaggerated to illustrate the multi-layered composition thereof. In one embodiment, the multi-layered sheet 126 comprises a base layer A on the external surface of the sheet which preferably is extruded from the primary extruder 112. A central barrier layer B is located in the very center of the coextruded sheet and preferably is extruded through the second coextruder 116. A pair of tie-layers C are located between the barrier layer B and the exterior layers A, which tie-layers C are extruded from coextruder 134.It should be noted that the aforementioned references to extrusion of the various layers A, B and C through extruders 112,116 and 134 is referring primarily to plastification of the solid polymer particles into a molten stream. The actual final extrusion of the molten stream occurs through die 122 after the molten streams from the three extruders have been combined in feed block 120.

In one preferred embodiment of the present invention, the base layers A were made up of a container polymer such as PET and the barrier layer B comprised a material such as EVOH. Since EVOH and PET are relatively incompatible and will not adhere to each other, a tie layer C was coextruded between the barrier and the base layers. The general composition of a tie layer C is a poly vinyl acetate or an ethylene vinyl acetate such as those manufactured by Mitsui Chemical Company of Japan and referred to as ADMER. An alternate adhesive for EVOH and PET would be that sold by DuPont Chemical Company under the trade name CXA.

In a second embodiment, a multi-layered sheet was formed for manufacturing containers comprising base layers A made of polypropylene with an EVOH barrier layer and tie layer C comprising an adhesive sold by Mitsui Chemical Corporation of Japan under the trademark Modic.

Referring now to Figures 4~6, there is illustrated the present invention embodied in a coextrusion/ container manufacturing line. In Figure 4, the coextrusion line 110 comprising main extruder 112 and coextruder 116 is illustrated feeding into feed block 120 and die 122. Acoextruded sheet 126 passes through chill rolls 128~132 to a pair of take-up rolls 138. Take-up rolls 138 provide a friction pulling device to maintain tension on the sheet 126 after it has passed through chill rolls 12#132. After the sheet 126 has exited through take-up rolls 138, it is run through a biaxial orienter 140 comprising a conventional sheet orienting system.In a sheet orienting system, the sheet is heated to its optimum orientation temperature and is stretched both laterally and longitudinally, then cooled, to provide optimum strengthening and barrier characteristics in the sheet. This is a conventional orientation system available commercially in the thermoplastic field today. Alternatively, the biaxial orienter 140 may be placed between the chill rolls and the take-up rolls to decrease the need for reheating the sheet material. In this instance, the temperature of the material coming offthe lower chill roll 132 is monitored and the coolant through the chill rolls is controlled in a very precise manner so that the material exiting the bottom chill roll is at the exact optimum orientation temperature.Then the material passes through the biaxial orienter which grips the sheet on all three open sides and stretches it biaxially in the maximum amount to provide optimum orientation. Thereafter, the stretched sheet is cooled while being held in its stretched configuration to prevent reshrinking of the sheet and loss of its orientation.

In Figure 6, the sheet from the orienter then passes through a slitter 142 whereupon it is slit into three or more primary strips D, E and F. The sides X and Y of the main sheet which are split off from the primary strips D, E and F are recycled by running them through a grinder and putting them back into a buried layer in the sheet through one of the coextruders. Each strip D, E and F then passes into the heat roll former where each strip is then rolled and welded into a cylindrical tube G, H and I. These continuous cylindrical tubes then pass into a precutter 146 which roughly cuts the tubes 147 into predetermined desirable tube lengths. The tube lengths 147 accumulate in a bin 148 and then are passed into a precise cutter 150 whereupon they are cut to exact lengths and given smooth, even ends.

The precise tube lengths 151 are then accumulated in a second accumulator 152 and from there are passed individually into a spinwelder 153 such as commercially known in the art and further described in the aforementioned incorporated Reissue Patent 29,448 to G. W. Brown et al, dated January 10, 1967.

In the spinwelder 153, formed container ends are supplied via conveyer 154 to be spinwelded into the precise tube sections 151. This forms containers such as illustrated in Figures 14-17. These containers after being spinwelded are then accumulated in hopper 156 and properly oriented for passing into a label printer 158. From the printer 158, the finished container passes through conveyer 160 to the filling line for receiving the liquid or solid food product to be contained therein. The spinwelder 153 and the printer 158 are commercially available items which can be purchased in the container industry.

One preferred embodiment utilizes a spinwelder designated as an AW-14 spinwelder manufactured by Vercon, Inc. of Garden Grove, California, and the printer 158 comprises a Van Dam printer manufactured and sold by Van Dam. U.S.A. of Camden, New Jersey.

Alternatively, and among one of the many advantages of the present invention, a flat printer may be used to print labels on the sheet prior to its being formed into cylindrical tubes. Thus would only require the placement of a conventional flatlabel printer either upstream or downstream of the sheet splitter 142. The printing of flat labels is well known in the container industry and is much easier, faster, and more accurate than the printing of labels on cylindrical and curved surfaces. The present invention allows the flat-printing of multiple labels directly on the thermoplastic walls of curved plastic containers before they become curved, a process not heretofore possible until this invention.

The container sections passing from accumulator 152 into spinwelder 153, comprise equal length cylindrical tube sections formed by the combination of the sheet coextruder, the biaxial orienter and the heat roll former and welder 144. From Figures 14~17 it can be seen that these cylindrical tubular sections may be formed into cans or bottles. In either instance, the bottom portion of the container, whether it be a can or a bottle, is primarily a circular disch having an upwardly facing U-shaped flange member for friction-welding, fusing, or cementing ths disc onto the cylindrical tube. The top of the container may be either a bottle top which preferably is formed by injection molding or a cap top comprising a tab-opening flat disc having a downwardly shaped U-shaped attachment flange.

Referring now to Figure 5, an alternate embodiment of the container forming line is illustrated in which a multiple layer sheet is formed having either a barrier polymer or else a metallic foil layer bonded on the inside or outside of the multiple layer sheet. In Figure 5, a primary extruder 210 is shown feeding a single layer feed block 212 and a single layer extrusion die 214. Located in the general vicinity above extruder 210 is a roll of barrier material 216 preferably comprising either polymer or a metallic foil. This layer of material 218 passes over a spreader roll 220 and merges with the primary extruder sheet 222 at chill roll assembly 224. A second extruder 226 having a feedblock 228 and an extrusion die 230 feeds a second sheet 232 of polymer into chill roll assembly 224.The two polymer sheets 222 and 232 converge on the outside of barrier layer 218 between the upper chill roll 234 and the center chill roll 236 whereupon they are pressed into a bonding relationship while still in a heated semi-soft state, thus providing a good adhesion between the two extruded layers and the barrier layer. The multi-layered sheet then passes overthefinal chill roll 238 and emerges from the chill roll assembly as a multi-layered sheet material 240. This material passes through take-up roll assembly 242 and thence into the slitter 142 and the heat roll former 144 of Figure 6.

In the embodiment of Figure 5, should a metallic foil layer be provided for the barrier material 218, then no orienter system should be utilized because of the lack of orientation capability in metallic foil.

On the other hand, if the barrier material 218 comprises a thermal polymer such as ethylene vinyl alcohol (EVOH) then the biaxial orienter 140 may be advantageously used either between the chill rolls and the take-up rolls or between the take-up rolls and the slitter. As previously mentioned, the biaxial orienter primarily comprises a mechanical stretching means that has the ability to grip both sides of the sheet and the free end of the sheet and pull in the two axial directions of the sheet. Thus the alternate embodiment of Figure 5 provides a multi layered barriered sheet similar to that of the system of Figure 4 utilizing a laminating system rather than a coextrusion system for bonding the sheet layers together. The advantage of the multiple layered sheet system of Figure 5 is that materials other than polymers can be placed in the sheet material.For example, a thin metallic foil such as aluminum foil, tin foil, or copper foil could be utilized by burying it within the polymer layers. The polymer layers are maintained at a temperature high enough to provide good adhesion to the metallic foil. Alternatively, a coextruder could be utilized for the single extruder 210 to provide a double layered sheet material with one layer being the container polymer and the second layer being an adhesive. Likewise, the second extruder 226 could be replaced with a coextruder for coextruding a double-layered material providing a container polymer having a layer of adhesive thereon. The adhesive layers are located such that both are facing inward while passing through the two chill rolls 234 and 236 and thus contact the barrier material 218 and provide good adhesion thereto.This would be particularly useful when utilizing a barrier material such as EVOH which is not readily compatible with polymers such as polypropylene and PET. In addition to the location of a foil material between two polymer materials, the invention can be utilized to provide a printed barrier material having a label thereon to be buried between the two clear polymer materials such as PET. This would eliminate the need for the printer 158 in the middle or at the end of the container line.

Referring now to Figures 7-13, one possible embodiment of a heat-roll4ormer/welder assembly 144 is disclosed. This illustration is schematic rather than true scale and is intended only to show the general principles of operation of such an assembly.

In the figures, two sets of parallel, coaxial rollers 310 and 312 are provided to contact the multi-layered sheet material 126 and gently curve it up, while it is being heated to its glass transition temperature, into a cylindrical tube. In Figure 7, the parallel rolls are generally flat and a second linearly displaced set of parallel rolls 314, 316 are provided downstream from the initial rolls 310,312. In Figure 8, the rolls have begun a certain amount of curvature to be placed into sheet 126. Figure 9 represents a semicircle of the sheet material formed by rolls 318 and a heated mandrel 320. In Figure 10 the material has been formed into a complete cylindrical tube by the action of rolls 322 and mandrel 320 which has become cylindrical at this point. Also illustrated in Figure 10 is a welding source 324 comprising any of the known conventional fusion and/or heating sources. For example, welding heat source 324 can be a flame, a lazer, a microwave element, a quartz heater or any equivalent means. Alternatively, welding source 324 can provide molten thermal polymer sprayed or streamed onto the seam area 125 in polymer 126. Another embodiment of the seaming process could utilize a fast-curing resin such as epoxy or any other acceptable liquid or semi-solid cement to join the two edges of the rolled tube.

The embodiment of Figure 10 shows what is known as a "butt-weld". Figure 11 is a side view of the final tube forming step shown in axial view 10.

Figure 12 is a schematic view of a different embodiment of the tube forming process in which a "lap-weld" is formed rather than the butt-weld of Figures 10 and 11. In Figure 12, one edge of the sheet is overlapped on top of the opposite edge in the final tube forming step and a heat-pressing roller 326 provides the sealing force for forming the cylindrical tube. Roller 326 actually comprises a series of rollers located axially along the seam area of the tube, as shown in Figure 13. A source of heat 324 is provided upstream of rollers 326 for preheating the seam area of the thermopolymer sheet. The heat source 324 may be of any applicable source such as radiant or radiowave heating.The rolls of Figure 13 are shown pressing the lap joint into a single dimensional seam by progressively flattening the overlapped section in its semi-molten state until the cylindrical tube section is completely formed. Thus the Figures 7-13 illustrate several embodiments of the tube forming assembly 144 of Figure 6.

In an alternate embodiment shown in Figure 22, a different type of welder is illustrated in axial view. In this embodiment, the sheet 126 is rolled over a cylindrical mandrel 320 similar to the previously described embodiments and the two edges of the sheet are brought together on the mandrel for a butt-weld. Just immediately prior to the edges contacting each other, they pass by an electrically heated resistance wire 330, such as nichrome wire, to which is connected an electrical power supply (not shown). The close transition of the polymer sheet sides to the heated wire brings them to a fusion temperature, whereupon they are pressed together immediately after passing the wire. This provides an excellent butt-weld with a minimum application of fusion energy to heat the polymer sheet.If desirable, a non-stick coating such as polytetrafluoroethylene, may be used on the heated wire to minimize sticking of the polymer to the wire if it should inadvertently touch the wire.

Figures 14~16 illustrate one type of container which is advantageously manufactured by the present invention. In these Figures, a bottle 401 is shown having a cylindrical tubular side wall 402 formed according to the above described process. A disc closure 404 is friction-welded, fused, or cemented into a bottom end of tube 402 and a top closure 403, comprising a bottle top having a threaded neck portion 407 and a fill ring 409 integrally formed thereon, is similarly affixed to the top of tube 402. The tubular well section 402 is illustrated as a singie-layer material but Figure 15 illustrates an alternate embodiment of the wall section 402 in which a triple-layered material is formed by means of lamination and/or coextrusion.

As previously mentioned, the wall of tubular section 402 may have any number of layers, from one to as high as nine, by the means of the multiple coextruders as shown in Figures 1 and 2.

Figure 17 illustrates the use of the seamed tube formed according to the above described process to manufacture a typical can 501. The can is made up of the seamed tubular cylindrical section 502 to which is attached a bottom closure 504 and a top closure 503. Top closure 503 has a pull opening tab 505 formed therein for opening the container. As previously mentioned, the bottle 401 and the can 501 have closures with peripheral U-shaped flanges thereon for friction-welding, cementing, or fusing to the tubular sections of the containers. Alternatively, the closure may be crimped on or cemented on, or any combination of the above.

Figures 1 > 21 illustrate different final roller configurations to obtain non-cylindrical uniform tubes. Figure 18 shows rollers and a mandrel for forming square tubing. Figure 19 illustrates a similar arrangement for making rectangular tubes; and Figure 20 shows the process for triangular tubing.

Other polygonal shapes can obviously be formed.

Figure 21 illustrates a non-cylindrical tube-forming assembly for making elliptically-shaped tubes.

Other arcuate tube shapes can likewise be formed.

Thus many types of non-cylindrical tube shapes can be formed into containers by the use of non-spin friction welding techniques such as oscillatory welding or by the use of heat fusion and/or adhesive bonding of the end closures to the tubes.

Thus, the present invention provides means for rapidly forming thermoplastic containers having barrier properties as well as orientation of the thermopolymer. The present process takes raw polymer pellets and turns it into finished containers having printed labels thereon if desired. The entire process is relatively compact and can be placed directly in the filling plant of the food process. Thus, the process eliminates the need for shipping empty containers from a container manufacturing plant to the filling plant which shipping process is extra newly uneconomical because of the light but bulky nature of empty containers. Also, the invention provides rapid, efficient and effective means for forming containers with a minimum of scrap material.The containers thus formed provide cylindrical wall sections capable of having multiple-layered barrier materials with polymer barriers, foil barriers or combinations thereof, as well as the capability of having oriented polymers in the container walls for providing extra strength while reducing the need for bulk polymer. The container forming process utilizes either extrusion, coextrusion, lamination, or a combination of these, of sheet material which is then rolled into seamed tubes and welded. The process provides continuous manufacture of tubular polymer material which is then cut to length and closed at the ends to provide finished containers. By utilizing large extruders which extrude sheets in widths of up to 52 inches or wider, a multiple tubular line can be formed off of one single extrusion assembly. Likewise, a multiple barriered tubular line can be formed off of a single coextrusion assembly. For example, in a 52 inch coextrusion line utilizing a primary extruder and a secondary coextruder, a three-layered barrier sheet can be formed 52 inches wide which can then be split into up to several different tube lines feeding from this single sheet. The tube lines are capable of forming soft drink cans or bottles in the popular 10 and 12 oz. sizes and illustrated in Figures 14 and 17.

This container is approximately 2.25 inches in diameter, requiring a strip of sheet about seven inches wide. Allowing for a certain amount of waste to be trimmed from each side of a 52 inch wide sheet, at least six strips can be cut from the wide sheet and possibly even seven strips. This would allow six or seven tube lines to be operated from a single sheet extruder. Thus whereas the aforementioned Hahn at al tubular extrusion process for the coextrusion of a tubular container wall is a distinct advantage over the prior art, the present invention even offers additional advantages in that up to five or more different tube lines can be formed from a single extrusion assembly by the use of slitters and tube welders.

Although a specific preferred embodiment of the present invention has been described in the detailed description above, the description is not intended to limit the invention to the particular forms or embodiments disclosed therein since they are to be recognized as illustrative rather than restrictive and it will be obvious to those skilled in the art that the invention is not so limited. For example, whereas rollers and a heated mandrel are shown for forming the tube from the sheet, it is obvious that a pair of parallel mandrels can be utilized rather than rollers or, rollers can be used entirely for the process rather than mandrels. Also, it is obvious that other types of seam-welding may be utilized than those disclosed, which known processes are available to those skilled in the art of thermoforming. Other configurations of tops and bottoms can also be utilized for forming the containers from the welded tubes. Likewise, different cutting means may be utilized to form the tubes to length such as laser cutting, sonic cutting, hot-knife cutting and rapid sawing. Other polymers than those disclosed m be utilized such as styrene acryonitrile (SAN), polyvinylidene chloride (PVdC), and copolymers of polyethylene and polypropylene.

Claims

1. A process for manufacturing thermoplastic articles having tubular bodies, which process comprises forming a sheet of thermoplastic material in a predetermined desirable thickness; trimming the said sheet into at least one continuous strip of predetermined desired width; heating the strip to a temperature at which the thermoplastic material may be shaped; rolling the heated strip into a continuous tube; sealing the two edges of the rolled strip together to form the tube; cutting sections of predetermined length from the tube; and, securing at least one end closure in each tube section to form a tubular article therefrom.

2. A process according to Claim 1, wherein the sheet forming step comprises melting the thermoplastic material in a mechanical extruder and extruding itthrough a sheet die.

3. A process according to Claim 1 or 2, wherein the heating step comprises maintaining the heat of extrusion of the sheet above its glass transition temperature from the extruder through the rolling step.

4. A process according to Claim 1, 2 or 3, wherein the sheet is formed of at least two different thermoplastic materials, each said material being located in a discrete layer in the sheet, the said layers being fixedly bonded together.

5. A process according to Claim 4, wherein the sheet forming step comprises coextruding a plurality of layers in a single multi-layered sheet.

6. A process accordimg to Claim 4, wherein the sheet forming step comprises laminating a plurality of layers into a single laminated sheet.

7. A process according to Claim 4, wherein the sheet forming step comprises laminating and coextruding at least three layers into a single bonded sheet.

8. A process according to Claim 7, wherein an interior layer of the sheet comprises a barrier polymer.

9. A process according to Claim 8, wherein the barrier polymer is selected from ethylene vinyl alcohol, polyvinylidene chloride, and styrene acrylonitrile.

10. A process according to any one of the preceding Claims, wherein the rolled tube is cylindrical.

11. A process according to any one of Claims 1 to 9, wherein the roller tube is non-cylindrical.

12. A process according to Claim 10, wherein the end opened closures is or are attached to the tube by spin welding.

13. A process according to Claim 11, wherein the end closure or end closures is or are attached to the tube by friction welding.

14. A process according to any one of the preceding claims, wherein the edges of the tube are sealed in a lap-joint.

15. A process according to any one of Claims 1 to 13, wherein the edges of the tube are sealed in a butt-joint.

16. A process according to any one of the preceding Claims, wherein the edges of the tube are sealed by heat fusion.

17. A process according to any one of Claims 1 to 15, wherein the edges of the tube are sealed by cementing.

18. A process according to any one of the preceding Claims, further comprising printing a label on the sheet after the sheet forming step.

19. A process according to Claim 18, wherein the printing step occurs prior to the rolling step.

20. A process according to Claim 7, wherein one interior layer of the sheet comprises a metallic foil.

21. A process according to Claim 7, wherein one interior layer of the sheet comprises a printed label.

22. A process according to any one of Claims 1 to 17, further comprising the step of orienting the sheet in at least one axial direction after the sheet has been formed.

23. A process according to Claim 22, further comprising the step of printing a label on the sheet after the said orienting step.

24. A process for manufacturing plastic containers, which method comprises forming a single sheet having at least three layers of polymer bonded together, with at least one of the layers consisting of a barrier polymer; slitting the sheet into a plurality of strips of predetermined desired width; heating the strips to a temperature above their glass transition temperature; and rolling each strip into a continuous tube about a longitudinal axis parallel to the edges of the strip.

25. A process according to Claim 24, wherein the sheet comprises five coextruded layers consisting of two outer layers of a structural polymer, a central barrier layer, and an intermediate layer of adhesive between each of said structural layers and the central layer.

26. A process according to Claim 25, wherein one of the outer layers comprises polypropylene, the other outer layer comprises a polypropylene/ ethylene copolymer, and the barrier layer comprises ethylene vinyl alcohol.

27. A process according to Claim 24, 25 or 26, wherein the securing step comprises friction welding.

28. A process according to any one of Claims 24to 27, further comprising the step of orienting the sheet in at least one axial direction after forming it.

29. A process according to any one of Claims 24 to 28, further comprising printing a label on the sheet after the sheet forming step.

30. A process according to any one of Claims 24 to 29, further comprising printing a label on the sheet after the forming step and prior to the rolling step.

31. A process according to any one of Claims 24 to 28, further comprising printing a label on each said tube after the rolling step.

32. A process according to Claim 28, further comprising printing a label on the sheet after the orienting step.

33. A process according to any one of Claims 24to 27, wherein one of the said layers has a label printed thereon.

34. A process for forming containers, which process comprises: extruding a sheet having at least one layer of a thermoplastic material; laminating at least one additional layer of material to the said extruded sheet to form a single sheet of multi-layered bonded material; heating the multilayered sheet to a non-melt softening temperature; trimming the sheet into at least one strip of continuous predetermined desirable width; rolling the strip into a tube wherein the edges of the strip are substantially parallel to the longitudinal axis of the formed tube; joining the edges to form an enclosed continuous tube; cutting predetermined desirable lengths from the tube; and, sealing at least one end enclosure to each length of tube to form containers therefrom.

35. A process according to Claim 34, wherein the laminating step further comprises adding a metallic foil layer to the extruded sheet and adding a second layer of thermoplastic material over the said foil layer.

36. A process according to Claim 34 or 35, wherein the said layers are heat-fused together.

37. A process according to Claim 34 or 35, wherein the said layers are cemented together.

38. A process according to Claim 34, wherein said extruding step comprises coextrusion of at least two layers of different thermopolymers.

39. A process according to Claim 34 further comprising the step of biaxially orienting the sheet after forming it.

40. A process for manufacturing thermoplastic articles having tubular bodies substantially as hereinbefore described with reference to the accompanying drawings.

41. Atubularcontaineror liketubulararticles whenever made by a process as claimed in any one of the preceding claims.