GB2107636A

GB2107636A - Method and apparatus for producing biaxially oriented hollow articles

Info

Publication number: GB2107636A
Application number: GB08224920A
Authority: GB
Inventors: Granville Hahn; Raleigh Rutledge
Original assignee: Cosden Technology Inc
Current assignee: Cosden Technology Inc
Priority date: 1981-09-04
Filing date: 1982-09-01
Publication date: 1983-05-05
Also published as: GB2107636B; SE8204998D0; CA1206315A; IT1152523B; NL8203448A; DK393682A; FR2512385B1; FR2512385A1; DE3232966A1; SE8204998L; IT8223112A0

Abstract

A hollow article (e.g. a bottle) made of a biaxially oriented thermoplastic is produced by heating a sheet of thermoplastic material (12) to a temperature above its orientation temperature; forcing the heated sheet by pressure into a first mold half (20); maintaining the sheet in contact with the surface of the mould half (20) to allow the sheet to reach its orientation temperature, and then forcing the sheet into the second mold half (18) by means of pressure. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing biaxially oriented hollow articles The present invention relates generally to method and apparatus for producing hollow articles from thermoplastic material and more especially pertains to method and apparatus for producing biaxially oriented articles from thermoplastic resinous materials. It is generally recognized that the strength characteristics of thermoformed plastic containers and hollow articles are materially enhanced when the thermoplastic material from which these articles are produced undergoes molecular orientation. This orientation can be provided by the use of pro oriented stock materials. However it is preferable to impart a molecular orientation in one or more directions to the final articles during the article forming process.

The most beneficial strength properties are achieved when the plastic material in the walls of the hollow article has been biaxially oriented in a relatively uniform or balanced manner. The material is biaxially oriented by stretching it proportionally the same extent along both coordinate axes of the plane of the material. The biaxial orientation of such material may be characterized by its very low birefringence value. However, the accomplishment of a biaxial orientation balanced in the coordinate directions is a complex task when done in conjunction with production of a hollow article having a varying cross-section.

Numerous methods have been utilized in the prior art for producing hollow articles from thermoplastic materials to produce articles exhibiting a certain degree of molecular biorientation. These methods generally involve a series of separate steps including the formation of a pre-form, a preliminary stretching of the pre-form, and a final pressure molding step to cause the stretched pre-form to conform to the final desired shape. Generally, using conventional methods, the pre-form, which is often termed a "parison", is typically preformed in one of two ways.

One method is to form a tubular parison by an extrusion process and the so-formed parison is then subjected to further shaping techniques. The second parison forming method is the most commercially used method and involves the forming of the parison by an injection molding process. After the parison is injection molded it is coolded and moved to separate final molding apparatus whereupon it is reheated and the final molding steps applied thereto.

One method of forming the final bottle with a biaxial orientation is to stretch the parison longitudinally along its axes while the parison is at its orientation temperature. This longitudinal axial stretching is accomplished by mechanical stretching means. In order to maintain the advantages of the biaxial orientation, both the mechanical stretching longitudinally and the radial stretching by pressure methods must be achieved at the orientation temperature and the article must not exceed the orientation temperature or the effects of the orientation will be neutralized. This process suffers from the disadvantage that mechanical stretching is non-uniform in character and does not obtain balanced biaxial orientation. This is particularly true along the leading edge of the mechanical stretching plug which contributes to a condition known as the "leading edge effect".Along this edge much greater stretching and deformation occurs than in areas spaced far from the edge. Also a deleterious thinning of the material can occur in the leading edge area degrading the quality of the finished container.

In a similar process, biaxial orientation is achieved with the pre-formed parison by subjecting the parison to a first blowing step to form a preliminary blown article having a shape generally the same as the final article but smaller in dimension. This preliminary blowing step is achieved while the material is above its orientation temperature, thereby obtaining no molecular orientation in the mate riai. The biaxial orientation is then accomplished when the pre-formed article is subjected to a final blowing step at the orientation temperature.

There are other processes for biaxially orienting a hollow article which include the utilization of a biaxially oriented sheet of material from which a vacuum forming or blow molding process forms the final article. The disadvantage with this process is that the orientation of the sheet material is adversely affected during the thermoforming stage. Also, this type of biaxial orientation is difficult to control in objects which are nonsymmetrical in cross-sectional configuration or in axial configuration.

There has existed in the container industry a long-felt need for a thermoformed thermoplastic container which can be used to satisfactorily package liquids and solids and maintain the freshness and aseptic quality of the contents. Such container must satisfy several strict criteria. It must have sufficient strength to safely withstand the internal pressures of pressurized beverages and/or the stresses and strains of shipment, including rough handling and droppage. Furthermore, the container must be attractive and non-toxic. The container must in many instances provide several barrier characteristics against the diffusion of various gases out of or into the products held in the container. For example, containers carrying both solid and liquid food products must have relatively high barriers against the infusion of oxygen from the surrounding atmosphere.

Likewise, carbonated beverages such as beer and soft drinks must have a barrier characteristic against the diffusion outward of the pressurized carbonation trapped in the liquid contents of the container. It has been found that a loss of as little as 15 percent of the total carbonation of soft drinks will be perceived by the consumer as "having gone flat". Thus the barrier characteristics of containers formed from thermoplastic materials must be very good in the area of oxygen and C02 barriers.

The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy. At the present time there are some plastic contain ers in the market containing carbonated beverages.

Some soft drinks have been marketed in plastic bottles in the one- and two-liter sizes. These bottles, which are made of polyethylene terephthalate (PET), do not provide a sufficient shelf life for total consumer satisfaction. There exists a high demand for bottles in the smaller range of from eight ounces up to one-half liter. Unfortunately, as the size of the bottle is reduced, its barrier properties are also reduced due to the larger surface-area-to-volume ratio of the smaller containers.

Also, the processes used to manufacture soft drink bottles in the one- and two-liter sizes, which are currently being marketed, are extremely complex and costly because of the many associated steps involved in forming the containers. These processes utilize a parison which has been injected molded in a first independent operation then cooled and subjected to a separate operation wherein the parisons are reheated and stretched with a mechanical rod then thermoformed to the final containers. Furthermore, the strength of thethermoformed one- and two-liter bottles leaves much to be desired in the bottom end area where the maximum stress occurs.

Thus the bottles are designed with basically a hemispherical bottom end to provide sufficient strength therein. This, in turn, necessitates the addition of a separate cap on the bottom end to provide a flat bottom surface for the bottles to stand upright alone. Additionally the bottom caps provide added strength in the weaker section of the container. The use of the injection-molding techniques to form the parisons substantially eliminates the possibility of forming multilayered walls in the containers for providing various properties to the containers.

For example, it may be desired to form a container having a multilayered wall wherein one of the layers provides strength to the wall, a second layer provides the necessary barrier characteristics, and a third layer provides the esthetic qualities desired in the container. It is not known how such a multilayered container could be formed uniformely in the injection-molding/parison type of process. Furthermore, due to the number of operations involved in the conventional beverage container forming process, it is an extremely expensive and time-consuming operation.

Thus the present invention provides a method and system for producing a biaxially oriented, hollow, thermoplastic article in a simplified and extremely rapid, but efficient, process. The present invention also discloses a highly efficient apparatus for forming a biaxially oriented hollow article from a multilayered thermoplastic material.

The method and system disclosed in the present invention utilizes a high pressure thermoforming system wherein sheet material is subjected to a downward blowing force to form a pre-form, which is then cooled for a determined period of time, and then an upward high-pressure force is applied to the pre-form to expand it into the final article shape. The assembly disclosed utilizes hydraulic pressure to clamp the sheet material, and a set of upper and lower mold cavities comprising porous mold metal or other metal structures capable of flowing gas therethrough. The system disclosed also utilizes a valving system comprising a six-way valve and an air system comprising a pressurized air source and a pair of air accumultaor tanks therein.The upper and lower mold assemblies utilize interchangeable mold sections for forming differently shaped articles, depending upon the particular needs and requirements of the container manufacturer.

The present invention utilizes a high pressure thermoforming system as opposed to the conventional vacuum forming system of the prior art. The assembly allows the formation of a pre-form and then the pressure forming of the final article in the same apparatus. This eliminates the costly parisonforming technique of the conventional thermoforming methods. Furthermore, the assembly allows a balanced biaxial orientation of the finished product which greatly enhances the strength and barrier characteristics. Furthermore, the present invention allows the use of a multilayered coextruded sheet material as a feedstock and results in a very uniform, multilayered, biaxially oriented thermoplastic container having the desired qualities of strength, esthetics and barrier properties.

Figure 1 is a schematic view of an apparatus line which is useful for carrying out the process according to the invention; Figures 2, 3, 4, and 5 are schematic representations of the orienting thermoforming steps according to the process of the present invention; Figure 6 is a perspective view of a sheet of thermoformed biaxially oriented hollow articles which have been produced according to the process of the present invention and which are not yet separated from one another; Figure 7 is a perspective view of a pre-form mold surface useful in the process of the present invention; Figure 8 is a perspective view of a plastic bottle manufactured in accordance with the present invention; Figure 9 is a perspective view of another shape of container manufactured according to the process of the present invention; ; Figure 10 is a schematic front elevational view of a thermoforming assembly; Figure 11 is a schematic side elevational view of the assembly of Figure 1; Figure 12 is a schematic top plan view of the assembly of Figures 1 and 2; Figure 13 is a cross-sectional front view of the molding blocks of the thermoforming assembly; Figures 14-19 are various plan views of removable molds; Figure 20 is a schematic view of the pressure valving system; Figure 21 is a cross-sectional view of a valve used in the pressure valving system; Figures 22-24 are various isometric views of a valve element for use in the valve of Figure 12; Figure 25 is an alternate embodiment of a mold for making a container top section; and, Figure 26 is a diagram showing the air, hydraulic, and electric control circuits for the entire system.

The present invention provides a process which is capable of blow molding hollow thermoplastic articles in a single forming-step procedure which are characterized by an optimum degree of biaxial orientation. The process is capable of operating at very short cycle times, which means that the hollow articles can be mass produced at a very high rate of speed and at low cost.

The process of the invention is applicable generalliy to any type of thermoplastic resinous material which can be extruded into sheet form and can be thermoformed. Both crystalline and amorphous polymers can be employed in the process of the invention. Examples of appropriate types of polymeric materials include the polyesters, such as polyethylene terephthalate; the vinyl aromatic or styrenic polymers, including substituted and unsubstituted styrene polymers and copolymers, high impact polystyrenes comprised of styrenorubbory polymer blends, graft copolymers and block copolymers, and ABS-type resins; polyolefins, such as polyethylene and polypropylene; nitrile-containing resins, such as copolymers containing a major proportion of acrylonitrile; acrylic materials, such as polymers and copolymers of acrylic and methacrylic acid esters; vinyl esters, such as polyvinyl chloride and vinylidene halide polymers; polyamides; and various blends and mixtures of these generally well known classes of polymeric materials.

The thermoplastic characteristics or properties of these classes of polymers are also well known to persons skilled in the art. For each particular polymer, there exists a so-called "orientation temperature range" or "stretch flow range", within which the polymer can be molecularly oriented upon stretching. This range lies somewhere below the melting temperature of a polymer which melts at a specific temperature, or below the crystalline melting range of a polymer which melts over a range of temperatures. The orientation temperature range also lies above the second order glass transition point, which is the temperature at which an essentially amorphous polymer, or a crystallizable polymer which can be quenched as an amorphous polymer, makes a transition from a glassy state to a rubbery state.It is in this rubbery state that the polymer in the form of a film can be oriented by stretching.

For each type polymer, the orientation temperature range will be different; however, it can be easily determined by simple experiments, or in the case of a large number of polymers, it can be looked up in a variety of reference sources. For example, a representative listing of polymer types and their orientation temperature ranges is given in British Patent No. 921,308, the disclosure of which is hereby incorporated by reference.

The basic process of blow molding is well known in the art for the production of hollow articles; however, this process has not been adapted for the production of biaxially oriented articles. In the introductory portion of the specification there has been described the special procedures used in the art to produce oriented hollow articles. A typical blow molding machine is capable of only very limited operating conditions, such as blowing pressures of up to only about 100 psi or 150 psi. These conventional machines are not suitable for carrying out the process of the present invention without being modified to enable higher blowing pressures and in other ways which will be explained below.

Referring now to the drawings, there is schematically illustrated in Figure 1 an apparatus line for carrying out the process according to the present invention. The line originates with a source of thermoplastic film or sheet, such as roll 10 of polymeric sheet material 12. This source of sheet material 12 can also comprise an extrusion device for producing the polymer sheet in a continuous operation as the present process is carried out.

The sheet material is then passed through a heater 14 which is suitable for raising the temperature of the polymer material in the sheet to a value which is above its second order glass transition temperature or its softening temperature, but which is lower than the melting temperature or melting range of the polymer.

The heated thermoplastic sheet is next transported into the blow molding apparatus schematically illustrated and identified by the reference numeral 16. The blow molding apparatus is characterized by upper and lower mold sections 18, 20 which are displaceable with respect to one another so as to be capable of opening and closing a plurality of mold cavities 22 formed therebetween. Upon closure of the upper and lower mold sections, the sheet of thermoplastic material is clamped between the two mold sections, and then a pressure differential is established on one or the other side of the plastic sheet, in order to force the sheet into the mold cavities and thereby thermoform it into the desired shape.

In accordance with the present invention, the blow molding apparatus is provided with a plurality of specially designed cavities 24 in the mold section opposite to the mold section which contains the mold cavities 22. One specially designed cavity 24 is positioned opposite to each mold cavity 22. Each special cavity 24 contains a pre-form mold surface having a predetermined configuration. One particular embodiment of such a pre-form surface, which is well suited for producing hollow, generally cupshaped articles from polyethylene terephthalate (PET), is illustrated in Figure 7. The configuration of these surfaces is not critical to the present invention, and surface configurations generally the same as that shown in Figure 8 can be used satisfactorily for producing hollow articles from other types of thermoplastic materials. A particular shape is imparted to these surfaces in order to optimize the uniformity in the wall thickness of the hollow article after it is blow molded.

The surfaces of pre-form mold portions 24 function primarily as heat exchange surfaces. After being clamped between the mold sections 18, 20, the thermoplastic sheet is blown toward and against the surfaces of pre-form mold portions 24. Upon being permitted to remain in contact with these surfaces for a predetermined period of time, which is dependent, inter alia, upon the temperature at which the surfaces are maintained, the polymer sheet is blown into mold cavities 22 by creating a positive pressure differential on the side of the sheet 12 2 opposite the mold cavities. After this, the mold sections are opened, and the blow molded sheet is advanced out of the apparatus. The individual stages of the molding step will be explained in more detail below with reference to Figures 2-5.

As the sheet exits from the blow molding apparatus 16, it now contains a plurality of hollow, blow molded articles formed therein, which are connected together by non-thermoformed web sections of the sheet 12. The hollow articles may all be of the same shape, or as shown in Figure 1, a portion of the articles can be of one configuration, e.g., a bottled top portion 26, whereas the remaining hollow articles may have a different configuration, e.g., a bottle bottom portion 28 adapted to be mated with the bottle top portion. This sheet of hollow articles is then introduced into a suitable trimming apparatus 26 wherein the interconnected hollow articles are severed from Dne another and trimmed of scrap thermoplastic material, which can be recycled, for example, to an extrusion device used to form the thermoplastic sheet 12.

The trimmed hollow articles exiting from the trimming apparatus 30 can be used just as they are, for example, as cups or as containers for food products. As a result of being able to efficiently produce such a container with biaxially oriented walls, it is possible to further reduce the thickness of the container walls without loss of strength properties. Hence, the amount of thermoplastic material used per container can be reduced to yield a savings in material costs.

On the other hand, the hollow articles exiting from the trimming apparatus can be further processed in order to convert them into more sophisticated types of containers. For example, in the embodiment illustrated in Figure 1 and in more detail in Figure 6, wherein bottle top and bottom portions are produced in the blow molding stage, the bottle portions can be subsequently joined together to produce integral bottles. This can be accomplished advantageously by introducing the bottle portions into a friction welding or so-called spin welding device 32.

In such a spin welding process, the container portions are placed into axial juxtaposition so they contact one another in the final desired configuration, and then the respective portions are rapidly rotated with respect to one another, in order to generate sufficient friction heat to cause the two portions to fuse or weld together. Such processes as well as suitable apparatus for carrying out these processes are disclosed, e.g., in U.S. Patent No.

3,216,874, No.3,220,908, No.3,297,504, No.

3,316,135, Re. 29,448, No.3,499,068, No.3,701,708 and No 3,759,770. The disclosures of these patents are hereby incorporated by reference. According to one embodiment of the present invention, a plastic bottle having a configuration such as that illustrated in Figure 8 results from spin welding together a bottle top half and a bottle bottom half.

In accordance with another embodiment of the invention, each of the mold cavities 22 in the blow molding device 16 has the same configuration, which is that ofthe entire top and sidewall portion of a bottle-like container such as illustrated, for example, in Figure 9. After exiting from the trimming device 30, these bottles-without-bottoms can be advantageously handled in a number of ways. If they are provided with a suitable bottom-to-top taper, a plurality of these articles can be nested one within the next. In this way the number of empty containers which can be transported in a given volume (e.g., truckload is multiplied many-fold in comparison to normal empty bottles.In addition, either with or without such a taper, these articles lend themselves excellently to high-speed printing processes, because the hollow article can be slipped over a mandrel to provide adequate support to enable a high-speed printing head to be applied with the force necessary for good quality printing. Either directly after exiting from the trimming apparatus, or after undergoing one or more intermediate processing and/or shipping stages, the hollow bottleswithout-bottoms can be subjected to a spin welding step in order to secure a generally planar bottom wall therein. A bottle-like container as illustrated in Figure 9 is the result.

With reference to Figures 2-5, the combined blow molding/biaxial orientation stage taking place within blow molding apparatus 16 will be described in more detail.

In Figure 2 sheet 12 is moved into the space between upper mold section 18 and lower mold section 20, the mold sections being spaced apart at this time. Sheet 12 has just left the heater 14 (Fig. 1), which can be a conventional oven, e.g., infrared, of the type associated with blow molding machines.

The temperature of the oven will, of course, depend upon the type of thermoplastic material which constitutes sheet 12. In the case of PET sheet material (e.g., 45 mils thick), the oven can be maintained at between about 610-630 F. The sheet 12 enters the heater and remains therein for several cycles of the machine, as the sheet is stepwise advanced through the heater toward the blow molding machine 16. A satisfactory residence time for PET sheet in the heater at the above temperatures is about 2 minutes. This is sufficient to heat the sheet 12 to a temperature above its softening temperature but below its melting temperature.

Suitable temperatures and residence times for other types of sheet material can be readily determined.

As shown in Figure 3, the upper and lower mold sections are then closed against one another in order to clamp sheet 12 firmly therebetween.

Although not shown in Figure 3, as the mold sections are closed the sheet 12 is initially displaced upwardly in its center portion by the surface 50 in the lower mold portions 24. This causes the sheet 12 to tent upwardly, so that it contacts only the upper or top portion of surface 50. Three-way valves 34 positioned below each of lower cavities 24 are then actuated to produce communication between the interior of cavity 24 and evacuation line 36, which can be connected to a vacuum source if desired. At the same tine, three-way valves 40 are actuated to cause a source of pressurized gas, preferably air, to communicate via lines 44 with the interior of each upper cavity 22. This blows the sheet 12 into contact with the convex surface 50 of the lower mold portions 24.

In Figure 7, two suitable configurations for surface 50 are illustrated. These configurations are suitable for forming the container portions illustrated in Figures 2-6.

The first surface takes the form of a shallow concave depression with a centrally located, slightly frustoconical cylinder having a rounded upper edge and a generally flat top projecting upwardly from the bottom of the concave depression. This first surface is especially suited for forming a partially longitudinally oriented thermoplastic pre-form adapted for ultimate fabrication into a biaxially oriented hollow bottom portion for the bottle illustrated in Figure 8.

The second surface has the form of a shallow concave depression having projecting from the bottom thereof a centrally located, rounded, hemi-ellipsoidal hump with a generally flat central top portion. This second surface is especially suited for forming a partially longitudinally oriented thermoplastic pre-form adapted for ultimate fabrication into a biaxially oriented hollow top portion for the bottle illustrated in Fig. 8. To aid in forming the threaded portion, it is advantageous to provide a series of concentric rings or other surface configuration in the flat central top portion, to hold a sufficient amount of polymer at this location. The shapes of the partially oriented pre-forms are designed to produce a highly uniform wall thickness in each of the top and bottom bottle portions when the respective bottle portions are blow molded to final shape.

The surface 50 of the lower mold portion 24 is at a temperature lower than the temperature of sheet 12 as it exits from heater 14. The temperature of surface 50 is chosen, in combination with the period of time during which the sheet 12 remains in contact with the surface 50, to impart to sheet 12 the optimum temperature for biaxially orienting the sheet during the next stage of the process, which is blowing sheet 12 into upper mold cavity 22. For example, in the case of the PET sheet discussed above, a temperature of about 200 F for surface 50 is appropriate to bring the material to its orienting temperature with a contact time of between about 0.2 and 0.4 second.

Once again, other surface temperatures and contact times can be readily determined.

When sheet 12 is initially blown against the lower mold portion 24, the sheet is at a temperature which is preferably higher than the optimum orientation temperature range for the material, although this is not necessarily the case. At such a higher temperature, the sheet can be blown against surface 50 with a relatively low pressure differential, for example, as low as about 40 psi. Typically, the pressure differential will be at least about 80 psi and may range up to about 200 psi. It is also contemplated that higher pressure, e.g., up to about 350 psi may also be used under certain circumstances, e.g., a larger surface area in surface 50. These latter pressures are, of course, considerably higher than the pressures used in conventional blow molding processes.During the initial blowing stage against lower portion 24, the sheet is typically not biaxially oriented, or at least not to any significant extent. Some orientation will invariably take place, but it is primarily uniaxial in the longitudinal direction.

After the sheet 12 has cooled to the desired temperature in contact with surfaces 50, the threeway valves 34 and 40 are actuated to reverse the pressure differential across the sheet. A gas at a very high pressure is introduced into lower cavities 24 via lines 38, as shown in Figure 4. At the same time the pressure in each upper cavity 22 is exhausted via lines 42, which may optionally also be connected to a vacuum source. It is preferred to use air as the gas, at a pressure of at least 200 psi and up to about 1000 psi. More preferably, the pressure of the air is between about 200 and 650 psi, in view of the fact that the molding equipment must be built quite massively to accommodate the higher pressures.

Such massive equipment is not only expensive, but is not well suited to the extremely rapid cycle times which can be achieved by the present process. Very suitable results can be achieved using air pressures of between about 250 and 400 psi.

The pressure differential applied across sheet 12 to force it into mold cavities 22 must be sufficiently high to produce a uniform biaxial orientation of the thermoplastic material. In other words, the blow of the material must be very rapid and complete, i.e., to form a completely shaped container having walls of uniform thickness. Furthermore, the pressure may not be too high, or this uniformity can also be adversely affected. The temperature of the inside surface of mold cavities 22 is simply chosen low enough to rapidly bring the material of sheet 12 below its softening temperature, e.g., below its second order glass transition temperature.

The foregoing temperature and timing considerations are determined to some degree by the overall cycle time for the apparatus. One of the significant advantages of the process according to the invention is that hollow articles can be prepared at very high rates of speed. It is possible, therefore, to operate the process with cycle times as low as about 1.2 seconds, i.e., from the entry of sheet 12 to the exit of the molded product and entry of a new section of sheet 12. Even cycle times as long as 6 seconds are faster than the conventional processes for forming biaxially oriented hollow articles. Typically, the process is operated with cycle times from about 1.5 or 2 seconds up to about 4 seconds.

This means that the contact time between sheet 12 and surfaces 50 of the lower mold cavities 24 is extremely short, e.g., on the order of from about 0.2 to about 0.4 second. However, this is not to say that shorter or longer contact times cannot be used if the appropriate temperatures are chosen for the sheet material and surface 50. There is no advantage to using longer contact times, but rather only the disadvantage of longer cycle times.

In Figure 5 is shown the final stage of the blowing process. Upper and lower mold sections 18, 20 are separated apart and the molded sheet 12 containing a plurality of upper bottle portions 26 and a plurality of lower bottle portions 28 is freed from the mold cavities and is transported out of the molding apparatus. A perspective view of a section of molded sheet 12 is illustrated in Figure 6. A completed bottle having these bottle top and bottom portions spin welded together is illustrated in a perspective view in Figure 8.

Obviously, the shape of upper mold cavities 22 can be chosen in any desired shape, depending on the shape of he hollow article sought to be produced.

An alternative bottle design is shown in perspective in Figure 9. The entire upper portion 60 of this bottle, included the threaded neck 62 is formed in the blow molding process according to the present invention.

Because of the slight upward taper in the walls, the bottomless container portions can be nested with other like articles for shipping and storage. At a subsequent time, the bottom 64 can be added by a spin welding process.

A further advantage of the present invention is that it opens up the possibility of employing specially tailored sheet materials, which can be produced by known sheet extrusion and coextrusion processes. For example, it is possible to employ multilayered coextruded sheet products which contain at least one layer of a plastic material having good barrier properties, e.g., Saran, polypropylene, high density polyethylene, nitrile-containing polymers, ethylene vinyl alcohol (EVAL) and Barex. The barrier layer can be on one surface of the multi-layer sheet, or sandwiched between other layers of different polymeric materials. For example, it is possible to sandwich a 5 mil layer of EVAL between two layers (25 and 15 mils) of PET. Many other combinations are possible, e.g., polystyrene and high impact polystyrene.These multi-layer sheets can be biaxially oriented without any difficulty by the process of the invention.

Referring now to Figure 10, a thermoforming assembly 100 is disclosed in a schematic end view.

Assembly 100 comprises a base pedestal 101 upon which is mounted a base 102, upward extending arms 103 attached to base 102, and a cross-bar member 104 extending transversely between arms 103, parallel to the top of base portion 102.

A bottom mold block 105 is fixedly secured in a mounting bed 106 attached to base 102. An upper mold block 107 is mounted above block 105 in a vertically movable position by suspension from cross-bar 104 through articulating linkages 108.

Guide rods 109 provide lateral stability of the movable upper block 107. A power source, such as a hydraulic cylinder 110, is provided between cross bar 104 and mold block 107, and is secured to each component.

Whereas a hydraulic cylinder is disclosed as a power source between the movable upper mold block and the stationary cross-bar 104, other known means for applying downward pressure and movemenu to mold block 107 can be utilized, such as a mechanical drive unit driven by electric or pneumatic power. Cylinder 110 utilizes a stationary shaft 111 mounting the cylinder 110. A movable plunger 112 exits the cylinder and connects to mold block 107.

Additional downward clamping forces can be supplied by attaching additional pressure cylinders to articulated arms 108. Additional power sources on arms 108 provide a more uniform clamping force on 107 to provide efficient clamping of block 107 on block 105.

A pressure reserve tank 113 is provided in close proximity to the lower mold block 105 to provide a sufficient charge of actuation air pressure for the thermoforming operation in the upper molds. Tank 113 provides a reserve air capacity to accumulate an initial charge to efficiently supply air to each of the mold cavities in the block. Likewise a second accumulatortank 114 is provided in the apparatus 100 and connected by air line 115 to the upper mold block 107 to accumulate compressed air and to provide actuating air pressure for the thermoforming operation accomplished in the lower mold cavities.

Referring nowto Figure 11,thethermoforming assembly 100 is shown in side plan view with the thermoforming subassembly 120 shown schematically. As evident in the side view, the base 102 is an extended table design having a series of rollers 121 rotatably mounted thereon driving spiked advance chain 122. Chain 122 is an endless chain which engages matching teeth on rollers 121 and further has upwardly extending spikes to grip the sheet material and pull itthroughthethermoforming assembly.

In addition to the chain-roller assembly mounted on bed 102, is a portable oven assembly 123 which may be moved into close proximity underlying and overlying the chain-roller assembly 121-122. The upper heating portion of oven 123 is shown above the rollers and the lower heating section 124 of the oven assembly is shown in phantom beneath the rollers. A sheet mount assembly arm assembly 125 is attached at the back end of base 102 and has upward extending arm mounting the roller spool 126 upon which is rotatably held a large roll of plastic sheeting 127.

Plastic sheet roll 127 feeds a layer of plastic sheet 128 onto rollers 121, and the upwardly extending spikes 122a of the pair of endless chains 122 puncture sheet 128 and secure it in the assembly 100. A motorized power source (Figure 26) drives a pair of geared rollers 129 which in turn, by means of external gear tooth engaged in chains 122, provide motivating power for driving gear chains 122 in a clockwise direction in Figure 11. This in turn, along with the action of spikes 122a, pulls sheet 128 into the heater section 123 of the assembly. Controlling the speed of the motor driving rollers 129 allows control of the heat and speed of sheet 128 through oven 123. At the opposite end of the assembly 100 from roller 126 is an article trimming device 130 comprising an upper movable trimming head 131 which is movable in a vertical direction, and serves to stamp or cut finished articles from the sheet 128 as it exits from the molding assembly 105, 107.

A control panel (Figure 26), utilizing solid state or microprocessor circuitry, controls all of the various mechanical and pneumatic operations of assembly 100 and trimmer 130. This control panel thus is operationally connected to the power drive for geared roller 129, the clamping action of cylinder 110, the compressed air supply to accumulator tanks 113 and 114, the six-way valving system (to be described hereafter), and the trimmer 130, The control panel uses control systems known in the art and available commercially. Preferably all operating parameters of the system can be programmed into the control panel and varied independently to achieve maximum operating efficiency of the entire assembly.The parameters preferably controlled include the speed of sheet 128 which is directly proportional to the speed and timing of drive gears 129, the timing of actuation of cylinder 110,the timing and magnitude of the air pressure surges from tanks 113 and 114, the movement back to the raised position of cylinder 110, and the trimming action ofarticlotrimmer 130, 131.Additional para- meters include the amount of heat generated in oven 123, 124 and the clamping force achieved in the upper mold block assembly 107, 108, 110. Another critical parameter is the residence time of the thermoformed sheet in both the lower mold 105 and upper mold 107. Dependent upon these residence times is the total time that mold 107 is clamped downward on mold 105 by the action of cylinder 110 and arms 108.Other parameters which have a bearing on the residence times, the clamping force, and the temperatures, include the sheet thickness of the thermoplastic material, the composition of the material, and whether or not the sheet material is a single resin or a coextruded sheet of two or more layers of resin bonded together. The forming pressures used would normally be adjusted upward if a thicker sheet is being formed. The optimum forming pressure for each sheet thickness can be determined with a minimum of experimentation by running a few cycles of the system and varying the forming pressures to obtain optimum forming operations.

Figure 12 is a top view schematic diagram of the assembly 100 showing the top of the oven 123 and indicating in phantom the rollers 121 and endless chains 122. Likewise, the top view illustrates the top of the molding block 107 with the actuating cylinder 110 and arms 108 removed to indicate the influx of pressurized air lines into the upper and lower molding blocks. Also the upper portion of trimmer 130 has been removed to show the individual trimming blades 132 for trimming individual articles.

Figure 13 illustrates the molding block assembly 105, 107 with the individual mold units removed.

The mold block assembly comprises a generally elongated rectangular metalic block member 107a and a similarly shaped lower block element 105a.

Each block element has a number of cavities 107b and 105b formed therein. A second set of cavities 107e and 105c are also formed in the upperand lower blocks. These cavities are generally cylindrical or other symmetrical shape and are adapted for receiving individual mold units which are set into the cavities in close-fitting relationship and provided with locking means such as allen-head screws or other type of threaded screw passing through the blocks 105 and 107 and projecting into cavities b and c. The cavities also are provided with air inlet passages d for providing pressurized thermoforming air into the mold units.

Figures 14 through 16 are various views of one of the pre-form mold units adapted for placement in cavity 105b or 105c of lower mold block 105.

Referring specifically to Figure 15, which is a side cross-sectional view of the mold cavity unit, the unit comprises a generally cylindrical body portion 140 shaped for snug fitting engagement in one of the cavities 105c orb. Although a cylindrical body is used for mold 140 for ease of manufacture, other symmetrical shapes such as rectangular, square, triangular, etc. could be utilized for this shape with complimentary shapes of cavities 1 05b and c. An upwardly extending flange portion 141 is integrally formed on body 140 and a lower tubular section 142 is formed on the opposite end from flange 141.

Tubular section 142 has an angular locking groove 143 formed around the periphery thereof for receiving the threaded locking screws passing through mold block 105. Along the top portion of mold 140 is a dished section 144 indented into the body comprising sloping walls 144a and a relatively flat bottom section 144b. One or more circumferential pressure locking grooves 145 are cut into flange 141 and extend around the periphery thereof, facing upward.

An upwardly extending pre-form center section 146 is located generally centrally in dish section 144 and is secured to mold 140 by an extended central bolt 147 which passes through an opening 148 centrally located in dished area 144. Athreaded nut 149 located on the lower threaded end 150 of bolt 147 abuts the lower side 151 of mold area 144b to retain bolt 147 and upper mold piece 146. Bolt 147 has an enlarged diametral head portion 151 opposite the threaded end 150 which abuts and clamps down mold section 146.Preferably the bore passage 152 through the center of mold section 146 is measurably larger in diameter than the diameter of bolt 147 to allow the passage of airtherebetween. Mold section 146 may be formed of a porous metal such as bronze or aluminum particularly manufactured to have communicating pores throughout, or may be made of a solid material such as aluminum or brass having a multitude of air holes drilled therethrough.

Similarly, a set of air passages 153 are drilled or otherwise formed through the dish portion 144b of the mold.

Figure 14 is a bottom view of mold 140 illustrating the retention nut 149, bolt 147,150 and the bottom side 151 of flat portion 144b. Air passages 153 are also illustrated in Figure 14. Figure 16 illustrates a top view of the pre-form mold of Figu res 14 and 15.

Figure 16 illustrates the mold 140, the clamping groove 145, sloped wall 144a, the flat dish portion 1 44b, and the vertical section 146 which is frustoco nical in configuration. Also disclosed is the bolt head 151 which secures the frustoconical upper mold piece 146 to the mold body 140.

Referring now to Figure 17, an alternate mold configuration is illustrated for use in the lower molding block 105. This mold utilizes the "negative" pre-form configuration as opposed to the "positive" configuration of the mold illustrated in Figures 14-16. In this embodiment a mold body 160 is formed of a cylindrical or other regular geometrical cross-sectional configuration adapted for closefit ting engagement in the mold block cavities 1 05c of mold block 105. Body 160 has an outwardly extend ing flange section 161 containing two V-shaped pressure retention grooves 162. The top surface of the mold 160 has a dished section 163 comprising an annular depression passing around the top surface of the mold.The central portion of the mold has a slighly elevated circular shoulder portion 164 defin ing the edges of a "crater-like" negative mold cavity 165. Cavity 165 extends downward substantially the entire length of body 160 and has a cupped bottom end 166 which has a number of air passages 167 formed therethrough. Body 160 also has a lower dished annular area 168 surrounding cupped end 166 and extending upwardly into body 160. A number of air passages 169 penetrate body 160 and communicate upper dished area 163 with lower dished area 168. Body portion 160 has an annular locking groove 160a formed perpherially therearound for engagement of one or more locking screws passing through mold block 105 for locking the mold 160 into the mold cavity.

Referring now to Figure 18, a composite upper mold assembly 170 is illustrated in side cross-sectional view. This assembly is formed of three separate sections for ease of manufacture, but may be formed of a single integral piece of material. Mold 170 preferrably is formed of an easily machinable material such as brass or aluminum, but can be of any acceptable solid heat-resistant material. The mold assembly 170 comprises an upper body section 170a, a lower body section 170b, and an air passage inner ring 170c. Upper section 107a is attached to lower section 170b by means of a threaded cylindrical connection at threads 171. Upper body portion 170a has an inwardly projecting annular shoulder 172 defining a downwardly facing abutment shoulder for ring 170c. Lower body portion 170b likewise has an upwardly facing annular shoulder 173 defining the lower seating place for ring 170c.The locations of shoulders 172 and 173 are arranged such that when threaded connection 171 is tightly engaged, ring 170c is snugly held between the two shoulders. Ring 1 70c is preferably formed of a porous metalic material such as porous bronze or porous aluminum to provide a wide area of airflow capacity. Passages 174 communicate through the wall of upper sleeve 170a into an annular air passage channel 175.

A set of small indentations 170e are formed peripherally around the inside of the mold, in the wall of cavity 178, to form projections on the outer surface of the finished contains. These projections will then be seated in similar indentations in the heads of a spin-welding system to grip the containers and prevent them from slipping in the spin-welder during spin-welding operations thereon.

Upper body section 170a has a second annular locking groove 176 passing circumferentially there- around for engagement by threaded locking means such as bolts or alien screws passing through upper mold block 107. Likewise an upper headspace 177 is formed in the top of mold portion 170a and com municateswith open bore 178 inside the mold by means of numerous air passages 179 bored therethrough. Lower mold section 170b further has an outwardly extending mounting flange 170d formed thereon.

Mold 170 is an upper mold for location in the upper mold block 107 and provides the finished configuration of a container bottom, whereas the molds of Figures 5-8 are pre-form molds used in the formation of an intermediate stage of the article being manufactured.

Figure 19 illustrates in side cross-sectional view one embodiment of an upper mold 180 adapted for snug-fitting engagement in upper mold block 107.

Whereas mold 170 was specifically designed to form a container bottom, mold 180 is adapted for forming a container top portion for later adjoinment with the bottom portion of the container formed in mold 170.

Mold 180 comprises a single integral bottom section 181 having a mounting flange 182 extending peripherially therearound. The internal cavity 183 of mold 180 is formed in the shape of a container top portion.

An annular locking channel 184 is formed peripherially in the wall of mold 180 and provides a groove or recess for a locking screw passing through mold block 107, and engaging in channel 184. A plurality of air relief passages 185 are formed through the wall of mold 180 to allow passage of air trapped in the mold by the thermoformed plastic article. Along the lower portion of mold cavity 183 are located a series of indentations 186 formed in the wall of the mold to provide small protruding shoulders on the molded article for engagement in a spin-welding apparatus.

At the top of the mold assembly 180 is a pair of sliding thread molds 187 and 188 which move together in the directions shown by the arrows to form the upper threaded mold cavity 189 for forming the threaded top of a bottle or other container having a threaded lid. The thread mold sections 187 preferably slide atop mold 180 and generally comprise together a cylindrical threaded mold cavity 189.

Thread molds 187 and 188 may be actuated by any conventional actuating means such as air cylinders, hydraulic cylinders, cammed means, chain drive, etc. When the top portion of the container has been thermoformed in cavity 183 and has hardened sufficiently, upper mold sections 187 and 188 are actuated in the direction opposite to the arrows indicated to disengage the upper thread mold from the finished threaded portion of the container top.

Referring now to Figure 25, an alternate embodiment 190 to the upper mold 180 is disclosed. Mold 190 is similar to mold 180 in all areas except in the thread forming portion at the top of the mold. In the mold of Figure 25, the body section 191 extends all the way to the top of the mold assembly. The thread portion of the container is formed by a spinable cylindrical threadforming sleeve 192 which is rotatably mounted in the upper portion 193 of mold 190.

Thread forming sleeve 192 may be of a cylindrical configuration mounted in close-fitting relationship in a cylindrical opening in mold 190. Sleeve 192 has a cavity 192a formed therein corresponding to the finished threaded configuration of the bottle or container top. A drive shaft 194 is integrally attached at the center line of sleeve 192 on the top thereof. A drive gear 195 is secured to shaft 194 and provides input of rotary motion to sleeve 192. Sleeve 192 has internal thread projections 196 formed in complimentary configuration to the desired thread configuration of a finished container top portion. Mold 190 also has a mounting flange 197 and internal indentations 198 similar to those of mold 180.

Referring now to Figures 21-24, a single three-way valve member 200 is illustrated in various views. In Figure 21 valve 200 comprises a generally rectangular block 201 having a packing or flange plate 202 attached thereto by means such as threads or bolts, and an internal generally hemispherical cavity portion 203. Extending outwardly in a coplaner relationship from three walls of block 201 are flow conduits 204a, 204e, and 204m. These may be of any cross-sectional shape but for ease of manufacture are cylindrical in shape in this instance. In the fourth coplaner side is an opening through which extends a valve member 205 having an upwardly extending shaft 205a and a valve ball 205b.

Figures 22-24 give various views of the valve member 205. A 90 degree valve passage 206 is formed through the center of valve ball 205b and comprises a downwardly extending passage section 206a and laterally extending passage section 206b.

These lateral and downwardly extending passages intersect the wall of ball 205b to form ports 207a and 207b. Valving of the conduits 204a, 204e, 204m is accomplished by rotation of shaft 205a as shown by the rotation arrow of Figure 21. Thus passage 206b is rotated from communication with the conduit 204a supplying pressurized air to the valve 201, 180 degrees, to the position "e" communicating with the exhaust air system. In both instances the passage "m" maintains constant communication with lower bore passage 206a. Thus in the position shown in Figure 21, conduit "m", which is attached to the manifold, is in communication by means of passage 206 with the air exhaust system through conduit "e".

By rotating shaft 205a 180 degrees, the pressurized air can be supplied from conduit "a" to the manifold via conduit "m".

Referring now to Figure 20, a pair of three-way valves such as that disclosed in Figure 21, and indicated as 200 and 210, are shown connected by a single body portion 220. Body portion 220 comprises a main body portion and a single, generally centrally located cavity 221 containing a shaft 230 extending inward and rotably mounted therein. The two valve members 205 of valves 200 and 210 are joined in a single shaft at 231. Input shaft 230 has a helical screw portion 232 formed thereon which engages a complimentary driven gear shaft at 231 joining valve members 205. Thus actuation of shaft 230 results in a simultaneous actuation of valves 200 and 210.

Valves 200 and 210 are placed in 180 degree phase relationship such that when valve 210 is communicating the manifold with the air supply, valve 200 is exhausting the manifold pressure into the exhaust system. Shaft 230 is connected to a power actuating means such as pneumatic or electric motor for simultaneously actuating valves 200 and 210. The actuating means connected to shaft 230 is arranged to provide 180 degrees rotation upon each actuating signal. This simultaneously rotates each of valves 200 and 210 180 degrees such that one side of the valving system is communicating the air supply to the manifold while simultaneously the opposite valving system is exhausting the manifold pressure into the exhaust system.Upon the next cycle of actuation and valves reverse their function and allow the manifold receiving air pressure to then exhaust and the manifold communicating with the exhaust to then be attached to the air supply. The valving system is arranged to provide valving for the two separate air supplies to the upper and lower mold blocks. Thus when the lower mold block is receiving pressurized air such as, for example, through valve 210 in Figure 20, the upper mold block is controlled by valve 200 and is in communication with the air exhaust system. Shaft 230 is preferably supported by a pair of bearing webs or support blocks 234 and 235.

Referring now to Figure 26, a typical schematic layout of the control system, the hydraulic system, and the air pressure system is disclosed. A control panel 300 containing conventional solid state and/or microprocessor circuitry is set up near the container-making apparatus. A high pressure air com pressor301 is provided to supply necessary air pressure to the various air operated elements. A hydraulic pump 302 is provided for supplying high pressure hydraulic fluid to the hydraulically driven elements.

Air compressor 301, by means of main supply line 303 passing through a master valve 304, supplies pressurized airtothermoforming blocks 105 and 107 through supply line 305. Line 305 connects to a four-way connector 306 supplying pressurized air to air pressure regulators 307,308, and 309. Regulator 309 supplies low pressure thermoforming air to supply line 310 which is connected to the low pressure accumulator 114. Regulator 308 supplies high pressure actuating air through high pressure line 311 to the high pressure accumulator tank 113.

Air compressor 301 is selected to supply air pressure as high as 600 PSIG or higher. Air pressure in line 305 preferably is in the range of 400 to 550 PSIG. Regulator 309 supplies low pressure air through line 310 at a pressure in the range of 100 to 200PSIG. Regulator 308 preferably supplies high pressure air in the range of 400 to 550 psig to accumulator 113. The high pressure air supply which accumulates in tank 113 is communicated by line 312 to the three-way valving system 210. From valving system 210 the high pressure supply line 313 leads directly to a tee connection supplying lower mold block 105.

Accumulator tank 114 supplies a high pressure air charge through line 314 to an electrically actuated valve 315, which in turn is in pneumatic connection with three-way valve assembly 200. Valve assembly 200 connects low pressure supply line 316 with a tee connection supplying mold block 107.

Air pressure regulator 307, receiving high pressure air through line 305, provides regulated air pressure to supply line 317 to electrically actuated valve 318 which in turn supplies at desirable times actuating airto air motor 320 via line 319. Actuating motor 320 drives a common shaft 205 between valves 200 and 210.

A second high pressure line 321 leading from air compressor 301 is connected to a fourth air pressure regulator 322 for supplying actuating air via line 323 to various assemblies on the thermoforming apparatus. Line 324 is connected to an electrically actuated sequencing valve 325 which supplies actuating air at desirable times through line 326 to actuating cylinder 327 of trimmer 130. Supply line 323 is also connected to a pair of electrically actuated valves 328 and 329 which supply compressed air to actuate the upper mold block air cylinders and the lower mold block air cylinders. Lower mold block valve 328 provides simultaneous air supplies to the articulated arm cylinders 330L and 330R. Simultaneously, central cylinder 110L receives air pressure through valve 328.

Upper control valve 329 simultaneously provides compressed air to upper mold block articulated arm cylinders 331 and 331 R. Simultaneously air is supplied to central cylinder 110U. This comprises a general description of one method of supplying pressurized air to the various air operated elements of the thermoforming assembly.

Hydraulic pump 302, which may be a motor-driven pump with an electric actuating motor 340 attached thereto, provides hydraulic fluid under pressure to line 341. This line passes through an electrically actuated sequencing valve 342 to provide hydraulic fluid to a double acting hydraulic cylinder 343 via first stage pressure line 344 and reverse stage pressure line 345. Spent hydraulic fluid is returned via line 346 to hydraulic pump 302. Hydraulic fluid is also supplied via line 347 to a mechanically actuated valve 348 which is actuated by movement of upper molding block 107. Valve 348 provides pressurized hydraulic fluid via lines 349 and 350 to augment the air pressure actuation of cylinders 331 and 331 R.

This augmenting hydraulic pressure occurs when mold block 107 reaches the lowermost end of its travel and serves to lock down mold block 107 in a pressurized configuration on block 105 immediately prior to the thermoforming process. Spent hydraulic fluid exits cylinders 331 and 331 R via return lines (not shown) to hydraulic pump 302.

Control panel 300 has various signal leads communicating to the various control actuators in the air pressure system and the hydraulic system. Electrical lead 360 provides an electrical actuating signal to air control valve 318 for actuating the air motor320 on valve system 200,210. A second signal lead 361 conveys an electrical signal from the control panel to the low pressure air supply valve 315. The third signal lead 362 conveys an electrical actuating signal to air pressure valve 325. Signal lead line 363 provides an electrical actuating signal for air pressure valve 328. Signal lead 364 provides an actuating signal for air valve 355 connected to the air drive cylinder 356, which in one embodiment is provided for spinning the top portions of the thermoplastic containers out of their respective mold cavities.Air is supplied to valve 355 via air pressure line 354 which in turn is tied into main air supply line 323.

Another electrical lead line 365 provides a signal from control panel 300 to the mechanical actuating valve 348 in the hydraulic system. The electrical signal transmitted by line 365 provides the shut-off mechanism to end the augmenting hydraulic pressure to the cylinders 331 after the thermoforming operation has been completed. Signal lead 366 provides an electrical actuating signal to air pressure valve 329 for actuating the three upper cylinders in the upper block assembly. Signal lead line 367 connects the control panel with the hydraulic actuating valve 342 for providing two different sources of hydraulic fluid to double-acting hydraulic cylinder 343. A final lead line 368 supplies an electrical signal from the control panel to oven 123 and has a feedback monitor to maintain constant oven temperature during operation of the thermoforming assembly.

Figure 26 illustrates a typical schematic diagram of the air pressure supply system, the hydraulic fluid supply system, and the signal generation system in the electrical control panel. Main electrical power is supplied externally to various parts of the system such as the hydraulic pump motor 340, oven 123, and air compressor motor 301.These sources of electrical power are not indicated in the schematic drawing of Figure 26 since they are easily supplied by one skilled in the art and are indirectly related to the control system.

Control panel 300 has a series of programmable internal timers for generating properly-timed signals to leads 360-368 for proper sequential operation of the aforementioned pneumatic, hydraulic, and electrical valves and controls. The structure and programming of such timers, to the extent not disclosed herein, is considered to be known by those skilled in the computer arts and therefore do not require further explanation.

Thus in typical operation, viewing Figures 10, 11, 12, and 26, a sheet of thermoplastic material such as, for example, PET (Polyethylene Terephthalate) is placed on feed roll 126 and fed onto feed chain 122.

The upwardly extending spikes 122a of feed chain 122 puncture the sides of sheet 128 and pull it onto rollers 121 thereby feeding it into the mold assembly 105, 107. Chain 122 is driven by engagement with a geared roller 129 having a drive gear 370 formed on the shaft thereof. An endless drive chain 371 engages gear 370 and also at its lower end engages a racheting drive gear 372. Racheting drive gear 372 is mounted on a shaft parallel to the shaft of roller 129 and is engaged in a rack 373 to provide rack-and-pinion arrangement between double acting cylinder 343 and gear 372.

The hydraulic fluid through line 345 activates cylinder 343 which drives cylinder shaft 344 and rack 373 to the left. This is a racheting action with respect to gear 372 and no movement of 371 is accomplished. An electrical signal from lead line 367 actuates sequencing valve 342 to switch hydraulic fluid to the opposite end of cylinder 343, thus driving the piston therein to the right, pulling rack 373 back to the right. This results in a geared rotation of gear 372 and a resulting movement in a counter-clockwise direction of endless chain 371. Chain 371 then rotates gear 370 which drives roller 129 and advances the thermoplastic sheet material 128 through the thermoforming assembly. Spent hydraulic fluid form cylinder 343 is returned via hydraulic line 346 to the pump chamber (not shown) of hydraulic pump 302.

During advancement of sheet 128 by means of chain 122, oven 123 receives a continuously#moni- tored signal for generating a controlled heat environment on both sides of sheet 128 as it progresses towards the molding assembly 105, 107. When a sufficient quantity of sheet 128 is brought into alignment between upper and lower molding blocks 105 and 107, double-acting cylinder 343 is reversed in direction, which stops the motion of chain 122 and consequently the motion of sheet 128.

At this time actuating signals are generated to activate the air cylinder system 110,331 to bring the upper mold block 107 down upon lower mold block 105. As mold block 107 contacts mold 105, mold 107 also contacts actuating valve 348 by means of a mechanial contact switch, thus providing augmented hydraulic fluid pressure to cylinders 331 which further locks 107 down on 105. Simultaneously, an electrical signal is generated to the lower cylinders 110,330 to provide upper pressure on lower block 105 to further insure high pressure sealing of mold blocks 105 and 107 together. At this point in time sheet 128, having progressed through oven 123, has been brought into the exact temperature range. This temperature preferably is that which gives the highest melt strength to the sheet above the maximum orientation temperature.Thus at this temperature, any stretching of forming of the sheet will produce no orientation. This is desirable since it will allow the formation of a "pre-form" on the lower pre-form molds 140.

The pre-forms are completed by cooling down into the orientation temperature range during their resi dense time on molds 140. This residence time is previously determined for each particular type of sheet resin utilized and is controlled by the actuation of valves 200,210, and 315.

The shape of pre-form molds 140 is selected so that the final pressureJorming step into the finished product shape (in molds 170 and 180) achieves optimum biaxial orientation in both the radial and axial directions.

In operation, the heated sheet is clamped between mold blocks 105 and 107 and is trapped by pressure grooves such as 145 and 162 between axially aligned upper and lower molds 180 and 140 respectively.

Valves 315 and 200 are actuated to provide a low pressure charge of air at about 160 PSIG into upper mold block 107. This air passes through air passages such as 179, 185, in the upper mold and blows the softened sheet material downward onto pre-form mold 140. This pressure is held during the predetermined residence time of 0.10 to 1.0- second and the mold absorbs heat from the sheet, cooling it down into the orientation range.

Then valves 315 and 200 are closed and valve 210 is actuated. This releases pressure in upper mold 107 and supplies a high-pressure charge of air through line 313 into lower mold block 105. This air preferably is in the range of about 500 PSIG and passes through passages, such as at 153, 167, and 169, in the lower molds. This air then blows the pliant sheet material into the upper molds 170, 180 whereupon it is biaxially oriented, i.e. stretched in the radial and axial directions. Upon contact with the upper molds, the material is further cooled below its thermoplastic temperature, solidifying in the upper molds.

At this time, at the end of the final residence time, the mold blocks are separated. The container sections having threaded neck portions are ejected from molds 180,190 by the sliding or spinning movement of the threaded portion of the mold as previously described. Shortly thereafter, drive rack 373 will engage gear 372 thereby imparting a translational movement to the sheet material, moving it out of the area of the mold blocks and into the trimmer 130.

The container sections are then trimmed from the excess sheet material by downward action of the trimmer and then conveyed into shipping or spinwelding operations. The simultaneous rotation of gears 195 by an endless chain connected to the spinner motor 356 spinsthethreaded portions 192 of the mold assemblies in a direction which would unthread the thermoplastic bottle portion seated therein. Since the container portions are still an integral part of the sheet material, the container portion will not spin with the movement of section 192.

Thus section 192 will be spinning in a counterclockwise direction looking downward form the top.

Since section 192 is entrapped in mold block 107, it cannot move upward off of the thermoplastic container section. Therefore the spinning movement of section 192 forces the container top downward out of the threaded section until it clears that section and falls out of the mold block 107. Needless to say, the timing of spinner 356 is such that the spinning operation does not begin until mold block 107 has been lifted from mold block 105. The separation of mold blocks 105 and 107 is achieved by the reverse action of double acting cylinders 330, 331, and 110.

This in turn is achieved by electronic signals from the control panel to the various air valves controlling the cylinder operation.

The result of applying high pressure airthrough lower mold block 105 to the thermoplastic pre-form material while the material is at its optimum orientation temperature is to force the material both axially and radially upward and outward into the upper mold cavities. This combined radial and axial expansion of the thermoplastic material while at its orientation temperature results in a balanced biaxial orientation of the finished thermoplastic container.

This is very desirable in a thermoplastic container because of the greatly improved tensile strengths in both radial and axial directions plus, it is believed, a significant improvement in barrier characteristics of the material.

After the mold blocks 105 and 107 are separated by the respective air charges and hydraulic movements, the drive cylinder 343 is actuated in the direction which rotates gear 372 counter-clockwise and drives chain 371. This advances chain 122, which in turn moves sheet 128 in the thermoforming apparatus. The movement of sheet 128 transfers a clear unformed section of the sheet to the area between mold blocks 105 and 107 and also passes the thermoformed section of sheet into trimmer 130 to separate the containers from the sheet material.

The separated finished containers may then be removed from the trimmer by conventional conveyance means and passed to a joining machine such as a spin-welder to permanently join the upper and lower container sections together. The excess sheet material from the trimmer may then be recirculated to a regrinder which in turn feeds an extruder for forming new sheet.

Thus the present invention discloses apparatus for quickly and efficiently forming biaxially oriented articles in a single-pass, continuously operating system. The present invention overcomes the difficulties of the prior art which require injection molding of a parison and then a thermoforming of the parison in a separate set of operations. The present invention provides apparatus for forming a pre-form and then immediately thereafter converting the pre-form into the final, biaxially oriented article. The elimination of the injection molding step by the present apparatus reduces the cost and time involved in forming the biaxially oriented article by a large percentage. The present invention provides finished containers and other thermoplastic articles having almost perfectly balanced biaxial orientation as measured by the birefringence values of the finished containers.By utilizing feedback and adjustable microprocessor circuits in the control panel, the present apparatus can be operated by a single operator or by no more than two personnel and can be adjusted during the operation to obtain maximum quality and quantity of the finished articles.

The present invention has been found useful for forming articles from such material as polystyrene and PET. The present invention also is capable of and has formed containers from coextruded sheet material having more than one layer of different resins in the material.

Although specific preferred embodiments of the invention have 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, mold blocks having up to twelve or more cavities instead of four could be utilized. Thus the invention is declared to cover all changes and modifications of the specific examples of the invention herein disclosed for purposes of illustration, which do not constitute departures from the spirit and scope of the invention.

Claims

1. A process for the production of a hollow article comprised of a biaxially oriented thermoplastic resinous material, comprising the steps of: providing a sheet of a thermoplastic material; heating said sheet of thermoplastic material to a temperature above the orientation temperature of the thermoplastic material;; clamping an area of the heated thermoplastic sheet between a first mold half and a second mold half, thefirst mold half containing a pre-form mold surface having a configuration predetermined to provide for a uniform wall thickness of the hollow article to be formed, said surface being at a temperature which is not higher than the orientation tempernature of the thermoplastic material, and the second mold half having a cavity which corresponds to the shape of the hollow article to be produced, forcing the heated thermoplastic sheet by pressure differential into the first mold half against said surface; maintaining the thermoplastic sheet in contact with said surface for a period of time sufficient to bring the thermoplastic sheet to its orientation temperature; and forcing the thermoplastic sheet into the second mold half by means of a pressure differential which is sufficient to cause the thermoplastic sheet to conform with the cavity in the second mold half to form a hollow article, with a force sufficient to substantially, molecularly orient the thermoplastic material in both the longitudinal and lateral directions.

2. A process according to Claim 1, wherein the thermoplastic material is heated to a temperature slightly above its orientation temperature.

3. A process according to Claim 2, wherein the thermoplastic sheet is maintained in contact with said surface for a period of time less than about 1 second.

4. A process according to Claim 3, wherein the thermoplastic sheet is maintained in contact with said surface for a period of time less than about 0.5 second.

5. A process according to Claim 4, wherein the thermoplastic sheet is maintained in contact with said surface for a period of time between about 0.1 and 0.5 seconds.

6. A process according to Claim 5, wherein the thermoplastic sheet is maintained in contact with said surface for a period of time between about 0.2 to 0.4 seconds.

7. A process according to Claim 1, wherein the thermoplastic sheet is forced against the first mold half by a pressure differential of from about 40 to 350 psi.

8. A process according to Claim 1, wherein the thermoplastic sheets is forced into the second mold half by a pressure differential of from about 200 to 1000 psi.

9. A process according to Claim 8, wherein said pressure differential for forcing the thermoplastic sheet into the second mold half is produced by injecting compressed air into the first mold half between said surface and the thermoplastic sheet.

10. A process according to Claim 1, wherein the thermoplastic material selected from a polyester, a polyolefin, a polyvinyl aromatic, a nitrile group-containing polymer, an acrylic polymer, a polyamide or a vinyl ester.

11. A process according to Claim 1, wherein the thermoplastic sheet is comprised of a plurality of layers of different polymeric material.

12. A process according to Claim 11, wherein the thermoplastic sheet comprises at least one layer of polyethylene terephthalate and at least one layer of ethylene vinyl alcohol.

13. A process according to Claim 1, wherein a plurality of hollow articles are simultaneously formed from a single thermoplastic sheet.

14. A process according to Claim 13, further comprising the step of separating the plurality of hollow articles from one another.

15. A process according to Claim 14, wherein at least one of said plurality of hollow articles comprises a container top portion and at least one of said plurality of hollow articles comprises a mating container bottom portion.

16. A process according to Claim 15, further comprising the step of uniting said container top portions and said container bottom portion to produce a container.

17. A process according to Claim 16, wherein said container comprises a carbonated beverage bottle.

18. A process according to Claim 16, wherein said uniting step comprises friction welding the container portions together.

19. Apparatus for forming biaxially oriented hollow thermoplastic articles from a sheet of material in a continuous operation, said apparatus comprising: an elongated horizontal bed; an endless-chain drive system along said bed, a heating oven arranged for heating at least a portion of said bed; a lower mold block at one end of said bed, and having at least one mold cavity formed therein; an upper mold block above and in alignmentwith said lower mold block, and having at least one mold cavity therein aligned vertically with a mold cavity in said lower mold block; pressure actuating means between said upper and lower mold blocks for clamping said mold blocks together with sufficient force to hold a gas pressure of up to at least about 600 PSIG therebetween;; a pre-form gas pressure system connected to a mold cavity of one of said mold blocks and arranged to inject thereinto a change of pressurized gas in the range of about 100 to about 200 PSIG; first timing means arranged to maintain said pre-form gas pressure a predetermined pre-form residence time; a final-form gas pressure system connected to a mold cavity of the other of said molding blocks and arranged to inject thereinto a charge of pressurized gas in the range of about 200 to about 1000 PSIG; second timing means arranged to maintain said final-form gas pressure a predetermined final-form residence time; valving means having actuating means thereon for controlling said preform and final-form gas pressure systems; and, adjustable control means for controlling said valving means and said residence times.

20. ThearticleJorming apparatus of claim 19 wherein said first residence time is about 0.10 to about 1.0 seconds and said valving means comprises a first, normally open valve, and a second, normally closed valve, said valves being operably interconnected, and coactuable by a single actuating means.

21. The article-forming apparatus of claim 19 further comprising a compressed air supply system for supplying said gas pressure to said actuating means and said pressure systems, valving means for controlling said air supply system, and adjustable valve control means for actuating said valving means.

22. The article-forming apparatus of claim 21 wherein said valve control means comprises a control panel having electronic timing means therein and electric signal leads connected to said valving means.

23. The article-forming apparatus of claim 19, 20, 21, or 22 further comprising hydraulic pressure-augmenting means between said upper and lower mold blocks for increasing the clamping pressure thereon.

24. The article-forming apparatus of claim 19, 20, 21, or 22 further comprising gas surge tanks in said gas pressure systems for providing a volumetric charge of air at a relatively constant pressure.

25. The article-forming apparatus of claim 19, 20, 21, or 22 wherein said upper and lower mold blocks each comprise from about 2 up to about 20 mold cavities, each said cavity containing a removable mold therein having air passage means therethrough.

26. The article-forming apparatus of claim 19,20, 21, or 22 wherein said upper and lower mold blocks each comprise from about 2 up to about 20 mold cavities, each said cavity containing a removable mold therein having air passage means therethrough, the cavities in one said block equalling in number and being vertically aligned with the cavities of said other block.

27. The article-forming apparatus of claim 19,20, 21, or 22 wherein said upper and lower mold blocks each comprise from about 2 up to about 20 mold cavities, each said cavity containing a removable mold therein having air passage means therethrough, the cavities in one block comprising pre form cavities which are equal in number and vertically aligned with the cavities in said other block which are final-form cavities; said final-form cavities being divided into at least one upper container-section-forming cavity and at least one lower container-section-forming cavity adapted to form upper and lower container sections capable of being spin-welded together.

28. The article-forming apparatus of claim 27 wherein said air passage means comprises a strong porous metal.

29. The article-forming apparatus of claim 19,20, 21, or 22 further comprising means for trimming thermoformed articles from thermoplastic sheet, and spin-welding means for welding together cylindrical sections of thermoplastic articles.

30. Athermoforming system for forming hollow, biaxially oriented articles from thermoplastic resin sheet material, said system comprising: a mold block assembly having a first mold block and a second mold block arranged to be tightly clamped together; at least one pre-form gas-pressure mold in one of said mold blocks; at least one final-form gas-pressure mold in the other of said mold blocks arranged for alignment with said pre-form gas-pressure mold; means for moving said mold blocks together and apart; means for holding said mold blocks together against pressures therein of up to 1000 PSIG; a first gas-pressure supply system connected to said final-form gas-pressure mold and arranged to provide pre-selected and timed volumetric charges of pressurized gas to said mold, in the range of from about 100 to about 300 PSIG;; a second gas-pressure supply system connected to said pre-form gas-pressure mold and arranged to provide pre-selected and timed volumetric charges of pressurized gas to said mold, in the range of from about 250 PSIG to about 1000 PSIG;

31. Thethermoforming system of claim 30furth- or comprising means for advancing thermoplastic resin sheet material between said mold blocks in periodic incremental lengths.

32. The thermoforming system of claim 31 further comprising heating means for heating said sheet material to a temperature above its orientation temperature but below its liquid melt temperature prior to its advancement between said mold blocks.

33. The thermoforming system of claim 30 or claim 32 further comprising a control system having signal generating means and adjustable variable timing means; said control system adapted for controlling said moving means, said holding means, said advancing means, said heating means, and said gas-pressure supply systems.

34. A thermoforming system for forming biaxially oriented hollow articles from resinous thermoplastic sheet material, said system comprising: a pair of opposed mold blocks each having at least one mold cavity therein; one of said mold blocks having a pre-form mold therein with gas passages therethrough; the other of said mold blocks having a final-form mold therein with gas passages therethrough; a low-pressure gas supply connected by low-pressure valve means to said final-form mold and adapted to supply a predetermined volumetric charge of pressurized gas in the range of about 100 to about 250 PSIG; a high-pressure gas supply connected by high pressure valve means to said pre-form mold and adapted to supply a predetermined volumetric charge of pressurized gas in the range of about 250 to about 1000 PSIG; closing and opening means on said opposed blocks; ; clamping means on said blocks adapted to clamp said blocks together sufficiently to seal against an internal pressure therein of at least about 600 PSIG; means for moving resinous sheet material in periodic increments between said molding blocks; means for preheating resinous sheet material to a temperature between its orientation temperature and its liquid melt temperature prior to the sheet advancing between said mold blocks; means for establishing predetermined residence times in each of said mold blocks; and, means for automatically sequentially operating said low-pressure and high-pressure valves, said opening and closing means, said clamping means, and said sheet moving means.