CA1077662A

CA1077662A - Apparatus for forming a laminated plastic article

Info

Publication number: CA1077662A
Application number: CA261,617A
Authority: CA
Inventors: Donald G. Sauer
Original assignee: National Can Corp
Current assignee: National Can Corp
Priority date: 1975-09-22
Filing date: 1976-09-21
Publication date: 1980-05-20
Also published as: JPS5256164A; CH619395A5; IT1070708B; NL7610476A; JPS5938092B2; FR2324435A1; GB1540496A; DE2642390A1; GB1540495A

Abstract

PROCESS AND APPARATUS FOR FORMING
A LAMINATED PLASTIC ARTICLE
Abstract of the Invention There is disclosed a process and apparatus for thermoforming laminated hollow articles including a plurality of processing stations wherein a thermoplastic material heated to a plastic state is selectively deposited area-wise on a sheet of thermoplastic material and wherein such resulting laminate portion of thermoplastic materials is positioned proximate to a female mold of a thermoforming apparatus including a plug assist for the subsequent forming of the laminated hollow articles.

Description

~77662 Field of the Invention This invention relates to a process and apparatus for molding hollow plastic articles from a sheet or strip of thermoplastic material, and more particularly to a novel process and apparatus for molding a laminated hollow plastic article.

sackground of the Invention Many processes have been advanced for manufacturing a hollow plastic article formed of a plurality of layers whereby the thus formed product is provided with an inner wall of a plastic material having certain desired properties and an outer wall of a plastic material exhibiting other desired properties. For example, in U.S. Patent No. 3,122,598 to Berger, there is disclosed a process for forming decorative plastic articles using injection molding techniques. In U.S. Patent No. 2,710,987 to Sherman, there is disclosed a method and apparatus for forming laminated plastic articles using extrusion blow molding techniques. In U.S. Patent No. 3,719,735 to Valyi, there is disclosed a process for blow molding a barrier container from a composite parison which is formed by injecting a thermo- ~
plastic material over a preformed liner. While such processes ~ -have produced acceptable hollow articles exhibiting such desired properties, such processes have not attained extensive commercial success since the equipment required to perform the processing steps is expensive, costly to operate, with excessive time cycles.
While thermoforming techniques have been used to form hollow articles utilizing a sheet of matexial comprised of one or more layers of plastic materials, none of such processes have been used commercially to form hollow articles exhibiting container-like properties, e.g. substantial resistance to oxygen permeation, resistance to carbon-dioxide diffusion, capable of storing products under moderate pressure over extended periods of time, and the like. Thermoforming techniques have been utilized to form a hollow product from a laminated sheet of material, however, such processes suffer from the inherent disadvantage of selective recovery of each thermoplastic material after thermoforming to permit effective recycling of component thermoplastic materials.
This invention is particularly concerned with thermo-forming techniques wherein a web or sheet of thermoplastic material is first softened by heat and then formed or shaped while in this stretchable plastic state by being drawn or pressed against the contours of a mold or die under the influence of a fluid pressure differential. The former techniques may be exemplified by the application of pressure within a pressure box produced by compressed air or the like, to press the softened material against the contours of a male mold while producing a low pressure from within the male mold. The later technique is exemplified by applying a vacuum from within a female mold while allowing atmospheric pressure (or a pressurized fluid) to shape the heat softened thermoplastic material against the surface of a female mold. For many purposes, a combination of these two techniques is preferred since such combination provides greater versatility and better control in the forming operation.

Statement of the Invention An apparatus for manufacturing a hollow article ~-having a plurality of layers, which comprises supply means for a sheet of thermoplastic material, means for selectively depositing a flowable thermoplastic material on said sheet of thermoplastic material, means for distributing said deposited thermoplastic material on said sheet of thermoplastic : . ' : , :

~077662 material, blow mold means for forming said hollow article utilizing a fluid medium, and means for removing said thus formed hollow article from said apparatus.

Br _f Description_of the Drawings The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment thereof in conjunction with the accompanying drawings with like reference numerals designating like parts in all figures in which:
Figure 1 is a schematic side elevational view, partially in section, of an apparatus embodying the principles of the present invention with some accessories omitted for greater clarity;
Figure 2 is a schematic top plan view of the apparatus of Figure l;
Figure 3 is a fragmental enlarged sectional elevational detail view taken substantially along the line 3-3 in Fig. 1 at a first station of the apparatus, showing means for the selective deposition of a mass of heated thermo-plastic material on a heated thermoplastic sheet;
Figure 4 is an enlarged fragmentary vertical sectional elevational detail view taken at a second station of ; the apparatus of Fig. 1, showing means for shaping the deposited thermoplastic mass on the thermoplastic sheet;
Figure 5 is an enlarged fragmentary vertical sectional elevational detail view of a third station of the apparatus of Figure 1 showing means for preforming, initial molding of the composite of thermoplastic materials;
Figure 6 is an enlarged fragmentary vertical sectional detail view of a fourth station of the apparatus, taken substantially along the lines 6-6 in Figure 1, for forming the hollow article from the composite of the thermoplastic . ~ - - :

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materials; and Figure 7 is a fragmentary enlarged vertical sectional detail view of a fifth station of the apparatus of Figure 1, adapted for cooling the formed article prior to ejection from the apparatus.

Detailed Description_of the Invention It will be appreciated that the type of thermo-plastic or thermoelastically deformable material employed in the present process is generally determined by the economics and duty to which the hollow article will eventually be placed.
Among the many thermoplastic resins suitable for various purposes and adaptable to thermoforming are high-impact poly-styrene, polybutadiene, styrenebutadiene blends or copolymers, polyvinylchloride and related vinyl polymers, polyallomers, nylon, formaldehyde polymers, polyethylene, polypropylene, nitrocellulose, cellulose acetate, cellulose proprionate, cellulose acetate, acetate butyrate, polymethymethacrylate, ethyl cellulose, benzyl cellulose and ester-esters of cellulose.
Referring now to Figures 1 and 2, there is illustrated a novel thermoforming assembly, generally indicated as 10, embodying the principles of the present invention and including a preforming section and a forming section, generally indicated as 12 and 14, respectively. It will be understood by one skilled in the art that the thermoforming assembly 10 is provided with the usual motor and timing assemblies including the usual instrumentation, timing circuits, safety features and the like for automatic and continuous operation of the assembly;
however, such assemblies are not shown in the interest of clarity. The preforming section 12 includes thermoplastic sheet supply roll assembly, heating stations, and operation stations A, Br and C, generally designated as 16, 18, 20, 22 and 24, respectively. The forming section 14 includes molding and - , .

cooling stations D and E, generally indicated as 26 and 28, respectively, as more fully hereinafter described.
The supply roller assembly 16 includes a shaft 30 journalled for rotation on supports 32 positioned on a foundation F. On the shaft 30, there is wound a sheet or strip of thermo-plastic material 34 selected for the specific properties to be imparted to one wall of the product. The heating section 18 is provided with a source of actinic electromagnetic radiation, such as infra-red lamp 36, as a means for softening the sheet of thermoplastic material prior to indexing into subsequent stations of the preforming section 12. For some applications, the heating section 18 is required, however it is generally contemplated that for most thermoforming operations, the latent heat of the molten thermoplastic material to be deposited on the sheet of thermoplastic material will be sufficient to heat areawise the underlying sheet of thermoplastic to a temperature at which said sheet may be thermoformed thereby eliminating the necessity of any such heating station. A sheet support assembly including drums 38 mounted on shafts 40 journalled for rotation in support trunnions 42 is positioned on foundation F. A chain belt 44 is mounted in an endless manner about the drums 38 to support the sheet of thermoplastic materials during passage through the preforming stages with retaining elements 46 being provided on the links forming the chain belt 44 to ensure for positive movement of the sheet 34 through the preforming section 12 of thermoforming assembly 10.
Referring now to Figure 3, station A (rotated by 90 from that of Figure 1) includes an extrusion assembly, a place-ment assembly and a support assembly, generally indicated as 50, 52 and 54 respectively. The extrusion assembly 50 is comprised of a barrel 56 having a cylindrically-shaped chamber 58 in which an extruder screw 60 is centrally disposed for forcing a plastic material therethrough, as known to one skilled in the art. The -.~ ~

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extrusion assembly 50 includes an L-shaped extrusion nozzle 62 suitably threaded within the barrel 56 and extending downwardly to a point above the thermoplastic sheet 34. The end of the nozzle 62 is machined to engage a gate plate 64 having an orifice 66 for controlling the amount of a heated thermoplastic material 68 selectively deposited on the sheet 34. For reciprocal movement, the gate plate 64 is mounted to a fluid cylinder 70 by a rod member 72.
The placement assembly 52 includes a chase 74 mounted to cylinder rods 76 associated with fluid cylinders 78.
The chase 74 is provided to establish a selective area portion of the thermoplastic sheet 34 on which the second thermoplastic material 68 is deposited in a plastic state. The chase 74 is provided with a suitable passage 80 for the circulation of an indirect heat transfer fluid to control the temperature thereof to aid in regulating the temperature of the material 68 prior to indexing of the thermoplastic sheet 34 to the next station. The support assembly 54 is comprised of a support shoe 82 including fluid passages 84 for the circulation of an indirect heat transfer media therethrough to control the temperature of the sheet 34 in station A. For reciprocal movement, the support shoe 82 is mounted to a fluid cylinder 86 by a cylinder rod 88.
Referring now to Figure 4 (station B), there is illustrated a guiding assembly, a shaping assembly, and a support assembly, generally indicated as 90, 92 and 94, respectively. The guiding assembly 90 is similar to the placement assembly 52 of Station A, and is comprised of a chase 96 including a passageway 98 for circulating an indirect heat transfer fluid. The chase 90 is reciprocally mounted to fluid cylinders 100 by cylinder rods 102.
The shaping assembly 92 includes a stamper foot 104 having an indirect heat transfer fluid conduit or passage means 106 and is mounted for reciprocal movement to a fluid cylinder 10'77662 108 by a rod 110. The peripheral configuration of the stamper foot 104 conforms closely to the inner configuration of the chase 96 to minimize escape of the second thermoplastic material 68 therebetween. Additionally, the contacting surface of the stamper foot 104 may be specially configured to distribute the second thermoplastic material 68 in a selected (or uneven) manner dependent on the shape of the product article with regard to the eventual distribution of thermoplastic materials.
The support assembly 94 includes a support shoe 112 having passages 114 for the circulation of an indirect heat transfer fluid therethrough. For reciprocal movement, the support shoe 112 is mounted to a fluid cylinder 116 by a cylinder rod 118.
Station C, referring to Figure 5, is provided with an initial molding assembly, generally indicated as 120, com-prised of a forming die assembly and a forming plate assembly, generally indicated as 122 and 124, respectively. For reciprocal movement the forming die assembly 122 includes a forming die 126 mounted to a fluid cylinder 128 by a cylinder rod 130. The forming plate assembly 124 is comprised of a forming plate 132 mounted for reciprocal movement to a fluid cylinder 134 by a cylinder rod 136. Both the forming die 126 and forming plate 132 are provided with passages 138 and 140, respectively, for circulating an indirect heat transfer medium therethrough.
The forming portion 14 of the assembly 10 of the present invention, referring to Figure 1, is comprised of a blowing station 26 ~station D) and the cooling station 28 (station E) mounted at circumferentially spaced locations on a rotary table assembly, generally indicated as 150, including a rotary table 152.
The blowing station 26, referring now to Figure 6, includes blow mold halves 154 mounted for horizontal movement to a vertically movable platen 156 in a manner known to one ;.. ~, .

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skilled in the art. Beneath the mold halves 154, there are disposed thread plates 158 mounted to fluid cylinders 160 by cylinder rods 162.
Each operating position of the rotary table 152 includes a piston 164 disposed within a chamber 166 in the rotary table 152 and is retained therein for vertical movement by a plate 168. Conduits 170 and 172 are formed in the rotary table 152 in fluid communication with the chamber 166 on either side of the piston 164. The piston 16~ is formed with a centrally disposed cylindrical passageway 174 within which an extendible core pin 176 is positioned for reciprocal movement. The core pin 176 is provided with a channel 178 and orifices 180 to permit the introduction of an expansion medium into the preform, as hereinafter more fully described. The end of the core pin 176 is provided with a conically-shaped support element 182.
To the upper surface of the piston 164, there is affixed a cylindrical sleeve 190 on which is mounted a top plate 192. A plate 194 including an edge abutment 195 and having a ring of resilient material 196 positioned thereon, is mounted for slidable engagement with the sleeve portion 190 of the plate 168. In a relaxed or non-operating mode, the resilient material 196 assumes a substantially cylindrical shape. However, in a compressed mode when the sleeve 190 is lowered, the material 196 is caused to be forced radially outwardly against the thermo-plastic materials to cause the thermoplastic materials to be forced against the thread plates 158 to thereby form a threaded portion 198 of the formed container 200, as more -fully hereinafter described.
Station 28, referring to Figure 7, is similar to station 26 as discussed with reference to Figure 6, except that ~ -the mold components constituting the system for forming the hollow article remain at station 26. At each station 28, there .
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is provided a retaining rod 204 having a conically-shaped end support element 206 and operatively associated with a fluid cylinder 208. As illustrated in Figure 2, four holding stations 28 are provided on the rotary table assembly 150.
Means may be provided for the removal of the formed container or article 200 from the table 152 onto a conveyor assembly (not shown) for subsequent inspection, filling, packaging and the like of the formed container.
In operation, the thermoplastic material 34 in sheet form is unwound from the supply roll assembly 16 in response to the movement of the chain 44 in accordance with the operational cycle of the machine, determined, inter alia, by the size and thickness of the article being formed, the types of thermoplastic materials, and the like. The sheet of thermo-plastic material 34 is heated to a plastic state during passage under the source 36 of actinic electromagnetic radiation.
The sheet 34 is indexed to station A whereat the chase 74 is caused to be lowered into contact with the sheet 34 by the action of the fluid cylinders 78. Simultaneously (or before or after), the support shoe 82 is raised to a contacting position with the underside of sheet 34 by actuation of the fluid cylinder 86.
Extrusion of the second thermoplastic material is initiated by placing orifice 66 of the gate 64 in co-axial alignment with the extrusion nozzle 62 with the screw 60 of the extrusion assembly 50 being caused to move forward in a manner known to one skilled in the art. After deposition of a controlled quantity of thermo-plastic material 68, the gate 64 is displaced in response to actuation of the fluid cylinder 70 to arrest the flow of material. The chase 74 and support shoe 82 are returned to an initial portion and the sheet of thermoplastic material 34 including thermoplastic material 68 is indexed to station B.

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- ~077662 At station B, referring to Figure 4, the support shoe 112 is raised in response to the actuation of the fluid cylinder 116 to a point whereat the support shoe 112 is in con-tact with the underside of the sheet of thermoplastic material 34. The chase 96 is lowered in contacting relationship with the sheet 34 in response to the actuation of the fluid cylinders 100 whereupon the stamper foot 104 is lowered by actuation of the fluid cylinder 108 to a point whereat the stamped foot causes the thermoplastic material 68 to be distributed over a select portion of the sheet 34. After a predetermined period, the stamper foot 104 is raised, the support shoe 112 is lowered and the chase 96 is moved vertically upwardly to an initial mode -~ -by successive actuation of fluid cylinders 108, 116 and 100, respectively, after which the sheet of thermoplastic material 34 is indexed to station C.
At station C, referring to Figure 5, the forming die 126 is moved vertically downwardly in response to fluid cylinder 128, with the forming plate 132 being essentially simultaneously raised by actuation of fluid cylinder 134 to form a preform 210. Upon completion of a predetermined time interval, the forming die 126 and the forming plate 132 are returned to a starting mode by actuation of fluid cylinders 128 and 134, respectively, and the sheet of thermoplastic material indexed to station D. -.
Referring to Figure 6, illustrating Station D of -the forming section of the apparatus 10, after indexing of the preform 210 into position, the die halves 154 and thread plates 158 are caused to be moved into operative association. Pressurized fluid is introduced into conduit 170 and thus into the portion of the chamber 166 above the piston 164 to cause the piston 164 to be moved vertically downward together with the sleeve 190 and plate 192 to cause the resilient material 196 to move outwardly ' ,, ., . ,' ' . "' ~" ' .. ~' ~' ' : , ~77~iZ

against the laminated plastic material thereby causing a portion of the preform 210 to be forced against the thread dies 158.
Thereafter, the blow pin 176 is caused to be moved vertically upwardly, together with the introduction of a pressurized fluid media through the passageway 178 and orifices 180 formed in the blow pin 176 causing the preform to be stretched and blown against the die 154. Pressurization is maintained for a predetermined time interval, after which pressurization is reduced to a level to support the blown article 200 against collapsing or further extension after separation and removal of the mold halves 154 and thread plates 158. After blowing, a compressed fluid is introduced into conduit 172 with conduit 170 being vented to the atmosphere to cause the piston 164 to return to an initial position whereby the resilient material 196 is returned to an uncompressed state and thereby assumes a substantially cylindrical configuration. The thread plates 158 are retracted by actuation of cylinders 160 and the mold halves 132 separated and returned to an initial position whereupon the rotary table 152 is indexed sixty degrees. It is to be noted that sheet 36 is cut at an angle represented by line 218 in Figure 2 by an assembly (not shown) during the processing functions of Station D to permit portions of the sheet 34 to revolve on the table 152 until final trimming and removal - of the article whereupon the residual material is removed and passed to subsequent processing operations (not shown) for reclamation of the thermoplastic materials.
At station E, the conically-shaped retainer 204 is lowered into contacting relationship with the bottom of the container 200 by actuation of the cylinder 208 with such contacting relationship being maintained through three subsequent indexes. At the last index, the hollow article 200 may be alternately trimmed from the residual material by increasing the pressure in conduit 172 to cause the piston 164 to be raised ~.. . .

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to an extent that the upper portion thereof is above the level of the rotary table 152 at which point trim dies 212, referring to Figure 7, are caused to be moved against each other by fluid cylinder assemblies 214 operatively associated with cylinder rods 216.
It will be understood by those skilled in the art that other methods and apparatus may be used to trim the product article either as part of the hereinabove described apparatus or downstream of product removal.
It will be understood by those skilled in the art that a plurality of stations A and B may be successively provided to form a laminate of more than two thermoplastic materials prior to formation of the preform at station C. For the formation of certain hollow articles, station C may be omitted. Additionally, while the invention has been described with reference to the formation of the hollow article in a female mold, it is contemplated that forming may be effected about a male mold.
The rotatable forming assembly, it is contemplated, may be used to form single layered hollow articles from a heated sheet of thermoplastic materials. As hereinabove mentioned, the latent heat of the molten thermoplastic material is preferably generally sufficient to heat the underlying sheet of thermoplastic material to a temperature for thermoforming (i.e. by the time such area reaches the molding station) thereby eliminating any requirements for heating such underlying sheet ; prior to selective deposition.
Numerous modifications and variations of the invention are possible in light of the above teachings and therefore the invention may be practiced otherwise than as particularly described.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for manufacturing a hollow article having a plurality of layers, which comprises:
supply means for a sheet of thermoplastic material;
means for selectively depositing a flowable thermoplastic material on said sheet of thermoplastic material;
means for distributing said deposited thermo-plastic material on said sheet of thermoplastic material;
blow mold means for forming said hollow article utilizing a fluid medium; and means for removing said thus formed hollow article from said apparatus.

2. The apparatus as defined in Claim 1 wherein said means for selective deposition includes an extruder means for depositing said flowable thermoplastic material.

3. The apparatus as defined in Claim 1 wherein said means for selective deposition includes a chase for restraining the flow of said moldable thermoplastic material.

4. The apparatus as defined in Claim l and additionally comprising die means for molding a preform from said materials prior to formation of said hollow article in said mold means.

5. The apparatus as defined in Claim 1 and additionally comprising means for supporting said sheet of thermoplastic material during selective deposition and distribution.

6. The apparatus as defined in Claim 1 and additionally comprising a second means for selectively depositing another moldable thermoplastic material and a second means for distributing said second moldable thermoplastic material.

7. The apparatus as defined in Claim 1 wherein said mold means is provided on a rotary table.

8. The apparatus as defined in Claim 1 wherein heating means are provided to raise the temperature of said sheet prior to selective deposition.

9. The apparatus as defined in Claim 1 wherein said mold means includes an extendible blow pin.

10. The apparatus as defined in Claim 9 wherein said mold means includes a support member for clamping a bottom portion of said hollow article with said extendible blow pin during cooling of said then formed hollow article.