US20020110612A1

US20020110612A1 - System and apparatus for injection molding articles with reduced crystallization

Info

Publication number: US20020110612A1
Application number: US09/877,680
Authority: US
Inventors: Robert Schad; Matthew Tai; Ali Mortazavi; Gordon Elliott; James Rodrigues; Barrie Drysdale
Original assignee: Husky Injection Molding Systems Ltd
Current assignee: Husky Injection Molding Systems Ltd
Priority date: 2001-02-09
Filing date: 2001-06-08
Publication date: 2002-08-15
Also published as: US20030091681A1; US20050230880A1; JP2002240109A; US6942480B2

Abstract

An injection molding system for the formation of molded articles with reduced crystallinity comprising a laser cutoff subsystem for the removal of an elongated vestige or sprue from the molded article.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to copending application, entitled “Method and Apparatus for Cutting Plastics Using Lasers”, filed contemporaneously herewith and incorporated herein by reference and Provisional Patent Application serial No. 60/267,859 filed Feb. 9, 2001, also incorporated herein by reference.[0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to injection molding systems and apparatus for the production of molded articles. More particularly, the invention relates to systems and apparatus specifically adapted for injection molding articles of substantially amorphous polyethylene terephthalate and similar materials, whereby the gate vestige is removed by a laser cutting system which produces a molded article with reduce crystallization.

2. Summary of the Prior Art

The use of polyethylene terephthalate (hereinafter referred to as “PET”) and similar materials as the materials of choice in the formation of numerous injection molded articles is well known in the art. For example, in the bottle and container industry, the blow molding of injection molded PET preforms has gained wide acceptance, and is experiencing strong growth. Among the reasons for this is the fact that PET and similar materials offer a wide range of desirable properties. Specifically, PET materials generally evidence high strength, good clarity, and low gas permeation characteristics. Further, PET materials are comparatively easy to recycle. Accordingly, they are desirable for use in retail packaging applications.

PET and similar materials, however, present molders with significant processing problems. These problems may be at least partially explained by the fact that these materials are considered to be what is known in the art as “crystallizable” materials. By this it is meant that the randomly oriented polymer chains of the amorphous phase of the material may be caused to form a highly ordered, crystalline structure in a controllable manner. This may be accomplished either by mechanical stretching of the material so as to cause an ordered orientation of its molecules and the formation of stress induced crystals, or by controlling the temperature of the material over time in a manner which induces crystal formation and growth. More particularly, as the temperature of the material is increased from the ambient, the material passes through a number of states. Specifically, the material in its so-called “glassy” (or rigid) state at ambient temperature upon heating will sequentially pass through a glass transition temperature range, a crystallization temperature range, and a crystal melting temperature range, before it reaches its molten state.

In the glassy state, existing crystals in the material are stable, and additional crystals cannot form because the molecules are too sluggish. This is to say that the molecules of the material lack the requisite energy to move about sufficiently to induce the creation of the intermolecular bonds necessary for crystal formation. In the glass transition temperature range (which for PET is typically between about 175.degree. F. and about 185.degree. F.), the material transforms from its glassy state to a rubbery state.

In the rubbery state, crystals tend to form and grow. The rate of this crystal formation and growth is both time and temperature dependent. More particularly, the rate of crystal formation and growth follows a substantially parabolic curve on a temperature versus time graph. It, therefore, will be recognized by those skilled in the art that for PET materials the rate of crystal formation and growth typically increases with temperature from about 185.degree. F. up to about 350.degree. F., and thereafter decreases to substantially zero at about 480.degree. F. Further, the extent of crystal formation and growth depends significantly upon the length of time during which the material is permitted to reside at any given temperature within its crystallization temperature range.

The crystal melting temperature range for PET extends between about 480° F. and about 490° F. Above about 490° F., the material exists in its molten state.

It is to be understood that the foregoing is a generalization of the crystallization properties of PET and similar materials. Variations in the properties of the particular material under consideration (such as its intrinsic viscosity, its diethylene glycol content, its water content and/or its comonomer or other additive content) may alter the melting point of the material, the crystallization behavior of the material, or both.

Furthermore, the breakdown product acetaldehyde is known to be generated in significant amounts whenever PET material is in a molten state. It is also well understood that slight changes in the melt temperature will significantly effect the rate of acetaldehyde generation. Since acetaldehyde is a potent flavorant, its presence in the melt material must be minimized during the injection molding of food or drink containers (or preforms therefor). If this is not done, detectable changes in the flavor or aroma of foods packaged in such articles (or in containers made from such preforms) may be induced. Heretofore, acetaldehyde minimization has been accomplished by maintaining the melt temperature as low as possible, while still allowing substantially clear articles (or preforms therefor) to be formed by so-called “runnerless” injection molding apparatus.

Injection molded preforms adapted for subsequent blow molding into a finally desired container form should consist of mostly amorphous material. This permits the preform to be blow molded into a desired shape easily and with a minimum of reheating. It also avoids the formation of undesireable cracks or a whitish haziness in the finished article/preform caused by the presence of excessive crystallized material therein. Further, the article/preform should have an acceptable acetaldehyde level, and be free from contaminants or defects.

In systems and apparatus for the “runnerless” injection molding of articles/preforms of the type alluded to above, a mold and a molten material transport means are commonly provided. The mold typically includes a first cavity extending inwardly from an outer surface of the mold to an inner end, an article formation cavity, and a gate connecting the first cavity to the article formation cavity. The gate defines an inlet orifice in the inner end of the first cavity, and an outlet orifice which opens into the article formation cavity.

The means for transporting the material extends from a melt source to the vicinity of the inlet orifice of the gate. These means typically include an elongated bushing residing at least partially within the first cavity. This bushing defines an elongated, axial passageway therethrough which terminates at a discharge orifice. A “gate area”, therefore, is defined by the assembled mold and bushing between the discharge orifice of the bushing and the outlet orifice of the gate. Ideally, this gate area is the portion of the system/apparatus in which the transition of the material from the molten phase present in the “runnerless” injection apparatus to the glassy phase of the completed article occurs during the time period between sequential “shots” of material.

Specifically, during the injection of a “shot” of molten material (i.e., melt), the melt flows from the discharge orifice of the bushing, through the gap between the discharge orifice of the bushing and the inlet of the gate, through the gate, and into the article formation cavity of the mold. Since the temperature of the melt is maintained above its maximum crystal melt temperature in the bushing, and the temperature of the mold is maintained well below the minimum glass transition temperature of the material, the majority of each shot cools quickly to its glassy state in the article formation cavity of mold. This results in the preform containing low crystallinity levels (i.e., an article made up of substantially amorphous PET or other similar crystallizable polymer) because the material temperature does not remain within its characteristic crystallization range for any appreciable length of time.

At the end of each “shot”, however, injection pressure commonly is maintained on the melt for between about 1 to 5 seconds in order to assure that the melt is appropriately packed into the article formation cavity of the mold. Thereafter, the injection pressure on the melt is released, and the article is allowed to cool in the mold for between about 10 to 15 seconds. Subsequently, the mold is opened, the article is ejected therefrom, and the mold is reclosed. The latter steps take on the order of about 5 to 10 seconds. It will be understood, therefore, that for correct system operation the temperature of the melt material must transition in the gate area of the system/apparatus during the time interval between successive material “shots” between its molten phase temperature and its glassy (rigid) phase temperature in a controlled manner.

Accordingly, thermal control of the temperature gradients in the material located in the gate area between successive “shots” of molten material is critical both to the prevention of stringing or drooling of melt material from the gate, and to the prevention of gate freeze-off. In addition, a failure to isolate the majority of the crystallized melt material formed during this transition within the vestige which extends outwardly from the completed article ejected from the mold may be detrimental not only to the efficiency of subsequent blow molding operations, but also to the quality of the final blow molded article for the reasons mentioned above.

To accomplish this thermal gate control, the art has heretofore adopted two alternative approaches. In the first of these alternatives, a mechanical melt shut off mechanism is provided by what is known as a “valve gate”. In the other alternative, the axial length of the gate is increased so as to ultimately form a vestige extending outwardly from the article/preform which is substantially longer than the comparatively short vestige normally resulting from “runnerless” injection molding operations.

The valve gate utilizes a pin which is axially movable in the bushing passageway. In a first retracted position, this pin allows melt material to flow through the bushing, into the gate area, and ultimately into the article formation cavity of the mold. In a second extended position, however, the distal end of the pin closes off the gate area, and thereby shuts off the flow of melt material therethrough. Specifically, the distal portion of the valve pin either may seal the inlet of the gate, or may substantially fill the volume defined by the gate so as to accomplish melt shut off.

This mechanism has several advantages. Principle among these is the preclusion of the potentially detrimental presence of melt material in the gate area between successive “shots”. The absence of melt material adjacent to the gate outlet prevents stringing of melt material between the gate and the vestige. Drooling of melt material from the gate between “shots” also is prevented for the same reason. In addition, the resulting vestige (if any) is of acceptably short length, and is composed primarily of substantially amorphous material. The latter result is achieved because the vestige is substantially thermally isolated from the melt transport means upon extension of the valve pin. Consequently, the vestige (if any) cools primarily under the influence of the surrounding gate portion of the mold which, as mentioned above, is maintained well below the minimum glass transition temperature of the material.

The elongated vestige alternative, on the other hand, evolved from the fact that the portion of the mold forming the gate walls in a conventional hot runner system is inadequate for controlling the crystallization of PET and similar crystallizable polymeric materials in the gate area during the time interval between successive material “shots”. More particularly, it will be understood that the metal (typically steel) forming the gate walls in a conventional hot runner system is located between the inner end of the first cavity of the mold adjacent to the inlet orifice of the gate and the portion of the article formation cavity of the mold adjacent to the outlet orifice of the gate. In such a system, the quantity and thermal conductivity properties of the metal defining the gate are not adequate to both (1) effectively withdraw heat from adjacent melt material in the article formation cavity of the mold in a manner which assures its amorphous nature in the completed article, and (2) at the same time effectively participate in the required melt material crystallization control in the gate area.

Accordingly, the axial length of the gate in some cases has been increased by artisans in the field of this invention so as to provide a gate wall structure capable of performing both of the above functions simultaneously. This, in turn, has resulted in the presence of an elongated sprue, or vestige, projecting from the finished article or preform.

The latter alternative has the advantage that the machine/mold designer can be relatively sure that substantially all crystallized material in the completed article/preform will be contained within the vestige. The resulting article/preform, however, may be adversely effected by the presence of the elongated vestige during the blow molding operation. Specifically, cracks may form at the vestige/article interface during the blow molding operation thereby ruining the blow molded article.

It is within this approach that significant effort has been employed to produce an injection molded article with an elongated vestige, and during post-processing, remove the elongated vestige. The prior art has seen numerous attempts at employing various cutting means including mechanical cutter means and grinding. These methods have generally proved unsuccessful due to low aesthetic quality and surface imperfections that are formed during the cutting process.

There exists a need for an improved injection molding system that allows for the use of an elongated sprue on a preform for reduced crystallinity that is subsequently cut off in a high speed manufacturing environment.

SUMMARY OF THE INVENTION

The primary objective of the invention is to provide an injection molded preform made of PET or similar material exhibiting reduced crystallinity through the use of an elongated sprue.

Another object of the invention is to provide a system and apparatus for removing an elongated sprue from an injection molded article by laser cutting.

A further object of the invention is to provide an improved injection molded preform with an improved surface finish in the area of the cut-off elongated sprue.

Still another feature of the present invention is to provide an injection molding system and apparatus that comprises an automatic recovery and recycling system of the cut-off elongated sprue material.

The foregoing objects are achieved by providing an injection molding machine which comprises a plurality of preform mold cavities for the formation of molded articles therein, the mold cavities comprise an elongated vestige feature whereby substantially all crystallinity occurs within the elongated vestige. Following the molding process, the preforms are placed in a conveyor like apparatus so that the elongated vestige of each preform is passed inline with at least one laser cutting apparatus. The energy of the laser is adjusted so that the elongated vestige is severed from the preform, thereby resulting in an improved preform with improved crystalline properties and acceptable surface finish in the area of the removed elongated vestige. The cut off elongated vestige is captured by a recycling system and remelted so that waste is minimized.

BREIF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified isometric view of an injection molding machine in accordance with the present invention; [0031]
FIG. 2 is an isometric view of the underside of the shuttle table in accordance with the present invention; [0032]
FIG. 3 is an enlarged isometric view of the laser cutting station with an array of preforms; [0033]
FIG. 4 is a partial detail view of the laser cutting station; [0034]
FIG. 5 is a detailed cross-sectional view of a typical preform [0035]
FIG. 6 is a top plan view of the laser system layout. [0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 5 which shows a blank [0037] 108, also termed preform, of a substantially amorphous thermoplastic material, preferably PET, having a mouth portion 122, a substantially conical portion 124 extending from the mouth portion, a substantially cylindrical portion 126, and a region of material 128 which, when forming the blank 108 into a container, forms the bottom of the container. The blank 108 has a central cavity 130 with a substantially cylindrical upper portion 132 and a substantially cylindrical lower portion 134, whose circumference is smaller than that of the upper portion 132. The transition between the upper and lower portions 132, 134 of the central cavity is a substantially conical transition portion 136. The cylindrical lower portion 134 is closed at its bottom, which is bulging outwards and comprises an elongated vestige or sprue 109. It is this elongated vestige 109 that will be severed from the preform 108 because it exhibits high crystallinity.
The [0038] preform 108 thus serves as starting material in the making of a blow-molded container for example a reusable bottle for beverages.
The [0039] mouth portion 122 has a threaded portion 138 and an annular gripping portion 140. The material forming the mouth portion 122 is designated A in FIG. 5. The conical portion 124 encloses the substantially cylindrical upper portion 132 of the central cavity of the blank 108. The cone of the conical portion 124 results from an increase of the thickness of this portion towards the bottom of the blank 108. The material of the blank 108 forming the conical portion 124 is designated B in FIG. 5.
The proximal part, with respect to the bottom of the blank [0040] 108, of the substantially cylindrical upper portion 132 of the cavity 130 is defined by a wall having a substantially uniform wall thickness in all parts of the cylindrical portion 126. The region of the substantially cylindrical portion is marked C in FIG. 5.
The region of [0041] material 128, which after reshaping of the blank 108 is intended to constitute the bottom of the container, has an increased wall thickness in the region of the transition portion 136 of the cavity of the blank 108, and maintains this wall thickness substantially throughout the entire region of the substantially cylindrical lower portion 134 of the cavity. The wall thickness of the blank 108 thereafter decreases in the closed bottom of the blank to have its minimum thickness in a central region of material 142 in the bottom of the blank 108. Reference D indicates the material of the blank 108 which in the resulting container is reshaped to form part of the bottom of the container, while reference E indicates the material of the blank 108 which substantially retains its shape when forming the container.
Referring now to FIG. 1, an [0042] injection molding system 10 according to the present invention is generally shown. The injection molding system 10 is comprised of an injection molding machine 12, a transport subsystem 14, a pick and place robot 16, a laser cutting station 18 and an inspection station (not shown). All of these subsystems work together to form a high speed manufacturing process for the production of injection molded articles, for example PET preforms 108.
In the preferred embodiment, the [0043] injection molding machine 12 is an index type machine with a rotary turret 36 for the production of PET preforms 108. As one skilled in the art will recognize however, any type injection molding machine may easily be adapted for use with the present invention.
[0044] Injection molding machine 10 generally includes a rotary turret 36 with a plurality of movable mold halves 37 a 37 d, a stationary mold half and platen 34 and injection unit 32, all positioned on base 30.
[0045] Injection molding system 10 may be used for molding a variety of different types of articles and accordingly, is not limited for use with any particular type of article. Preforms are referred to throughout this description by way of example only.
While the rotary turret [0046] 36 is shown throughout this description as rotatable on a horizontal axis, and this is the preferred embodiment, it is feasible that a similar design of a movable turret block providing the clamping action may be provided which is rotatable on a vertical axis. Accordingly, this invention is not considered limited to the horizontal axis feature.
As shown in FIG. 1, rotary turret [0047] 36 is preferably longitudinally movable on base 30 via a set of bearings blocks 43 attached to the bottom of a pair of turret fittings 46. Base 30 includes linear bearings 44 which engage bearing blocks 43 and counteract upward forces and tipping forces that may act on the turret block assembly. Rotary turret 36 is rotatable preferably by a rotational drive 41 in communication with belts and pulleys, preferably an electric servo drive motor and preferably on a horizontal axis H through arcuate sectors preferably of substantially 90.degrees. Preferably, the rotational drive is connected via a belt drive 39 to axis H for rotating the rotary turret 36, as shown in FIG. 1, while the electric servo drive motor is preferably mounted on one of turret fittings 46 extending from base 30.
As shown in FIG. 1, rotary turret [0048] 36 includes a plurality of movable mold halves, i.e. movable mold halves 37 a-37 d each of which includes a plurality of mold cores 45 a-45 d, respectively, each set having at least one mold core, adapted for engagement with a set of mold cavities 40, each set including at least one mold cavity and located in stationary mold half and platen 34. Preferably, four movable mold halves or faces 37 a-37 d are provided on rotary turret 36, although any number supportable by the size of the rotary turret 36 can be used. Sets of mold cores 45 a-45 d are adapted to be rotated into horizontal and vertical alignment with sets of mold cavities 40.
Referring still to FIG. 1, rotary turret [0049] 36 includes sets of ejector pistons or stripper rings 33 a-33 d, and a system for the operation thereof, which operate on sets of mold cores 45 a-45 d and strippers positioned on movable mold halves 37 a-37 d, respectively. Accordingly, sets of ejector pistons or stripper rings 33 a-33 d are positioned within rotary turret 36 and parallel to sets of mold cores 45 a-45 d and perform the function of stripping the mold cores of finished molded articles, for example, preforms, such as those shown in FIGS. 4 and 5. Each movable mold half 37 a-37 d and platen 34 includes at least one ejector piston in each set 33 a-33 d for stripping finished articles from sets of mold cores 45 a-45 d. For the detailed design of the ejector piston or stripper ring system for use with sets 33 a-33 d, reference is made to U.S. Pat. No. 5,383,780, issued Jun. 24, 1995, to the assignee of the present invention, for incorporation by reference of a design of the ejector piston or stripper ring system, particularly column 4, line 29, to column 7, line 6, and FIGS. 1-8. Preferably, the ejector piston or stripper ring system is actuated via the hydraulic services supplied to the rotary turret 36, as discussed below. The hydraulically actuated ejector piston or stripper ring system actuated by on board hydraulic services is the preferred design, however, other designs may be used.
Rotary turret [0050] 36 is movable backward and forward along linear bearings 44 on base 30 via piston/cylinder assemblies 38 positioned in stationary mold half and platen 34, as shown in FIG. 1. Preferably four piston/cylinder assemblies 38, as shown in FIG. 1 are used which are positioned in the corners of stationary mold half or platen 34. Each piston/cylinder assembly 38 is attached to tie bars 47, respectively, which tie bar 47 acts as the piston shaft. Accordingly, tie bars 47 extend from the piston/cylinder assemblies 38 and are connected at an opposite end to rotary turret 36. In order to move rotary turret 36 backward and forward relative stationary mold half and platen 34, pressurized fluid is forced into cylinders assemblies 38. The side of the cylinder assemblies 38 in which pressurized fluid is forced against, determines the direction in which rotary turret 36 moves relative stationary mold half and platen 34, that is, either into an open or closed position. Tie bars 47 pass through the turret fittings 46 and are attached thereto via retaining nuts.
Services S, shown in FIG. 1, are provided to rotary turret [0051] 36 via a rotary union 31. Accordingly, as rotary turret 36 rotates, services S are continuously supplied to the movable mold halves 37 a-37 d. Such services S include the supply of electricity, pressurized fluid, cooling fluids, and hydraulic fluids, etc. For using these services, rotary turret 36 also includes the required circuitry and control valves (not shown) on board and movable and rotatable with the turret block.
Injection unit [0052] 32, preferably in the form of a reciprocating screw injection unit, is connected with stationary mold half and platen 34 positioned on base 30 for providing melt to the mold cores for molding. Injection unit 32 is preferably movable into and out of engagement with stationary mold half and platen 34 by means of carriage cylinders (not shown) on rollers and hardened ways, similar to as described above for use with rotary turret 36.
Still referring to FIG. 1, the [0053] transport subsystem 14 comprises an inside and outside track 48 a and 48 b mounted to the base 30 and running from under the rotary turret 36 to a position of easy access by the pick and place robot 16. A motor 50 is attached to one end of the inside track 48 a which is in communication with a shaft 54 which runs between the inside and outside track 48 a and 48 b. Attached at each end of the shaft 54 is a pair of belts 52 which run the entire length of the tracks 48 a and 48 b. Attached to the inside surface of each track 48 a and 48 b is a second pair of linear bearings 56 which interface with a plurality of bearing blocks 60 (FIG. 2) rigidly affixed to a shuttle table 58. Each belt 52 is attached to the shuttle table 58 such that the shuttle table 58 is operatively positioned (back and forth) through the use of the motor 50 along tracks 48 a and 48 b. In this arrangement, the shuttle table is controllably positioned beneath the rotary turret 36 to accept the molded preform 108. Once the shuttle table 58 is filled with preforms 108, it is operatively positioned at a far end of the tracks 48 a and 48 b for easy access by the pick and place robot 16.
Referring now to FIG. 2, the shuttle table [0054] 58 comprises a horizontal surface 62 with a plurality of holes 64 arranged to interface with the movable mold halves 37 a-37 d of the rotary turret 36. Inserted in each hole 64 is a spacer 66 sized to accept the molded preform 108. In the preferred embodiment, the spacers are made from a soft plastic material to minimize the scratching of the preform 108 that may occur during the handoffs from the shuttle table 58.
In the preferred embodiment, the shuttle table [0055] 58 must translate upwardly to interface with and catch the plurality of molded preforms 108 when they are released by the rotary turret 36. To accomplish this motion, a servo-motor 68 is mounted beneath the horizontal surface 62 and in communication with a pair of ball screws 70. Each ball screw 70 is attached to opposite ends of the horizontal surface 62 and grounded to an inside and outside support 74 a and 74 b. A second belt 72 runs between the ball screws 70 such that the servo-motor 68 controls both ball screws 70 for raising and lowering the horizontal surface 62 of the shuttle table 58.
Once the shuttle table [0056] 58 has received a plurality of preforms 108, the table 58 moves away from the injection molding machine 12 and aligns with the robot 16. The robot 16 comprises a frame 80 which carries a pick-up table 84 along a trackway 82. The pickup table 84 interfaces with the shuttle table 58 with a plurality of air operated fingers 86 which are inserted into each preform 108. The pick up table 84 is moved under precise control in a manner similar to the way the shuttle table 58 is moved and therefore won't be further described herein. In the preferred embodiment, once the air operated fingers 86 are positioned inside the preforms 108, air is communicated to the fingers 86, causing them to expand and grab on the inside surface of the preforms 108. There are myriad methods for picking up the preforms 108, and the forgoing is just an example of one of these methods and should not be read to limit the scope of the invention.
Once the plurality of [0057] preforms 108 are retrieved by the pick up table 84, the table translates to a distal location so that the preforms are aligned with a singulator 88. The singulator 88 is a flat plate with a continuous serpentine groove 89 machined therein. The serpentine groove 89 is designed to accept a plurality of different preform sizes. Once the preforms 108 are properly seated in the groove 89 by the pick up table 84, the air in the fingers 86 is removed and the plurality of preforms 108 are released into the groove 89. Now the preforms 108, which were in individual holes, have been placed into the continuous groove 89 allowing them to be easily slid in a linear fashion to be picked up by an inline, single file conveyor 90.
Referring to FIGS. 3 and 4, the [0058] preforms 108 travel down the conveyor 90 to the laser cutting station 18. The laser cutting station 18 comprises a rotary track 92 which accepts the preforms from the conveyor 90 and spins them in a circular fashion past a plurality of laser beams 103. The rotary track 92 comprises a circular holder 96 with a plurality of pockets to accept the preforms 108 from the conveyor 90. The rotational speed of the rotary track 92 is matched with the linear speed of the conveyor 90 so that preforms 108 are quickly and easily transferred into the pockets of the circular holder 96. As the rotary track 92 rotates (and before the preform aligns with the first laser beam 103), a segmented top plate 94 is lowered into contact with the top surface of the preform 108 and forces the bottom of the preform 108 to interface with a lower shield 98. In this arrangement, the elongated vestige 109 is now properly aligned with the plurality of laser beams 103 as they travel around with the rotary track 92. The elongated vestige 109 travels past each laser beam 103 in rapid succession, thereby severing the vestige 109 from the preform 108. The now severed vestige 109 drops into a reclamation bin 112, where the vestige 109 will be later re-melted and recycled.
The [0059] shield 98 is specifically designed to both protect the main body of the preform 108 from damage by the laser and also maintain a given length of remaining vestige. Testing has shown that without the shield 98, energy from the laser 102 can cause inadvertent damage to the body of the preform 108. In addition, international quality inspection criteria dictate the required length of any remaining vestige. Using the shield 98 insures the laser cuts the elongated vestige 109 at the proper location.
Referring to FIG. 6, the various optical components which comprise the laser cutting setup are generally shown. Two [0060] lasers 102 are each aligned such that the laser beam passes first through a splitter 106 a and 106 b respectively. The splitters 106 a and 106 b are designed to reflect half of the laser beam power at 90 degrees from the entering beam, and allow the other half of the laser beam power to continue on to a mirror 118 a and 118 b where the remaining laser beam power is also reflected at 90 degrees from the entering beam. In the preferred embodiment, the optimum laser cutting set up was found to be two 500W CO₂lasers focused inline with the elongated vestige 109. In this arrangement, four laser beams, each with approximately 250 watts of power are transmitted to a bank of focusing lenses 104 a-104 d. Positioners 120 a-120 d are attached to each lens 104 and allow for minute adjustments to the focused laser beam for machine set. In the preferred embodiment, a CO2 laser operating at a predetermined pulse, for example around 100 kHz, and with a focused beam width of a predetermined diameter, for example about 0.05-0.25 mm, was found to work best.
A buy product of the laser cut is a very fine dust which tends to accumulate on the outside surface of the preform. The [0061] shield 98 helps to prevent this dust from accumulating on the preform and a brush 115 is mounted in the path of the shield 98 to wipe the dust off. Alternatively, or in combination, forced air could be blown over the preforms as the cut is made, or an electrical charge could be placed on the preforms to repel the flying plastic dust.
The unload [0062] conveyor 116 accepts the preforms 108 in a linear fashion after they have been cut and transfers them to an inspection station (not shown) where each preform is inspected for compliance with quality control standards.
It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. For example, the exact placement and splitting of the laser beams is susceptible to myriad variations, and any such variation is fully contemplated by the present invention. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims. [0063]

Claims

What is claimed is:

1. An injection molding machine for the production of a molded article exhibiting reduced crystallinity properties comprising:

an injection unit for the communication of a molten material to at least one mold cavity;

said mold cavity forming said molded article with a sprue thereon;

a transport subsystem for the communication of said molded article from said mold cavity to a laser cutting station;

said laser cutting station comprising at least one laser aimed at a predetermined position of said sprue, wherein said laser severs said sprue from said molded article.

2. The injection molding machine of claim 1 further comprising a rotary turret, said rotary turret comprising a plurality of mold halves whereby each mold halve is successively positioned for the receipt of said molten material from said injection unit for the formation of said molded articles.

3. The injection molding machine of claim 1 further comprising a robot for the movement of said molded articles from said transport subsystem to a serpentine track where each molded article is passed by said laser station in a single file line.

4. The injection molding machine of claim 3, further comprising a conveyor attached to an end of said serpentine track for the communication of said molded articles to a rotary table, said rotary table moving said molded article past said laser station at a predetermined rotational speed.

5. The injection molding machine of claim 4, wherein said predetermined rotational speed is variable.

6. The injection molding machine of claim 4, wherein said rotary table further comprises;

an array of holders for the removable receipt of said molded articles;

a plate to hold said molded articles in said holders;

a shield with a plurality of holes for insertion of said sprue before said molded article is moved past said laser cutting station;

a motive force for passing each of said molded articles passed said laser cutting station at a predetermined rate.

7. The injection molding machine of claim 1, wherein said transport subsystem further comprises:

a shuttle table, said shuttle table comprising a plurality of holes for the receipt of said molded articles from said mold cavities;

a track running from under said injection molding machine to a predetermined position away from said injection molding machine;

said shuttle table running in a back and forth motion on said track to align with said mold cavities at a first distal end of said track, and align with a robot at a second distal end of said track;

said robot in communication with said shuttle table for the removal of said molded articles from said shuttle table to a conveyor;

said conveyor moving said molded articles passed said laser cutting station.

8. The injection molding machine of claim 7, wherein each of said plurality of holes includes

a spacer for reduction of surface blemishes on said molded articles that may occur during the insertion of said molded articles in said plurality of holes.

9. The injection molding machine of claim 7, wherein said robot further comprises:

a frame for the suspension of a trackway over said second distal end of said track;

a pickup table suspended from said frame riding back and forth on said trackway selectably aligning with said shuttle table and said conveyor;

a plurality of fingers extending from said pickup table, selectably inserted into said plurality molded articles, each finger expandable by the communication of a fluid to said fingers for gripping each said molded article.

10. The injection molding machine of claim 9, wherein each of said plurality of fingers comprises an elastic bladder in communication with an air supply.

11. The injection molding machine of claim 1, wherein said molded article is a PET preform.

12. The injection molding machine of claim 1, wherein said laser cutting station further comprises at least one splitter for the formation of at least two laser beams aimed to be in communication with said sprue of each said molded article.

13. The injection molding machine of claim 1, wherein said laser comprises a CO₂laser.

14. The injection molding machine of claim 1, wherein said laser has a power output of at least 500 watts.

15. The injection molding machine of claim 1, wherein said laser has a predetermined power output required to achieve a predetermined cut quality.

16. The injection molding machine of claim 1, wherein said laser emits a beam having a predetermined diameter.

17. The injection molding machine of claim 16, wherein said predetermined diameter is between 0.05-0.25 mm.

18. The injection molding machine of claim 1, wherein said laser cutting station further comprises:

two lasers each emitting a beam of at least 500 watts of power;

two splitters in the path of each said beam, each said splitter creating two beams for a total of four beams, wherein each said splitter communicates a first of said beams to a first location coincident with said sprue as it travels along said conveyor and further communicates a second of said beams to a mirror;

said mirror communicating said second beam to a second location coincident with said sprue as it travels further along said conveyor.

19. The injection molding machine of claim 1, wherein said sprue is elongated.

20. The injection molding machine of claim 1, further comprising a flowing fluid in communication with said molded articles to reduce the deposition of vaporized plastic created by said laser on said molded article.

21. The injection molding system of claim 1, further comprising an electrical charge applied to said molded articles to repel the deposition of vaporized plastic created by said laser on said molded article.