WO1996019330A1

WO1996019330A1 - Transforming physical characteristics of a moldable material

Info

Publication number: WO1996019330A1
Application number: PCT/US1994/014605
Authority: WO
Inventors: Jean-Pierre Ibar
Original assignee: Thermold Partners L.P.
Priority date: 1994-12-19
Filing date: 1994-12-19
Publication date: 1996-06-27
Also published as: AU1552895A

Abstract

A molding process is provided for molding a solid product from a moldable material in a mold. At least two spaced-apart reciprocating devices (50, 52) are provided which are in communication with the moldable material, and each includes a drivable member reciprocable within a chamber. The reciprocating devices (50, 52) exert a stress tensor prior to, and in the course of, solidifying. This stress tensor is created by reciprocating the drivable member with respect to another drivable member in accordance with a predetermined program (58), in a manner selected from: (a) at the same frequency, at a different amplitude and out of phase, (b) at the same frequency, at a different amplitude and in phase, (c) at a different frequency and at the same amplitude, and (d) at a different frequency and at a different amplitude. The moldable material is cooled to form a solid product during packing.

Description

6/19330 PCIYUS94/1

1 -

"TRANSFORMING PHYSICAL CHARACTERISTICS OF A MOLDABLE MATERIAL"

Field of the Invention This invention relates to a means for transforming the physical characteristics of a moldable material during a molding process. Particularly, the present invention relates to molding processes wherein a stress tensor is exerted onto a moldable material prior to, and in the course of, it solidifying.

Background of the Invention

In the past few decades, there have been many improvements in classical molding technologies. One such improvement pertains to the control of certain fabrication variables prior to and/or during the molding process in order to modify the end-use performance of the finished product. Such techniques enable skilled practitioners to improve the physical characteristics of the finished product by enabling them to control the material's morphological structure. Examples of methods and apparatuses which can transform the physical characteristics of a material, by controlling the influence of rheological parameters prior to and/or during a molding process, are set out in U.S. Letters Patent 4,469,649, U.S. Letters Patent 4,925,161, U.S. Letters Patent 4,994,220 and U.S. Letters Patent 5,074,772. U.S. Patent 4,469,649 is incorporated herein by reference. 0 PCI7US94/14605

According to the ABSTRACT of U.S. Patent 4,469,649, the invention therein relates, at least in part, to a process and apparatus which mod¬ ifies the morphological structure of a molded material by varying temperatures during- the molding process simultaneously with at least one other rheological parameter such as hydrostatic pressure, shear stress, mechanical vibration (frequency or amplitude), dielectric vibration (frequency or amplitude) for dielectric materials and electromagnetic properties for metallic materials. Notwithstanding the disclosure in U.S. Patent 4,469,649, the U.S. Patent Office granted U.S. Patent 4,925,161, U.S. Patent 4,994,220 and U.S. Patent 5,074,772, each of which relates to a process which modifies the morphological structure of a molded material by varying temperatures during the molding process simultaneously with shear stress. The difference between U.S. Patent 4,469,649 and the other aforementioned patents is that the latter group of patents disclose specific methods in which to apply a shear stress. As is well known, the molding industry is constantly looking for different ways in which to control the morphological structure and/or physical properties of a moldable material prior to and/or during the molding process. This need has prompted the discovery of the molding processes disclosed herein.

Summary of the Invention

One object of this invention is to provide a means for transforming the physical characteristics of a moldable material during a molding process.

Another object of this invention is to provide a molding processes wherein a stress tensor is exerted onto a moldable material prior to, and in the course of, it solidifying.

Yet another object of this invention is to provide a molding process which controls certain fabrication variables prior to and/or during the molding process in order to modify the end-use performance of the finished product.

These and other objects are achieved through the advent of a process for molding a solid product from a moldable material. In this process, a moldable material is supplied into a mold until said mold's cavity is filled. Then, at each of at least two spaced-apart regions of the moldable material, a reciprocating device is provided.

Each reciprocating device is in communication with the moldable material. Moreover, each reciprocating device includes a drivable member reciprocable within, and relative to, a chamber.

The reciprocating devices are designed to manipulate the moldable material by exerting a stress tensor thereon prior to, and in the course of, it solidifying within the mold's cavity. This manipulation is created by recipro- eating the drivable member of each reciprocating device, with respect to another drivable member, in a manner selected from the group consisting of: (a) at the same frequency, at a different amplitude and out of phase, (b) at the same fre¬ quency, at a different amplitude and in phase, (c) at a different frequency and at the same amplitude, and (d) at a different frequency and at a different amplitude. Moreover, while the moldable material is being manipulated in accordance with one of the aforementioned manners, the frequency, amplitude and/or phase shift of the drivable members can be constant, variable and/or intermittent.

The temperature of the mold can be increased and/or decreased prior to, and in the course of, the material contained therein solidifying. This allows the monitoring of the cooling rate during the cooling of the moldable material to change. It also allows the internal temperature of the mold to be set at the time of feeding the moldable material therein.

After the stress tensor has been applied in accordance with a predetermined program, but before the moldable material solidifies within the mold, a packing force is exerted thereon. As this packing force is applied, the moldable material is solidified. The solid product is then extracted from the mold's cavity.

The morphological structure of the resulting solid product (e.g., percentage crystallinity, orientation, free volume content, texture, etc.), from which the physical properties depend (e.g., tensile strength, tensile modulus, etc.), is different from that of a product made from the identical process but which does not employ one of the manipulation techniques disclosed herein. Therefore, by varying the parameters of the present invention, skilled artisans can have a greater degree of control over the resulting product's structure and/or properties.

Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art upon reading the specification and the appended claims which follow. A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily ascertained as the invention becomes better understood by reference to the following detailed description, when considered in connection with the accompanying figures briefly described below.

Brief Description of Drawings FIGURE 1 represents a schematic illustration of a conventional injection molding apparatus and mold.

FIGURES 2 to 4, inclusive, illustrate schematic illustrations of a manifold including one embodiment of a reciprocation means interposed between an injection molding apparatus and a mold in accordance with the present invention.

FIGURE 5 is a detailed illustration of the manifold illustrated in Figures 2 to 4, inclusive. FIGURE 6 is a cross-sectional side elevation of the manifold illustrated in Figure 5 taken along line 6-6.

FIGURE 7 is a general schematic of one embodiment of the invention illustrating a system designed to control a reciprocation pattern in accordance with the present invention. FIGURE 8 represents a schematic illustration of an injection molding apparatus which can be used when practicing the present invention.

FIGURE 9 represents a schematic illustration of a portion of a hot-runner molding system which can be used when practicing the present invention.

FIGURE 10 is a front view of the portion of the hot-runner molding system illustrated in Figure 9.

FIGURE 11 represents a schematic illustration of a portion of a cold-runner molding system which can be used when practicing the invention. FIGURE 12 is a front view of the portion of the cold-runner molding system illustrated in Figure 11.

FIGURE 13 represents a schematic illustration of a portion of a cold-runner molding system which can be used when practicing the present invention, and which employs more than two reciprocating drivable members. FIGURE 14 is a front view of the portion of the cold-runner molding system illustrated in Figure 13.

FIGURE 15 is a graph which illustrates the action of two drivable members acting at different frequencies and amplitudes on a melt.

Definitions

The term "frequency" as used herein refers to the number of times a particular drivable member oscillates per second.

The term "amplitude" as used herein refers to the maximum longitudinal distance traveled by a drivable member during half of an oscillation cycle.

The term "phase" as used herein refers to the relative motion of one drivable member with respect to another which is oscillating at the same frequency.

As used herein, the term "stress tensor" refers to a matrix which comprises two essential components — a compressive force and a shear stress. Detailed Description of the Invention

The present invention relates to a process for molding a solid product from a moldable material.

In this novel process, a moldable material is supplied into a mold. The mold is designed in such a manner that, at each of at least two spaced-apart regions of the moldable material, there is a reciprocating device.

Each reciprocating device includes a drivable member which is reciprocable within, and relative to, a chamber. These reciprocating devices are designed to manipulate the moldable material prior to, and in the course of, its solidifying within the mold's cavity by exerting a stress tensor on the moldable material.

This manipulation is created by reciprocating the drivable members of each reciprocating device, with respect to one another, in a specific manner.

After the manipulation has been applied in accordance with a predetermined program, but before the moldable material solidifies, a packing force is exerted thereon.

This packing force is maintained until the material solidifies . Once solidified, the solid product is extracted from the mold's cavity.

It is also within the purview of this invention to exert packing forces on the moldable materials prior to and/or intermittently throughout the reciprocation pattern. Packing forces can be exerted on the moldable material by the action of any one of the reciprocating devices and/or the means by which the molten material is introduced into the reciprocating devices (e.g., an injection screw). When practicing this invention, any suitable method can be used to supply the moldable material into the mold. The preferred method will depend, in part, upon the specific molding technique employed. Moreover, if desired, at least a portion of the moldable material can be supplied into the mold by at least one reciprocating device. The reciprocating devices of the present invention generally include a drivable member which is reciprocable within, and relative to, a chamber. This chamber is designed to be in direct or indirect communication with the moldable material, when the material is confined within the mold's cavity. The drivable members and their respective chambers can have any configuration which enables one to practice this invention. Examples of suitable drivable members include, without limitation, oscillating pistons (see, e.g., Figure 2), oscillating injection screws (see, e.g., Figure 3) and the like, and/or any combination thereof. In order to practice this invention, there must be at least two such reciprocating devices present. Moreover, these reciprocating devices must be at spaced-apart regions of the mold's cavity.

In the embodiment of the invention wherein at least a portion of the moldable material is supplied into the mold by a reciprocating device, conven- tional methods can be used to supply the moldable material into the reciprocating device's chamber. Thereafter, the drivable member is moved in such a manner that it expels the moldable material from its chamber and forces this expelled material into the mold's cavity.

As indicated above, after the mold's cavity is completely filled with a moldable material, the material can, optionally, be packed into the mold. Thereafter, the reciprocating devices are employed to manipulate the moldable material in accordance with the present invention. This manipulation is per¬ formed prior to, and in the course of, the moldable material solidifying within the mold. As also indicated above, while the moldable material is reciprocated in accordance with a specific pattern, it is within the purview of this invention to, optionally, exert a packing pressure thereon.

In accordance with the present invention, the manipulation of the moldable material is performed by reciprocating the drivable member of each reciprocating device, with respect to any other drivable member, in one of four different manners. These are as follows: (a) at the same frequency, at a differ- ent amplitude and out of phase, (b) at the same frequency, at a different amplitude and in phase, (c) at a different frequency and at the same amplitude, and (d) at a different frequency and at a different amplitude. Moreover, while the moldable material is being manipulated in one of the aforementioned manners, the frequency, amplitude and/or phase shift of the drivable members can remain constant, be variable and/or be intermittent throughout the molding process. If the mode of manipulating the moldable material varies, the drivable members must still operate in one of the aforementioned manners.

When practicing this invention, the various drivable members can be reciprocated at any suitable frequency. The preferred frequency will depend, at least in part, upon the size of the drivable members, the number of recipro¬ cating means, the amplitude of the drivable members, the location of the drivable members, and the like, as well as the desired effects on the resulting product. Those skilled in the art, after reading this specification, will be able to determine the optimum frequency which best suits their specific needs.

Notwithstanding the above, the frequency ( ) at which the various drivable members are reciprocated typically ranges from between about 1 to about 120 Hz. Preferably, the drivable members are reciprocated at a frequency rang¬ ing from between about 1 to about 100 Hz, and more preferably, from between about 1 to about 80 Hz.

When practicing the present invention, one drivable member is reciprocated at a frequency of (fi) and at least one other drivable member is reciprocated at a frequency of (f₂). Frequencies (fj) and (f₂) each can range from about 1 to about 120 Hz. When frequencies (f_}) and (f₂) are the same, the drivable members must operate at a different amplitude. On the other hand, when frequencies (f_}) and (f₂) are different, the drivable members can operate at the same or at a different amplitude.

When practicing this invention, the various drivable members can be reciprocated at any suitable amplitude. The preferred amplitude will depend, at least in part, upon the size of the drivable members, the number of recipro¬ cating means, the frequency of the drivable members, the location of the drivable members, and the like, as well as the desired effects on the resulting product. Those skilled in the art, after reading this specification, will be able to determine the optimum amplitude which best suits their specific needs.

Notwithstanding the above, the amplitude (a) at which the various drivable members are reciprocated is such that they generate a compressive force within the mold ranging from between about 100 to about 20,000 psi. Preferably, the drivable members are reciprocated at an amplitude such that they generate a compressive force within the mold ranging from between about 100 to about 15,000 psi, and more preferably, from between about 100 to about 10,000 psi.

When practicing the present invention, one drivable member is reciprocated at an amplitude of (a,) and at least one other drivable member is reciprocated at an amplitude of (a₂). Amplitudes (a_t) and (a₂) are such that they generate a compressive force within the mold ranging from between about 100 to about 10,000 psi.

When amplitudes (a,) and (a₂) are the same, the drivable members must operate at a different frequency. On the other hand, when amplitudes (a,) and (a₂) are different, the drivable members can operate at the same or at a different frequency.

It should be noted that, when two drivable members operate at the same frequency, at the same amplitude and 3.14 radians out of phase with one another (see, e.g., U.S. Patent 4,952,161), the reciprocation pattern does not generate any significant compressive force within the mold. Notwithstanding the disclosure in U.S. Patent 4,952,161, it has been discovered that the morphological structure of the resulting solid product (e.g., percentage crystallinity, orientation, free volume content, texture, etc.), from which the physical properties depend (e.g., tensile strength, tensile modulus, etc.), can be modified by reciprocating the drivable members in a manner which not only creates a shear stress, on the moldable material, but also simultaneously generates a compressive force thereon. As indicated above, manipulating a moldable material in such a manner is referred to herein as ex¬ erting a stress tensor thereon.

One of the objects of this invention is to exert a specific stress tensor by separately monitoring and controlling the stress tensor's individual components (i.e., shear stress and compressive force). The shear stress compo¬ nent affects the orientation of the moldable material, where as the compressive force component affects the material's temperature. The proper mixture of these two components in time, as the frequency, amplitude and phase of the drivable members are varied during heating and cooling, results in an original history pattern which modifies the morphology and thus the physical properties of the resulting product.

In accordance with the present invention, when at least two drivable members are reciprocated at the same frequency, they can be recipro- cated either "in phase" or "out of phase" with each other. The phase shift between two such drivable members can range from 0 to 6.28 radians.

When the phase shift is at the values of 0 or 6.28 radians, the drivable members are oscillating in phase with each other. On the other hand, when the phase shift is at an amount ranging from between a value slightly greater than about 0 radians to a value slightly less than 6.28 radians, the drivable members are oscillating out of phase with each other.

The various drivable members which are reciprocated at the same frequency, can be oscillated at any suitable phase shift, or at none at all (i.e., in phase). The preferred phase shift will depend, at least in part, upon the size of the drivable members, the number of reciprocating means, the amplitude of the drivable members, the frequency of the drivable members, the location of the drivable members, and the like, as well as the desired effects on the resulting product. Those skilled in the art, after reading this specification, will be able to determine the optimum phase shift which best suits their specific needs.

Notwithstanding the above, when the various drivable members are reciprocated at the same frequency, at a different amplitude and out of phase with each other, the phase shift therebetween typically ranges from between about 0.79 to about 5.50 radians. Preferably, the drivable members are reciprocated at a phase shift ranging from between about 1.57 to about4.71 radians, and more preferably, from between about 2.36 to about 3.93.

The maximum phase shift occurs at 3.14 radians. Accordingly, with all other variables being the same, the greatest amount of shear will result when the drivable members are reciprocating at a phase shift of 3.14 radians. As indicated above, the stress tensor is exerted on the moldable material by reciprocating the drivable members of each reciprocating device, with respect to another drivable member, in one of four different manners. While the stress tensor is being exerted in accordance with this invention, the frequency, amplitude and/or phase shift of the individual drivable members can be constant, varied and/or intermittent throughout the molding process. For example, when practicing this invention, a specific frequency, amplitude and phase shift that two or more drivable members will reciprocate with respect to one another is selected. The selected parameters must fall within one of the aforementioned manners of exerting a stress tensor on a moldable material. These settings are referred to herein as a specific "reciprocation pattern".

In accordance with the present invention, a reciprocation pattern can be designed to remain constant throughout the molding process. On the other hand, it is also within the purview of this invention to have this reciprocation pattern vary and/or be intermittent throughout the molding process. However, it should be noted that, if the reciprocation pattern varies during a molding process, the drivable members must always operate, with respect to one another, in one of the four aforementioned manners.

In the embodiment of the present invention wherein the reciproca- tion pattern varies during the molding process, the frequency, amplitude and/or phase shift of at least one drivable member can vary, for example, from a low value to a high value, or vice versa. This variation can occur linearly, exponen¬ tially, randomly and/or intermittently.

Moreover, the variance of one drivable member can be either the same or different from that of another drivable member. For example, a varying reciprocation pattern in accordance with the present invention can result from the parameters of only one drivable member varying while those of all other drivable members remain the same, the parameters of at least two drivable members varying in the same manner, and/or the parameters of at least two drivable members varying in different manners.

As can be appreciated by those skilled in the art, there are many different reciprocation patterns which can be used when practicing this invention. Each pattern will modify the properties of the resulting product in its own specific manner. The preferred pattern will depend, in part, upon the desired end results. After reading this specification, those skilled in the art will be able to determine the specific reciprocation pattern which best suits their needs through simple experimentation. For example, this can be done by noting the physical properties of a material which was molded in accordance with a par- ticular reciprocation pattern.

Then, subsequent materials are prepared in accordance with the present invention wherein one of the stress exertion parameters (e.g., frequency, amplitude and/or phase shift) is changed. By comparing the morphological structure and/or the physical properties of these subsequent materials with those of the first material, a skilled artisan can see how the variance of a specific stress exertion parameter affects the particular material ' s morphological structure . This information can then be used to determine how the stress exertion parameters must be modified in order to produce a product having the desired morphological structure and/or physical properties. Once the parameters have been established, the results can be easily reproduced by using the same reciprocation pattern under similar circumstances.

For example, by using thermal analysis instruments such as a Differential Scanning Calorimeter (DSC) and/or a Thermal Stimulated Current/Relaxation Map Analysis (TSC/RMA) spectrometer, skilled artisans should note a significant difference in the specific heat traces during heating at rate of 10°C per minute which is characteristic of morphological changes occurring during the molding process. Moreover, skilled artisans should also note a significant difference in the relative positions of the melting temperature, glass transition temperature and secondary transitions, as shown in the TSC/RMA peaks. Furthermore, through such a thermal analysis of the resulting molded products, skilled artisans should observe that there is a significant difference in the intensity of the peeks which demonstrate, for example, that the product pre¬ pared in accordance with the present invention has a free volume distribution which has been altered. When the phase shift varies during the molding process, each drivable member can be programmed in the following manner:

Bj = Ao -I- A, sin (fit + b,) B₂ = A'₀ + A sin (f_xx + b'j)

wherein B, is the phase of one drivable member and B₂ is the phase of another drivable member, and wherein A^t), A'₀(t), A,(t), A',(t), /,(-), /,(t), b,(t) and b',(t) are functions of time.

The variables which can be inserted into these equations are selected such that the resulting reciprocation pattern will induce changes in the thermal history of the final product throughout the interaction between the propagation of the pressure/shear waves induced by the drivable member through the visco-elastic medium represented by the moldable material during the molding process.

In one preferred embodiment, the frequency of a particular drivable member is twice that of another drivable member. Moreover, the amplitude of the higher frequency drivable member is smaller but varies faster than that of the other drivable member.

When the amplitude varies during the molding process, the amplitude average may vary exponentially in a preferred embodiment with the inverse of absolute temperature in the following manner to account for viscosity changes in the plastic:

A₁₀ exp (B/T) wherein B is a constant which depends upon the material molded in accordance with the present invention, and wherein T is the average temperature of the molded material throughout the molding process.

Any suitable means can be employed to reciprocate the drivable members. Examples of suitable means include, without limitation, hydraulic devices, pneumatic devices, mechanical devices, electrical devices, electromag¬ netic devices and any combination thereof. The preferred method of reciprocating the drivable members will depend, in part, upon the resources available to the person practicing this invention and the type of drivable member selected.

The stress tensor exerted upon the moldable material by the reciprocating means can occur for any suitable period of time. The preferred period of time will depend, in part, upon the size of the drivable members, the number of reciprocating means, the amplitude of the drivable members, the frequency of the drivable members, the location of the drivable members, and the like, as well as the desired effects on the resulting product. Those skilled in the art, after reading this specification, will be able to determine the optimum time period over which to exert the stress tensor which suits their specific needs. The manner in which the stress tensor is applied to the moldable material is established by a predetermined program. Specifically, prior to manipulating the moldable material in accordance with the present invention, a specific reciprocation pattern is determined. This would include not only determining specific starting frequencies, amplitudes, phase shift parameters and time parameters, but also determining whether these initial settings will vary and be intermittent during the molding process, determining at what temperatures certain modifications occur when varying parameters such as Ao(t), A'₀(t), A^t),

A'ι(t), _!(t), ι(t), b,(t) and b',(t), and determining whether packing forces will be exerted onto the moldable material prior to, and/or intermittently throughout, the reciprocation pattern. These determinations are based, in part, upon the tem- perature of the moldable material as measured by a suitable temperature sensing device (e.g., an infrared temperature sensing device). As indicated above, after reading this specification, these determinations can be made by those skilled in the art through the use of simple deductive experimentation and reasoning. After the stress tensor has been applied in accordance with a predetermined program, but before the moldable material solidifies, a packing force is exerted thereon. As this packing force is being applied, the moldable material cools to form a solid product.

The packing force exerting onto the moldable material after, and optionally prior to and/or during, the reciprocation pattern can be applied by any suitable means known to those skilled in the art. For example, the packing force can be applied by a packing device (e.g., an extrusion screw, a piston, etc.), by at least one of the reciprocating means, and/or by any combination thereof.

After the product is solidified, it is extracted from the mold's cavi- ty. The manner in which the solid product is extracted depends, in part, upon the specific type of mold, molding process and/or molding apparatus.

The morphological structure of the resulting solid product (e.g., percentage crystallinity, orientation, free volume content, texture, etc.), from which the physical properties depend (e.g., tensile strength, tensile modulus, etc.), is different from that of a product made from the identical process but which did not employ one of the manipulation techniques disclosed herein. Accordingly, by varying the parameters of the present invention, skilled artisans now have a greater degree of control over the resulting product's structure and/or properties. When practicing this invention, sensors can be used to monitor certain physical characteristics of the moldable material during the molding process. These sensors can be designed to send information to a data processor. The data processor can be designed to monitor and control the reciprocation pattern during the molding process. The molding process of this invention is suitable for application to a moldable material which comprises a polymer material (e.g., an organic polymer material). Moreover, the process may be applied to thermosettable polymer materials (e.g., those formed in situ by Reactive Injection Molding (RIM) processes).

This process can also be applied to thermoplastic polymer materi¬ als. Examples of such materials include, but are not limited to those which are amorphous, certain polyesters, free radical-polymerized polystyrene, polymers of (meth)acrylate esters and poly(ether-sulphones), those which may be, or become during molding, semicrystalline polymer materials, as well as semi- crystalline polymer material which can be effectively oriented.

The molding process of this invention is also particularly suitable for application to polymer material which comprises a liquid crystalline, prefer¬ ably a thermotropic liquid crystalline, polymer (e.g., liquid crystalline polyester, preferably a liquid crystalline aromatic polyester).

Blends of one or more of thermoplastic polymers, including one or more liquid crystalline polymers, may be molded by the process of this inven¬ tion. Moreover, the moldable material used in the molding process of this invention may comprise a filler (e.g., a fibrous filler such as glass or carbon fiber). Preferred filled molding compositions include glass fiber-filled polypropylene and poly(aryleιherketone) and, carbon fiber-filled poly(aryletherketone) and nylon.

At high loadings (e.g., from 50 to 80% by volume of filler), the resulting molded articles can be subjected to controlled heat treatment to convert them into sintered ceramic or metal products. Moreover, when a second, anisotropic, refractory filler is present (e.g., a refractory fibrous filler), such products subjected to the process of the present invention will have oriented fibers.

When practicing the present invention, the moldable material introduced into the mold should not be too fluid during the varying stress stage. Polymer materials having a melt flow index (MFI) ranging from between about 4 to about 10, preferably from between about 5 to about 6, are very suitable. For example, in some instances, when the MFI is greater than 10 the molten material tends to be too fluid to enable sufficient work to be done on it during the stress varying stage. On the other hand, when the MFI is below 4, the material tends to be too intractable.

The present invention can be used with any molding apparatus wherein a moldable material is introduced into a mold. It is most advantageous when the molding apparatus is an injection molding device or a transfer molding device.

Referring now to Figure 1, a conventional ("prior art") injection molding machine 10 is illustrated. This machine includes a drivable injection screw 12 mounted for rotation about, and for oscillation along, its axis within a substantially coaxially extending elongate cavity 13 of a cylindrical, heatable barrel 14. Downstream from the screw, the elongate cavity communicates within a nozzle 15 and bushing 16. Upstream from the screw, the elongate cavity com¬ municates with a feed hopper 17 containing polymer feedstock 19.

Bushing 16 is designed to mate with mold 18. Mold 18 defines cavity 20 which communicates with screw cavity 13 via channel 22. Figures 2-4 illustrate an embodiment of the present invention having two reciprocating devices. These devices are in the form of pistons reciprocable within cylinders.

In Figure 2, bushing 16 mates with manifold 24 which houses the reciprocating devices. Bushing 16 communicates with an axially-symmetric, bifurcated channel 26, each branch of which leads into cylinders 28 and 30. Mounted in these cylinders are axially-slidable, drivable pistons 32 and 34, respectively. Each of cylinders 28 and 30 communicate downstream with axially aligned twin nozzles 36 and 38, respectively. Nozzles 36 and 38 mate with mold 35. Mold 35 is designed to include a double sprued, double gated bar mold cavity 20. Sprues 40 and 42 communicate with the bushings 46 and 48 of the twin nozzles, respectively.

In use, the mold tooling is first assembled. A suitable demolding agent is generally applied to the surfaces defining the mold cavity. The mold is then closed and brought to temperature.

Granular polymer feedstock is fed from the feed hopper into the elongate cavity and heated by the cylindrical barrel heater. The molten polymer feedstock is further heated, plasticized, and rendered substantially homogeneous by rotation of the injection screw.

When the molten polymer feedstock is determined to be of the desired viscosity, it is injected into manifold 24, by rotation and downstream translation of the injection screw. The molten polymer feedstock enters manifold 24 via bifurcated channels 26. When pistons 32 and 34 are positioned in the manner illustrated in Figure 2, the molten polymer feedstock passes, successively, through cylinder 30, nozzle 38, sprue 42, mold cavity 20, sprue 40, nozzle 36 and finally into cylinder 28. Further transport beyond cylinder 28 is prevented by piston 32 blocking channel 26. When the mold cavity, sprues and cylinders are filled with molten polymer feedstock, the injection screw is stopped from rotating.

As can be seen, manifold 24 splits the single feed from nozzle 15 into the desired number of separate feeds. In the example illustrated in Figures 2-4, the feed has been split into two identical channels.

In Figure 3, pistons 32 and 34 are reciprocated in accordance with a reciprocation pattern encompassed by the present invention. This specific recip¬ rocation pattern exerts a stress tensor on the molten polymer feedstock in the mold cavity, sprues and cylinders. If any shrinkage occurs during the mampulation and/or cooling process, it can be compensated for by further molten polymer feedstock being fed into the mold cavity from manifold 24 and injection screw 10. It should be noted that it is also within the preview of this inven¬ tion to pack the molten material into the mold prior to initiating the reciprocation pattern. If this preliminary packing is performed, it can be accomplished by the continual rotation of screw 12, the inward movement of piston 32 and/or 34, and/or any combination thereof.

After the desired stress tensor has been exerted on the moldable material in accordance with the present invention, and before the material solidifies, pistons 32 and 34 are preferably reciprocated in phase with each other to provide a packing force auxiliary to that of injection screw 10. This packing force is maintained until the polymer feedstock in the gate has solidified (see, Figure 4).

After the polymer has sufficiently solidified, it is removed from the mold. The resulting plastic material has a unique structure and unique properties which were created due to the specific reciprocation pattern. Figure 5 is a detailed illustration of manifold 24 without pistons

32 or 34. Moreover, Figure 6 is a cross-sectional side elevation of Figure 5 taken along line 6-6.

Figure 7 illustrates one method of controlling the reciprocation pattern and monitoring its effect on the material contained within a mold cavity in accordance with the present invention. In Figure 7, pistons 50 and 52 are reciprocated by motors 54 and 56, respectively. Motors 54 and 56 can regulate the piston's frequency, amplitude and phase orientation.

The apparatus illustrated in Figure 7 also includes a means for controlling the temperature within the mold, manifold and/or injection screw. This is represented by temperature adjuster 57.

Temperature adjuster 57 can be a single device which controls the temperature in the mold, manifold and/or injection screw collectively or a series of devices which make these temperature adjustments independently. For sake of simplicity, Figure 7 represents the temperature adjusting device as a single unit even though it is understood that the temperature within the mold, manifold and/or injection screw will generally be different.

Temperature adjuster 57 can be used to increase, decrease or maintain a constant temperature within the mold, manifold and/or injection screw. This temperature control can be accomplished by any suitable means known to those skilled in the art. For example, temperature adjuster 57 can employ the implementation of the following: (a) hot and cold oil circulated through passages in the mold, manifold and/or injection screw, (b) resistance cartridges positioned within the mold, manifold and/or injection screw, (c) hot pipes inserted into the mold, manifold and/or injection screw, and/or (d) fluid which is embedded in the mold, manifold and/or injection screw and whose temperature can be con¬ trolled by dielectric means.

Central processing unit (CPU) 58 is connected to frequency controller 60, amplitude controller 62, phase controller 64 and temperature adjuster 57. Controllers 60, 62 and 64 are connected to motors 54 and 56. It should be noted that controllers 60, 62 and 64 can be part of CPU 58 and/or part of motors 54 and 56.

Preferably, CPU 58 has programmed therein various reciprocation patterns wherein each pattern results in the final product having a specific mor- phological structure and/or physical properties. These reciprocation patterns also take into consideration specific temperature patterns.

Accordingly, by inputting into CPU 58 the desired structure and/or properties of the final product, CPU 58 will send the appropriate signals to con¬ trollers 60, 62 and 64 which, in turn, cause pistons 50 and 52 to reciprocate in accordance with a specific reciprocation pattern. CPU 58 will also send the ap¬ propriate signal to temperature adjuster 57 which maintains the proper temperature pattern 41 in the mold, manifold and/or injection screw during the selected reciprocation pattern.

In order to monitor the effect that the specific reciprocation and temperature patterns have on the moldable material, sensors 66, 67 and 68 are positioned accordingly. These sensors are connected to CPU 58. CPU 58 can be programmed to modify and/or regulate the reciprocation and temperature patterns based, in part, on the information received from sensors 66, 67 and 68.

Sensors 66, 67 and 68 can be designed to monitor any desirable processing parameter such as compressive force, temperature, viscosity, etc. Moreover, similar sensors can be placed anywhere along the polymer flow path and/or at specific locations within the mold.

Figure 8 represents a schematic illustration of an injection molding apparatus which can be used when practicing the present invention. In Figure 8, injection screws 70 and 72 are used as the reciprocating means.

In this specific embodiment, injection screws 70 and 72 mate with mold 74. Mold 74 defines cavity 76 which communicates with injection screws 70 and 72 via conduits 78 and 80, respectively.

In the embodiment illustrated in Figure 8, granular feedstock is fed from the feed hopper into the elongate cavity of each injection screw. These screw cavities are heated to melt the feedstock into a molted polymer.

When the molten polymer is determined to be of the right viscosi¬ ty, it is injected into mold cavity 76, by rotation and downstream translation of either one, or both of the injection screws. When mold cavity 76 and conduits 78 and 80 are filled with molten polymer feedstock, injection screws 70 and 72 are reciprocated in accordance with one of the reciprocation patterns encompassed by the present invention. This reciprocation creates a shear force on the molten material within cavity 76 while, simultaneously, exerting a compressive force thereon. Shrinkage of the polymer feedstock during cooling can be compensated for by further molten polymer feedstock being fed into cavity 76 from injection screw 70 and/or 72.

After the desired stress has been exerted on the moldable material in accordance with the present invention, but before the material solidifies, injec¬ tion screws 70 and/or 72 are reciprocated such as to provide a packing force on the molten material within cavity 76. This packing force is maintained until the polymer feedstock has solidified.

Once the molten polymer has sufficiently solidified, it is removed from the mold cavity. The resulting plastic material has unique properties which were created due to the specific reciprocation pattern.

In the embodiment illustrated in Figure 8, there is no manifold interposed between the reciprocating devices and mold 74. However, it is within the purview of the invention to substitute pistons 32 and 34 in Figures 2-4 with screws 70 and 72. Similarly, it is also within the purview of the invention to substitute screws 70 and 72 in Figure 8 with pistons 32 and 34.

Figures 9 and 10 represent a schematic illustration of a portion of a hot-runner-molding system which can be used when practicing the present invention. Specifically, Figure 9 represents a cross-sectional view of the hot- runner molding system illustrated in Figure 10 taken along line 9-9. In Figure 9, the drivable members are pistons 82 and 84. These pistons are designed to reciprocate in cylinders 86 and 88, respectively.

In the specific embodiment illustrated in Figure 9, pistons 82 and 84 are driven by hydraulic plungers 90 and 92, respectively. Pistons 82 and 84 can, however, be driven by any suitable means known to those skilled in the art. In operation, molten polymer feedstock is fed through feed channel

94 into hot-runner channel 96. From channel 96, the molten feedstock successively fills cylinders 86 and 88 and mold cavity 98.

After channels 94 and 96, cylinders 86 and 88, and mold cavity 98 are completely filled with the molten material, pistons 82 and 84 are recipro- cated in one of the reciprocation patterns encompassed by the present invention. The specific reciprocation pattern is continued for a predetermined period of time until the desired results are achieved. Thereafter, pistons 82 and 84 are recipro¬ cated in a manner to exert a packing force on the molten material within cavity 98. This packing force is maintained until the molten material in cavity 98 0 PCI7US94/14605

- 24 -

solidifies. Then, after the material has sufficiently solidified, it is removed from the mold cavity.

Figures 11 and 12 represent a schematic illustration of a portion of a cold-runner molding system which can be used when practicing the present invention. Specifically, Figure 11 represents a cross-sectional view of the cold- runner molding system illustrated in Figure 12 taken along line 11-11.

In Figure 11, the drivable members are pistons 118 and 120. These pistons are designed to reciprocate in cylinders 110 and 112, respectively.

In the specific embodiment illustrated in Figure 11, pistons 118 and 120 are driven by hydraulic plungers 122 and 124, respectively. As with the embodiment illustrated in Figures 9 and 10, pistons 118 and 120 can be driven by any suitable means known to those skilled in the art.

In operation, molten polymer feedstock is fed through feed channel

100 into cold-runner channel 102. Thereafter, the molten polymer enters mold cavity 104 via gates 106 and 108. Moreover, as the molten polymer fills cavity

104, it also flows into cylinders 110 and 112 via conduits 114 and 116, respectively.

After the molten polymer has completely filled conduit 100, runner 102, mold cavity 104, conduits 114 and 116, and cylinders 110 and 112, pistons 118 and 120 are reciprocated in one of the reciprocation patterns encompassed by the present invention. The specific reciprocation pattern is continued for a predetermined period of time until the desired results are achieved. Thereafter, pistons 118 and 120 are reciprocated in such a manner to exert a packing force on the molten material within cavity 104. This packing force is maintained until the molten polymer solidifies . Then, after the material has sufficiently solidified , it is removed from the mold cavity.

Figures 13 and 14 represent a schematic illustration of a portion of a cold-runner molding system which can be used when practicing this inven¬ tion, and which employs more than two reciprocation devices. Specifically, Figure 13 is a cross-sectional view of the cold-runner molding system illustrated in Figure 14 taken along line 13-13.

In Figures 13 and 14, the drivable members are pistons 156, 158, 160 and 162. These pistons are designed to reciprocate in cylinders 140, 142, 144 and 146, respectively.

In the specific embodiment illustrated in Figures 13 and 14, pistons

156, 158, 160 and 162 are driven by hydraulic plungers. Figure 13 shows hydraulic plungers 155 and 157 for pistons 156 and 160, respectively. As with the embodiments illustrated in Figures 9-12, pistons 156, 158, 160 and 162 can be driven by any suitable means known to those skilled in the art.

In operation, molten polymer is fed through feed channel 130 into cold-runner channel 132. Thereafter, the molten polymer flows into mold cavity

134 via gates 136 and 138. Moreover, as the molten polymer fills cavity 134, it also flows into cylinders 140, 142, 144 and 146 via conduits 148, 150, 152 and 154, respectively.

After the molten polymer has completely filled conduit 130, runner

132, mold cavity 134, conduits 148, 150, 152 and 154 and cylinders 140, 142,

144 and 146, the pistons are reciprocated in one of the reciprocation patterns encompassed by the present invention. The specific reciprocation pattern is continued until the desired results are obtained. Thereafter, the pistons are reciprocated in such a manner to exert a compressive force on the molten material contained within cavity 134. This compressive force is maintained until the molten material solidifies. Then, after the material has sufficiently solidified, it is removed from the mold cavity. Figure 15 is a graph which illustrates the action of two drivable members acting at different frequencies and amplitudes on a melt. Specifically, in this graph, P_d is the dynamic pressure (peak to peak) on a molten polymer at a given point of the mold as measured by a suitable pressure sensor. Each point along the graph represents the apparent mass of the system in vibration which should be compared with the mass of the piston vibrating.

When P_d is zero, the apparent mass is infinity. Therefore, no vibration energy is transmitted to the plastic. Rather, all is transmitted into the frame, mold, etc.

The graph also shows that the apparent mass is frequency depen- dent. This implies that the transmitted energy into the plastic is a function of frequency in a non-Newtonian manner.

Since the amplitude of the signal is also a rheological parameter that may vary during cooling, it is more appropriate to have several pistons each of which is designed to work in a specific frequency range. Thereafter, the signals from this plurality of pistons from the melt are combined together.

It is evident from the foregoing that various modifications, which are apparent to those skilled in the art, can be made to the embodiments of this invention without departing from the spirit or scope thereof. Having thus described the invention, it is claimed as follows.

Claims

THAT WHICH IS CLAIMED IS:

1. A molding process for molding a solid product from a moldable material, said process comprises:

(a) supplying a molten moldable material into cavity of a mold;

(b) providing at each of at least two spaced-apart re¬ gions of the moldable material within the mold, a reciprocating means in communication with the moldable material, each reciprocating means comprising a drivable member reciprocable within, and relative to, a chamber;

(c) exerting a stress tensor on the moldable material prior to, and during, it solidifying by reciprocation of the drivable member of each reciprocating means, with respect to another drivable member the reciprocation of the drivable member having frequency amplitude, and phase components, in a manner selected from the group consisting of:

(i) at the same frequency, at different amplitudes and out of phase,

(ii) at the same frequency, at different amplitudes and in phase,

(iii) at different frequencies and at the same amplitude, and

(iv) at different frequencies and at different amplitudes;

(d) exerting a packing force on the moldable material prior to, and in the course of, it solidifying;

(e) solidifying the moldable material while the packing force is being applied to form a solid product; and (f) extracting the solid product from the cavity of the mold.

2. A process as recited in claim 1 wherein at least a portion of the stress tensor exerted on the moldable material in step (c) is caused by re¬ ciprocating the drivable member of each reciprocating means, with respect to the other drivable member or drivable members, at the same frequency, at a different amplitude and out of phase.

3. A process as recited in claim 1 wherein at least a portion of the stress tensor exerted on the moldable material in step (c) is caused by re¬ ciprocating the drivable member of each reciprocating means, with respect to the other drivable member or drivable members, at the same frequency, at a different amplitude and in phase.

4. A process as recited in claim 1 wherein at least a portion of the stress tensor exerted on the moldable material in step (c) is caused by re¬ ciprocating the drivable member of each reciprocating means, with respect to the other drivable member or drivable members, at a different frequency and at the same amplitude.

5. A process as recited in claim 1 wherein at least a portion of the stress tensor exerted on the moldable material in step (c) is caused by re¬ ciprocating the drivable member of each reciprocating means, with respect to the other drivable member or drivable members, at a different frequency and at a different amplitude.

6. A process as recited in claim 1 wherein at least a portion of the packing force exerted on the moldable material in step (d) is caused by at least one of the drivable members.

7. A process as recited in claim 1 wherein the drivable member of at least one reciprocating means comprises a reciprocable piston, and wherein the chamber of the same reciprocating means comprises a cylinder in communication with an inlet in the mold through which the molten material enters the cavity of the mold.

8. A process as recited in claim 1 wherein the drivable member of at least one reciprocating means comprises a reciprocable extrusion screw, and wherein the chamber of the same reciprocating means comprises a cylinder in communication with an inlet in the mold through which the molten moldable material enters the cavity of the mold.

9. A process according to claim 1 wherein at least two of the drivable members are reciprocated out of phase with each other by an amount ranging from between a value slightly greater than 0 radians to a value slightly less than 6.28 radians.

10. A process according to claim 9 wherein at least two of the drivable members are reciprocated out of phase with each other by an amount ranging from between about 0.79 to about 5.50 radians.

11. A process according to claim 10 wherein at least two of the drivable members are reciprocated out of phase with each other by an amount ranging from between about 1.57 to about 4.71 radians.

12. A process according to claim 11 wherein at least two of the drivable members are reciprocated out of phase with each other by an amount ranging from between about 2.36 to about 3.93 radians.

13. A process according to claim 12 wherein at least two of the drivable members are reciprocated out of phase with each other by about 3.14 radians.

14. A process according to claim 1 wherein at least one of the drivable members is reciprocating at a frequency (f_}) ranging from between about 1 to about 120 Hz, and wherein at least one other drivable member is recip¬ rocating at a frequency (f₂) ranging from between about 1 to about 120 Hz.

15. A process according to claim 14 wherein at least one of the drivable members is reciprocating at a frequency (f,) ranging from between about 1 to about 100 Hz, and wherein at least one other drivable member is reciprocating at a frequency (f₂) ranging from between about 1 to about 100 Hz.

16. A process according to claim 15 wherein at least one of the drivable members is reciprocating at a frequency (/j) ranging from between about 1 to about 80 Hz, and wherein at least one other drivable member is reciprocating at a frequency (f₂) ranging from between about 1 to about 80 Hz.

17. A process according to claim 1 wherein the molding process comprises an injection molding apparatus.

18. A process according to claim 1 wherein the molding process comprises a transfer molding apparatus.

19. A process according to claim 1 wherein the moldable material comprises a polymer material.

20. A process according to claim 1 wherein at least one of the drivable members is reciprocating at an amplitude (a,) such that it generates a pressure within the mold ranging from between about 100 to about 20,000 psi, and wherein at least one other drivable member is reciprocating at an amplitude ( ₂) such that it generates a pressure within the mold ranging from between about 100 to about 20,000 psi.

21. A process according to claim 20 wherein at least one of the drivable members is reciprocating at an amplitude (α_;) ranging from between about 100 to about 15,000 psi, and wherein at least one other drivable member is reciprocating at an amplitude (a₂) such that it generates a pressure within the mold ranging from between about 100 to about 15,000 psi.

22. A process according to claim 21 wherein at least one of the drivable members is reciprocating at an amplitude (α_;) ranging from between about 100 to about 10,000 psi, and wherein at least one other drivable member is reciprocating at an amplitude (a₂) such that it generates a pressure within the mold ranging from between about 100 to about 10,000 psi.

23. A process according to claim 1 wherein a preliminary packing force is exerted onto the moldable material in said mold prior to step (c).

24. A process according to claim 1 wherein an intermediate packing force is exerted onto the moldable material in said mold during step (c).

25. A process according to claim 24 wherein a preliminary packing force is exerted onto the moldable material in said mold prior to step (c).

26. A process according to claim 1 further comprising control¬ ling temperature of the mold during steps (c), (d) and (e).

27. A process according to claim 26 further comprising controlling the temperature of the mold prior to step (a).

28. A process according to claim 27 further comprising controlling the stress tensor exerted during step (c) and the packing force exerted during step (d).

29. A process according to claim 28 wherein temperature and pressure sensors are employed to monitor at least the following: the temperature of the mold prior to step (a), the temperature of the mold during steps (c), (d) and (e), the stress tensor exerted during step (c), and the packing force exerted during step (d).

30. A process according to claim 29 wherein a central process unit is interfaced with the temperature and pressure sensors, and wherein the central processing unit is employed to control at least the following: the tempera¬ ture of the mold prior to step (a), the temperature of the mold during steps (c), (d) and (e), the stress tensor exerted during step (c), and the packing force exerted during step (d).

31. A molding process for molding a solid product from a moldable material said process comprising the steps of:

(a) supplying a molten moldable material into a cavity of a mold;

(b) providing at each of at least two spaced-apart regions of the moldable material within the mold, a reciprocating means in communication with the moldable material, each reciprocating means comprising a drivable member reciprocable within, and relative to a chamber;

(c) exerting a stress tensor on the moldable material prior to, and during, solidification by reciprocation of the drivable member of each reciprocating means, with respect to another drivable member, said stress tensor having a shear and a compressive component; and

(d) extracting the solid product from the cavity of the mold.