HK1020030B - Process and apparatus for forming plastic articles - Google Patents

Description

Method and apparatus for molding plastic articles

RELATED APPLICATIONS

This application has priority to U.S. provisional application No.60/044,454, filed on 3/20/97.

Background

The present invention relates to an improved method and apparatus for molding articles from molten material, including an innovative injection valve gating apparatus and an injection valve gating method for injection molding articles of different shapes.

Different arrangements for valving the liquid flow have been proposed in the prior art for regulating the flow of thermoplastic material from such a source to the mould cavity space. In many cases, the flow of melt into the cavity space at a hot or cold runner nozzle and through an injection gate can be satisfactorily regulated by a valve stem located in the nozzle melt channel. The valve stem is actuated by a movable device, typically located on the injection mold back plate, to open or close the melt passage to the cavity space. This method has several disadvantages when used in multi-cavity injection molding for molding desired articles, such as meltable preforms molded from a single or multiple materials. One disadvantage is that the system requires the use of multiple valve stems. In such a configuration, the single actuation of the valve stems creates a problem that causes all of the valve stems to be opened or closed simultaneously. Secondly, the valve stem tends to separate the streams of molten material, thus creating a so-called "reject lines". In addition, the actuation of the valve stem is problematic for multiple material injection lances when at least two materials are injected into the same cavity space. One known approach to solving the first two problems is to use a side valve gate structure that includes a gate orifice. The gate orifice is shown in U.S. patent No.4,108,956 to Lee.

The method shown in Lee is not very efficient. While it serves to address the first and second disadvantages described above, it does not simplify the design and operation of the injection mold. In fact, this approach complicates injection mold design and operation. The structure for valving the liquid flow of Lee involves the use of a reciprocatable slide member having at least one opening. The slide is positioned between a source of thermoplastic material, such as a hot runner outlet or injection nozzle, and an injection molding gate. As seen in both patents, the movable valve carries a hot sheet stock of molded plastic material thereon as the valve moves from the valve open position to the valve closed position. In the cooling step, the sheet blank is solidified. The presence of such a sheet blank in the valve opening requires a device comprising some additional and specially made mechanism for removing the sheet blank from the opening. If the sheet blank is not removed from the valve opening, it is brought back to the gate area with the next shot and injected into the cavity space. In many applications, this is not allowed because it reduces the profile and strength characteristics of the molded article. In multi-material molding, mixing of two or more different materials must be avoided, and the requirements in this respect become more stringent.

In Lee, a movable mechanical spray device driven by a pneumatic device (which is as complex as a similar component used to move an existing valve stem) is mounted on the molding device to remove cold chip blanks from the valve openings. Other devices not shown in the Lee patent must also be used to remove the sheet stock from the injection mold. In systems employing multi-cavity injection molding, such as injection molding with more than 16 cavities made by the assignee of the subject application, the use of such devices is difficult. For example, injection molds become very large and bulky if they must be equipped with movable mechanical injection devices. Furthermore, additional detection means are required to ensure that the sheet blanks have actually been ejected from each opening.

The apparatus as shown in the Lee patent also presents an economic disadvantage in that the sheeted blank becomes scrap and can be used to make molded articles if it is not formed into a sheeted blank. In addition to the sheet slug removal and waste problems, these systems also face the potential problem of molten plastic material flowing between the valve, adjacent injection mold plate and the surface of the hot runner housing. If the molten plastics material flows between these surfaces and stays on them, there is a possibility that the operation of the valve and the device itself may be interrupted while the plastics material solidifies.

The more recent valve gating apparatus of Lee has previously been used to control the flow of melt from a mechanical injection nozzle to an injection mold such as shown in U.S. patent No.3,632,729 to Bielfeldt. Of course, the valved structure shown in the Lee patent is not designed for the purpose of providing the liquid supply to the liquid supply of No.4,863,665; 5,200,207, respectively; 5,143,733, respectively; 5,112,212; 4,863,369, respectively; 4,808,101, respectively; 4,775,308, respectively; 4,717,324; 4,701,292, respectively; and 4,657,496 U.S. patents, all assigned to the assignee of the present application and incorporated herein by reference, disclose valves for opening a gate in a material injection lance. The Lee method cannot be used in the molding of a variety of materials because it would produce too much scrap material composed of different materials. Furthermore, the need to handle more than one type of sheet stock is technically and cost prohibitive.

In the prior art, a reciprocating cutting blade is used to remove shaped gate marks from a parison (preform). Such a system is shown in U.S. patent No.4,380,423 to Aoki. Although the Aoki patent discusses the problem of removing gate vestige from an already molded article, it does not discuss the critical issue of how to open and close the flow path of molten material from a runner system to an injection mold without forming shaped gate vestige that must be cut in a subsequent molding operation. Similar to Lee's sheet stock, the shaped gate vestige shown in the Aoki patent represents a significant waste of valuable resin in causing the above-mentioned problems.

There is a need for a simpler and more efficient injection valve gating structure for a multi-material injection nozzle. There is also a need for an injection valve gating arrangement for injecting multiple or single materials in which the flow of molten material from a hot or cold runner system or injection nozzle to an injection mold can be interrupted without causing waste of the material being molded. Furthermore, there is a need for an injection valve gating arrangement that does not necessarily include a movable and/or a mechanical injection device for removing molded plastic material from the valve.

Summary of the invention

It is a primary object of the present invention to provide a simpler and more efficient valve gating apparatus and method for controlling a hot or cold runner injection nozzle that is easier to manufacture, operate and use for injection molding of improved articles.

It is another object of the present invention to provide a valve gating apparatus and method wherein the valve gating apparatus is located outside of the injection nozzle.

It is another object of the present invention to provide a valve gating apparatus and method wherein a thin, movable knife switch is used in place of a valve gate stem, the knife switch including a fixed bore, minimum volume gate orifice.

It is another principal object of the present invention to provide a valve gating apparatus and method wherein substantially no material is diverted from the flow of molten material by the movable gate orifice during the injection process.

It is another principal object of the present invention to provide a simpler and more efficient valve gating apparatus and method of the above character for both single material and multi-material injection molding.

It is another object of the present invention to provide an apparatus and method for molding plastic articles substantially free of gate vestige from a single or multiple materials.

It is another object of the present invention to provide an apparatus and method for molding plastic articles without crystallinity from a single or multiple materials.

It is another object of the present invention to provide an apparatus and method for molding plastic articles without bond lines.

The invention is carried out in an injection mold having one or more injection nozzles that direct at least one molten material stream having a desired tubular flow pattern toward one or more mold cavities. More particularly, the present invention discloses a thin movable valve gating structure located outside a single material or multi-material injection nozzle and a method of gating a valve for an injection mold in which substantially no material deviates from the melt flow during the transfer of the molten material from the single material or multi-material injection nozzle to the cavity space. Thus, movement of the valve gating device produces substantially no residual material. Many advantages are obtained according to the invention and with a sheet blank that is substantially free of material residues in the injection mold. For example, injection molds with fewer mechanical or movable devices are simpler to design and manufacture, easier to install, operate and maintain, and do not require additional equipment to eliminate or cut gate marks after the article is molded. In addition, little molten material is wasted and the injection mold can be operated in a smaller, clean shop environment. Furthermore, the molded article has a higher mechanical resistance and a higher aesthetic value.

According to the present invention there is provided an apparatus for forming a moulded article broadly comprising: an injection mold having one or more cavity spaces and an injection gate communicating with the cavity spaces; one or more injection lances for feeding molten plastics material into the injection mould cavity space, the injection lances having at least one lance outlet aligned with an injection moulding gate; movable valve gating means, such as a knife switch, located between the injection gate and the at least one nozzle outlet and having an orifice therein, the orifice having a minimum volume; means for moving the valve gate means between a first position in communication with the nozzle outlet and the injection gate and causing the molten plastic material to flow from the at least one outlet to the injection gate and a second position in which the flow from the at least one nozzle outlet to the injection gate is interrupted, the valve gate means being sufficiently thin that substantially no plastic material is carried or deflected by the valve gate means during movement of the valve gate means between the first and second positions.

According to the present invention, there is provided a method for forming a moulded article comprising the steps of: feeding at least one molten material from an injection nozzle through at least one nozzle outlet to a cavity space through an injection gate substantially aligned with the at least one nozzle outlet; and substantially preventing waste of molten plastic material during the molding process by mounting a thin, movable valve gate opening means with an aperture therein between the injection gate and the at least one nozzle outlet, and moving the valve gate opening means between a first position in communication with the at least one nozzle outlet and the injection gate and allowing the molten plastic material to flow from the at least one outlet to said injection gate and a second position in which flow from the at least one nozzle outlet to the injection gate is interrupted, and substantially no plastic material is displaced by the thin valve gate opening means during movement of the valve gate opening means between the first and second positions.

The apparatus and method of the present invention have found particular application in injection molding systems that include multiple material injection nozzles for injecting two or more materials into a cavity space. The valve gating apparatus of the present invention may be designed to inject material into the cavity space sequentially or simultaneously, since the valve gating apparatus is thin enough that it does not substantially carry the material being molded and does not form residual material that needs to be processed as it moves between positions. The valve gating apparatus according to the present invention may have more than one gate hole when injecting multiple materials.

According to another aspect of the invention, the valve gating device is desirably mounted in close proximity to the cavity space so as to minimize the height of the remaining gate vestige. According to another aspect, the gating device needs to be maintained at a temperature such that substantially no crystallinity forms in the region of the molded article proximate the injection molding hole or gate. When injecting a material such as PET, no bond lines are formed in the molded article. The valve gating device may be a single knife switch, a disc member or a cup member, the knife switches preferably being flexible knife switches movable in opposite directions. A plurality of driving means for moving the valve gating device individually or together may be mounted on one or both sides thereof. Furthermore, because there is no valve stem inside the injection nozzle melt channel of the present invention, the molded article does not have a knit line and a faster injection molding cycle can be achieved.

Additional features and advantages of the invention will be described hereinafter.

Brief Description of Drawings

The invention may be more readily understood by reference to the following drawings, in which:

FIG. 1 is a cross-sectional view of a multi-cavity injection mold according to the present invention;

FIGS. 2A and 2B are a top view and a perspective view, respectively, of a knife switch valve according to the present invention;

FIG. 3 is an enlarged detail view of a nozzle, knife switch and injection mold of the present invention;

FIG. 4 is a partial cross-sectional view of a preform for a molded article made according to the present invention;

FIGS. 5A, 5B and 5C illustrate another embodiment of the present invention with a single valve gating device acting on each injection mold cavity;

FIG. 6A shows another embodiment of a valve open gate structure according to the present invention;

FIG. 6B illustrates a valve opening gate structure for use in a system having a plurality of injection lances in accordance with the present invention;

FIGS. 7A-7D illustrate additional blade switch configurations of the present invention;

FIG. 8 shows a frame assembly for supporting a plurality of knife switches for simultaneous movement;

FIGS. 9A-9D illustrate another embodiment of the present invention;

FIG. 10 further illustrates an embodiment for injecting two materials sequentially or simultaneously;

FIG. 11 is a top view of a disc-shaped valve gating structure;

FIG. 12 is a cross-sectional view of a side-gated nozzle and rotary valve gate structure;

FIG. 13 is a perspective view of a three material hot runner nozzle system including a valve open gate configuration according to the present invention;

FIG. 14 is a cross-sectional view of a three material spout used in the embodiment of FIG. 13;

FIG. 15 is a bottom view of a valve open gate knife switch that can be used with the three material nozzle of FIG. 13;

FIG. 16 illustrates another embodiment of a valve open gate knife switch that can be used with the three material nozzle of FIG. 13;

FIG. 17 is a cross-sectional view of a three-slot injection molding gate for use with the three material nozzle of FIG. 16;

FIG. 18 is a cross-sectional view of a three material preform made with the system of FIG. 13;

FIG. 19 is a cross-sectional view of another two-material nozzle system with a valve opening gate structure according to the present invention;

FIG. 20 is a top view of a valve gate knife switch for use in the system of FIG. 19;

FIG. 21 is a cross-sectional view of a two-material preform made with the system of FIG. 19;

FIG. 22 is a schematic of a valve gate knife switch with a thermocouple and a heater therein;

FIGS. 23A-23C illustrate a dual knife-shaped switch valve gate configuration; and

fig. 24A-24C illustrate the use of a valve gated knife switch having multiple thicknesses.

Description of The Preferred Embodiment

According to a preferred embodiment of the present invention, the valve gating device is a novel, flexible, thin knife switch valve that is preferably actuated using a moving device that runs across the knife switch. The moving means pulls the knife switch and the gate opening thereon into and out of alignment with the injection molding gate and the injection nozzle outlet. In this way, no axial mechanical or compressive stresses are generated in the valve gate during the sliding movement of the knife switch valve. In another embodiment of the invention, the valve gating device is comprised of a thin somewhat rigid knife switch valve that is preferably actuated by a moving device that operates only at one end of the knife switch valve. This is recommended for viscous materials that have less adhesion to the knife switch or bottom cavity injection molding. The sliding movement of the knife switch valve occurs in a plane that is substantially perpendicular to the flow of the molten material, such as resin, and the injection gate. The opening of the injection mold gate has an axis that is substantially parallel to the flow of the molten material.

According to the present invention, the valve gating device does not substantially carry any material being molded when moving between the two positions. To achieve this, the valve gating device must have a minimum thickness. The minimum thickness is selected such that each aperture in the valve gating device retains a minimum volume of material, and preferably no material. In its lateral movement, the volume V of material collected by the diameter D of the orifice can be determined according to the following equation:

the volume of the holes must be minimal during the cooling of the injection mold in order to leave substantially no molten material that becomes a cold slab. There are at least three ways to achieve this: the diameter D is the smallest and the knife switch thickness T at the gate area is the smallest or both. Considering that the diameter of the hole has a certain value in practice, a knife switch is chosen whose thickness is sufficient to prevent the formation of a sheet blank. Therefore, the actual thickness of the blade switch is determined by the following equation (1):

Tmin＝4Vmin/(πD²)

wherein Tmin is the minimum thickness;

vmin — the minimum volume of the pore; and

d-the diameter of the hole.

With the same practical approach we also point out that: in most cases, the knife switch thickness Tmin at the gate area should be less than the diameter D of the hole.

Tmin＜Dmin

A valve gating device having a thickness Tmin may close off the flow of hot molten plastic material substantially without creating a scrap piece blank and without diverting the molten material as the valve gating device moves between open and closed positions. The valve gating device may have a thickness from 0.01mm to 2 mm. Tests with different molten materials, different injection molding parameters, different drive means, different material knife switches and different injection mold designs have shown that: a valve gating device thickness of less than 0.3mm may ensure that substantially no material remains in the bore of the valve gating device.

According to the present invention, the driving piston pulls the knife switch valve to move in one or both directions in the process of opening and closing the opening gate. The inventive sliding blade-type switching valve can be used effectively in a multi-cavity injection molding, by which all melt channels can be closed simultaneously.

As is known in the art, injection molding typically has two methods of interrupting the communication between the nozzle and the cavity. In the so-called hot runner method, the flow of molten resin to the mold cavity is interrupted by "solidifying" the mold gate area after the injection step and before opening the injection mold. In the so-called valve gating method, a movable valve gate stem located in the melt channel is driven to open and close the gate. Both of these methods have several disadvantages. In the hot-runner approach, the size of the injection mold gate is limited to a smaller diameter to allow the gate to cool. The operating temperature and pressure window is also limited to a range that does not cover a large number of applications. In the valve gated approach, the presence of a valve stem at the melt channel creates a so-called knit line in the molded article. They cannot be effectively applied in several applications, especially when it is applied to molded articles where the so-called open gate vestige must be very small and must be substantially free of crystallinity.

FIG. 1 shows a multi-cavity injection molding assembly 10 having a cavity plate 12 and a core plate (not shown). The cavity plate 12 may include one or more cavity spaces 32 and 34. The mechanical nozzle 16 feeds molten material to a hot runner passage 18 located in a manifold 20. The nozzle 16 and/or manifold 20 may include a plurality of heating elements 22 to maintain the plastic material in the hot runner passage at a suitable temperature. The hot runner channel 18 feeds molten plastic material to injection lances 24, 26 which contain melt channels 28, 30, respectively. The cavity spaces 32 and 34 are comprised of the cavity plate 12 and mold cores 36 and 38, respectively. Cooling channels 40, 42, each supplied with a cooling medium from a medium source (not shown), are used to solidify the molten material. Other parts of the injection molded assembly are known in the art and are not shown here.

Injection lances 24, 26 feed molten plastic material to cavities 32 and 34 through injection gates 44, 46, respectively.

A slidable knife switch valve 48, shown in detail in fig. 2A and 2B, including apertures 50, 52 thereon, is mounted between the injection lances 24, 26 and the cavity spaces 32 and 34. The knife switch 48 is actuated by cylinders 56, 58 on either side of the knife switch 48 to slide laterally in the direction of arrow 54 to open communication between the melt channels 28, 30 and the cavities 32, 34 when the knife switch bores 50, 52 are aligned with their respective melt channels and cavities, and to close communication when the knife switch bores 50, 52 are out of alignment with their respective melt channels and cavities.

The thickness 60 of the knife switch 48 is minimal, typically 0.02mm to 2mm, so that no plastic material (cold blade blank) is diverted when the knife switch slides to close the gate after the injection molding process. The width 62 of knife switch 48 depends on the particular injection molded design. A gap 64 (see enlarged view of fig. 3) defined between the nozzle 24 and the mold 12 allows the knife switch 48 to slide between the nozzle and the mold but prevents leakage of the plastic material during injection. The knife switch is flexible but, since both its ends are fixed, it is in a rigid state and does not bend during its sliding movement.

As shown in fig. 4, the molded plastic article 66 is formed to be substantially free of gate vestige 68 having a minimum thickness 70 and width 72.

In the embodiment of fig. 5A, the shorter individual knife switches 74, 76 are each individually actuated from one side by only a single air cylinder 82, 84 to open and close the individual nozzles 78, 80. Fig. 5B and 5C show top views of individual knife switches 74, 76 with holes 86, 88. Shorter single blade switches are less flexible and are easier to drive from only one side.

Fig. 6A shows another compact embodiment of a single knife switch 90, the single knife switch 90 bypassing the rollers 92, 94 and being driven by air cylinders 96, 98. Other components are not shown in fig. 6A. The advantages of this driving method are: the piston is perpendicular to the injection mold parting line, which reduces the size of the injection mold.

Fig. 6B shows another compact embodiment in which a single knife switch 90 bypasses the rollers 92, 94 and is driven by air cylinders 96, 98. In this embodiment, there are three injection lances 101, 103 and 105 for injecting molten material through three spaced apart injection gates 115 into a single, large arcuate cavity space 107. The knife switch 90 has three apertures 109, 111 and 113 for alignment with the outlets of the injection nozzles 101, 103 and 105 and the corresponding injection mold gates 115 to allow the molten material to flow into the cavity space 107 simultaneously. This can be used for large parts with curvature, for example, car bumpers.

Fig. 7A-7D show other blade switch configurations. Fig. 7A is a top view and fig. 7B is a side view of a blade switch 104 with apertures 106, each opening lined with a material 108 different from the blade switch material to achieve different characteristics.

Fig. 7C and 7D are top and side views of knife switch 110 with aperture 112 including septum 114 in aperture 112 to form a split aperture that can be used to inject more than one material into a single mold cavity.

In the embodiment of fig. 8, a plurality of knife switches 120 are mounted on a frame 116 mounted on a rack 118 that is moved by a pinion (not shown) and that can move back and forth with the frame for a plurality of injection molds.

Fig. 9A-9D illustrate different mechanisms for driving the knife switches 122, 124 having apertures 126, 128 using mechanical means, e.g., a friction drive like motors 130, 132, rather than pneumatic components.

The embodiment of figure 10 shows a lance 134 and lance outlets 137 and 139 with two passages 136, 138 for different plastics materials a and B respectively. The knife switch 140 has a single opening 142. Knife switch 140 is moved to align aperture 142 with outlet 137 and injection gate 143 in a first position and with outlet 139 and injection gate 143 in a second position. Knife switch 140 is moved further to misalign aperture 142 with either outlet 137 or outlet 139. This structure can be implanted with material a and then with material B. The knife switch 140 may be moved using any of the mechanisms described above. In addition, knife switch 140 may also be positioned to allow both materials A and B to be injected through aperture 142 and into injection mold gate 143 simultaneously. In most applications, one material forms the central portion and the other material forms the surface portion. In preform applications, one material may be virgin PET and the other material may be recycled PET.

Instead of a knife switch, the valve gating device may be a gating disk, as shown in fig. 11. As previously described, the degating disk 150 is mounted between a nozzle outlet 154 and an injection mold gate (not shown). The degating disk 150 may have one or more holes 152. The number of holes 152 depends on the number of nozzle outlets and injection mold gates that mate with the degating disk 150. Where the disk 150 has a plurality of orifices 152, the orifices may be used to valve gate a single injection nozzle or to valve gate more than one nozzle simultaneously. Further, where the disk 150 has a plurality of holes 152, the holes may be of different sizes. The diameter of the degating disk 150 is determined by the configuration of the nozzle outlet and the injection mold gate with which it must be mated.

In operation, degating disk 150 preferably rotates between a first position in which apertures 152 are aligned with the nozzle outlets and the injection mold gates to flow molten plastic material from the nozzle outlets through the injection mold gates to the cavity space, and a second position in which apertures 152 are not aligned with the nozzle outlets and the injection mold gates. Any suitable means known in the art (not shown) may be used to rotate the gate disk 150 between the first and second positions. A defined gap between each injection nozzle outlet and the injection gate may allow part 150 to rotate without leaking molten plastic material.

The thickness of the disc-shaped member 150 is determined by the foregoing equation. The disc-shaped member 150 is sufficiently thin that substantially no plastics material is carried by the disc-shaped member and no plastics material sheet blanks are formed in the aperture 152 during movement of the member between the first and second positions. In this way, no waste of molten plastic material is incurred. Nor does plastic material flow between the components and interfere with the operation of the disc-shaped components.

FIG. 12 shows another embodiment of the invention for gating a side-gated nozzle 160, the nozzle 160 having one or more outlets 162, 164 perpendicular to the main flow of molten material. In this embodiment, the valve gating apparatus includes a rotating cup-shaped gating member 166. As shown in fig. 12, the degating member 166 includes holes 168 and 170 in sidewalls 172 and 174. Each bore 168 and 170 communicates with outlets 162 and 164 and an injection molding gate (not shown).

Sprueled part 166 preferably rotates between a first position in which holes 168, 170 are aligned with nozzle outlets 162 and 164 and the injection molding gate to flow molten plastic material from the nozzle outlets through the injection molding gate to the cavity space, and a second position in which holes 168, 170 are not aligned with nozzle outlets 162, 164 and the injection molding gate. Any suitable means known in the art (not shown) may be used to rotate gate member 166 between the first and second positions. For example, an elongated drive plate 175 with a rack portion 173 may be provided. The rack portion 173 is engaged with a pinion 171 connected to the gate opening part 166. A suitable member (not shown) is connected to carrier 175 to move it back and forth to rotate gate member 166 via the action of rack 173 and pinion 171. In a multi-cavity injection mold, each nozzle tube 160 is surrounded by a gating member 160 and drive plate 175 will interact with pinion 171 of each gating member 166. A defined spacing between each injection nozzle outlet and the injection gate may allow for the rotation of sprueled part 166 without leaking molten plastic material.

The thickness of each sidewall 172, 174 is determined by the preceding equation. Each sidewall is sufficiently thin so that substantially no plastic material is carried by the sidewall and no plastic material sheet stock is formed in the holes 168 and 170 during movement of the degating member 166 between the first and second positions. In this way, no waste of molten plastic material is incurred. Nor does plastic material flow between the components and interfere with the operation of the gate opening components 166.

The valve gating structure of the present invention has found particular application in injection molding systems in which multiple materials are injected into a cavity space to form multiple material articles, such as multiple material preforms as shown in fig. 18 and 21. Referring now to FIG. 13, an injection molding system 200 capable of forming an article comprised of three different materials is illustrated. The system 200 is described in U.S. patent No.4,863,665, which is incorporated by reference. System 200 includes three sources of molten material, extruders A, B and C. The portion of the hot runner system exiting extruder B is shown in solid lines, the portion of the system originating from extruder C is shown in dashed lines, and the portion of the system originating from extruder A is shown in dotted lines. In general operation, a first material, such as virgin PET, from extruder A, used to form the exterior surface of an article, is first injected into the cavity space 204. Subsequently, a second material, for example, EVOH insulating resin, from an extruder C is injected into the cavity space 204. Next, a third material, e.g., regrind PET or any other desired fill resin, from extruder B is injected into cavity space 204.

Extruder B supplies molten material B to a heated manifold 206 which communicates with injection nozzle 202 via hot runners or passages 210,212, 214 and 216, respectively. Reference numerals 218, 220, 222 and 224 denote spool valves which are operated to control the injection of injection canisters or injection cylinders 226, 228, 230 and 232.

Correspondingly, a hot manifold 234 supplying the second material C exits the extruder C through hot runners or passages 236, 238, 240, and 242 to each nozzle 202. The spools 244, 246, 248 and 250 control the injection shot cans 252, 254, 256 and 258.

A hot manifold 260 supplying a third material a is drawn from extruder a through hot runners 262, 264, 266, and 268 directly to each nozzle 202.

The operation of the system for supplying three materials to the spout 202 is explained in more detail in the' 665 patent and, here, will not be repeated.

Referring to FIG. 14, the injection nozzle includes three passages 270, 272 and 274 for materials A, B and C, respectively. The passages 270, 272 and 274 terminate in openings 276, 278 and 280, respectively. In addition, the centerline of the channel 270 is spaced a distance D from the centerline of the channel 272_ABThe centerline of the passage 272 is spaced a distance D from the centerline of the passage 274_AC。

The system also includes an injection gate 282 for flowing molten material into the cavity space 204.

However, the system 200 differs from the system of U.S. patent No.4,863,665 in that it includes a laterally moving valve gate knife switch 284 according to the present invention. As shown in fig. 14 and 15, knife switch 284 is mounted between injection nozzle outlets 276, 278, and 280 and injection mold gate 282. As previously described, the knife switch 284 is sufficiently thin that substantially no molten material is carried by the valve gate knife switch 284 during its movement.

Knife switch 284 may have one aperture 286 for each injection nozzle 202. The knife switch may be moved laterally by an air cylinder (not shown) to sequentially align each of the apertures 286 with the outlets 276, 278 and 280 in the respective injection lances 202. One sequence that may be used is to align each aperture 286 with an exit port 278 so that material a is fed into injection mold gate 282 and then into the cavity space. Each aperture 286 is then moved into alignment with an outlet 276 to allow material B to be fed into cavity space 204 through injection gate 282. Each aperture 286 is then aligned with an outlet 280 to allow material C to be fed into cavity space 204 through injection gate 282. Finally, knife switch 284 may be moved to a position in which each aperture 286 is not aligned with any of outlets 276, 278, and 280 in the respective injection nozzle 202 and the flow of molten material into cavity space 204 is interrupted.

As shown in FIG. 16, valve gate knife switch 284 may have a determined distance D_ABAnd D_ACThe three holes 290, 292, and 294 are spaced apart in part, which may be done in either the injection sequence described above or in the following sequence: c is implanted/A + B is implanted or A + B is implanted/C is implanted or A-B-C is implanted sequentially.

Fig. 17 illustrates another type of injection molding gate 282' that can be used with the injection nozzle of fig. 14. As shown, the injection mold gate 282' may have three channels 300, 302, and 304 aligned with the outlets 276, 278, and 280, respectively.

Fig. 18 shows a three material preform formed of materials A, B and C that can be made using the system of fig. 13-16.

Referring to fig. 19, there is illustrated one injection lance 134' for injecting two materials a and B. Injection lance 134 ' is similar to that of fig. 10 in that it has passages 136 ' and 138 ' that terminate in outlets 137 ' and 139 '. Materials a and B are fed into a cavity space through outlets 137 ' and 139 ' and injection gate 143 '. As previously described, the valve gate knife switch 140 'has a hole 142' for allowing the sequential injection of materials A and B. As shown in fig. 19 and 20, the knife switch 140' may also have a portion with two holes 310 and 312 to allow for the simultaneous injection of materials a and B. This configuration can be used to accomplish the following implant sequence: (1) injecting A/injecting A + B; and (2) implant B/implant A + B. Valve gate knife switch 140' may be used to complete other sequences. A two material preform that can be made using the open gate valve structure of fig. 19 and 20 is shown in fig. 21.

There are some resin materials that require additional heat and better temperature control during the injection process. In this case, it is necessary to install a heater and a thermocouple to the valve opening gate structure. While how this is done will be discussed in the context of one of the above embodiments, it should be appreciated that: a heater and thermocouple arrangement may be incorporated into any of the valve gate arrangements described herein.

Referring to fig. 22, a side valve gate knife switch 48 is provided with a heater 320, e.g., a chip heater, and a thermocouple 322 on one surface thereof. The heater 320 may be used to ensure that the resin material receives the heat required for it to be properly injected. The thermocouple 322 can measure the temperature near the orifice 46, thereby allowing the injection system to achieve better temperature control. The thermocouple may be any suitable thermocouple known in the art, such as a thin plate thermocouple. The heater 320 and thermocouple 322 may be mounted on one surface of the knife switch 48 in any suitable manner known in the art.

Referring to fig. 23A-23C, instead of using a single valve gate knife switch, it may be desirable for some applications to use two knife switches 340 and 342 that are movable in opposite directions. As shown, knife switches 340 and 342 have an aperture 344 and 346, respectively. Knife switches 340 and 342 are movable from a first position (fig. 23B) in which apertures 344 and 346 are not aligned to a second position (fig. 23C) in which apertures 344 and 346 are aligned to allow material from an injection nozzle 348 to flow into a cavity space (not shown). Any suitable means known in the art (not shown) may be used to move knife switches 340 and 342 between the first and second positions. It is believed that: this method provides more flexibility in selecting the optimum thickness of the knife switch to prevent the formation of a sheet blank.

Although various blade switch configurations having constant thickness have been shown, one blade switch having multiple thicknesses T and Tmin as shown in FIGS. 24A-24C may be used. This is because in some applications, the critical thickness Tmin is only required near the injection gate and its hole 400 to prevent sheet stock formation. In this configuration, a first thickness T is selected to provide the knife switch 48' with sufficient strength to avoid bending it during lateral movement. A second thickness Tmin necessary to avoid forming the slab is located on the knife switch portion near each injection molding gate orifice 400. These portions of knife switch 48 ' having thickness Tmin include knife switch apertures 50 ' and 52 '. The second thickness is selected to prevent formation of a sheet blank, as previously described. It may also vary injection parameters or a function of the molding material.

As can be seen from fig. 24A and C, the length L of the thickness Tmin is greater than the width M of the gate hole 400. This creates a gap 402 that is slightly larger than the diameter D of the apertures 50 ' and 52 ' to allow the knife switch 48 ' to move from a valve open position to a valve closed position. In the valve open position, molten material can flow through the spout outlet 404 through the injection molding gate orifice 400 and into the cavity space 406; in the valve closed position, the flow of molten material is interrupted without any leakage after each injection step. As best seen in fig. 24B, both apertures 50 'and 52' are offset from the midpoint of length L by the need to provide a gap 402.

It should 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 and arrangement of parts, as well as details of operation. The present invention includes all modifications falling within the spirit and scope defined by the claims.

Claims (38)

1. An apparatus for forming a molded article, comprising:

at least one injection mold (12) having a cavity space (32, 34) and an injection mold gate (44, 46) in communication with said cavity space;

an injection nozzle (24, 26) for supplying at least one stream of molten material to said at least one injection mold, said injection nozzle having at least one nozzle outlet substantially aligned with said injection mold gate;

a movable valve opening gate arrangement (48, 74, 76, 90, 104, 110, 120, 140, 284, 140 ', 48', 150, 166) between the injection molding gate and the at least one nozzle outlet and having at least one aperture (50, 52, 86, 88, 106, 112, 126, 128, 142, 152, 168, 170, 286, 290, 292, 294, 310, 312, 346, 344, 50 ', 52') therein;

means (56, 58, 82, 84, 96, 98, 171, 173, 130, 132) for moving the valve gate opening means between a first position in which the at least one aperture is in communication with the at least one nozzle outlet and the injection mold gate to allow molten material to flow from the at least one outlet to the injection mold gate and a second position in which the flow of molten material from the at least one outlet to the injection mold gate is interrupted; and

the thickness of the valve gating device is from 0.01mm to 2mm such that substantially no material is carried by the valve gating device and no residual scrap material is formed during movement of the valve gating device between the first and second positions.

2. The apparatus of claim 1, wherein: the valve gating device has a thickness Tmin defined by the equation:

Tmin＝4Vmin/(πD²)

wherein Tmin is the minimum thickness;

vmin — the minimum volume of the pore; and

d-the diameter of the hole.

3. The apparatus of claim 1, wherein: the valve gating apparatus includes a knife switch (48, 74, 76, 90, 104, 110, 120, 140, 284, 140 ', 48') having the at least one aperture therein.

4. The apparatus of claim 3, wherein: the blade switch (48, 74, 76, 90, 104, 110, 120, 140, 284, 140 ', 48') is laterally slidable in a direction substantially perpendicular to the injection mold gate.

5. The apparatus of claim 1, forming a plastic article (60) in the mold cavity, a portion (68) of the article being in contact with the valve gating apparatus, wherein: the portion of the article in contact with the valve gating device is substantially flat and substantially no knit line is formed in the article such that substantially no crystallinity occurs in the region of the molded article proximate the injection gate.

6. The device of claim 4, comprising a defined gap between the injection nozzle and the injection mold that allows the knife switch to slide without leaking plastic material.

7. The apparatus of claim 1, wherein: each bore (106) is lined with a material (108) different from the valve gating device.

8. The apparatus of claim 1, wherein: each aperture (112) includes a baffle (114) therein to provide a bisecting aperture.

9. The apparatus of claim 4, including a plurality of knife switches (120) supported by a frame (116).

10. The apparatus of claim 1 further comprising:

a plurality of injection lances (101, 103, 105) for injecting molten material into a cavity space (107), each of said injection lances having an outlet;

the valve gating apparatus includes a flexible blade switch (90) having a plurality of apertures (109, 111, 113); and

each of the apertures is aligned with the respective outlet in a first position to allow the molten material to flow from the injection nozzle into the cavity space.

11. The apparatus of claim 1, wherein: the valve gating apparatus includes two knife switches (340, 342) movable in opposite directions, each knife switch having an aperture (344, 346) therein.

12. The apparatus of claim 1 further comprising:

each of said injection lances (134, 134 ', 202) having a plurality of channels (136, 138, 136 ', 138 ', 270, 272, 274) for receiving a plurality of materials to be molded;

each of said channels terminating in an outlet; and

the injection mold gate (282') has a plurality of channels (300, 302, 304) for mating with the outlet.

13. The apparatus of claim 1, wherein: the valve gating apparatus includes a laterally sliding knife switch having a bore therein, the knife switch being slidable for sequential injection of the material.

14. The apparatus of claim 1, wherein: the valve gating apparatus includes a laterally sliding knife switch (284, 140 ') having more than one aperture (290, 292, 294, 310, 312, 142') therein, the knife switch being movable for sequential and simultaneous injection of the materials.

15. The apparatus of claim 1, wherein: the valve gating apparatus includes means (320) for heating the molten material as it flows through the at least one aperture and means (322) for sensing the temperature of the molten material flowing through the at least one aperture (322).

16. The apparatus of claim 15, wherein: the valve gating apparatus includes a knife switch (48) having at least one aperture (46), and the heating means and sensing means are mounted on a surface of the knife switch proximate each of the apertures.

17. The apparatus of claim 1, wherein: the valve gating apparatus includes a disk (150) having at least one aperture (152) that is rotatably movable between the first and second positions.

18. The apparatus of claim 1, wherein: the injection lance comprises a plurality of outlets (162, 164) substantially perpendicular to the main flow of molten material through the injection lance, and the valve gating device comprises a rotary member (166) having the same number of apertures (168, 170) as the number of outlets, and rack and pinion means (171, 173) for rotating the rotary member between the first and second positions.

19. The apparatus of claim 1, wherein: the valve gating apparatus includes a knife switch (48') having a first portion with a first thickness sufficient to substantially prevent bending thereof and at least a second portion with a second thickness sufficiently thin to allow substantially no material to be carried by the knife switch and no residual scrap to form when the knife switch is moved between the first and second positions.

20. The apparatus of claim 19 further comprising:

each of said second portions having a bore (50 '52') for mating with an opening (400) in a respective injection mold gate;

the bore has a diameter (D);

each of said second portions having a length (L) greater than the width of a respective injection gate to form a gap (402); and

the gap is larger than the diameter of the hole.

21. A method for injection molding an article substantially free of scrap material, comprising the steps of:

supplying at least one molten material from an injection nozzle (24, 26) through at least one nozzle outlet and through an injection gate substantially aligned with the at least one nozzle outlet to a cavity space (32, 34) of an injection mold (12);

substantially eliminating waste of molten material during molding by mounting a thin, movable valve gate opening device (48, 74, 76, 90, 104, 110, 120, 140, 284, 140 ', 48', 150, 166, 340, 342) having an orifice (50, 52, 86, 88, 106, 112, 126, 128, 142, 152, 168, 170, 286, 290, 292, 294, 310, 312, 346, 344, 50 ', 52') therein between an injection mold gate and the at least one nozzle outlet and moving the valve gate opening device between a first position in which the orifice is in communication with the at least one nozzle outlet and the injection mold gate to permit flow of molten material from the at least one nozzle outlet to the injection mold gate and a second position in which flow from the at least one nozzle outlet to the injection mold gate is interrupted without any of the molten material during movement of the valve gate opening device between the first and second positions The melting material is conveyed by the thin valve gating device.

22. The method of claim 21, wherein: the installing step includes providing a knife switch valve (48, 74, 76, 104, 110, 120, 140, 284, 140 ', 48') with an aperture, and the moving step includes sliding the knife switch valve laterally.

23. A method according to claim 21, comprising determining the valve gating device thickness Tmin by the equation:

Tmin＝4Vmin/(πD²)

wherein Tmin is the minimum thickness;

vmin — the minimum volume of the pore; and

d-the diameter of the hole.

24. The method of claim 22 including sliding the knife switch laterally in a direction generally perpendicular to the injection gate.

25. The method of claim 21, the plastic article being formed substantially without crystallinity in the injection gate region.

26. A method according to claim 21, forming a plastic article (60) in the cavity space and a portion (68) of the article being in contact with the valve gating device, characterized by: the portion of the article in contact with the valve gating device is substantially flat and substantially no knit line is formed in the article.

27. The method of claim 21, including the step of forming a defined gap between the injection nozzle and the injection mold that allows the valve gating device to move without leaking plastic material.

28. The method of claim 21, wherein: the mounting step includes mounting a disk (150) having at least one aperture (152) between the nozzle outlet and the injection mold gate, and the moving step includes rotating the disk between the first and second positions.

29. The method of claim 21 further comprising:

the injection lance (160) having a plurality of outlets (162, 164);

said mounting step includes providing a rotating member (166) having the same number of apertures (168, 170) as said number of outlets; and

the moving step includes rotating the rotating member between the first and second positions.

30. The method of claim 21, further comprising:

providing an injection nozzle (202, 134') having a plurality of channels for receiving different materials to be molded, each channel terminating in a nozzle outlet;

said mounting step includes mounting a thin, laterally movable knife switch valve (284, 140') having a single orifice (142, 286) between an injection molding gate and said nozzle outlet; and

sequentially feeding the different materials to the injection mold gate by moving the knife switch between positions where the holes are sequentially aligned with the different outlets.

31. The method of claim 21, further comprising:

providing an injection nozzle (202, 134') having a plurality of channels for receiving different materials to be molded, each channel terminating in a nozzle outlet;

said mounting step includes mounting a thin, laterally movable knife switch valve (284, 140 ') having a plurality of apertures (290, 292, 294, 310, 312, 142') between an injection molding gate and said nozzle outlet; and

sequentially supplying the different materials to the injection molding gate by moving the knife switch between positions where one of the holes is sequentially aligned with one of the different outlets.

32. The method of claim 31, further comprising:

different materials are simultaneously fed to the injection mold gate by moving the knife switch to a plurality (310, 312) of positions in the bore aligned with a plurality of the outlets.

33. A system for injection molding a plurality of articles, comprising:

a plurality of cavity spaces (204);

-an injection gate (143, 143 ', 282') per said cavity space;

means (134, 134', 202) for supplying at least two molten materials (A, B, C) to each of said cavity spaces via said injection gates;

a valve gate arrangement (140, 140', 284) movable between each of said injection gates and said feeder arrangement;

the movable valve gating device has a plurality of apertures (142, 142', 286, 310, 312);

means (56, 58) for moving the valve gating device between at least one open position and one closed position; in an open position, said bore communicates with said injection gate to allow flow of at least one of said molten materials to each of said cavity spaces, and in a closed position, flow of said molten materials to said cavity spaces is interrupted; and

the valve gating device is sufficiently thin that substantially no molten material is carried by the valve gating device during movement of the valve gating device between the positions.

34. The system of claim 33, wherein: the valve gating apparatus includes a knife switch having a plurality of holes therein.

35. The system of claim 33, wherein: the feeding device comprises a plurality of injection lances, each of said injection lances having at least two channels (136, 138, 136 ', 138', 270, 272, 274) for receiving at least two different materials; it also includes a plurality of extruders (A, B, C) in communication with each of the injection lances (202) through hot runner passages and each of the extruders supplying one of the materials to each of the injection lances.

36. The system of claim 35, wherein: each of said materials is sequentially fed into said cavity space through said aperture in said valve gating device.

37. The system of claim 35, wherein: each of said materials is simultaneously fed into said cavity space through said apertures (290, 292, 310, 312) located in said valve gating device.

38. The system of claim 35, wherein: each of the injection lances has two passages (136, 138, 136 ', 138', 270, 272, 274) for receiving two different materials, and each passage terminates in a respective lance outlet (137, 139, 137 ', 139', 276, 278, 280).