TW201417986A - Method for injection molding at low, substantially constant pressure - Google Patents

Abstract

Disclosed herein are methods of injection molding at low, substantially constant melt pressures. Embodiments of the disclosed method now make possible a method of injection molding that is more energy-and cost-effective than conventional high-velocity injection molding processes. Embodiments of the disclosed method surprisingly allow for the filling of a mold cavity at low melt pressure without undesirable premature hardening of the thermoplastic material in the mold cavity and without the need for maintaining a constant temperature or heated mold cavity. Heretofore, it would not have been expected that a constant pressure method could be performed at low pressure without such premature hardening of the thermoplastic material when using an unheated mold cavity or cooled mold cavity.

Description

Injection molding method at low and substantially constant pressure

The present invention relates to a method for injection molding, and more particularly to an injection molding method for use at low and substantially constant pressure.

Injection molding is a technique commonly used to mass produce parts made of fusible materials, most commonly made of plastic. During a repeated injection molding process, a thermoplastic resin, most commonly in the form of small beads, is introduced into one of the injection molding machines that melts the resin beads under heat and pressure. The molten resin is strongly injected into one of the cavities having a specific cavity shape. The ejected plastic is held in the cavity under pressure, cooled and then demolded into a solidified component having a shape that substantially replicates the cavity shape of the mold. The mold itself may have a single cavity or a plurality of cavities. Each cavity can be connected to a flow channel by a gate that directs the flow of molten resin into the cavity. Once formed, the component can have one or more gates. Large components typically have two, three or more gates to reduce the flow distance that the polymer must travel to fill the molded part. One or more gates per cavity may be located anywhere on the component geometry and have any cross-sectional shape, such as a cross-sectional shape that is substantially circular or shaped to have an aspect ratio of 1.1 or greater. Therefore, a typical injection molding process involves four basic operations: (1) heating the plastic in the injection molding machine to flow under pressure; and (2) injecting the molten plastic to the two mold halves defined by the closure. In one or several cavities between them; (3) when the pressure is under, the plastic is cooled in the cavity or the cavities And hardening; and (4) opening the mold halves to cause the part to be ejected from the mold.

The molten plastic resin is ejected into the cavity and the molten plastic resin is strongly pushed through the cavity by the injection molding machine until the plastic resin reaches the position farthest from the gate in the cavity. The resulting length of the part and the wall thickness are one of the shapes of the cavity.

While it may be desirable to reduce the wall thickness of the injection molded part to reduce the plastic content of the final part and thus the cost, using a conventional injection molding procedure to reduce wall thickness can be an expensive and a significant task, particularly for less than 1.0. The wall thickness of the millimeter is designed. When a liquid plastic resin is introduced into an injection mold in a conventional injection molding process, the material adjacent to the wall of the cavity immediately begins to "cold" or solidify or solidify, because the liquid plastic resin is cooled to a low level. At a temperature at one of the non-flowing temperatures of the material and the portion of the liquid plastic becomes static. As the material flows through the mold, a layer of boundary material is formed against the side of the mold. As the mold continues to fill, the boundary layer continues to thicken, eventually closing the material flow path and preventing additional material from flowing into the mold. When the mold is cooled (a technique for reducing the cycle time of each component and increasing the amount of machine production), the plastic resin on the wall of the mold is intensively cooled.

It is also desirable to design a component and corresponding mold such that the liquid plastic resin flows from the region having the thickest wall thickness toward the region having the thinnest wall thickness. Increasing the thickness in certain areas of the mold ensures that sufficient material flows into areas where strength and thickness are required. This "thick to thin" flow path requirement can result in inefficient use of plastics and a higher part for the manufacturer of injection molded parts The cost of the part is due to the fact that additional material must be molded into the part of the part where the material is not necessary.

One method for reducing the wall thickness of a component is to increase the pressure of the liquid plastic resin as it is introduced into the mold. By increasing the pressure, the forming machine can continue to force the liquid material into the mold before the flow path has closed. However, increasing pressure has both cost and performance negatives. Due to the increased pressure required to form the assembly, the forming equipment must be strong enough to withstand additional pressure, which is usually equivalent to being more expensive. A manufacturer may have to purchase new equipment to accommodate the increased pressure. Thus, a reduction in one of the wall thicknesses of a given component can result in significant capital expenditure to complete manufacturing via conventional injection molding techniques.

Additionally, when the liquid plastic material flows into the exit mold and is cold set, the polymer chain remains at a high stress level where the polymer is in liquid form. Such "in-forming" stresses can result in components that undesirably warp or sink after forming, have reduced mechanical properties, and have reduced chemical resistance. Controlling and/or minimizing reduced mechanical properties is particularly important for injection molded parts such as thin walled tubs, living hinge components, and outer casings.

According to an embodiment of the invention, a method comprises: (a) filling an unpressurized cavity of a forming device with a shot comprising a molten thermoplastic material; and (b) using the molten thermoplastic material The melt fill maintains the melt pressure substantially constant at less than 6000 psi during substantially the entire cavity. The shot comprising the molten thermoplastic material has an ejection of one of the shots including the molten thermoplastic material immediately after exiting into the mold cavity One of the front pressures of the melt pressure. An inner portion of the cavity that is spaced apart from the most intermediate surface of one of the cavities comprising the molten thermoplastic material by at least 2 mm is maintained at a temperature of less than about 100 °C. The thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes.

In accordance with another embodiment of the present invention, a method of ejecting a shot comprising a molten thermoplastic material into a cavity of a forming apparatus at a low and substantially constant pressure comprises: (a) including the melting The shot of the thermoplastic material is ejected into the cavity such that the pressure of one of the shots comprising the molten thermoplastic material increases immediately after injection to a melt pressure; and (b) substantially fills the entire cavity The melt pressure of the shot comprising the molten thermoplastic material is maintained at a substantially constant pressure of less than 6000 psi. An inner portion of the cavity that is spaced apart from the most intermediate surface of one of the cavities comprising the molten thermoplastic material by at least 2 mm is maintained at a temperature of less than about 100 °C. The molten thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes.

According to still another embodiment of the present invention, a method comprises: (a) filling a cavity by ejecting a shot comprising a molten thermoplastic material into a cavity of a molding apparatus; and (b) using The melt pressure comprising the molten thermoplastic material fills substantially the entire cavity to maintain the melt pressure substantially constant at less than 6000 psi. The cavity has a cavity pressure. The shot comprising the molten thermoplastic material has a pre-ejecting pressure that is not equal to one of the cavity pressures prior to exiting into the mold cavity. The shot comprising the molten thermoplastic material has one of the pressures immediately before exiting into the cavity Melt pressure. The thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes.

In accordance with another embodiment of the present invention, a method of ejecting a shot comprising a molten thermoplastic material into a cavity of a forming apparatus at a low and substantially constant pressure comprises: (a) including the melting The shot of the thermoplastic material is ejected into the cavity such that a pressure of one of the shots comprising the molten thermoplastic material after injection is immediately increased to a melt pressure; and (b) is comprised of the molten thermoplastic material The shot fills substantially the entire cavity while maintaining the melt pressure of the shot comprising the molten thermoplastic at a substantially constant pressure of less than 6000 psi and maintaining one of the pressures at atmospheric pressure at atmospheric pressure . The molten thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes.

In accordance with yet another embodiment of the present invention, a method of ejecting a shot comprising a molten thermoplastic material into a cavity of a forming apparatus at a low and substantially constant pressure comprises: (a) including the molten thermoplastic The shot of material is ejected into the cavity such that a pressure of one of the shots comprising the molten thermoplastic material after injection is immediately increased to a melt pressure; and (b) the molten thermoplastic material is included The shot fills substantially the entire cavity while maintaining the melt pressure of the shot comprising the molten thermoplastic at a substantially constant pressure of less than 6000 psi and maintaining a vacuum in the cavity. The molten thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes.

The embodiments set forth in the drawings are illustrative and illustrative in nature and not It is intended to limit the subject matter defined by the scope of the patent application. The following detailed description of the illustrative embodiments may be understood as

All of the pressures disclosed herein are gauge pressures that are indicative of the pressure of the pressure system relative to the surrounding pressure.

Disclosed herein is an injection molding process at low and substantially constant melt pressures. Embodiments of the disclosed method now enable a more energy efficient and cost effective injection molding process than conventional high speed injection molding procedures. Surprisingly, embodiments of the disclosed method allow a cavity to be filled at low melt pressure without the thermoplastic material undesirably prematurely hardening in the cavity and without the need to maintain a constant temperature or heated cavity. As explained in detail below, those skilled in the art have not anticipated that a constant pressure process can be performed at low pressures without the premature hardening of the thermoplastic material when using an unheated cavity or a cooled cavity.

Embodiments of the disclosed method also allow for the formation of high quality, ejected molded parts that do not experience undesirable sinking or warping, without the need to balance the pre-extrusion cavity pressure and the pre-extrusion pressure of the thermoplastic material. Thus, embodiments of the disclosed methods can be performed using cavity atmospheric pressure and eliminate the need to include a pressurized member in the cavity.

Embodiments of the method can also produce high quality, injection molded parts that have significantly less sensitivity to changes in temperature, viscosity, and other such properties of thermoplastic materials than conventional high pressure injection molding processes. In one embodiment, this may advantageously allow for the use of blends of recycled plastic (eg, post-consumer recycled plastic) and batch-to-batch variations inherently having material properties. A thermoplastic material formed from plastic.

Additionally, the low melt pressures used in the disclosed methods allow for the use of low cost, high thermal conductivity cavity materials that are more cost effective and energy efficient. For example, the cavity can be formed from a material having a surface hardness of less than 30 Rockwell C (Rc) and a thermal conductivity greater than 30 BTU/HR FT °F. In one embodiment, the cavity may be formed from an aluminum alloy, such as 6061 Al and 7075 Al.

Embodiments of the disclosed method may further allow for the formation of high quality thin walled components. For example, embodiments of the method can be used to form a molded part having a ratio of one to more than one hundred of a molten thermoplastic flow length to thickness (L/T). It is contemplated that embodiments of the method may also form a shaped part s having a ratio of L/T of greater than 200 and in some cases greater than 250.

When the length L of one of the flow channels is divided by the thickness T of one of the flow channels being greater than 100 (i.e., L/T > 100), the shaped part is generally considered to be thin-walled. For a cavity having a more complex geometry, the T dimension can be integrated over the length of the cavity 32 from the end of the gate 102 to the cavity 32 and the end of the gate 102 to the cavity 32 can be determined. The longest flow length is used to calculate the L/T ratio. The L/T ratio can then be determined by dividing the longest flow length by the average part thickness. In the case where one of the cavities 32 has more than one gate 30, the L/T ratio is determined by integrating L and T for portions of the cavity 32 filled by each individual gate, and a given mode The overall L/T ratio of the well is the highest L/T ratio calculated for any of the gates.

FIG. 1 illustrates an exemplary injection molding apparatus 10 for use with embodiments of the disclosed procedures. The injection molding device 10 usually includes an injection system System 12 and a clamping system 14. A thermoplastic material can be introduced into the injection system 12 in the form of, for example, colloidal particles 16. The colloidal particles 16 can be placed into a hopper 18 which feeds the colloidal particles 16 into a heated cylinder 20 of one of the injection systems 12. After being fed into the heated cylinder 20, the colloidal particles 16 can be driven by a reciprocating screw 22 to the end of the heated cylinder 20. Heating of the heated cylinder 20 and compression of the colloidal particles 16 by the reciprocating screw 22 causes the colloidal particles 16 to melt to form a molten thermoplastic material. The molten thermoplastic material is typically treated at a temperature of from about 130 °C to about 410 °C.

The reciprocating screw 22 forces the molten thermoplastic material toward a nozzle 26 to form a shot comprising a molten thermoplastic material 24 that will be ejected into the cavity 32 of a mold 28. The cavity 32 is formed between the first mold portion 25 of the mold 28 and the second mold portion 27, and the first mold portion 25 and the second mold portion 27 are held together under pressure by a press or mold clamping unit 34. . The press or clamping unit 34 applies a clamping force that is greater than the force exerted by the injection pressure to separate the two mold halves to cause the first mold when the molten thermoplastic material 24 is ejected into the cavity 32. The portion 25 is held together with the second mold portion 27. To support such clamping forces, the clamping system 14 can include a mold frame and a mold base formed from a material having a surface hardness of greater than about 165 BHN and preferably less than 260 BHN. However, materials having a surface hardness BHN value greater than 260 can be used as long as the material can be easily machined, as discussed further below.

Once the shot comprising the molten thermoplastic material 24 is ejected into the cavity 32, the reciprocating screw 22 stops traveling forward. Molten thermoplastic material 24 takes the mold The pockets 32 are externally shaped and the molten thermoplastic material 24 is cooled inside the mold 28 until the thermoplastic material 24 solidifies. Once the thermoplastic material 24 has solidified, the press 34 releases the first mold portion 25 and the second mold portion 27, the first mold portion 25 and the second mold portion 27 being separated from each other, and the finished member can be ejected from the mold 28. Mold 28 can include a plurality of cavities 32 to increase overall productivity. The shapes of the cavities in the plurality of cavities may be the same, similar or different from each other. (The latter can be regarded as a family of mold holes).

The method generally includes ejecting a shot comprising a molten thermoplastic material into a cavity 32 to fill the cavity. Referring to Figure 2, at t1 (before injection), the shot comprising the molten thermoplastic material has a pre-embedding pressure. As used herein, the pre-ejection pressure of a shot comprising a molten thermoplastic material refers to the thermoplastic material after it has been heated to a molten state in a heated cylinder and is ready to be shot and just to include a shot of molten thermoplastic material. The pressure before it is ejected into the cavity or in one of the runners or feed systems in fluid communication with the nozzle and cavity. The pre-ejection pressure of the shot comprising the molten thermoplastic material is not equal to the pressure of the cavity prior to ejection. In one embodiment, the cavity may be at atmospheric pressure prior to ejection, for example, as shown in Figures 2 and 4. In another embodiment, the cavity may have a slight positive pressure, as shown in FIG. In yet another embodiment, a vacuum may be included in the cavity.

As illustrated in Figure 2, after injection into the cavity during t2, the pressure of the shot comprising the molten thermoplastic material is increased to a pressure greater than one of the pre-extrusion pressures of the shot comprising the molten thermoplastic material. Referring again to FIG. 1, for example, the ejection of the shot comprising the molten thermoplastic material can include flattening the reciprocating screw 22 toward the nozzle 26 in the direction of arrow A in FIG. The shifting forces the shot comprising the molten thermoplastic material 24 through the nozzle 26 and into the cavity 32. In various embodiments, the shot 24 comprising molten thermoplastic material can be ejected through a gate 30 into a cavity 32 of a mold 28 that directs the flow of molten thermoplastic material 24 to the cavity 32. For example, the cavity 32 can be formed between the first mold portion 25 of the mold 28 and the second mold portion 27. The first mold portion 25 of the mold 28 and the second mold portion 27 can be held together under pressure by a press 34.

Referring again to Figure 2, at time t3, substantially the entire cavity or the entire cavity is filled with a shot comprising molten thermoplastic material. The melt pressure is maintained at a substantially constant pressure of less than 6000 psi during substantially the filling of the entire cavity. The term "substantially constant pressure" as used herein with respect to melt pressure of a thermoplastic material means that a deviation from a baseline melt pressure does not result in a meaningful change in the physical properties of the thermoplastic material. For example, "substantially constant pressure" includes, but is not limited to, pressure changes that do not materially change the viscosity of the thermoplastic material from which it is melted. In this regard, the term "substantially constant" encompasses a deviation of about 30% from a baseline melt pressure. For example, the term "approximately 4600 psi substantially constant pressure" includes pressure fluctuations in the range of about 6000 psi (30% higher than 4600 psi) to about 3200 psi (30% lower than 4600 psi). The melt pressure can be considered to be substantially constant as long as a melt pressure fluctuates from the pressure by no more than 30%. For example, substantially constant pressure may fluctuate from melt pressure (as an increase or decrease) from about 0% to about 30%, from about 2% to about 25%, from about 4% to about 20%, to about 6% to About 15% and about 8% to about 10%. Other suitable fluctuations include about 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% and 30%. The fluctuations are illustrated in Figure 2 as one of the desired melt pressures ΔP. Without wishing to be bound by theory, it is believed that maintaining a substantially constant pressure as defined herein prevents the retardation of the melt leading edge as the molten thermoplastic material flows into the cavity. Such dynamic flow conditions may advantageously allow the shot comprising the molten thermoplastic material to maintain uniform flow and landfill conditions to the final fill point of the mold without the melt material having cold or other stalls. As illustrated in Figures 3 and 4, the melt pressure during substantially the filling of the entire cavity can be increased or decreased, for example, at a constant rate, respectively, and as long as substantially the entire cavity is filled. The maximum increase or decrease in melt pressure during the period is not greater than 30% of the desired melt pressure, which is considered to be substantially constant. Again, this fluctuation is illustrated in Figures 3 and 4 as one of the desired melt pressures ΔP.

Referring to Figure 5 and as discussed in detail below, once substantially the entire cavity is filled (at time t3), the melt pressure can be reduced to a stacking pressure to fill the remainder of the cavity (at time t3') . The stacking pressure can be maintained substantially constant until the entire cavity is filled.

Once the cavity is completely filled, the melt pressure and cavity pressure (if necessary) are reduced to atmospheric pressure at time t4 and the cavity can be opened. During this time, the reciprocating screw 22 stops traveling forward. Advantageously, the low and substantially constant pressure conditions allow the shot comprising the molten thermoplastic material to be rapidly cooled inside the mold, which in various embodiments may occur substantially simultaneously with the discharge of the melt pressure and the cavity to atmospheric pressure. . Thus, the injection molded part can be quickly ejected from the mold after filling the cavity with the shot comprising the molten thermoplastic material.

A sensor can be located near the fill end in the cavity. This sensor can provide an indication of when the leading edge of the mold is near the fill end in the cavity. The sensor senses temperature, pressure, optical or other means of identifying the presence of the polymer. When the sensor measures pressure, this measurement can be used to communicate with the central control unit to provide a target "filling pressure" for one of the formed components. The signal generated by the sensor can be used to control the molding process so that changes in material viscosity, mold temperature, melt temperature, and other variations affecting the fill rate can be adjusted by the central control unit. These adjustments can be made immediately during the molding cycle or can be corrected in subsequent cycles. In addition, the readings can be averaged over several cycles and then used by the central control unit to adjust the molding process. In this way, the current injection cycle can be corrected based on measurements occurring at an earlier time point during one or more cycles. In one embodiment, sensor readings can be averaged over many cycles to achieve program consistency.

Melt pressure

As used herein, the term "melt pressure" refers to a pressure comprising one of a molten thermoplastic material as it is ejected into a cavity of a forming apparatus and filled into the cavity. The melt pressure of the shot comprising the molten thermoplastic material is maintained substantially constant at less than 6000 psi during substantially the filling of the entire cavity. The melt pressure of the shot comprising the molten thermoplastic material during substantially the filling of the entire cavity is significantly less than that used in conventional injection molding procedures and recommended by the manufacturer of the thermoplastic material used in the injection molding process. Body pressure. For example, other suitable melt pressures include less than 5000 psi, less than 4500 psi, less than 4000 psi, and small At 3000 psi. For example, the melt pressure can be maintained at from about 1000 psi to less than 6000 psi, from about 1500 psi to about 5500 psi, from about 2000 psi to about 5000 psi, from about 2500 psi to about 4500 psi, from about 3000 psi to about 4000 psi. And a substantially constant pressure in the range of from about 3000 psi to less than 6000 psi.

As set forth above, a "substantially constant pressure" means that the melt pressure from the desired melt pressure fluctuates upwardly or downwardly by no more than the desired melt pressure during filling of substantially the entire cavity with the shot comprising the molten thermoplastic material. One of the pressures. For example, substantially constant pressure may fluctuate from melt pressure (as an increase or decrease) from about 0% to about 30%, from about 2% to about 25%, from about 4% to about 20%, to about 6% to About 15% and about 8% to about 10%. Other suitable fluctuations include about 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% And 30%. The fluctuations are illustrated in Figure 2 as one of the desired melt pressures ΔP. Referring to Figures 3 and 4, the melt pressure during substantially the filling of the entire cavity can be increased or decreased, for example, at a constant rate, respectively, and as long as the melt is substantially during the filling of the entire cavity. The maximum increase or decrease in pressure is not greater than 30% of the desired melt pressure, which is considered to be substantially constant. Again, this fluctuation is illustrated in Figures 3 and 4 as one of the desired melt pressures ΔP. In yet another embodiment, the melt pressure during substantially the filling of the entire cavity may increase within one of the times t3 and then decrease within the remainder of time t3. This fluctuation can be considered as a substantially constant pressure as long as the maximum increase or decrease in melt pressure during filling is not greater than 30% of the desired melt pressure.

A pressure sensor, for example, disposed at the exit point, can be used to measure the melt pressure of the shot comprising the thermoplastic material after exiting into the mold cavity. As used herein, an "ejection point" is a molding apparatus that includes a location of a molten thermoplastic material into a cavity. For example, for a forming device having a single cavity coupled to one of the nozzles, the exit point can be at or adjacent to the nozzle. Another option is for a molding device having a plurality of cavities and a sprue system for transporting molten thermoplastic material from the nozzle to each of the cavities, the ejecting point can be a sprue system and an individual The point of contact between each of the cavities. The shot comprising the molten thermoplastic material is maintained at a substantially constant melt pressure as it is delivered through the sprue system. In general, the sprue system maintains one of its melt temperatures through a heated runner system when delivering a shot comprising molten thermoplastic material to the cavity.

The melt pressure of the shot comprising the thermoplastic material during substantially the filling of the entire cavity may, for example, be measured by using a pressure sensor disposed at the nozzle and after exiting into the cavity Immediately maintain a constant pressure at the nozzle to maintain. In another embodiment, the melt pressure of the shot comprising thermoplastic material during substantially the filling of the entire cavity can be measured using a pressure sensor disposed in the cavity opposite the gate.

The cavity fill percentage is defined as the % of the cavity filled on a volume basis. Therefore, if a cavity is filled with 95%, the total volume of the filled cavity is 95% of the total volume of the cavity. At least 70%, at least 72%, at least 74%, at least 76%, at least 78%, at least 80%, at least 82%, at least 84%, at least 86%, at least 88%, at least at least 80% of the cavity is filled with the molten thermoplastic material. 90%, at least 92%, at least 94%, at least 96%, at least At 98% or at least 99%, substantially the entire cavity is filled. For example, when the molten thermoplastic material is filled from about 70% to about 100%, from about 75% to about 99%, from about 80% to about 97%, or from about 90% to about 95% of the cavity, substantially the entire mold The hole is filled. The percentage of the cavity filled with the shot comprising the molten thermoplastic material can be determined, for example, by placing a pressure sensor in the cavity corresponding to the desired fill point of the filled cavity. The pressure sensor alerts the operator when the shot comprising the molten thermoplastic material has reached the desired fill percentage.

Referring to Figure 5, in one embodiment, once substantially the entire cavity is filled (at the end of time t3), a reduced melt pressure can be used to fill and stack the remainder of the cavity (time) T3'). Once substantially the entire cavity is filled, the melt pressure of the shot comprising the molten thermoplastic material can be reduced to less than one of the melt pressures of the melt pressure to provide an ideal pressure for filling the remainder of the cavity and Prevent excessive pressurization or excessive filling of the cavity. The remainder of the cavity can be filled while maintaining the melt pressure of the shot comprising the molten thermoplastic material substantially constant at the stacking pressure. For example, the landfill pressure can be at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least at least the melt pressure. 95% or at least 99%.

In another embodiment, once substantially the entire cavity is filled, the melt pressure can be increased to fill and fill the remainder of the cavity.

Maintaining a constant constant pressure

In one embodiment, a hydraulic pressure is applied to the shot comprising the molten thermoplastic material 24 to include the molten thermoplastic material 24 at the melt temperature. The shot is ejected into the cavity. Hydraulic pressure may be applied, for example, by translating the reciprocating screw 22 in the direction of arrow A in FIG. 1 toward the nozzle 26 to force the shot comprising the molten thermoplastic material 24 through the nozzle 26 and into the cavity 32. pressure. The melt pressure of the shot comprising the molten thermoplastic material 24 after the injection into the cavity 32 and the melt pressure of the shot of the molten thermoplastic material 24 during the filling of the cavity 32 is then monitored and adjusted to exit the mold by monitoring the melt pressure of the shot comprising the molten thermoplastic material 23 after injection into the cavity 32. The hydraulic pressure applied to the shot comprising the molten thermoplastic during the cavity maintains the melt pressure substantially constant during filling of the shot comprising the molten thermoplastic material 24 into the cavity 32. The melt pressure can be monitored using a pressure sensor disposed at the injection point (e.g., nozzle 26) and in the cavity 32.

A controller 50 is communicatively coupled to a sensor 52 and a screw control member 36. Controller 50 can include a microprocessor, a memory, and one or more communication links. Controller 50 can be coupled to sensor 52 and screw control 36 via wired connections 54, 56, respectively. In other embodiments, controller 50 may allow controller 50 and sensor 52 and screw control 36 via a wireless connection, a mechanical connection, a hydraulic connection, a pneumatic connection, or known to those skilled in the art. Any other type of communication connection for communication between the two is coupled to sensor 52 and screw control 56.

In the embodiment of FIG. 1, sensor 52 measures one (directly or indirectly) a pressure sensor that melts the melt pressure of thermoplastic material 24 in nozzle 26. The sensor 52 produces an electrical signal that is transmitted to the controller 50. The controller 50 then commands the screw control 36 to advance the screw 22 at a rate that maintains a substantially constant melt pressure of one of the molten thermoplastic materials 24 in the nozzle 26. Although the sensor 52 can directly measure the melt pressure, the sensor 52 can measure the melt pressure. Other properties of the molten thermoplastic material 24, such as temperature, viscosity, flow rate, and the like. Likewise, the sensor 52 need not be located directly in the nozzle 26, but rather the sensor 52 can be located anywhere within the firing system 12 or mold 28 that is fluidly coupled to the nozzle 26. The sensor 52 need not be in direct contact with the ejected fluid, and another selection system can be in fluid communication and can sense the pressure of the fluid and/or other fluid characteristics. If the sensor 52 is not located within the nozzle 26, an appropriate correction factor can be applied to the measured characteristic to calculate the melt pressure in the nozzle 26. In still other embodiments, the sensor 52 need not be disposed at a location that is fluidly coupled to the nozzle. Rather, the sensor can measure the clamping force generated by the clamping system 14 at a mold parting line between the first mold portion 25 and the second mold portion 27. In one aspect, controller 50 can maintain pressure based on input from sensor 52.

Although an active closed loop controller 50 is illustrated in FIG. 1, other pressure regulating devices may be used in place of the closed loop controller 50. For example, a pressure regulating valve (not shown) or a pressure relief valve (not shown) can replace controller 50 to regulate the melt pressure of molten thermoplastic material 24. More specifically, the pressure regulating valve and the pressure relief valve prevent overpressure of the mold 28. Another alternative mechanism for preventing overpressure of the mold 28 is to activate one of the alarms when an overpressure condition is detected.

Thus, in another embodiment, the forming apparatus section includes a pressure relief valve disposed between an injection point and a cavity. The pressure relief valve has a predetermined pressure set point equal to one of the desired melt pressures for injection and filling of the cavity. By forcing a pressure to a shot comprising a molten thermoplastic material to force a molten thermoplastic material at a melt pressure above one of a predetermined set point The shot passes through a pressure relief valve to maintain a substantially constant melt pressure during injection and filling of the cavity. The pressure relief valve then reduces its melt pressure as it passes through the pressure relief valve and exits into the cavity. The reduced melt pressure of the shot comprising the molten thermoplastic material corresponds to the desired melt pressure for filling the cavity and is maintained substantially constant by a predetermined set point of the pressure relief valve.

In one embodiment, the melt pressure is reduced by diverting a portion of the shot comprising the thermoplastic material to one of the outlets of the pressure relief valve. The diverted portion of the shot comprising the thermoplastic material can be maintained in a molten state and can be reincorporated into the injection system, for example, through a heated cylinder.

Cavity

The forming device comprises a mold having at least one cavity. The mold can comprise any suitable number of cavities. Embodiments of the methods disclosed herein advantageously allow the use of molds having asymmetrically oriented mold cavities and/or mold cavities having different shapes. Despite the asymmetry in the cavity configuration, the use of low and substantially constant fill pressure for embodiments of the method may allow each cavity to be filled under balanced landfill conditions. Thus, despite the asymmetric orientation, high quality, ejected molded parts can be formed in each of the mold cavities. The ability to asymmetrically configure the cavity of a mold can advantageously allow for a high cavity density in a mold, thereby allowing an increased number of injection molded parts to be formed by a single mold and/or allowing one of the sizes of the mold to be reduced. small.

Cavity pressure

As used herein, "cavity pressure" refers to the pressure within a closed cavity. Can be used, for example, by a pressure sensor placed inside the cavity Measure the cavity pressure. In an embodiment of the method, the cavity pressure is different from the pre-ejection pressure of the shot comprising the molten thermoplastic material prior to injecting the shot comprising the molten thermoplastic material into the cavity. For example, the cavity pressure can be less than the pre-ejection pressure of the shot comprising the molten thermoplastic material. In another embodiment, the cavity pressure can be greater than the pre-ejection pressure of the shot comprising the molten thermoplastic material. For example, the cavity pressure prior to injection may differ from (before or less than) the pre-ejection pressure of the shot comprising the molten thermoplastic material by at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, At least 40% or at least 50%. In one embodiment, the cavity pressure differs (greater than or less than) from the pre-extrusion pressure of the shot comprising the molten thermoplastic material by at least 15 psi. Referring to Figures 2 and 4, in various embodiments, the cavity pressure prior to ejection can be at atmospheric pressure. In other embodiments, for example, as shown in FIG. 3, the cavity pressure may have a pressure greater than one of atmospheric pressure. In yet another embodiment, the cavity can be maintained in a vacuum prior to ejection.

In various embodiments, the cavity pressure can be maintained substantially constant during the filling of substantially the entire cavity with the shot comprising the molten thermoplastic material. As used herein, a "substantially constant cavity pressure" is one or more of a pressure that does not fluctuate by more than 30% from the desired melt pressure during filling of substantially the entire cavity with a shot comprising a molten thermoplastic material. . For example, substantially constant pressure may fluctuate from melt pressure (as an increase or decrease) from about 0% to about 30%, from about 2% to about 25%, from about 4% to about 20%, to about 6% to About 15% and about 8% to about 10%. Other suitable fluctuations include about 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% And 30%. Referring to Figure 2, for example, may include melting The injection of the thermoplastic material maintains the cavity pressure at a substantially constant atmospheric pressure during substantially the entire cavity. Referring to Figure 3, for example, the cavity pressure can be maintained substantially constant at a pressure greater than atmospheric pressure equal to one of the pre-extrusion pressures of the cavity. In another embodiment, the cavity pressure can be maintained at a substantially constant pressure that is greater than one of the pre-extrusion pressures of the cavity. For example, a suitable cavity pressure for filling a cavity includes, for example, from about 50 psi to about 500 psi.

The cavity can include, for example, one or more vents for maintaining the cavity pressure substantially constant. The vents can be controlled to open and close to maintain a substantially constant cavity pressure.

In one embodiment, a vacuum may be maintained in the cavity during injection and filling of substantially the entire cavity with the shot comprising the molten thermoplastic material. Maintaining a vacuum in the cavity during injection can advantageously reduce the amount of melt pressure required to fill the cavity, as there is no air that is pumped from the cavity during filling. The lack of air resistance to flow and the increased pressure drop between melt pressure and fill end pressure can also result in a greater flow length of one of the shots comprising molten thermoplastic material.

Referring to Figure 5, in another embodiment, the cavity pressure can be increased during filling of substantially the entire cavity with a shot comprising a molten thermoplastic material. For example, the cavity pressure may increase in proportion to the displacement volume of the cavity during filling. The increase in cavity pressure can occur, for example, at a substantially constant rate. The cavity may include an exhaust port for maintaining the increased cavity pressure below a predetermined set point. The predetermined set point can be, for example, a melt pressure comprising an injection of molten thermoplastic material. The predetermined set point can also be (For example) a pressure above which may damage the cavity or adversely affect the quality of the injection molded part.

Once the cavity is completely filled with the shot comprising the molten thermoplastic material and the material has cooled, the cavity pressure can be discharged (if necessary) to atmospheric pressure and the mold can be opened to release the ejected molded part.

Cavity temperature

In an embodiment of the method, the cavity is maintained at room temperature or cooled prior to injection and filling of the cavity with a shot comprising molten thermoplastic material. Although the cavity surface may increase the temperature immediately after contact with the molten thermoplastic material, it is spaced at least 2 mm, at least 3 mm, at least 4 mm, at least 5 mm from the most intermediate surface of the cavity contacting the shot comprising the thermoplastic material. The inner portion of one of the cavities at least 6 mm, at least 7 mm, at least 8 mm, at least 9 mm, or at least 10 mm is maintained at a lower temperature. Typically, this temperature is less than the no-flow temperature of the thermoplastic material. As used herein, "no flow temperature" means the temperature at which the viscosity of the thermoplastic material is so high that it cannot be effectively flowed. In various embodiments, the inner portion of the mold can be maintained at a temperature of less than about 100 °C. For example, the internal portion can be maintained at from about 10 ° C to about 99 ° C, from about 20 ° C to about 80 ° C, from about 30 ° C to about 70 ° C, from about 40 ° C to about 60 ° C, and from about 20 ° C to about 50 ° C. a temperature. Other suitable temperatures include about 10 ° C, 15 ° C, 20 ° C, 25 ° C, 30 ° C, 35 ° C, 40 ° C, 45 ° C, 50 ° C, 55 ° C, 60 ° C, 65 ° C, 70 ° C, 75 ° C, 80 ° C, 85 ° C, 90 ° C, 95 ° C or 99 ° C. In one embodiment, the inner portion can be maintained at a temperature of less than 50 °C. In one embodiment, the inner portion can be maintained at less than 30 ° C a temperature.

Up to now, when filling at a low constant pressure, the filling rate is reduced relative to the conventional filling method. This means that the polymer will be in contact with the cooled forming surface for a longer period of time before the mold will completely fill. Therefore, more heat will need to be removed before filling, and it is expected that this will cause the material to consolidate before the mold fills up. It has been unexpectedly discovered that the thermoplastic material will flow when subjected to low and substantially constant pressure conditions, although one portion of the cavity is below the no-flow temperature of the thermoplastic material. It will generally be appreciated by those skilled in the art that such conditions will cause the thermoplastic material to freeze and block the cavity rather than continuing to flow and fill the entire cavity. Without wishing to be bound by theory, it is believed that the low and substantially constant pressure conditions of embodiments of the disclosed methods allow for dynamic flow conditions throughout the cavity during filling (i.e., constantly moving melt front) . There is no hysteresis in the flow of the molten thermoplastic material as it flows to fill the cavity, and therefore, there is no consolidation of the flow, although at least a portion of the cavity is below the no-flow temperature of the thermoplastic material. Additionally, it is believed that due to dynamic flow conditions, the molten thermoplastic material can maintain a temperature above one of the no-flow temperatures due to shear heating, although it is subjected to such temperatures in the mold cavity. It is further believed that dynamic flow conditions prevent the formation of crystalline structures in the thermoplastic material as it begins the cold set process. The crystalline structure increases the viscosity of the thermoplastic material, which prevents proper flow of the filling cavity. The reduction in crystal structure formation and/or crystal structure size may allow one of the thermoplastic material's viscosity to decrease as the thermoplastic material flows into the mold cavity and experiences a lower temperature of the mold below the material's no-flow temperature.

In various embodiments, the mold can include maintaining the entire cavity below One of the temperatures of one of the non-flowing temperatures cools the system. For example, even the surface of the cavity that contacts the shot comprising the molten thermoplastic material can be cooled to maintain a lower temperature. Any suitable cooling temperature can be used. For example, the mold can be maintained substantially at room temperature. Incorporating such cooling systems can advantageously enhance the rate at which the formed injection molded part is cooled and ready to eject from the mold.

Thermoplastic material:

A wide variety of thermoplastic materials can be used in the low and substantially constant pressure injection molding process of the present invention. In one embodiment, the molten thermoplastic material has a melt flow index from about 0.1 g/10 minutes to about 500 g/10 minutes (measured by ASTM D1238 performed at a temperature of about 230 C at a pressure of 2.16 kg) ) define one of the viscosities. For example, for polypropylene, the melt flow index can range from about 0.5 g/10 minutes to about 200 g/10 minutes. Other suitable melt flow indices comprise from about 1 g/10 minutes to about 400 g/10 minutes, from about 10 g/10 minutes to about 300 g/10 minutes, from about 20 g/10 minutes to about 200 g/10 minutes, about 30 g/10 min to about 100 g/10 min, about 50 g/10 min to about 75 g/10 min, about 0.1 g/10 min to about 1 g/10 min or about 1 g/10 min to about 25 g/10 minutes. The MFI of the material is selected based on the application and use of the shaped article. For example, a thermoplastic having a MFI of from 0.1 g/10 minutes to about 5 g/10 minutes can be suitably used as a preform for injection stretch blow molding (ISBM) applications. A thermoplastic material having an MFI of from 5 g/10 minutes to about 50 g/10 minutes can be suitably used as a cover and outer casing for packaging articles. Thermoplastic materials having an MFI of from 50 g/10 minutes to about 150 g/10 minutes are suitable for use in the manufacture of buckets or drums. With 150 g/10 points The thermoplastic material of the MFI, which is one of about 500 g/10 minutes, can be adapted to a shaped article having a very high L/T ratio, such as a sheet. Manufacturers of such thermoplastic materials generally teach that the materials should be injection molded using melt pressures in excess of 6000 psi and typically well in excess of 6000 psi. Embodiments of the low and constant injection molding process of the present invention advantageously allow for use at melt pressures below 6000 psi and possibly below 6000 psi, as compared to conventional teachings regarding injection molding of such thermoplastic materials. Thermoplastic materials and treatments form high quality, injection molded parts.

For example, the thermoplastic material can be a polyolefin. Exemplary polyolefins include, but are not limited to, polypropylene, polyethylene, polymethylpentene, and polybutene-1. Any of the foregoing polyolefins may be derived from bio-based materials such as sugar cane or other agricultural products used to produce a bio-polypropylene or bio-polyethylene. The polyolefin advantageously exhibits shear thinning when in a molten state. Shear thinning reduces one of the viscosities when the fluid is placed under compressive stress. Shear thinning can beneficially allow the flow of thermoplastic material to be maintained throughout the injection molding process. Without wishing to be bound by theory, it is believed that a thermoplastic material, and in particular the shear thinning nature of the polyolefin, results in less variation in material viscosity when the material is treated at low pressure. Thus, embodiments of the method of the present invention may be less sensitive to, for example, variations in thermoplastic materials resulting from colorants and other additives and processing conditions. Sensitivity to this reduction in batch-to-batch variation in the properties of the thermoplastic material may also advantageously allow for the use of embodiments of the method of the invention to treat post-industrial and post-consumer recycled plastic. Post-industrial and post-consumer recycled plastics are derived from finished products that have been cycled through their useful life as a consumer product and would have been disposed of as a solid waste. This again Blends of recycled plastic and thermoplastic materials inherently have significant inter-batch variations in their material properties.

For example, the thermoplastic material can also be a polyester. Exemplary polyesters include, but are not limited to, polyethylene terephthalate (PET). The PET polymer can be derived from bio-based materials such as sugar cane or other agricultural products used to produce a portion or complete bioPET polymer. Other suitable thermoplastic materials include copolymers of polypropylene and polyethylene and polymers and copolymers of thermoplastic elastomers, polyesters, polystyrenes, polycarbonates, poly(acrylonitrile-butadiene-styrene) ), poly(lactic acid), bio-based polyester (such as poly(ethylene glycolate), polyhydroxyalkanoate, poly(ethylene glycolate) (considered as one of PET replacement or drop-in replacement) ), polyhydroxyalkanoates, polyamines, polyacetals, ethylene-α-olefin rubbers, and styrene-butadiene-styrene block copolymers. The thermoplastic material can also be a blend of a plurality of polymeric and non-polymeric materials. For example, the thermoplastic material can be a blend of high, medium, and low molecular polymers that produces a multimodal or bimodal blend. Multimodal materials can be designed in such a way that one of the thermoplastic materials with superior flow properties and satisfactory chemical/physical properties can be produced. The thermoplastic material can also be a blend of a polymer and one or more small molecule additives. For example, the small molecule can be a monooxane or other lubricating molecule that improves the flow of the polymeric material when added to the thermoplastic.

Other additives may include: inorganic fillers such as calcium carbonate, calcium sulfate, talc, clay (eg, nano clay), aluminum hydroxide, CaSiO3, glass formed into fibers or microspheres, crystalline alumina (eg, quartz, Microcrystalline cerium oxide (novacite), microcrystalline), magnesium hydroxide, mica, sodium sulfate, zinc bismuth White, magnesium carbonate, iron oxide; or organic fillers such as rice husks, straw, hemp fibers, wood flour or wood, bamboo or sugar cane fibers.

Other suitable thermoplastic materials include: renewable polymers, such as non-limiting examples of polymers produced directly from the organism, such as polyhydroxyalkanoates (eg, poly(beta-hydroxyalkanoates), poly(3-hydroxybutans) Acid esters - co--3-hydroxyvalerate, NODAX (registered trademark) and bacterial cellulose; polymers extracted from plants, crops and forest crops and biomass, such as polysaccharides and their derivatives (eg, gums, fibers) , cellulose ester, chitin, chitosan, starch, chemically modified starch, cellulose acetate particles), proteins (eg, zein, whey protein, gluten, collagen), lipids, lignin And natural rubber; thermoplastic starch derived from starch or chemical starch, and general-purpose polymers derived from monomers and derivatives of natural sources, such as bio-polyethylene, bio-polypropylene, poly-trimethylene terephthalate, polylactic acid, NYLON 11, alkyd resin, succinic acid based polyester and biopolyethylene terephthalate.

Suitable thermoplastic materials may comprise one or several blends of different thermoplastic materials such as those cited above. The different materials may also be a combination of one of the materials derived from the original biologically derived or petroleum derived materials or the recycled materials of the biologically derived or petroleum derived materials. One or more of the thermoplastic materials in a blend may be biodegradable. And for non-blended thermoplastic materials, the material can be biodegradable.

An exemplary thermoplastic resin is provided in the chart below along with its recommended operating pressure range:

Although one of the embodiments relates to substantially filling the entire cavity with a shot comprising a molten thermoplastic material while including a molten thermoplastic material The melt pressure of the shot is maintained at a substantially constant pressure of less than 6000 psi, but certain thermoplastic materials benefit from the present invention at different constant pressures. Specifically: PP, nylon, PC, PS, SAN, PE, TPE, PVDF, PTI, PBT, and PLA at a substantially constant pressure of less than 10,000 psi; ABS at a substantially constant pressure of less than 8000 psi; a substantially constant pressure PET at less than 5800 psi; a substantially constant pressure acetal copolymer at less than 7000 psi; plus substantially less than 10,000 psi or 8000 psi or 7000 psi or 6000 psi or 5800 psi Constant pressure poly(ethylene furoate) polyhydroxyalkanoate, furfuric acid polyethylene (also known as PEF).

As explained in detail above, the disclosed embodiments of the low and substantially constant pressure method may achieve one or more of the conventional high pressure injection molding procedures, prior art high constant pressure injection molding procedures, and prior art lower pressure injection molding procedures. advantage. For example, embodiments include a procedure that eliminates the need to balance one of the need for cavity and thermoplastic material pre-ejection pressure, is more cost effective and more efficient, allows for the use of one of the atmospheric pressures of the cavity, and thus eliminates the need for pressurized components Simplified mold structure, the ability to use lower cost and high thermal conductivity cavity materials that are more cost effective and easier to machine, less sensitive to changes in temperature, viscosity and gas material properties of thermoplastic materials. The method and the ability to produce high quality, injection molded parts at low pressure without prematurely hardening the thermoplastic material in the cavity and without the need to heat or maintain a constant temperature in the cavity.

In one example, the sample part is formed using a low constant pressure program that is less than 6000 PSI of the injection pressure. The sample is isolated from the injection molded part using a common laboratory microtome. From each shot molded part to Four samples are missing. The profile of the sample is then prepared to expose the constituent layers (skin, core, etc.) of each sample.

The synchrotron measurement is performed by the DORIS III with the MAXIM detector ensemble under the German Electronic Synchrotron (DESY) beam line G3, that is, the first measurement is obtained by the point average scintillation counter to obtain the sample diffraction. Overview. The spatially resolved diffracted image is then acquired by a MAXIM position sensitive camera (a 2D detector Hamamatsu 4880 with a multi-channel board [MCP] in front of its CCD sensor).

Synchrotron measurement reveals that an injection molded part having a specific thickness formed using a low constant pressure process exhibits a different and discernible additional oriented polypropylene microcrystalline strip or zone in the core of the part (see the figure below). Red arrow). This additional oriented material zone can be seen in parts that are formed using steel or aluminum molds. The use of a component that is conventionally formed using a higher pressure program typically has a reduced number of orientation bands when compared to forming a component using a low constant pressure process.

Parts molded using a low constant pressure program can have less stress in the forming process. In a conventional procedure, a combination of a speed controlled filling procedure and a higher transfer or conversion to one of the pressure controls can result in a component having a high level of undesired forming stress. If the stacking pressure is set too high in a conventional procedure, the part will typically have an overfilled gate area. The stress in the forming can be visually evaluated by placing the component on a crossed polarization metering station. The birefringence observed in the molded part can be used to observe the difference in stress during forming. Typically, this observation is a pattern of stress lines in the part. It is generally undesirable to have a large number of lines of stress lines and/or unevenness.

It should be noted that the terms "substantially", "about" and "about" may be used herein to mean the degree of inherent uncertainty attributable to any quantitative comparison, value, measurement or other representation. The terms are also used herein to indicate that the quantitative representation may vary from one of the stated reference, but does not result in a change in one of the basic functions of the subject matter in question. Unless otherwise defined herein, the terms "substantially", "about" and "about" mean that the specified quantity, value, measurement, or other representation may be within 5% of the stated reference.

It should now be apparent that various embodiments of the products illustrated and described herein can be produced by a low and substantially constant pressure forming process. Although specific reference has been made herein to a product for consuming a consumer product or a consumer product product itself, it should be understood that the molding method discussed herein may be suitable for combination in the consumer goods industry, the food service industry, the transportation industry, medical care. Used in products used in industry, toy industry and similar industries. Moreover, those skilled in the art will recognize that the teachings disclosed herein can be combined with in-mold decoration, insert molding, in-mold assembly, and the like for constructing a stack, multi-material mold (including rotation and core return). Mold).

The relevant portions of all documents cited in the Detailed Description of the Invention are hereby incorporated by reference. In addition, if any meaning or definition of a term in this document is inconsistent with any meaning or definition of the term in a document incorporated by reference, the meaning or definition assigned to the term in this document is quasi.

Although the specific embodiments have been illustrated and described herein, it is understood that various modifications may be made without departing from the spirit and scope of the claimed subject matter. He changed and modified. In addition, although various aspects of the claimed subject matter are set forth herein, it is not necessary to utilize such aspects in combination. Accordingly, the scope of the appended claims is intended to cover all such modifications and modifications

10‧‧‧Injection molding device

12‧‧‧Injection system

16‧‧‧gel

18‧‧‧ hopper

20‧‧‧heated cylinder

22‧‧‧Reciprocating screw

24‧‧‧Metal thermoplastic materials

25‧‧‧First mould part

26‧‧‧Nozzles

27‧‧‧Second mold part

28‧‧‧Mold

30‧‧‧gate

32‧‧‧ cavity

34‧‧‧ Press or clamping unit

36‧‧‧ Screw control parts

50‧‧‧Controller/active closed-loop controller

52‧‧‧ sensor

54‧‧‧Wired connection

56‧‧‧Wired connection

1 illustrates a schematic elevational view of one of the high speed injection molding machines in accordance with one or more of the embodiments shown and described herein; FIG. 2 is a low and substantially constant pressure in accordance with an embodiment of the present invention. One of the pressure-variation curves of one of the injection molding methods is schematically illustrated; FIG. 3 is a schematic diagram of one of the pressure-volume curves of one of the injection molding methods at a low and substantially constant pressure according to another embodiment of the present invention. 4 is a schematic illustration of one of the pressure-volume curves of one of the injection molding methods at low and substantially constant pressure in accordance with an embodiment of the present invention; and FIG. 5 is in accordance with yet another embodiment of the present invention. One of the pressure-variation curves of one of the injection molding methods at low and substantially constant pressure is schematically illustrated.

10‧‧‧Injection molding device

12‧‧‧Injection system

16‧‧‧gel

18‧‧‧ hopper

20‧‧‧heated cylinder

22‧‧‧Reciprocating screw

24‧‧‧Metal thermoplastic materials

25‧‧‧First mould part

26‧‧‧Nozzles

27‧‧‧Second mold part

28‧‧‧Mold

30‧‧‧gate

32‧‧‧ cavity

34‧‧‧ Press or clamping unit

36‧‧‧ Screw control parts

50‧‧‧Controller/active closed-loop controller

52‧‧‧ sensor

54‧‧‧Wired connection

56‧‧‧Wired connection

Claims (13)

A method of ejecting a shot comprising a molten thermoplastic material into a cavity of a forming apparatus at a low and substantially constant pressure, the method comprising: (a) the shot comprising the molten thermoplastic material Ejecting into the cavity such that one of the shots comprising the molten thermoplastic material after injection is immediately increased to a melt pressure; and (b) substantially including the molten thermoplastic during filling of the entire cavity The melt pressure of the shot of the material is maintained at a substantially constant pressure of less than 6000 psi, wherein: at least 2 mm is spaced from the most intermediate surface of the one of the cavities contacting the shot comprising the molten thermoplastic material. One of the interior portions of the cavity is maintained at a temperature of less than about 100 ° C and the molten thermoplastic material has a melt flow index of from 0.1 g/10 minutes to about 500 g/10 minutes. The method of claim 1, wherein the inner portion of the cavity is maintained at a temperature of about 30 ° C or less. The method of claim 1 wherein the mold cavity is maintained at less than about 100 ° C by flowing a cooling liquid through at least a portion of the mold cavity when the shot comprising the molten thermoplastic material is injected into the mold cavity. One of the temperatures. The method of claim 1, wherein the ejecting comprises: ejecting the shot into the cavity when the cavity pressure is at atmospheric pressure. The method of claim 1, wherein the ejecting comprises: ejecting the shot into the cavity when the cavity pressure is not pressurized. A method comprising: (a) filling a cavity by ejecting a shot comprising a molten thermoplastic material into a cavity of a forming device, the cavity having a cavity pressure comprising the molten thermoplastic The shot of the material has a pre-ejecting pressure that is not equal to one of the cavity pressures prior to exiting into the mold cavity, and the shot comprising the molten thermoplastic material has an amount immediately after exiting into the mold cavity, immediately before the ejection One of the pressures of the melt pressure; and (b) maintaining the melt pressure substantially constant at less than 6000 psi when the entire mold cavity is filled with the shot comprising the molten thermoplastic material, wherein the thermoplastic material has One melt flow index from 0.1 g/10 min to about 500 g/10 min. The method of claim 6, wherein the pre-extrusion pressure of the shot comprising the molten thermoplastic material exceeds the cavity pressure. The method of claim 7, wherein the cavity pressure is atmospheric pressure. The method of claim 6, wherein the pre-extrusion pressure of the shot comprising the molten thermoplastic material is less than the cavity pressure. The method of claim 6 wherein the cavity pressure is at least 15 psi greater or less than the pre-ejection pressure of the shot comprising the molten thermoplastic material. The method of claim 10, wherein the cavity pressure is maintained substantially constant within a range of from about 50 psi to about 500 psi during filling of the entire mold cavity with the shot comprising the molten thermoplastic material. The method of claim 6 wherein during the filling of substantially the entire cavity with the shot comprising the molten thermoplastic material, the cavity pressure increases in proportion to a displacement volume of the cavity. The method of claim 6, further comprising: discharging the cavity to atmospheric pressure after filling the entire cavity with the shot comprising the molten thermoplastic material.