巴西专利BR112013029234B1 method and apparatus for substantially constant pressure injection molding of thin-walled parts

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专利摘要:
METHOD AND APPARATUS FOR SUBSTANTIALLY CONSTANT PRESSURE INJECTION MOLDING OF THIN WALL PARTS. It is a substantially constant pressure injection molding method and machine that forms molded parts by injecting molten thermoplastic material into a mold cavity at substantially constant pressures. As a result, the mold cavity is filled with thermoplastic material at the end of the mold cavity.
公开号:BR112013029234B1
申请号:R112013029234-2
申请日:2012-05-21
公开日:2021-07-06
发明作者:Gene Michael Altonen；Michael Thomas Dodd；Natalia Ramon-Martinez；Kimberly Nichole Mcconnell；Danny David Lumpkin；Vincent Sean Breidenbach；John Russell Lawson
申请人:Imflux, Inc.；
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[001] The present application is a non-provisional application claiming the priority benefit of provisional patent applications US 61/488,564; 61/488,547; 61/488,553; 61/488,555; 61/488,559; 61/602,650; 61/602,781; and 61/641,349, filed on May 20, 2011, May 20, 2011, May 20, 2011, May 20, 2011, May 20, 2011, February 24, 2012, February 24, 2012 and 2 of May 2012, respectively. Provisional Patent Applications Nos. US 61/488,564; 61/488,547; 61/488,553; 61/488,555; 61/488,559; 61/602,650; 61/602,781; and 61/641,349, are incorporated herein by reference. TECHNICAL FIELD
[002] The present invention relates to apparatus and methods for injection molding and, more particularly, to apparatus and methods for producing injection molded thin-walled parts at a substantially constant injection pressure. BACKGROUND OF THE INVENTION
[003] Injection molding is a technology commonly used for high volume manufacturing of parts produced from meltable materials, most commonly parts produced from thermoplastic polymers. During a repetitive injection molding process, a plastic resin, most often in the form of small microspheres or pellets, is introduced into an injection molding machine that melts the resin microspheres under heat, pressure and shear. The now molten resin is force-injected into a mold cavity that has a particular cavity shape. The injected plastic is held under pressure in the mold cavity, cooled and then removed as a solidified part that has a shape that essentially replicates the mold cavity shape. The mold itself can have a single cavity or multiple cavities. Each cavity can be connected to a flow channel by a port, which directs the flow of molten resin into the cavity. A molded part can have one or more ports. It is common for large parts to have two, three or more ports to reduce the flow distance the polymer must travel to fill the molded part. The one or multiple ports per cavity can be located anywhere in the part geometry, and have any cross-sectional shape such as being essentially circular or being shaped with an aspect ratio of 1.1 or more. Thus, a typical injection molding procedure comprises four basic operations: (1) heating the plastic in the injection molding machine to allow it to flow under pressure; (2) injecting the molten plastic into a mold cavity or cavities defined between two mold halves that have been closed; (3) allow the plastic to cool and harden in the cavity or cavities while under pressure; and (4) opening the mold halves to cause the part to be ejected from the mold.
[004] During the injection molding process, the molten plastic resin is injected into the mold cavity and the plastic resin is injected into the cavity, forcibly, by the injection molding machine until the plastic resin reaches the location in the cavity farther from the door. After that, the plastic resin fills the cavity from the back of the end towards the door. The wall thickness and resulting length of the part is a result of the shape of the mold cavity.
[005] In some cases, it may be desirable to reduce the wall thickness of injected molded parts to reduce the plastic content and thus the cost of the final part. Reducing wall thickness using a conventional variable high pressure injection molding process can be an expensive and non-trivial task. In fact, conventional variable high pressure injection molding machines (eg machines that inject molten plastic resin between about 55.2 MPa and about 137.9 MPa (about 8,000 psi and about 20,000 psi)) have a practical limit to how the thin walls of a part can be molded. Conventional variable high pressure injection molding machines generally cannot mold parts that have a thin wall ratio (as defined by an L/T ratio shown below) greater than about 200. In addition, the molding of walled parts thin with thin wall ratios greater than 100, requires pressures at the high end of the current capacity and therefore presses that are capable of handling these high pressures.
[006] When filling a thin-walled part, current industrial practice is to fill the mold cavity at the highest possible rate that the molding machine can achieve. This approach ensures that the mold cavity is filled before the polymer "freezes" in the mold, and provides the shortest possible cycle time as the polymer is exposed to the cooled mold cavity as quickly as possible. This approach has two drawbacks. The first is that achieving very high fill speeds requires very high power loads, and that requires very expensive molding equipment. Additionally, most electric presses are unable to deliver enough power to achieve these high fill rates, or require very complicated and expensive drive systems that substantially increase the cost of molding equipment, making them economically impractical. .
[007] The second disadvantage is that high filling rates result in very high pressures. These high pressures result in the need for very high clamping forces to keep the mold closed during filling and these high clamping forces result in very expensive molding equipment. High pressures also require very high strength injection molds, typically produced from hardened tool steels. These high strength molds are also very expensive and may be economically impractical for many molded components. Even with these substantial disadvantages, the need for injection molded thin-walled components remains high as these components use less polymeric material to construct the molded part, resulting in savings that more than offset the higher equipment costs. Additionally, some molded components require very thin design elements to perform properly, such as design elements that need to flex, or design elements that need to match very small features.
[008] As a liquid plastic resin is introduced into an injection mold in a conventional variable high pressure injection molding process, the material adjacent to the cavity walls immediately begins to "freeze" or solidify, or cure, and not In the case of crystalline polymers, the plastic resin starts to crystallize, due to the fact that the liquid plastic resin cools to a temperature below the temperature without material flow and the liquid plastic portions become stationary. This frozen material adjacent to the mold walls narrows the flow path that the thermoplastic travels as it advances toward the end of the mold cavity. The thickness of the layer of frozen material adjacent to the mold walls increases as the filling of the mold cavity progresses, causing a progressive reduction in the cross-sectional area through which the polymer must flow to continue filling the mold cavity. As the material freezes, it also shrinks, going away from the mold cavity walls, which reduces the effective cooling of the material by the mold cavity walls. As a result, conventional variable high pressure injection molding machines fill the mold cavity with plastic very quickly and then maintain a compaction pressure to force the material out, against the sides of the mold cavity in order to to intensify cooling and to maintain the correct shape of the molded part. Conventional variable high pressure injection molding machines typically have cycle times consisting of up to about 10% of the injection time, about 50% of the compaction time and about 40% of the cooling.
[009] As the plastic freezes in the mold cavity, conventional variable high pressure injection molding machines increase the injection pressure (to maintain a substantially constant volumetric flow rate due to the smaller cross-sectional flow area). Increasing pressure, however, has disadvantages both in terms of cost and performance. As the pressure needed to mold the component increases, the molding equipment needs to be strong enough to withstand the additional pressure, which generally equates to being more expensive. A manufacturer may have to purchase new equipment to accommodate these increased pressures. Thus, a decrease in the wall thickness of a given part can result in significant capital expenditures for carrying out fabrication using conventional injection molding techniques.
[010] US document No. 5,853,630, entitled "Low Pressure Method for Injection Molding a Plastic Article", is directed to inject a plastic material into a mold cavity to fill the mold cavity with precision under low pressure and to avoid filling the mold cavity with plastic material.
[011] US document no. 5,935,505 is intended for the manufacture of thin wall components using resin with good fluidity, impact performance and modulus.
[012] The US document No. 2008/0143006 is directed to the control and gradual decrease of an injection rate of the injection material of a plastic molding system.
[013] The document US No. 5,419,858 is directed to obtaining a uniform quality of injection molded plastic parts regardless of the flow properties of the molding resin.
[014] In an effort to avoid some of the disadvantages mentioned above, many conventional injection molding operations use plastic material with shear thinning to improve flow characteristics of the plastic material in the mold cavity. As the plastic material with shear thinning is injected into the mold cavity, the shear forces generated between the plastic material and the mold cavity walls tend to reduce the viscosity of the plastic material, thus allowing the plastic material to flow more freely and easily into the mold cavity. As a result, you can fill thin-walled parts quickly enough to prevent the material from freezing completely before the mold is completely filled.
[015] The reduction in viscosity is directly related to the magnitude of shear forces generated between the plastic material and the feed system, and between the plastic material and the mold cavity wall. As such, manufacturers of these shear thinning materials and operators of injection molding systems drive higher injection molding pressures in an effort to increase shear, thereby reducing viscosity. Typically, high output injection molding systems (eg, Class 101 and 30 systems) inject plastic material into the mold cavity at melt pressures typically of 103.4 MPa (15,000 psi) or more. Plastic material manufacturers with shear thinning teach injection molding operators to inject plastic material into mold cavities above a minimum melt pressure. For example, polypropylene resin is typically processed at pressures greater than 41.4 MPa (6,000 psi) (the recommended range of polypropylene resin manufacturers is typically greater than 41.4 MPa to about 103.4 MPa (6,000 psi) at about 15,000 psi)). Press manufacturers and processing engineers typically recommend processing polymers with shear thinning at the top end of the range, or significantly greater, to achieve maximum potential shear thinning, which is typically greater than 103 .4 MPa (15,000 psi), to extract maximum thinning and more satisfactory flow properties from the plastic material. Thermoplastic polymers that lower shear viscosity are generally processed in the range of more than 41.4 MPa to about 206.8 MPa (6,000 psi to about 30,000 psi). Even with the use of plastic whose viscosity decreases under shear, there is a practical limit to variable high pressure injection molding of thin-walled parts. This limit is currently in the range of thin walled parts that have a thin wall ratio of 200 or more. Furthermore, even parts that have a thin wall ratio between 100 and 200 can become cost prohibitive, as these parts generally require injection pressures between about 103.4 MPa and about 137.9 MPa (about 15,000 psi and about 20,000 psi).
[016] High production injection molding machines (ie, class 101 and class 30 molding machines) that produce thin-walled consumer-oriented products exclusively use molds that have the largest mold part produced from high hardness materials. High production injection molding machines typically produce 500,000 cycles per year or more. Industrial quality production molds need to be designed to withstand at least 500,000 cycles per year, preferably more than 1,000,000 cycles per year, more preferably more than 5,000,000 cycles per year, and most preferably even more 10,000,000 cycles per year. These machines have multi-cavity molds and complex cooling systems to increase production rates. Materials with high hardness have a greater ability to withstand repeated high pressure pressing operations than materials with lower hardness. However, materials with high hardness, like most tool steels, have relatively low thermal conductivities, generally less than 34.6 W/(m*K) (20 BTU/HR FT °F). which leads to extended cooling times as heat is transferred through the molten plastic material through the material with high hardness.
[017] Even with the increasing injection pressure ranges of existing variable high pressure injection molding machines, a practical limit remains of around 10 of 200 (L/T ratio) for molding thin-walled parts in conventional high variable pressure injection molding machines (eg 137.9 MPa (20,000 psi)), and thin walled parts that have a thin wall ratio between about 100 and about 200 can be prohibitive in terms cost for many manufacturers. BRIEF DESCRIPTION OF THE DRAWINGS
[018] The embodiments shown in the drawings are illustrative and exemplary in nature and are not intended to limit the subject defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where similar structures are indicated with similar reference numbers and in which:
[019] Figure 1 illustrates a schematic view of an injection molding machine with substantially constant pressure, built in accordance with the description;
[020] Figure 2 illustrates an embodiment of a thin-walled part formed in the injection molding machine with substantially constant pressure of Figure 1;
[021] Figure 3 is a graph of pressure vs. cavity time for the substantially constant pressure injection molding machine of Figure 1, superimposed against a pressure vs. graph. cavity time for a conventional variable high pressure injection molding machine;
[022] Figure 4 is another graph of pressure vs. cavity time for the substantially constant pressure injection molding machine in Figure 1, superimposed against a pressure vs. graph. cavity time for a conventional variable high pressure injection molding machine, with the graphs illustrating the percentage of filling time devoted to certain filling steps;
[023] Figures 5A-5D are side cross-sectional views of a portion of a thin-walled mold cavity at various stages of filling by a conventional variable high pressure injection molding machine; and
[024] Figures 6A-6D are side cross-sectional views of a portion of a thin-walled mold cavity at various stages of filling by the substantially constant pressure injection molding machine of Figure 1.
[025] Figure 7 shows a graph illustrating peak power and peak vs. flow rate. percentage mold cavity filling for conventional high variable pressure processes and for substantially constant pressure processes; and
[026] Figure 8 shows a graph where the disclosed substantially constant pressure injection methods and devices also require less power for the given L/T ratios than conventional high variable pressure injection molding systems. DETAILED DESCRIPTION
[027] The modalities of the present invention refer, in general, to systems, machines, products and methods of production of products by injection molding and, more specifically, to systems, products and methods of production of products by substantially constant pressure injection molding.
[028] The term "low pressure", as used herein with respect to the melt pressure of a thermoplastic material, means melt pressures in an adjacency of a nozzle of an injection molding machine of 41.4 MPa (6,000 psi) and below.
[029] The term "substantially constant pressure", as used herein with respect to a melt pressure of a thermoplastic material, means that deviations from a baseline melt pressure do not produce significant changes in the physical properties of the thermoplastic material. For example, "substantially constant pressure" includes, but is not limited to, pressure variations for which the viscosity of the molten thermoplastic material does not change significantly. The term "substantially constant" in this respect includes deviations of approximately 30 % of a baseline melt pressure For example, the term "a substantially constant pressure of approximately 31.7 MPa (4600 psi)" includes pressure fluctuations within the range of about 41.4 MPa (6,000 psi) (30% above 31.7 MPa (4600 psi)) to about 22.1 MPa (3200 psi) (30% below 31.7 MPa (4600 psi)) A melt pressure is considered to be substantially constant provided that the melting pressure does not fluctuate more than 30% with respect to the stated pressure.
[030] The term "fusion bracket", as used herein, refers to the portion of an injection molding machine that contains molten plastic in fluid communication with the nozzle of the machine. The fusion support is heated so that a polymer can be prepared and maintained at a desired temperature. The fusion bracket is connected to a power source, for example a hydraulic cylinder or electric servo motor, which is in communication with a central control unit, and can be controlled to advance a diaphragm to force molten plastic through the nozzle of the machine. The molten material then flows through the sprue system into the mold cavity. The fusion support can have a cylindrical cross section, or have alternative cross sections that will allow a diaphragm to force the polymer under pressures that can range from as low as 0.69 MPa (100 psi) to pressures of 275, 8 MPa (40,000 psi) or more through the machine nozzle. The diaphragm can optionally be integrally connected to a reciprocating screw with steps designed to plasticize the polymer material prior to injection.
[031] The term "high L/T ratio" generally refers to L/T ratios of 100 or more and more specifically to L/T ratios of 200 or more. The calculation of the L/T ratio is defined below.
[032] The term "peak flow rate" generally refers to the maximum volumetric flow rate as measured at the nozzle of the machine.
[033] The term "peak injection rate" generally refers to the maximum linear velocity that the injection plunger travels in the process of forcing the polymer into the feed system. The piston can be a reciprocating screw, as in the case of a single-stage injection system, or a hydraulic piston as in the case of a two-stage injection system.
[034] The term "plunger rate" refers, in general, to the linear velocity that the injection plunger goes through in the process of forcing the polymer into the feed system.
[035] The term "flow rate" generally refers to the volumetric flow rate of polymer as measured at the nozzle of the machine. This flow rate can be calculated based on the spool rate and spool cross-sectional area, or measured with a suitable sensor located on the machine nozzle.
[036] The term "percent cavity fill" generally refers to the percentage of the cavity that is filled on a volumetric basis. For example, if a cavity is 95% filled, then the total volume of the mold cavity that is filled is 95% of the total volumetric capacity of the mold cavity.
[037] The term "melting temperature" refers, in general, to the temperature of the polymer that is kept in the melt support, and in the material feed system when a hot sprue system is used, which keeps the polymer in a molten state. The melting temperature varies from material to material, however it is understood that a desired melting temperature is generally within the ranges recommended by the material manufacturer.
[038] The term "door size" generally refers to the cross-sectional area of a door, which is formed by the intersection of the sprue and the mold cavity. For hot sprue systems, the port can be an open design where there is no positive interruption of material flow in the port, or a closed design where a valve pin is used to mechanically stop material flow through the port into the cavity. (commonly called a valve port). Door size refers to the cross-sectional area, for example, a door diameter of 1 mm refers to a door cross-sectional area that is 1 mm at the point where the door meets the cavity. mold. The cross section of the door can be any shape desired.
[039] The term "ratio of intensification" refers, in general, to the mechanical advantage that the injection power supply has over the injection plunger that forces the molten polymer through the nozzle of the machine. For hydraulic power supplies, it is common for the hydraulic ram to have a 10:1 mechanical advantage over the injection ram. However, the mechanical advantage can range from much lower ratios such as 2:1 to much higher mechanical advantage ratios such as 50:1.
[040] The term "peak power" generally refers to the maximum power generated while filling a mold cavity. Peak power can occur at any point in the fill cycle. Peak power is determined by the product of the plastic pressure as measured at the machine nozzle multiplied by the flow rate as measured at the machine nozzle. Power is calculated by the formula P = p * Q, where p is the pressure and Q is the volumetric flow rate.
[041] The term "volumetric flow rate" generally refers to the flow rate as measured at the nozzle of the machine. This flow rate can be calculated based on the piston ratio and the cross-sectional area of the piston, or measured with a suitable sensor located in the nozzle of the machine.
[042] The terms "filled" and "complete," when used in relation to a mold cavity that includes thermoplastic material, are interchangeable and both terms mean that the thermoplastic material has stopped flowing into the mold cavity.
[043] The term "dose size" generally refers to the volume of polymer to be injected from the fusion support to completely fill the mold cavity or cavities. The Dose Size volume is determined based on the temperature and pressure of the polymer on the fusion support just prior to injection. In other words, dose size is a total volume of molten plastic material that is injected into one stroke of an injection molding plunger at a given temperature and pressure. The dose size may include injection of molten plastic material into one or more injection cavities through one or more ports.
[044] The dose of molten plastic material can also be prepared and injected by one or more fusing supports.
[045] The term "hesitation" refers, in general, to the point at which the velocity of the flow front is sufficiently minimized to allow a portion of the polymer to fall below its temperature without flow and begin to freeze.
[046] The term "electric motor" or "electric press", when used herein, includes electric servo motors and electric linear motors.
[047] The term "Peak Power Flow Factor" refers to a normalized measurement of peak power required by an injection molding system during a single injection molding cycle and Peak Power Flow Factor can be used to directly compare the power requirements of different injection molding systems. The Peak Power Flow Factor is calculated by first determining the Peak Power, which corresponds to the maximum molding pressure product multiplied by the flow rate during the filling cycle (as defined herein) and then , from determining the dose size for the mold cavities to be filled. The Peak Power Flow Factor is then calculated by dividing the peak power by the dose size.
[048] The term "percent cavity fill" is defined as the percentage (%) of the cavity that is filled on a volumetric basis. Thus, if a cavity is 95% filled, then the total volume of the mold cavity that is filled is 95% of the total volumetric capacity of the mold cavity.
[049] Referring to the Figures in detail, Figure 1 illustrates an exemplary substantially constant pressure injection molding apparatus for the production of thin-walled parts in high volumes (for example, a class 101 injection mold or 30, or an "ultra high productivity mold"), specifically thin-walled parts that have an L/T ratio of 100 or more. The substantially constant pressure injection molding apparatus generally includes an injection system 12 and a pressing system 14. A thermoplastic material can be introduced into the injection system 12 in the form of thermoplastic pellets. 16. The thermoplastic pellets 16 can be placed in a feed hopper 18, which feeds the thermoplastic pellets 16 into a heated cylinder 20 of the injection system 12. The thermoplastic pellets 16, after being fed into the heated cylinder 20, can be driven to the end of the heated cylinder 20 by a reciprocating screw 22. Heating the heated cylinder 20 and compacting the thermoplastic pellets 16 by the reciprocating screw 22 causes the thermoplastic pellets 16 to fuse together, forming a molten thermoplastic material 24.
[050] The molten thermoplastic material is typically processed at a temperature of about 130°C to about 410°C.
[051] The reciprocating screw 22 forces the molten thermoplastic material 24 toward a nozzle 26 to form a dose of thermoplastic material, which will be injected into a mold cavity 32 of a mold 28 through one or more ports. The molten thermoplastic material 24 can be injected through a port 30, which directs the flow of the molten thermoplastic material 24 to the mold cavity 32. In other embodiments, the nozzle 26 may be separated from one or more ports 30 by a power system (not shown). The mold cavity 32 is formed between the first and second mold sides 25, 27 of the mold 28 and the first and second mold sides 25, 27 are held together under pressure by a press unit or press 34. The unit press or press 34 applies a pressing force during the molding process that is greater than the force exerted by the injection pressure that acts to separate the two mold halves 25, 27, thus maintaining the first and second mold sides 25, 27 together as molten thermoplastic material 24 is injected into mold cavity 32. In a typical variable high pressure injection molding machine, the press typically exerts 206.8 MPa (30,000 psi) or more due to fact that the pressing force is directly related to the injection pressure. To withstand these pressing forces, the pressing system 14 can include a mold frame and a mold base.
[052] Once the dose of molten thermoplastic material 24 is injected into the mold cavity 32, the reciprocating screw 22 interrupts the forward path. The molten thermoplastic material 24 takes the shape of the mold cavity 32 and the molten thermoplastic material 24 cools within the mold 28 until the thermoplastic material 24 solidifies. Once the thermoplastic material 24 has solidified, the press 34 releases the first and second mold sides 25, 27, the first and second mold sides 25, 27 being separated from each other, and the finished part can be ejected from mold 28. Mold 28 can include a plurality of mold cavities 32 to increase overall production rates. The shapes of the cavities of the plurality of mold cavities can be identical, similar or different from each other. (The latter can be considered a family of mold cavities).
[053] A controller 50 is communicatively connected to a sensor 52 situated near the nozzle 26 and a screw control 36. The controller 50 may include a microprocessor, a memory and one or more communication links. Controller 50 may also optionally be connected to a sensor 53 situated adjacent one end of mold cavity 32. This sensor 32 may provide an indication of when the thermoplastic material approaches the end of filling in mold cavity 32. sensor 32 can sense the presence of thermoplastic material through optical, pneumatic, mechanical or otherwise sensing a pressure and/or temperature of the thermoplastic material. When the pressure or temperature of the thermoplastic material is measured by sensor 52, that sensor 52 can send a signal indicative of pressure or temperature to controller 50 to provide a target pressure for controller 50 to hold in the mold cavity. 32 (or nozzle 26) as filling is completed. This signal can generally be used to control the molding process so that variations in material viscosity, mold temperatures, melt temperatures, and other variations that influence the fill rate are adjusted by controller 50. These adjustments can be made immediately during the molding cycle, or corrections can be made in subsequent cycles. In addition, one can average several signals over a number of cycles and then use it to make adjustments to the molding process by controller 50. Controller 50 can be connected to sensor 52 and/or sensor 53 and to the control of screw 36 via wire connections 54, 56, respectively. In other embodiments, controller 50 can be connected to sensors 52, 53 and screw control 56 via a wireless connection, a mechanical connection, a hydraulic connection, a pneumatic connection or any other type of connection. communication known to the person skilled in the art that allows controller 50 to communicate with both sensors 52, 53 and with screw control 36.
[054] In the embodiment of Figure 1, the sensor 52 is a pressure sensor that measures (directly or indirectly) the melt pressure of the molten thermoplastic material 24 in the vicinity of the nozzle 26. The sensor 52 generates an electrical signal that is transmitted to controller 50. Controller 50 then commands screw control 36 to advance screw 22 at a rate that maintains a substantially constant melting pressure of the molten thermoplastic material 24 in nozzle 26. Although sensor 52 can measure directly at melt pressure, sensor 52 can measure other characteristics of the molten thermoplastic material 24, such as temperature, viscosity, flow rate, etc., which are indicative of melt pressure. Similarly, sensor 52 need not be located directly on nozzle 26, but instead sensor 52 can be located anywhere within injection system 12 or mold 28 that is fluidly connected with the nozzle 26. If sensor 52 is not located within nozzle 26, the appropriate correction factors can be applied to the measured characteristic in order to calculate an estimate of the fusion pressure at nozzle 26. Sensor 52 need not be in direct contact with nozzle injected fluid and may alternatively be in dynamic communication with the fluid and have the ability to sense fluid pressure and/or other fluid characteristics. If sensor 52 is not located within nozzle 26, suitable correction factors can be applied to the measured characteristic in order to calculate the melt pressure at nozzle 26. In still other embodiments, sensor 52 need not be disposed at one location. that is fluidly connected to the mouthpiece. Instead, the sensor could measure the pressing force generated by the pressing system 14 on a mold dividing line between the first and second mold pieces 25, 27. In one aspect, the controller 50 can maintain pressure accordingly. with the input of sensor 52. Alternatively, the sensor could measure an electrical power demand by an electric press, which can be used to calculate an estimate of the pressure at the nozzle.
[055] Although an active closed loop controller 50 is illustrated in Figure 1, other pressure regulating devices can 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 the controller 50 in order to regulate the melt pressure of the molten thermoplastic material 24. More specifically, the pressure regulating valve and the pressure relief valve can prevent overpressurization of mold 28. Another alternative mechanism to prevent overpressurization of mold 28 is an alarm that activates when an overpressurization condition is detected.
[056] Returning to Figure 2, an exemplary molded part 100 is illustrated. The molded part 100 is a thin-walled part. In general, molded parts are considered thin-walled when a flow channel length L divided by a flow channel thickness T is greater than 100 (ie, L/T > 100). For mold cavities that have a more complicated geometry, the L/T ratio can be calculated by integrating the dimension T along the length of the mold cavity 32 from a port 30 to the end of the mold cavity. 32, and determining the longest flow length from port 30 to the end of mold cavity 32. The L/T ratio can then be determined by dividing the longest flow length by the average part thickness. In the case where a mold cavity 32 has more than one gate 30, the L/T ratio is determined by integrating L and T for the portion of mold cavity 32 filled by each individual gate and the L ratio. /T overall for a given mold cavity is the highest L/T ratio that is calculated for any of the ports. In some injection molding industries, thin walled parts can be defined as parts having an L/T > 100, or having an L/T > 200. The flow channel length L is the longest flow length, as measured from port 30 to end 104 of the mold cavity. Thin-walled parts are specifically prevalent in the consumer-oriented 5 product industry.
[057] High L/T ratio parts are commonly found in molded parts that have average thicknesses less than about 10mm. In consumer-oriented products, products that have high L/T ratios generally have an average thickness of less than about 5mm. For example, while automotive bumper panels, which have a high L/T ratio, generally have an average thickness of 10mm or less, tall drinking cups that have a high L/T ratio generally have an average thickness of 10mm or less. generally an average thickness of about 5mm or less, containers (such as tubes or bottles) that have a high L/T ratio generally have an average thickness of about 3mm or less, bottle cap closures that have a high L/T ratio generally have an average thickness of about 2 mm or less and individual toothbrush bristles that have a high L/T ratio generally have an average thickness of about of 1 mm or less. The substantially constant pressure devices and processes disclosed herein are particularly advantageous for parts having a thickness of 5mm or less and the disclosed processes and devices are more advantageous for thinner parts.
[058] Thin-walled parts with high L/T ratios present certain obstacles in injection molding. For example, the fineness of the flow channel tends to cool the molten thermoplastic material before the material reaches the end of the flow channel 104. When this occurs, the thermoplastic material freezes and does not flow, resulting in an incomplete part. To overcome this problem, traditional injection molding machines inject the molten thermoplastic material at very high pressures, typically 5 greater than 103.4 MPa (15,000 psi), so that the molten thermoplastic material quickly fills the mold cavity before it has the chance to cool and freeze. This is one reason why manufacturers of thermoplastic materials teach to inject at very high pressures. Another reason traditional injection molding machines inject at high pressures is increased shear, which increases flow characteristics, as discussed above. These very high injection pressures require the use of very rigid materials to form the mold 28 and feed system, among other things.
[059] When filling under constant pressure, it was generally thought that filling rates would need to be reduced compared to conventional filling methods. This means that the polymer would be in contact with the cooled molding surfaces for longer periods before the mold was completely filled. Thus, it would be necessary for more heat to be removed before filling, and this would be expected to result in the material freezing before the mold is filled. It has been unexpectedly found that the thermoplastic material will flow when subjected to substantially constant pressure conditions, regardless of whether a portion of the mold cavity is below the no-flow temperature of the thermoplastic material. In general, it would be expected by the person skilled in the art that such conditions would cause the thermoplastic material to freeze and clog the mold cavity rather than continuing to flow and fill the entire mold cavity. Without being bound by theory, it is believed that the substantially constant pressure conditions of disclosed method and device modalities allow conditions of dynamic flow (i.e., constantly moving melt front) throughout the entire mold cavity during the fill. There is no hesitation in the flow of the molten thermoplastic material as it flows to fill the mold cavity and thus no opportunity for flow freezing, regardless of the fact that at least a portion of the mold cavity is below the no-flow temperature of the thermoplastic material.
[060] Additionally, it is believed that, as a result of the dynamic flow conditions, the molten thermoplastic material has the ability to maintain a temperature higher than the temperature without flow, despite being subjected to such temperatures in the cavity of mold as a result of heating by shear. It is also believed that dynamic flow conditions interfere with the formation of crystal structures in the thermoplastic material, as this initiates the freezing process. Crystal structure formation increases the viscosity of the thermoplastic material, which can prevent proper flow from filling the cavity. The reduction in crystal structure formation and/or crystal structure size can allow a decrease in the viscosity of the thermoplastic material as it flows into the cavity and is subjected to a low mold temperature that is below the no-flow temperature of the material.
[061] The disclosed substantially constant pressure injection molding methods and systems may use a sensor (such as sensor 53 in Figure 1 above) situated near one end of the flow position (ie, near one end mold cavity) to monitor changes in material viscosity, changes in material temperature, and changes in other material properties. Measurements from this sensor can be communicated to the controller to allow the controller to correct the process in real time to ensure that the fusion front pressure is relieved before the fusion front reaches the end of the mold cavity, the which can cause mold flashing, and other pressure and power spikes. In addition, the controller can use sensor measurements to adjust peak power and peak flow rate points in the process to achieve consistent processing conditions. In addition to using sensor measurements to fine-tune the process in real time during the current injection cycle, the controller can also adjust the process over time (eg over a plurality of injection cycles). In this way, the current injection cycle can be corrected based on measurements that occur during one or more cycles at a previous point in time. In one modality, one can average sensor readings over many cycles in order to achieve process consistency.
[062] In various embodiments, the mold can include a cooling system that keeps the entire mold cavity at a temperature below the no-flow temperature. For example, even mold cavity surfaces that come in contact with a dose comprising molten thermoplastic material can be cooled to maintain a lower temperature. Any suitable cooling temperature can be used. For example, mold 5 can be kept substantially at room temperature. The incorporation of such cooling systems can advantageously enhance the rate at which the injection molded part so formed is cooled and ready for ejection from the mold. Thermoplastic material:
[063] A variety of thermoplastic materials can be used in the pressure injection molding methods and devices substantially set out in the description. In one embodiment, the molten thermoplastic material has a viscosity, as defined by the melt flow index of about 0.1 g/10 min to about 500 g/10 min, as measured by ASTM D1238 performed at a temperature of about 230°C with a weight of 2.16 kg. For example, for polypropylene, the melt flow index can be in a range from about 0.5 g/10 min to about 200 g/10 min.
[064] Other suitable melt flow indices include about 1 g/10 min to about 400 g/10 min, about 10 g/10 min to about 300 g/10 min, about 20 to about 200 g/10 min, about 30 g/10 min at about 100 g/10 min, about 50 g/10 min at about 75 g/10 min, about 0.1 g/10 min at about 1 g/10 min, or about 1 g/10 min to about 25 g/10 min. The material's MFI is selected based on the application and use of the molded article. For example, thermoplastic materials with an MFI of 0.1 g/10 min to about 5 g/10 min may be suitable for use as preforms for Injection Stretch Blow Molding (ISBM) applications ). Thermoplastic materials with an MFI of 5 g/10 min to about 50 g/10 min can be suitable for use as closures and closure systems for packaging articles. Thermoplastic materials with an MFI of 50 g/10 min to about 150 g/10 min can be suitable for use in the manufacture of buckets or tubes. Thermoplastic materials with an MFI of 150 g/10 min to about 500 g/10 min may be suitable for molded articles that have extremely high L/T ratios such as a thin board. Manufacturers of such thermoplastic materials generally teach that materials should be injection molded using melt pressures above 41.4 MPa (6000 psi) and often well above 41.4 MPa (6000 psi) psi). Contrary to conventional teachings regarding injection molding of such thermoplastic materials, the modalities of the injection molding method and device set out in the description advantageously allow the formation of quality injection molded parts with the use of such thermoplastic materials and processing at melt pressures below 41.4 MPa (6,000 psi), and possibly far below 41.4 MPa (6,000 psi).
[065] The thermoplastic material can be, for example, a polyolefin. Exemplary polyolefins include, but are not limited to, polypropylene, polyethylene, polymethyl pentene and polybutene-1. Any of the aforementioned polyolefins could give rise to bio-based raw materials, such as sugar cane or other agricultural products, to produce a biopolypropylene or biopolyethylene. Polyolefins advantageously demonstrate thinning under shear when in a molten state. Shear thinning is a reduction in viscosity 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 being bound by theory, it is believed that the thinning under shear properties of a thermoplastic material, and in particular polyolefins, result in less variation in the viscosity of materials when the material is processed at constant pressures. As a result, the method and device embodiments of the description may be less sensitive to variations in the thermoplastic material, for example, resulting from dyes and other additives, as well as processing conditions. This decreased sensitivity to batch-to-batch variations of thermoplastic material properties can also advantageously allow post-industrial and post-consumer recycled plastics to be processed using the method and device modalities of the description. Post-industrial, and post-consumer recycled plastics are derived from end products that have completed their life cycle as a consumer item and would otherwise have been disposed of as a solid waste product. Such recycled plastic, and blends of thermoplastic materials, inherently have significant lot-to-lot variation in their material properties.
[066] The thermoplastic material can also be, for example, a polyester. Exemplary polyesters include, but are not limited to, polyethylene terephthalate (PET). The PET polymer could give rise to bio-based raw materials, such as sugar cane or other agricultural products, to produce a polymer of partially or completely PET. Other suitable thermoplastic materials include polypropylene and polyethylene copolymers, and thermoplastic elastomer polymers and copolymers , polyester, polystyrene, polycarbonate, poly(acrylonitrile-butadiene-styrene), polylactic acid, biobased polyesters such as polyethylene furanate, polyhydroxyalkanoate, polyethylene furanoate, (considered an alternative to, or compatible replacement for, PET), polyhydroxyalkanoate, polyamides, polyacetals, ethylene-alpha olefin rubbers, and styrene-butadiene-styrene block copolymers. The thermoplastic material can also be a blend of multiple polymeric and non-polymeric materials. The thermoplastic material can be, for example, a blend of high, medium and low molecular weight polymers that produce a multimodal or bimodal blend. The multimodal material can be designed in such a way that it results in a thermoplastic material that has superior flow properties and has, in addition, satisfactory chemical-physical properties. The thermoplastic material can also be a blend of a polymer with one or more small molecule additives. The small molecule could be, for example, a siloxane molecule or another lubricating molecule that, when added to the thermoplastic material, improves the fluidity of the polymeric material.
[067] Other additives may include inorganic fillers such as calcium carbonate, calcium sulfate, talcs, clays (eg, nanoclays), aluminum hydroxide, CaSiO3, glass formed into fibers or microspheres, crystalline silicas (eg, quartz, novacite, crystal lobite), magnesium hydroxide, mica, sodium sulphate, lithopone, magnesium carbonate, iron oxide; or, organic fillers such as rice husks, straw, hemp fiber, wood flour, or wood, bamboo or sugar cane fiber.
[068] Other suitable thermoplastic materials include renewable polymers as non-limiting examples of polymers produced directly from organisms such as polyhydroxy alkanoates (eg poly(beta-hydroxy alkanoate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate, NODAX (trademark)), and bacterial cellulose; polymers extracted from plants, agricultural and forestry, and biomass, such as polysaccharides and their derivatives (for example, gums, cellulose, cellulose esters, chitin, chitosan, starch, chemically starch modified, cellulose acetate particles), proteins (eg, zein, whey, gluten, collagen), lipids, lignins and natural rubber; thermoplastic starch produced from chemically modified starch or starch and current polymers derived from monomers and derivatives of natural origin, such as biopolyethylene, biopolypropylene, polytrimethylene terephthalate, polylactic acid, NYLON 11, alkyd resins, polyesters based on succinic acid and terephthale of biopolyethylene.
[069] Suitable thermoplastic materials may include a blend or blends of different thermoplastic materials as in the examples mentioned above. Also, different materials can be a combination of materials derived from virgin or petroleum-derived bio-derived materials, or recycled materials from bio-derived or petroleum-derived materials. One or more of the thermoplastic materials without a blend may be biodegradable. And, for thermoplastic materials other than blends, this material can be biodegradable.
[070] Exemplary thermoplastic resins are provided, along with their recommended operating pressure ranges, in the following Table:

[071] Although more than one of the modalities involves substantially filling the entire mold cavity with the dose comprising the molten thermoplastic material while maintaining the melt pressure of the dose comprising the molten thermoplastic material at a substantially constant pressure, specific thermoplastic materials benefit from the invention at different constant pressures. Specifically: PP, nylon, PC, PS, SAN, PE, TPE, PVDF, PTI, PBT, and PLA at a substantially constant pressure less than 68.9 MPa (10,000 psi); ABS at substantially constant pressure less than 55.2 MPa (8,000 psi); PET at substantially constant pressure less than 39.9 MPa (5,800 psi); acetal copolymer at substantially constant pressure less than 48.3 MPa (7,000 psi); plus polyethylene furanate polyhydroxyalkanoate, polyethylene furanoate (also known as PEF) at substantially constant pressure less than 68.9 MPa, or 55.2 MPa, or 48.3 MPa or 41.4 MPa, or 39.9 MPa (10,000 psi, or 20 8,000 psi, or 7,000 psi or 6,000 psi or 5,800 psi).
[072] As described in detail above, the disclosed substantially constant pressure method and device modalities can achieve one or more advantages over conventional variable high pressure injection molding processes. For example, the modalities include a more cost effective and efficient process that eliminates the need to balance pre-injection pressures of the mold cavity and thermoplastic materials, a process that allows the use of atmospheric mold cavity pressures and, thus, simplified mold structures that eliminate the need for pressurizing means, the ability to use mold cavity materials of lower hardness, high thermal conductivity that are lower cost and easier to machine, a more robust processing method which is less sensitive to variations in temperature, viscosity, and other material properties of the thermoplastic material, and the ability to produce quality injection molded parts at substantially constant pressures without prematurely quenching the thermoplastic material in the mold cavity and without the need to heat or maintain constant temperatures in the mold cavity.
[073] In one example, sample parts were molded using a substantially constant pressure process below 41.4 MPa (6,000 psi) of injection pressure.
[074] The samples were isolated from the injection molded parts using a common laboratory microtome. At least four samples were taken from each injection molded part. The cross-section of the samples was then prepared to expose the compositional layers (skin, core, etc.) of each sample.
[075] The synchroton measurements were taken on the beamline G3 Deutsches Elektronen Synchrotron (DESY) to DORIS III with the MAXIM detector set, that is, the first measurements were taken by the point averaging scintillation counting device a in order to obtain diffraction overviews of the sample. The spatially separated diffraction images were then taken by the MAXIM position-sensitive camera (a 2D Hamamatsu 4880 detector with a multi-channel plate [MCP] in front of its CCD sensor).
[076] Synchroton measurements revealed that injection molded parts having a certain thickness, which were molded using a substantially constant pressure process, show a distinct and discernible extra band or zone of polypropylene crystallites oriented in the part core. This extra zone of oriented material can be seen in parts molded using steel or aluminum molds. Parts molded using a conventional larger variable pressure process usually have a reduced number of oriented bands when compared to a part molded using a substantially constant pressure process.
[077] Parts molded using a substantially constant pressure process may have less stress under molding. In a conventional variable high pressure process, the speed-controlled filling process combined with a larger transfer or change to control pressure can result in a part with high stress under undesirable molding. If the compaction pressure is set to be too high in a conventional process, the part will often have a super-compacted port region. Stress under molding can be visually assessed by placing the parts on a cross polarized light table. The birefringence observed in molded parts can be used to observe differences in stress under molding. Typically this is seen as patterns of stress lines in the part. The increased number of lines and/or non-uniformity of stress lines is typically undesirable.
[078] Returning to Figure 3, a typical pressure and time curve for a conventional variable high pressure injection molding process is illustrated by the dashed line 200. In contrast, a pressure and time curve for the molding machine by constant pressure injection revealed is illustrated by solid line 210.
[079] In the conventional case, the melt pressure is rapidly increased to well over 103.4 MPa (15,000 psi) and then maintained at a relatively high pressure, over 103.4 MPa (15,000 psi), for a first time period 220. The first time period 220 is the filling time at which the molten plastic material flows into the mold cavity. Thereafter, the melt pressure is decreased and maintained at a lower but still relatively high pressure, typically 68.9 MPa (10,000 psi) or more, for a second time period 230. The second time period 230 is a compaction time in which the melt pressure is maintained to ensure that all gaps in the mold cavity are filled again. After compaction is complete, the pressure can optionally be lowered again for a third time period 232, which is the cool-down time. The mold cavity in a conventional high pressure injection molding system is compacted from the back end of the flow channel to the port. Material in the mold typically freezes near the edge of the cavity, so the completely frozen region of material moves progressively towards the port location or locations. As a result, the plastic near the end of the mold cavity is compressed for a shorter period of time and with reduced pressure than the plastic material that is closest to the port location(s). Part geometry, such as very thin cross-sectional areas midway between the door and the end of the mold cavity, can also influence the level of compaction pressure in the mold cavity regions. Inconsistent compaction pressure can cause inconsistencies in the final product, as discussed above. Furthermore, conventional plastic compaction at various solidification stages results in some non-optimal material properties, eg molding stresses, sinking, and non-optimal optical properties.
[080] The substantially constant pressure injection molding system, on the other hand, injects the molten plastic material into the mold cavity at a substantially constant pressure for a filling time period 240. The injection pressure in the example of Figure 3 is less than 41.4 MPa (6,000 psi). However, other modalities may use higher pressures as long as the pressure is substantially constant during the molding process. After the mold cavity is filled, the substantially constant pressure injection molding system gradually reduces the pressure. pressure over a second period of time 242 as the molded part is cooled. By using substantially constant pressure, the molten thermoplastic material maintains a continuous molten flow front that advances through the port's flow channel towards the end of the flow channel. In other words, the molten thermoplastic material remains in motion along the mold cavity, which prevents premature freezing. In this way, the plastic material 5 remains relatively uniform at any point along the flow channel, which results in a more uniform and consistent end product. By filling the mold with relatively uniform pressure, the finished molded parts form crystalline structures that can have more satisfactory mechanical and optical properties than conventionally molded parts. Furthermore, parts molded at constant pressure exhibit different characteristics than the skin layers of conventionally molded parts. As a result, molded parts under constant pressure can have more satisfactory optical properties than conventionally molded parts.
[081] Now, referring to Figure 4, the various fill stages are broken down as percentages of total fill time. For example, in a conventional variable high pressure injection molding process, the filling period 220 constitutes about 10% of the total filling time, the compaction period 230 constitutes about 50% of the filling time. -total fill and cool-down period 232 constitutes about 40% of the total fill time. On the other hand, in the substantially constant pressure injection molding process, the filling period 240 constitutes about 90% of the total filling time while the cooling period 242 only constitutes about 10% of the filling time. total. The substantially constant pressure injection molding process needs less cooling time due to the fact that the molten plastic material cools as it flows into the mold cavity. Thus, by the time the mold cavity is filled, the molten plastic material has cooled significantly, though not enough to freeze in the central cross section of the mold cavity, and there is less total heat to be removed to complete. the freezing process. Additionally, due to the fact that the molten plastic material remains liquid throughout the fill, and compaction pressure is transferred through this molten central cross section, the molten plastic material remains in contact with the mold cavity walls (in opposition to the freezing and shrinking of the opposite direction). As a result, the substantially constant pressure injection molding process described herein is able to fill and cool a molded part in less time than a conventional variable high pressure injection molding process.
[082] Peak power and peak flow rate vs. percentages of mold cavity filling are illustrated in the graph of Figure 7 for conventional high variable pressure processes and for substantially constant pressure processes.
[083] In the substantially constant pressure process, the peak power load occurs at a time approximately equal to the time the peak flow rate occurs, then steadily decreases throughout the fill cycle. More specifically, peak power and peak flow rate occur at the first 30% fill and preferably at the first 20% fill and even more preferably at the first 10% fill. By making the peak power and peak flow rate occur during the start of filling, the thermoplastic material is not subjected to extreme conditions when it is closest to freezing. This is believed to result in superior physical properties of the molded parts.
[084] The power level generally decreases slowly through the fill cycle after the peak power load. Additionally, the flow rate generally decreases slowly through the fill cycle after the peak flow rate due to the fact that the fill pressure is kept substantially constant. As illustrated above, the peak power level is less than the peak power level for a conventional process, typically 30 to 50% lower and the peak flow rate is less than the peak flow rate for a conventional process, in general, 30 to 50% smaller.
[085] Similarly, peak power loading for a conventional variable high pressure process occurs at a time approximately equal to the time at which the peak flow rate occurs. However, unlike the substantially constant process, the peak power and flow rate for the conventional variable high pressure process occurs in the final 10% to 30% fill, which subjects the thermoplastic material to extreme conditions as in the freezing process. . Also unlike the substantially constant pressure process, the power level in the conventional variable high pressure process generally decreases rapidly through the fill cycle after peak power loading. Similarly, the flow rate in a conventional variable high pressure process generally decreases rapidly through the fill cycle after the peak flow rate.
[086] In the disclosed method and device for molding a part with a high L/T ratio, the part is molded by injecting a molten thermoplastic polymer into a mold cavity at an increasing flow rate to achieve an injection pressure and then decreasing the flow rate over time to keep the injection pressure substantially constant. The substantially constant injection pressure method and device is particularly advantageous when molding thin-walled parts (eg parts having an L/T ratio > 100) and when using larger dose sizes ( for example, greater than 50 ml, and in particular more than 100 ml). It is specifically advantageous that the maximum flow rate occurs within the first 30% cavity fill, preferably within the first 20% cavity fill and even more preferably within the first 10% of cavity filling. By adjusting the filling pressure profile where the maximum flow rate occurs within preferred cavity filling ranges, the molded part will have at least part of the physical advantages described above (eg, more satisfactory strength, more satisfactory optical properties, etc. .) due to the fact that the crystal structure of the molded part is different from a conventionally molded part. Furthermore, due to the fact that products with a high L/T ratio are thinner, these products require less pigment to impart a desired color to the resulting product. Also, in non-pigmented parts, parts will have less noticeable deformities due to more consistent molding conditions. Using no or less pigment saves costs.
[087] Alternatively, peak power can be adjusted to maintain a substantially constant injection pressure. More specifically, the fill pressure profile can be adjusted to make peak power occur in the first 30% of cavity fill, preferably in the first 20% of cavity fill, and even more preferably , in the first 10% of cavity filling. Adjusting the process to make the peak power occur within the preferred ranges and then to have a decreasing power over the remainder of the cavity fill results in the same benefits to the molded part that were described above that say with respect to the adjustment of the peak flow rate. Furthermore, adjusting the process in the manner described above is particularly advantageous for thin-walled parts (eg L/T ratio > 100) and for larger serving sizes (eg more than 50 ml, in particular more 100 ml).
[088] The substantially constant pressure injection methods and devices disclosed in this document also require less power for the given L/T ratios than conventional high variable pressure injection molding systems, as illustrated in the chart below.
[089] As illustrated in Figure 8 (by the dashed line), the substantially constant injection pressure methods and devices disclosed in this document require less power (ie, have a lower peak power flow factor) to fill a given mold cavity than conventional variable high pressure injection molding processes for any L/T ratio between 100 and 250, and this ratio extends to L/T of 300, and 400 L/T and greater. In fact, the disclosed substantially constant injection pressure methods and devices require less power than that calculated by the formula: Y = 0.7218x + 129.74 where Y = peak power flow factor; and X - L/T ratio
[090] In all cases, conventional high variable pressure injection molding systems require more power than calculated by the formula above.
[091] Referring now to Figures 5A-5D and 6A-6D, a portion of a mold cavity is illustrated as it is filled by a conventional variable high pressure injection molding machine (Figures 5A-5D) and as is filled by an injection molding machine with substantially constant pressure (Figures 5A-5D).
[092] As illustrated in Figures 5A-5D, as the conventional variable high pressure injection molding machine begins to inject molten thermoplastic material 24 into a mold cavity 32 through port 30, the high injection pressure tends to inject the molten thermoplastic material 24 in the mold cavity 32 at a high rate of velocity, which causes the molten thermoplastic material 24 to flow in laminates 31, more commonly called laminar flow (Figure 5A). These outermost laminates 31 adhere to the mold cavity walls and subsequently cool and freeze, forming a frozen boundary layer 33 (Figure 5B), before the mold cavity 32 is completely filled. As the thermoplastic material freezes, however, it also shrinks away from the mold cavity wall 32, leaving a gap 35 between the mold cavity wall and the boundary layer 33. This gap 35 reduces the cooling efficiency of the mold. The molten thermoplastic material 24 also begins to cool and freeze in the vicinity of port 30, which reduces the effective cross-sectional area of port 30. In order to maintain a constant volumetric flow rate, the injection molding machine is high. Conventional variable pressure needs to increase the pressure to force the molten thermoplastic material through the narrowing port 30. As the thermoplastic material 24 continues to flow into the mold cavity 32, the boundary layer 33 becomes thicker (Figure 5C). Eventually, the entire mold cavity 32 is substantially filled by the thermoplastic material that is frozen (Figure 5D). At this point, the conventional high pressure injection molding machine needs to maintain a compaction pressure to push the indented boundary layer 33 back against the walls of the mold cavity 32 in order to increase cooling.
[093] An injection molding machine with substantially constant pressure, on the other hand, flows molten thermoplastic material into a mold cavity 32 with a constantly moving flow front 37 (Figures 6A-6D). The thermoplastic material 24 behind the flow front 37 remains molten until the mold cavity 37 is substantially filled (i.e. 99% or more filled) before freezing. As a result, there is no reduction in the effective cross-sectional area of port 30, and a constant injection pressure is maintained. Furthermore, because the thermoplastic material 24 is fused behind the flow front 37, the thermoplastic material 24 remains in contact with the walls of the mold cavity 32. As a result, the thermoplastic material 24 cools (without freezing) during filling portion of the molding process. As such, the cooling portion of the injection molding process does not need to be as long as a conventional process.
[094] Due to the fact that the thermoplastic material remains molten and keeps moving in the mold cavity 32, less injection pressure is required than in conventional molds. In one modality, the injection pressure can be 41.4 MPa (6,000 psi) or less. As a result, injection systems and pressing systems don't have to be as powerful. For example, the disclosed substantially constant injection pressure devices may use presses that require lower pressing forces, and a correspondingly smaller press power supply. Furthermore, the disclosed injection molding machines, because they require less power, may employ electric presses, which are generally not powerful enough to be used in conventional class 101 and 102 injection molding machines, which mold thin-walled parts at variable high pressures. Even when electric presses are sufficient to be used in some simple molds with few mold cavities, the process can be improved with the disclosed substantially constant injection pressure methods and devices, as smaller, less expensive electric motors can be used. The constant pressure injection molding machines disclosed may comprise one or more of the following types of electric presses, a direct drive servomotor press, a dual motor belt driven press, a double motor belt driven press, a dual motor and a dual motor ball drive press that has a power rating of 149.14 kW (200 hp) or less. test data
[095] A mold viscosity test was completed for a test mold, which was used to generate the data in the force vs. graph. L/T This test determined that the optimal injection rate was 15.2 cm/sec (6" per second). An additional rate of 20.3 cm/s (8" per second) was performed to illustrate the relationship between the injection rate. 5 and the molding pressure. As mentioned above, current industrial practice is to inject the maximum rate that the molding press is capable of achieving. The data below illustrates that increasing injection rate leads to substantial increases in molding pressures, as indicated by data runs of 20.3 cm/s (8" per second). Injection at even faster rates like 25.4 cm (10" per second), 50.8 cm/s (20" per second) or faster will lead to substantial increases in pressure. Test data is summarized in the Tables below.

[096] In comparing the peak flow rate and peak power levels required to mold an injection molded part, melt temperatures and mold temperatures should be consistent between the conditions run for the constant pressure process and conventional. Furthermore, these temperature settings should generally be based on the resin manufacturer's recommended temperatures or within appropriate ranges to ensure that the resin is processed as intended by the manufacturer.
[097] The presented substantially constant pressure injection molding machines advantageously reduce the total cycle time for the molding process while increasing the part quality. Furthermore, the substantially constant pressure injection molding machines presented can employ, in some embodiments, electric presses, which are generally more energy efficient and require less maintenance than hydraulic presses.
[098] Additionally, the disclosed substantially constant pressure injection molding machines are able to employ more flexible support structures and more adaptable application structures such as larger print roll widths, increased tie rod spacing, tie rod elimination binding, lighter weight construction to facilitate faster movements and unnatural balanced feeding systems. In this way, the disclosed substantially constant pressure injection molding machines 5 can be modified to fit application needs and are more easily customizable for particular molded parts.
[099] Additionally, the substantially constant pressure injection molding machines and methods presented allow molds to be produced from softer materials (eg, materials that have an Rc less than 30), which may have conductivities higher thermals (eg, thermal conductivities greater than 34.6 W/(m*K) (20 BTU/HR FT °F)), which leads to molds with improved cooling capabilities and more uniform cooling.
[0100] It should be noted that the terms "substantially", "about" and "approximately" unless otherwise specified may be used in the present invention to represent the inherent degree of uncertainty that can be attributed to any comparison, value, measurement, or other quantitative representation. These terms are also used in the present invention to represent the degree to which a quantitative representation may vary from a stated reference, without resulting in a change in the basic function of the subject matter. Unless otherwise defined in the present invention, the terms "substantially," "about" and "approximately" mean that the comparison, value, measurement, or other quantitative representation may fall within 20% of the stated reference.
[0101] It should be evident that the various embodiments of the products illustrated and described herein can be produced by a substantially constant low pressure molding process. While particular reference is made in the present invention to products for containing consumer goods or the consumer goods products themselves, it should be evident that the molding method discussed here may be suitable for use in conjunction with products for use in the manufacturing industry. consumer goods, the food service industry, the transportation industry, the medical industry, the toy industry, and the like. In addition, those skilled in the art will recognize that the teachings disclosed herein can be used in the construction of stack molds, multiple material molds including core and rotational back molds, in combination with inner mold decoration, insert molding, in the assembly mold, and the like.
[0102] All documents cited in the Detailed Description of the Invention are, in their relevant part, incorporated herein by reference. Citation of any document is not to be construed as an admission that it represents prior art with respect to the present invention. If any meaning or definition of a term in this written document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition ascribed to the term in this written document shall take precedence.
[0103] Although particular modalities have been illustrated and described here, it should be understood that various other alterations and modifications can be made without departing from the spirit and scope of the claimed subject matter. Furthermore, although various aspects of the claimed subject matter have been described here, these aspects need not be used in combination. Therefore, it is intended that the 5 appended claims cover all such changes and modifications that fall within the scope of the claimed subject matter.

权利要求:
Claims (10)
[0001]
1. A method of injection molding a thin walled part at substantially constant pressure, the method comprising the steps of: operating an injection system (12) to advance molten thermoplastic material (24) into a mold cavity (32 ), whereby the mold cavity (32) has an L/T ratio of 100 or more and the thermoplastic material has a dose size of more than 50cc and operates at an increasing power (0-t1) until a pressure of predetermined injection is reached; and characterized in that it further comprises: adjusting a fill pressure profile to cause the power of the injection system (12) to culminate within the first 30% of the mold cavity (32) being filled (t1); and reducing power (t1-100) until the mold cavity (32) is substantially filled with thermoplastic material to maintain a substantially constant injection pressure.
[0002]
2. Method according to claim 1, characterized in that the peak power occurs before the cavity is 20% filled.
[0003]
3. Method according to claim 1, characterized in that the peak power occurs before the cavity is 10% filled
[0004]
4. Method according to any one of claims 1 to 3, characterized in that reducing includes reducing to maintain substantially constant injection pressure less than 4138.4 N/cm2 (422 kilograms force per square centimeter).
[0005]
5. Method according to any one of claims 1 to 4, characterized in that operating includes the operation to maintain a substantially continuous and moving flow front of thermoplastic material that moves without hesitation as the thermoplastic material advances through the mold cavity (32).
[0006]
6. Method according to any one of claims 1 to 5, characterized in that operating includes filling the mold cavity (32) by at least 99% before a flow front of the thermoplastic material starts to freeze.
[0007]
7. Method according to any one of claims 1 to 6, characterized in that operating includes the operation to advance the molten thermoplastic material (24) to the mold cavity (32) which has an L/T ratio of 200 or more.
[0008]
8. Method according to any one of claims 1 to 7, characterized in that operating includes the operation to advance the molten thermoplastic material (24) to the mold cavity (32) which has an L/T ratio of 250 or more.
[0009]
9. Method according to any one of claims 1 to 8, characterized in that operating includes the operation of the injection system (12), and the thermoplastic material has a dose size greater than 50 cc.
[0010]
10. Method according to any one of claims 1 to 9, characterized in that operating includes the operation of the injection system (12), and the thermoplastic material has a dose size greater than 100 cc.

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法律状态:
2018-04-03| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

2019-11-12| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

2020-04-07| B25A| Requested transfer of rights approved|Owner name: IMFLUX, INC. (US) |

2020-10-06| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application [chapter 6.1 patent gazette]|

2021-05-18| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

2021-07-06| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 21/05/2012, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

申请号 | 申请日 | 专利标题

US201161488555P| true| 2011-05-20|2011-05-20|

US201161488553P| true| 2011-05-20|2011-05-20|

US201161488559P| true| 2011-05-20|2011-05-20|

US201161488547P| true| 2011-05-20|2011-05-20|

US201161488564P| true| 2011-05-20|2011-05-20|

US61/488,547|2011-05-20|

US61/488,553|2011-05-20|

US61/488,555|2011-05-20|

US61/488,564|2011-05-20|

US201261602781P| true| 2012-02-24|2012-02-24|

US201261602650P| true| 2012-02-24|2012-02-24|

US201261641349P| true| 2012-05-02|2012-05-02|

US61/641,349|2012-05-02|

PCT/US2012/038846|WO2012162245A1|2011-05-20|2012-05-21|Method and apparatus for substantially constant pressure injection molding of thinwall parts|

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