Patent Application
20080303185
The present invention generally relates to, but is not limited to, molding systems, and more specifically the present invention relates to, but is not limited to, (i) a molding-system process for making a product having reduced susceptibility to warpage, and (ii) a molding-system process for making a product having reduced susceptibility to warpage, and (iii) other arrangements according to the Summary.
Examples of known molding systems are (amongst others): (i) the HyPET™ Molding System, (ii) the Quadloc™Molding System, (iii) the Hylectric™ Molding System, and (iv) the HyMET™ Molding System, all manufactured by Husky Injection Molding Systems (Location: Canada; www.husky.ca).
Parts that are made from a thermoplastic composite, which contains high-aspect ratio reinforcements (such as: glass, carbon, natural or basalt fibers, amongst other equivalent materials), may experience warpage. An example of such a part is a door-module carrier. The high-aspect ratio may be in the range from about 5 to about 1000. Warpage is due to differential shrinkage in a “flow” direction and a “cross-flow” direction induced by fiber orientation in the two directions. However, fiber orientation alone does not necessarily trigger warpage. Local differences in shrinkage and hence internal stresses and warpage occur when orientation (that is, angle of orientation and degree of orientation) changes from point to point. Fibers orient in the flow direction and restrict shrinkage in the flow direction, which is then compensated by an increased shrinkage of the polymer in the transverse direction, which leads to warpage. Factors that influence fiber orientation have an impact on warpage; and such factors include: (i) gate location, (ii) injection-compression molding, (iii) lower fiber concentration, and (iv) resin viscosity, etc.
Options that may be used to reduce warpage include: (i) gating, and/or (ii) flow pattern in injection compression. Gating can be used to minimize fiber orientation; a part with a large number of gates spread evenly over the surface will have short flow lengths, will fill primarily with radial flow patterns, and will pack uniformly; however, part geometry may restrict this option, and cost of additional drops on a hot runner may be prohibitive. Flow pattern in injection compression will: (i) have short flow lengths, (ii) fill primarily with radial flow patterns, and (iii) pack more uniformly than injection; this option helps to reduce warpage; however, this option may require additional post-molding steps (such as: trimming or punching holes) that result in wastage, extra manufacturing steps, and increased part cost.
A common method to reduce warpage is to add a small amount of flake reinforcements such as mica or talc in addition to the fibers. The mica or talc has an aspect ratio that is greater than 1 but less than 20; usually, this does not include a particulate that has aspect ratio of 1, such as calcium carbonate. Usage of flake-type reinforcements, which have a lower aspect ratio than long fibers, result in a degree of shrinkage that tends to be more isotropic (that is, less warpage); however, mechanical properties, such as tensile strength or impact strength, are reduced.
According to a BASF Plastics Brochure (Technical Information for Experts 05/99e; Title: Warpage Characteristics of Fiber-reinforced Injection-molded Parts), there are marked differences in the shrinkage characteristics of un-reinforced and glass-fiber reinforced thermoplastics. The design rules applicable to un-reinforced plastic parts for minimizing warpage have only limited validity for glass-fiber reinforcement. The dominant determining factor in this case is the orientation of the fibers. In order to be in a position to take any possible warpage into consideration as early as the design phase or to optimize the warpage behavior of prototype parts, the causes and mechanisms of fiber orientation together with their effects on shrinkage behavior must be known. This understanding allows the derivation of design rules and measures for the minimization of warpage. The summary of design rules are: (i) aim for a uniform direction of flow (that is, direction of orientation), (ii) gate oblong parts in a longitudinal direction, (iii) aim for and/or emphasize symmetry, (iv) avoid ribs or walls transverse to a direction of flow, (v) position the end of a flow path in corners, (vi) take account of transverse orientation at an end of a flow path and along edges, (vii) aim for flow lines which are as blunt as possible (that is, pay attention to strength), (viii) avoid flow lines on free-standing webs or displace them into corners, and/or (ix) retain the freedom to make changes.
According to pages 29 to 33 of Chapter 4 (Causes of Molded-Part Variation: Material) associated with a publication titled “Handbook of Molded Part Shrinkage and Warpage” (Author: Jerry M. Fisher; ISBN: 2002014824), a common misunderstanding is that the shrinkage values listed on data sheets are a direct indication of potential part warpage. A more reliable indication of warp would be the differential shrinkage obtained by subtracting shrinkage in a flow direction from that in a transverse direction. This is equally valid for semi-crystalline and amorphous resins, but greater attention to differential shrinkage is required with semi-crystalline plastics. Fillers also influence the shrinkage by offsetting some volume of polymer with a low-shrinking filler particle. The shrinkage of resins containing isotropic fillers (such as glass beads or powders) will be more isotropic than resins containing high-aspect-ratio fillers (like fibers or platelets). This results from orientation of the fillers in a flow path during filling, and the restricted shrink along a long axis of the filler particles. Fibers are known to create excessive warp as the restricted shrink in a flow direction is compensated by an increased shrink of the polymer in a transverse direction.
U.S. Pat. No. 6,844,059 (Inventor: Heinz et al.; Published: 2005 Jan. 18) discloses a long-fiber-reinforced polyolefin structure that is also termed “a pellet”. The long-fiber-reinforced polyolefin structure of length being greater than or equal to 3 millimeters (mm) includes: a) from 0.1 to 50% by weight of at least one amorphous cycloolefin polymer, b) from 0.1 to 90% by weight of at least one polyolefin other than a), c) from 5.0 to 75% by weight of at least one reinforcing fiber, and d) up to 10.0% by weight of at least one additive which is different from components a)-c), wherein the percentages are based on the total composition. The moldings of the invention have reduced warpage and increased precision of fit. The object is to provide a long-fiber-reinforced polyolefin structure with very good mechanical properties, good heat resistance, and low water absorption, and also low warpage. The long-fiber-reinforced polyolefin structure is made by a process which includes: I) inducting a fiber bundle through a flat die charged with a melt made from said amorphous cycloolefin polymer a), said polyolefin other than a) (b) and, optionally, from said additive d), II) conducting the immersed fiber bundle through a shaping die, III) cooling the fiber bundle, IV) post forming the fiber bundle, and V) cutting the fiber bundle perpendicular to its running direction to give the length of the structure or winding the fiber bundle up in the form of a continuous structure.
Column 9 lines 44 to 51 (of U.S. Pat. No. 6,844,059) indicates that “a small rod-shaped 45 structure of a certain shape. The length of the rod-shaped structure is from 3 to 100 mm, preferably from 4 to 50 mm, and particularly preferably from 5 to 15 mm. The diameter the rod-shaped structure, also termed a pellet, is from 1 to mm, preferably from 2 to 8 mm, and particularly preferably from 3 to 6 mm”.
Column 9 lines 52 to 56 (of U.S. Pat. No. 6,844,059) indicate that “a process where the components are mixed in an extruder, and the reinforcing fiber is wetted by the melt, and the resultant material is then pelletized. The resultant pellets may be mixed with dye 55 and/or pigment and further processed to give the component”.
Column 9 lines 60 to 64 (of U.S. Pat. No. 6,844,059) indicates that “A shaped article is molded from the molten, where appropriate colored, long-fiber reinforced polyolefin pellets in a manner known per se, such as injection molding, extrusion, blow molding, or compression with plastification”.
Column 11 lines 11 to 20 (of U.S. Pat. No. 6,844,059) indicates that “moldings of this type may also be obtained by mixing long-fiber-reinforced polyolefin structures which are currently commercially available with pellets made from amorphous cycloolefin polymer, and then producing the moldings by the known processes from this mixture of pellets, in such a way that the content of amorphous cycloolefin polymer in the pellet mixture and in the moldings produced therefrom corresponds to the content of amorphous cycloolefin polymer in the polyolefin structures of the invention”.
It appears that according to U.S. Pat. No. 6,844,059, the long-fiber-reinforced polyolefin structure is a pellet having, in combination, a polyolefin, an amorphous cycloolefin polymer and a reinforcing fiber.
According to a first aspect of the present invention, there is provided a molding-system process, including: a receiving operation, including receiving a polymer unit, a cyclic olefin copolymer unit and a reinforcement unit, the polymer unit and the reinforcement unit being separate from each other prior to the polymer unit and the reinforcement unit being received, the received polymer unit, cyclic olefin copolymer unit and reinforcement unit are to be converted into a molding material, the molding material to be transferred into a mold, and in response the mold forming a product having reduced susceptibility to warpage.
According to a second aspect of the present invention, there is provided a molding-system process, including: (i) a receiving operation, including receiving a polymer unit, a cyclic olefin copolymer unit and a reinforcement unit, the polymer unit and the reinforcement unit being separate from each other prior to the polymer unit and the reinforcement unit being received, (ii) a converting operation, including converting the polymer unit, the cyclic olefin copolymer unit and the reinforcement unit into a molding material, and (iii) a transferring operation, including transferring the molding material into a mold, and in response the mold forming a product having reduced susceptibility to warpage.
According to a third aspect of the present invention, there is provided a molding system, including: (i) means for receiving a polymer unit, a cyclic olefin copolymer unit, and a reinforcement unit, the polymer unit and the reinforcement unit being separate from each other prior to the polymer unit and the reinforcement unit being received, (ii) means for converting the cyclic olefin copolymer unit, the polymer unit and the reinforcement unit into a molding material, and (iii) means for transferring, including transferring the molding material into a mold, and in response the mold forming a product having reduced susceptibility to warpage.
According to a fourth aspect of the present invention, there is provided a molding system, including: (i) a receiver configured to receive a polymer unit, a cyclic olefin copolymer unit and a reinforcement unit, the polymer unit and the reinforcement unit being separate from each other prior to the polymer unit and the reinforcement unit being received, (ii) a converter coupled to the receiver, the converter configured to receive the cyclic olefin copolymer unit, the polymer unit and the reinforcement unit from the receiver, the converter configured to convert the cyclic olefin copolymer unit, the polymer unit and the reinforcement unit into a molding material, and (iii) a transfer mechanism coupled to the converter, the transfer mechanism configured to transfer the molding material from the converter to a mold, and in response the mold forming a product having reduced susceptibility to warpage.
A technical effect, amongst other technical effects, of the aspects of the present invention is improved quality associated with a molded article.
A better understanding of the non-limiting embodiments of the present invention (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the non-limiting embodiments along with the following drawings, in which:
The drawings are not necessarily to scale and are sometimes illustrated by phantom lines, diagrammatic representations and fragmentary views. In certain instances, details that are not necessary for an understanding of the embodiments or that render other details difficult to perceive may have been omitted.
The following is a listing of the elements designated to each reference numeral used in the drawings:
According to U.S. Pat. No. 6,844,059, the long-fiber-reinforced polyolefin structure (hereafter referred to as the “LFRP structure”) is a pellet having, in combination: (i) a polyolefin, (ii) an amorphous cycloolefin polymer, and (iii) a reinforcing fiber. It appears that (based on U.S. Pat. No. 6,844,059) the LFRP structure, which is an input to a molding process, is manufactured before it is used as an input to the molding process; specifically, the LFRP structure is manufactured and then it is purchased for use as an input to a molding system or the molding process. A significant drawback, as identified by the inventor, to the arrangement associated with U.S. Pat. No. 6,844,059 is that it may be costly for a manufacturer of molded parts to purchase these “pre-manufactured” pellets (that is, the LFRP structures) for use as an input to the molding process. In sharp contrast to U.S. Pat. No. 6,844,059, according to the non-limiting embodiments, costs associated with purchasing raw material inputs (that is, the inputs to the molding system) are reduced because the material inputs include: (i) a cyclic olefin copolymer, (ii) a polymer, and (iii) a reinforcement material. The cyclic olefin copolymer may hereafter, from time to time, be referred to as the “COC”. The polymer may also be called a thermoplastic or a thermoset. The reinforcement material includes any one of: glass, carbon, natural or basalt fibers, amongst others equivalent items. It may be advantageous to merely add the cyclic olefin copolymer, the polymer and the reinforcement material to an extruder or a hopper of a molding system so that in this manner, (i) warpage of the molded part is reduced, and (ii) costs associated with obtaining and using the inputs are reduced as much as possible. According to the inventor, the it appears that the subject matter associated with U.S. Pat. No. 6,844,059 teaches away from the non-limiting embodiments.
According to non-limiting variants, (i) the reinforcement unit 6 includes a shape having an aspect ratio greater than 1, (ii) the polymer unit 2 includes the cyclic olefin copolymer unit 4 prior to the polymer unit 2 being received by the molding system, (iii) the reinforcement unit 6 includes the cyclic olefin copolymer unit 4 prior to the reinforcement unit 6 being received by the molding system, or (iv) the polymer unit 2, the cyclic olefin copolymer unit 4 and the reinforcement unit 6 are all separate from each other prior to the polymer unit 2, cyclic olefin copolymer unit 4 and the reinforcement unit 6 being received by the molding system.
According to a non-limiting variant: (i) the receiving operation 12 further includes receiving an additive 8, which is depicted in
According to a non-limiting variation, the receiver 221 is further configured to receive the additive 8, and the converter 223 is further configured to convert the polymer unit 2, the cyclic olefin copolymer unit 4, the reinforcement unit 6 and the additive 8 into the molding material.
The receiver 221 includes: (i) a hopper assembly 224, and (ii) a feed throat 225. The hopper assembly 224 is configured to receive the polymer unit 2, the cyclic olefin copolymer unit 4 and the reinforcement unit 6. The feed throat 225 is coupled to the hopper assembly 224.
The converter 223 includes: (i) a screw structure 222; (ii) a motor 226, and (iii) a controller 260. The motor 226 is coupled to the screw structure 222. The motor 226 is configured to drive the screw structure 222 (for example, to rotate and/or translate the screw structure 222). The screw structure 222 is configured to convert the polymer unit 2, the cyclic olefin copolymer unit 4 and the reinforcement unit 6 into the molding material (by using friction). The controller 260 includes a computer program product 262. The computer program product 262 is used for carrying a computer program embodied in a computer-readable medium. The readable medium is adapted (that is, the readable medium includes instructions) to direct (that is, instruct) the controller 260 so that the controller 260 controls the motor 226, so that, in turn, the motor 226 may actuate the screw structure 222 so as to perform the process 10 of
The transfer mechanism 241 includes an extruder assembly 220. The extruder assembly 220 includes: (i) a barrel 228, and (ii) a machine nozzle 243. The barrel 228 is connected with the feed throat 225. The barrel 228 is configured to receive the screw structure 222. The machine nozzle 243 is connected with an output of the barrel 228. The machine nozzle 243 is configured to convey the molding material away from the barrel 228 toward the mold 50.
According to a non-limiting variant, the system 200 further includes: (i) a stationary platen 242, (ii) a movable platen 244, and (iii) a clamp assembly 280. The stationary platen 242 is configured to support a stationary mold portion 52 of the mold 50. The movable platen 244 is configured to support a movable mold portion 54 of the mold 50. The movable platen 244 is movable relative to the stationary platen 242 so as to close the stationary mold portion 52 against the movable mold portion 54. Once the mold portions 52, 54 are closed, a mold cavity is defined that is used to receive the molding material. The clamp assembly 280 is configured to apply a clamping force to the stationary platen 242 and to the movable platen 244 so that the stationary mold portion 52 remains closed against the movable mold portion 54 as the mold 50 receives the molding material under pressure. The clamp assembly 280 includes: (i) rods 284 extending between respective corners of the platens 242, 244, (ii) nuts 282 for securing respective rods 284 to respective corners of the movable platen 244, and (iii) clamp units 286 coupled to respective rods 284 at respective corners of the stationary platen 242. The clamp units 286 are connected to ends of respective rods 284 opposite to respective nuts 282. The clamp unit 286 is configured to apply a clamping force to the rod 284, so that in this manner the clamping force may be applied or transmitted to the platens 242, 244. According to a non-limiting variant, the mold 50 includes a plurality of mold cavities, and a hot runner 230 that is configured to connect the machine nozzle 243 so as to fill the plurality of mold cavities with the molding material. Since the mold 50 wears out and is replaced with a new or refurbished mold, the system 200 and the mold 50 may be supplied by different vendors. In addition, since the mold 50 and the hot runner 230 are matched together (for performance reasons), once vendor may supply the hot runner 230 while another vendor supplies the system 200.
The receiver 321 includes: (i) a hopper assembly 324 and (ii) a feed throat 325. The hopper assembly 324 is configured to receive the polymer unit 2, the cyclic olefin copolymer unit 4 and the reinforcement unit 6. The feed throat 325 is coupled with the hopper assembly 324. The hopper assembly 324 may include three separate hoppers each of which separately receives an input or a single hopper used to receive all the inputs (the same may be said for the hopper assembly 224 of
The converter 323 includes: (i) a multiple-screw structure 322 (such as a double screw), (ii) a motor 326, and (iii) a controller 360. The multiple-screw structure 322 is configured to convert the polymer unit 2, the cyclic olefin copolymer unit 4 and the reinforcement unit 6 into the molding material. The motor 326 is coupled to the multiple-screw structure 322. The motor 326 is configured to drive the multiple-screw structure 322. The controller 360 includes a computer program product 362 for carrying a computer program. The computer program is embodied in a computer-readable medium that is adapted to direct the controller 360 to control the motor 326, so that the motor 326 may actuate the multiple-screw structure 322 so as to perform the process 10 of
The transfer mechanism 341 has or includes an extruder assembly 320. The extruder assembly 320, includes: (i) a barrel 328, (ii) a conduit 350, (iii) a manifold 352, (iv) a machine nozzle 343, and (v) a shooting pot 355. The barrel 328 is coupled with the feed throat 325. The barrel 328 is configured to receive the multiple-screw structure 322. The conduit 350 is connected with an output of the barrel 328. The conduit 350 is configured to convey the molding material away from the barrel 328 and toward the mold 50. The manifold 352 is connected with the conduit 350. The manifold 352 is configured to receive the molding material from the conduit 350. The machine nozzle 343 is connected with the manifold 352. The shooting pot 355 is connected with the manifold 352. The manifold 352 is further configured to: (i) convey, when switched to do so, the molding material to the shooting pot 355 while not conveying the molding material to the machine nozzle 343, and (ii) convey, when switched to do so, the molding material from the shooting pot 355 to the machine nozzle 343 while not conveying the molding material to the conduit 350. The shooting pot 355 includes a piston 356 that is receivable in the shooting pot 355. The piston 356 is configured to shoot the molding material toward the mold 50 via the manifold 352 and the machine nozzle 343. According to a non-limiting variant, the mold 50 includes a plurality of mold cavities, and a hot runner 330 that is configured to connect the machine nozzle 343 so as to fill the plurality of mold cavities with the molding material.
In summary: the discontinuous process includes having the multiple-screw structure 322 of the extruder assembly 320: (i) rotate to make molding material, but (ii) stop rotating while the manifold 352 shuts off so that the shooting pot 355 may translate to inject the molding material into a mold (while avoiding back flow of molding material back into the extruder assembly 320).
According to a variant, the continuous process (not depicted) includes: continuously operating the multiple-screw structure 322 of the extruder assembly 320, and using a buffer (not depicted) between the extruder assembly 320 and the shooting pot 355; in operation: (i) while the extruder assembly 320 fills the buffer with molding material, the shooting pot 355 shoots a shot into a mold, and (ii) while the buffer empties itself into the shooting pot 355, the extruder assembly 320 continues to make more molding material and buffering the molding material in the extruder assembly 320 on a temporary basis. There are patents and technical articles that disclose how to perform the continuous process by using two shooting pots that are alternately filled and emptied wherein the manifold directs the melt flow accordingly.
It will be appreciated that any one of the computer program products 262, 362 (of
According to a non-limiting variant, the system 300 further includes: (i) a stationary platen 342, (ii) a movable platen 344, and (iii) a clamp assembly 380. The stationary platen 342 is configured to support a stationary mold portion 52 of the mold 50. The movable platen 344 is configured to support a movable mold portion 54 of the mold 50. The movable platen 344 is movable relative to the stationary platen 342 so as to close the stationary mold portion 52 against the movable mold portion 54. Once the mold portions 52, 54 are closed, a mold cavity is defined that is used to receive the molding material. The clamp assembly 380 is configured to apply a clamping force to the stationary platen 342 and to the movable platen 344 so that the stationary mold portion 52 remains closed against the movable mold portion 54 as the mold 50 receives the molding material under pressure. The clamp assembly 380 includes: (i) rods 384 extending between respective corners of the platens 342, 344, (ii) nuts 382 for securing respective rods 384 to respective corners of the movable platen 344, and (iii) clamp units 386 coupled to respective rods 384 at respective corners of the stationary platen 342. The clamp units 386 are connected to ends of respective rods 384 opposite to respective nuts 382. The clamp unit 386 is configured to apply a clamping force to the rod 384, so that in this manner the clamping force may be applied or transmitted to the platens 342, 344. According to a non-limiting variant, the mold 50 includes a plurality of mold cavities, and a hot runner 330 that is configured to connect the machine nozzle 343 so as to fill the plurality of mold cavities with the molding material. Since the mold 50 wears out and is replaced with a new or refurbished mold, the system 300 and the mold 50 may be supplied by different vendors. In addition, since the mold 50 and the hot runner 330 are matched together (for performance reasons), once vendor may supply the hot runner 330 while another vendor supplies the system 300.
The description of the non-limiting embodiments provides non-limiting examples of the present invention; these non-limiting examples do not limit the scope of the claims of the present invention. The non-limiting embodiments described are within the scope of the claims of the present invention. The non-limiting embodiments described above may be: (i) adapted, modified and/or enhanced, as may be expected by persons skilled in the art, for specific conditions and/or functions, without departing from the scope of the claims herein, and/or (ii) further extended to a variety of other applications without departing from the scope of the claims herein. It is to be understood that the non-limiting embodiments illustrate the aspects of the present invention. Reference herein to details and description of the non-limiting embodiments is not intended to limit the scope of the claims of the present invention. Other non-limiting embodiments, which may not have been described above, may be within the scope of the appended claims. It is understood that: (i) the scope of the present invention is limited by the claims, (ii) the claims themselves recite those features regarded as essential to the present invention, and (ii) preferable embodiments of the present invention are the subject of dependent claims. Therefore, what is to be protected by way of letters patent are limited only by the scope of the following claims:
