WO2004052615A1

WO2004052615A1 - Method of in-mould coating an injection-moulded article incorporating positioning of the article prior to coating

Info

Publication number: WO2004052615A1
Application number: PCT/US2003/037359
Authority: WO
Inventors: John Thompson
Original assignee: Omnova Solutions Inc.
Priority date: 2002-12-10
Filing date: 2003-11-21
Publication date: 2004-06-24
Also published as: AU2003294448A1

Abstract

A method for providing a coated molded article is provided. A first thermoplastic composition is injected into a mold cavity (16) at a first pressure. The first composition continues to be injected into the mold cavity (16) at a second pressure that is less than the first pressure. A third pressure is applied to the injected first composition that is less than the second pressure and allows the first composition to form a molded article. A fourth pressure that is higher than the third pressure is applied to the molded article to position it within mold cavity (16) after it achieves a sufficient modulus to resist injection pressure. A second composition is injected into the mold cavity (16) onto at least one surface of the molded article after it achieves a sufficient modulus to support the second composition.

Description

METHOD OF IN-MOULD COATING AN INJECTION-MOULDED ARTICLE INCORPORATING POSITIONING OF THE ARTICLE PRIOR TO COATING BACKGROUND INFORMATION

[0001] The present invention relates to a method for coating a molded article or substrate with an in-mold coating (IMC) composition, more particularly to a method that includes the step of positioning the molded thermoplastic article within its mold cavity prior to injecting the IMC composition onto the molded article in the mold cavity.

[0002] Molded thermoplastic and thermoset articles, such as those made from polyolefins, polycarbonates, polyesters, polystyrenes and polyurethanes, are utilized in numerous applications including those for the automotive, marine, recreation, construction, office products, and outdoor equipment industries. [0003] Often, application of a surface coating to a molded article is desirable.

For example, molded articles may be used as one part in multi-part assemblies. To match the finish of the other parts in such assemblies, the molded articles may require application of a surface coating that has the same finish properties as the other parts. Coatings may also be used to improve surface properties of the molded article such as uniformity of appearance, gloss, scratch resistance, chemical resistance, weatherability, and the like. Also, surface coatings may be used to facilitate adhesion between the molded article and a separate finish coat to be later applied to the molded article. [0004] Numerous techniques have been developed to apply surface coatings to molded plastic articles, many of which involve applying a surface coating to molded articles after they are removed from their molds. These techniques are often multi-step processes involving surface preparation followed by spray-coating the prepared surface with paint or other finishes. [0005] In contrast, in-mold coating provides a means of applying a surface coating to molded articles prior to ejection from the mold. In-mold coating can eliminate the separate manufacturing process of applying a coating to an article upon its ejection from its mold, thereby reducing overall manufacturing cost. [0006] Molds used with thermoplastics and thermosets usually are designed like a clam shell, having mated halves that meet at a parting line. One of the mated halves typically remains stationary whereas the other typically is movable between closed and open (retracted) positions. To form a molded article, the movable half is moved to its closed position and held closed under a clamping force thereby forming a contained molding cavity. Molten material is injected into the molding cavity. Molded articles are formed by thoroughly filling the cavity with the substrate-forming composition and allowing it to sufficiently cool and solidify. During the entire molding process, the movable mold half is maintained in its closed position. After molding, the mold halves are opened and a finished, molded article ejected therefrom. [0007] Owing to differences in mold design and molding conditions, processes where the mold is parted prior to injection of an IMC composition generally are not used for the coating of injection molded articles. When molding such articles, maintaining pressure on the movable mold half to keep the cavity closed and prevent resin from escaping along the parting line generally is necessary. Further, it is often necessary to maintain pressure on the resinous material during molding. Such packing the mold helps to provide a more uniform crystalline or molecular structure in the molded article. Without packing, the physical properties of the molded article tend to be impaired. [0008] Because injection molding does not permit the mold to be parted or cracked prior to injection of the IMC composition into the mold cavity, the IMC composition is injected under sufficient pressure to compress the molded article in all areas to be coated. The compressibility of the molded thermoplastic article dictates how and where the IMC composition covers it. The process of coating an injection molded article with a liquid IMC composition is described in detail and the interested reader is directed to, e.g., U.S. Patent No. 6,617,953 and U.S. Patent Publications 2002/0039656 and 2003/0082344, all expressly incorporated herein by reference.

[0009] The method and apparatus used to physically inject the liquid IMC composition into the molding cavity of an injection molding machine during the molding of an article, also referred to herein as a dispense and control method and apparatus, is described in Intl. Appl. No. PCT/US03/33186 filed October 17, 2003, expressly incorporated herein by reference. The dispense and control apparatus provides a delivery system for injecting an IMC composition into the cavity of a pair of mold halves on an injection molding machine and a means for controlling the delivery system.

[0010] Often, the dispense and control apparatus must produce a relatively high pressure for injecting IMC composition into the cavity and forcing it across one or more surfaces of the molded article to be coated. The high injection pressure may be needed because the molded article may be tightly packed within the mold cavity, which obviously has finite dimensions. After a substrate-forming material has been injected into the mold cavity filling the same to a predetermined extent to produce a quality part, the molded part is compressed within the cavity and a relatively high amount of resistance is present between the molding surfaces of the mold cavity and the outer surfaces of the molded article. To interpose IMC composition between the molding surfaces and the outer molded article surfaces, a high injection pressure may be needed. The relatively high pressure needed to inject the IMC composition may cause an undesirable stress or pressure to be exerted against the molded article being coated, which could cause undesirable surface blemishes in the coated article. [0011] Thus, a method of forming and in-mold coating a molded article that reduces the required IMC composition injection pressure is desirable.

SUMMARY OF THE INVENTION

[0012] Briefly, the present invention provides a method for providing a coated molded article. A first composition is injected into a mold cavity at a first pressure, then continues to be injected into the mold cavity at a second pressure that is below the first pressure. To the injected first composition is applied a third pressure that is less than the second pressure and that allows the first composition to form a molded article. To the molded article is applied a fourth pressure that is higher than the third pressure so as to position the article within the mold cavity. An IMC composition is injected into the mold cavity onto at least one surface of the molded article after it achieves a sufficient modulus to support the IMC composition. The IMC composition cures on the surface(s) of the molded article so as to provide the coated molded article.

[0013] The method promotes the flow of IMC composition on a surface of a molded article and reduces stress or pressure exerted on the molded article by an IMC composition injection device. More particularly, the method takes advantage of the ability to resituate a molded article in its mold cavity to permit IMC composition to be applied with less effort than heretofore utilized. The method draws on the ability to place pressure or exert a force on the molded article to create an area of lowered resistance between walls of the mold cavity and the molded article. The method of the present invention has the ability to produce coated parts having excellent surface characteristics and capable of being used as-is without further coating or painting, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a side view of one molding apparatus suitable for use in or with the method of the present invention.

[0015] FIG. 2 is a partial cross-section through a vertical elevation of a mold cavity. [0016] FIG. 3 is a perspective view of an IMC composition dispense and control apparatus adapted to be connected to the molding apparatus of FIG. 1 and suitable for use in or with the present method.

[0017] FIG. 4 is a graph which visually portrays pressures exerted by the molding apparatus of FIG. 1 and the dispense and control apparatus of FIG. 3 over various periods of time.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0018] Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting the same and like reference numerals are used to indicate like or corresponding parts throughout the several figures, FIG. 1 shows a molding apparatus or injection molding machine 10 according to a preferred embodiment of the present invention. The molding apparatus 10 includes a first mold half 12 and a second mold half 14. The first mold half 12 preferably remains in a stationary or fixed position. In FIG. 1 , the movable mold half 14 is shown in an open position. The movable mold half 14 is movable to a closed position wherein the first and second mold halves mate with one another to form a contained mold cavity 16 of a finite and substantially fixed volume therebetween (See FIG. 2). More specifically, moid halves 12,14 mate along surfaces 18 and 20 (FIG. 1) when the molding apparatus is in the closed position, forming a parting line 22 (FIG. 2) therebetween and around cavity 16.

[0019] Movable mold half 14 reciprocates generally along a horizontal axis relative to the first or fixed mold half 12 by action of a clamping mechanism 24 with a clamp actuator 26 such as through a hydraulic, pneumatic or mechanical actuator as known in the art. The clamping pressure exerted by clamping mechanism 24 preferably has an operating pressure in excess of the pressures generated or exerted by either one of a first composition injector 30 and a second composition injector 32. In a preferred embodiment, the pressure exerted by clamping mechanism 24 ranges generally from about 15 to about 100 MPa (2000 to 15,000 psi), preferably from about 25 to about 85 MPa (4000 to 12,000 psi), and more preferably from about 40 to about 70 MPa (6000 to 10,000 psi) of the mold surface. [0020] In FIG. 2, mold halves 12,14 are shown in a closed position abutting or mating with one another along parting line 22 to form mold cavity 16. The design of mold cavity 16 obviously can vary greatly in size and shape according to the desired end product or article to be molded. Mold cavity 16 generally has a first surface 34 on second mold half 14 and a corresponding or opposite second surface 36 on first mold half 12. First mold half 12 defines a first orifice 38 connecting to cavity 16 that allows first composition injector 30 to inject its composition into cavity 16. Similarly, second mold half 14 defines a second orifice 40, also connecting to cavity 16, that allows second composition injector 32 (FIG. 1) to inject its composition into cavity 16. [0021] First composition injector 30 is that of a typical injection molding apparatus. More specifically) first composition injector 30 is generally capable of injecting a flowable composition, generally a thermoplastic resin or polymer, into mold cavity 16. Owing to space constraints, first injector 30 is positioned to inject material from fixed half 12 of the mold. First composition injector 30 could be reversed and placed in movable mold half 14. Second composition injector 32 generally is capable of injecting an IMC composition into mold cavity 16 to coat the molded article formed therein. In the illustrated embodiment, second injector 32 is shown positioned in movable mold half 14. However, second injector 32 alternatively can be positioned in stationary mold half 12. [0022] First composition injector 30 is shown in a "backed off' position but obviously can be moved in a horizontal direction so that a nozzle or resin outlet 42 of first injector 30 mates with mold half 12. In the mated position, injector 30 is capable of injecting its contents into mold cavity 16. For purposes of illustration only, first composition injector 30 is shown as a reciprocating-screw machine. Nozzle 42 optionally has a valve (not shown) at the open end thereof and screw 46 generally has a non-return valve (not shown) to prevent the backflow of material into screw 46.

[0023] First composition injector 30 is not limited to the embodiment shown in FIG. 1 but can be any apparatus capable of injecting a resinous composition into mold cavity 16. For example, the injection molding machine can have a mold half movable in a vertical direction or may be a "stack-mold" with center injection. Other suitable injection molding machines include many of those available from, e.g., Cincinnati-Milacron, Inc. (Cincinnati, Ohio); Battenfeld Injection Molding Technology (Meinlerzhagen, Germany); Engel Machinery Inc. (York, Pennsylvania); Husky Injection Molding Systems Ltd. (Bolton, Canada); and BOY Machines Inc. (Exton, Pennsylvania). [0024] FIG. 3 shows an IMC composition dispense and control apparatus 60 capable of being connected to molding apparatus 10 for providing coating capabilities and controls therefor. Control apparatus 60 includes an container receiving cylinder 62 for holding an IMC container filled with an IMC composition, such as that U.S. Patent No. 5,777,053. Control apparatus 60 further includes a metering cylinder or tube 64 adapted to be in fluid communication with IMC container when received in receiving cylinder 62. An air-driven transfer pump 66 is provided on control apparatus 60 and is capable of pumping IMC composition from receiving container 62 to metering cylinder 64. [0025] Metering cylinder 64 is selectively fluidly connectable to second injector 32 on molding apparatus 10. Metering cylinder 64 includes a hydraulic means such as a hydraulic piston for evacuating IMC composition from metering cylinder 64 and directing the evacuated IMC composition to second injector 32. A return line (not shown) is connected to second injector 32 and to receiving container 62 to fluidly communicate therebetween.

[0026] Control apparatus 60 further includes an electrical box 74 capable of being connected to a conventional power source. Electrical box 74 includes a plurality of controls 76 and a touch pad controller 78 thereon for controlling dispensing IMC composition to mold cavity 16. A compressed air connector (not shown) is provided on control apparatus 60 for connecting control apparatus 60 to a compressed air line. Compressed air is used to drive transfer pump 66 and remove IMC composition from control apparatus 60 and its fluid communication lines during a cleaning or evacuation. Additionally, air can be used to move a solvent through the communication lines for cleaning purposes. [0027] Apparatus 60 includes a remote sensor (not shown) that is adapted to be positioned, in the preferred embodiment, on one of mold halves 12,14. The sensor can be a conventional rocker switch that sends a signal to apparatus 60 upon actuation. The sensor is positioned on one of mold halves 12,14 such that it is actuated upon mold closure. The signal sent from the sensor is used to initiate a timer on apparatus 60. Alternatively, the sensor can be placed in another location to indicate when mold closure. [0028] Alternatively, molding apparatus 10 may be equipped with a sensor or sensor means that has the ability to generate a signal upon closure of mold halves 12,14. A conventional signal transfer cable could be connected between molding apparatus 10 and control apparatus 60 for communicating the signal to control apparatus 60. Such an arrangement would eliminate the need for connecting an independent sensor to one of mold halves 12,14. [0029] To prepare for injecting IMC composition into mold cavity 16, a container of a desired IMC composition is placed in receiving cylinder 62. Metering cylinder 64 is fluidly connected to second injector 32. Return line 68 is fluidly connected to second injector 32 and receiving cylinder 62. Control apparatus 60 is connected to a suitable power source such as a conventional 460 volt AC or DC electrical outlet to provide power to electrical box 74. Control apparatus 60 is also connected to a compressed air source to provide a pneumatic means for evacuating IMC composition from apparatus 60 and its fluid communication lines when a cleaning operation is desirable and/or moving a solvent through apparatus 60 and its fluid communication lines. The sensor is appropriately positioned on one of mold halves 12,14 as described above. [0030] A first, preferably thermoplastic, composition is placed in hopper 44

(FIG. 1) of molding apparatus 10. The present method can be practiced with any flowable material that can be injection molded. Suitable thermoplastic materials include, but are not limited to, nylon, acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polystyrene, polycarbonate, acrylic, acetal, polyolefins such as polyethylene and polyethylene, polypropylene, and polyvinyl chloride (PVC). The foregoing list is not meant to be exhaustive. [0031] First injector 30 is moved into nesting or mating relation with fixed mold half 12. Through conventional means, e.g., using heated extruder barrel 48 and rotating screw 46, first injector 30 heats first composition above its melting point and directs heated first composition toward nozzle 42 of first injector 30. Mold halves 12,14 are closed by clamp mechanism 24 thereby creating contained mold cavity 16 having a substantially fixed volume. In the closed position, clamping mechanism 24 maintains a clamping pressure sufficient to maintain mold halves 12,14 in closed relation even when the first composition and the second composition are injected into mold cavity 16 under pressure. Also prior to injecting the first composition, first injector 30 is moved into nesting or mating relation with first mold half 12.

[0032] As described above, the sensor of control apparatus 60 is positioned on one of mold halves 12,14 such that when mold halves 12,14 are closed together the sensor sends a signal to control apparatus 60 indicating that mold halves 12,14 are closed and that the molding process has begun. Upon receipt of the signal, hereinafter T₀, control apparatus 60 initiates the timer contained therein. The timer is used to track elapsed time from T₀. At predetermined elapsed time intervals, control apparatus 60 actuates and controls various IMC related functions to insure that the IMC composition is delivered to mold cavity 16 at a desired point in the molding process. Thus, control apparatus 60 operates simultaneously with molding apparatus 10.

[0033] After T₀, the molding process continues and a nozzle valve (not shown) of nozzle 42 is moved to an open position for a predetermined amount of time to allow a quantity of the first composition to enter mold cavity 16. Screw 46 provides a force or pressure that urges or injects first composition into mold cavity 16 until the nozzle pin is returned to its closed position. First composition is filled and packed into mold cavity 16. Once mold cavity 16 is filled and packed, molded first composition is allowed to cool thereby forming a molded article. [0034] After first composition has been injected into mold cavity 16 and the surface of the molded article to be coated has cooled below the melt point or otherwise reached a temperature or modulus sufficient to accept or support an IMC composition but before the surface has cooled too much such that curing of the IMC composition would be inhibited, a predetermined amount of a second composition which is an IMC composition is ready for injection into mold cavity 16 through second orifice 40 (FIG. 2) of second composition or IMC composition injector 32. This point in the molding process, hereinafter T|_MC. can be characterized as an elapsed time from T₀. For second injector 32 to inject the IMC composition precisely at T|_Mc, apparatus 60 has to perform several functions at precise times between T₀ and T|_MC. Each of these functions occurs at a predetermined elapsed time relative to T₀.

[0035] One such function is filling metering cylinder 64 with a desired amount of IMC composition. This function occurs a predetermined elapsed time from T₀ but in advance of T|_Mc- Thus, at the pre-selected elapsed time, control apparatus 60 opens a valve (not shown) that permits fluid communication between the IMC composition-filled container and metering cylinder 64. Transfer pump 66 then pumps IMC composition from the container to metering cylinder 64. When metering cylinder 64 is filled a desired amount, the valve closes to prevent more IMC composition from entering the cylinder. The amount of IMC composition entering cylinder 64 is selectively adjustable.

[0036] After metering cylinder 64 is filled and just prior to T|_MC, control apparatus 60 opens a pin or valve (not shown) on second injector 32 to allow fluid communication between second injector 32 and mold cavity 16. The pin is normally biased or urged toward a closed position, i.e., flush to the mold surface, but is selectively movable toward the open position by control apparatus 60.

Specifically, in a preferred embodiment, an electrically powered hydraulic pump (not shown) of control apparatus 60 is used to move the pin. Very shortly thereafter, at TI _C. the hydraulic means of metering cylinder 64 evacuates IMC composition contained therein and delivers it to second injector 32, where it passes through orifice 40 and into mold cavity 16.

[0037] The mold is not opened or undamped before IMC composition is introduced; mold halves 12,14 maintain a parting line 22 and generally remain a substantially fixed distance relative to one another while first and second compositions are injected into mold cavity 16. Thus, the substantially fixed volume of mold cavity 16 is constant and maintained throughout the molding and coating steps. When injected, the IMC composition spreads from the mold surface and coats a predetermined portion or area of the molded article. Very shortly after the IMC composition is fully injected into mold cavity 16, apparatus 60 allows the valve of second injector 32 to return to its closed position, thereby preventing further injection of IMC composition into mold cavity 16. [0038] After the predetermined amount of IMC composition is injected into mold cavity 16 and covers or coats the predetermined area of the article or substrate, the coated substrate can be removed from the mold. However, before the mold halves 12,14 are parted, the IMC composition is cured by components present within the coating composition. The cure is optionally heat activated, from sources including the substrate or mold halves 12,14 which are at or above the curing temperature of the IMC composition. Cure temperature will vary depending on the IMC composition utilized. As mentioned above, the IMC composition is injected before the molded article has cooled to the point below where proper curing of the coating can be achieved. The IMC composition requires a minimum temperature to activate the catalyst present therein which causes a crosslinking reaction to occur, thereby curing and bonding the coating to the substrate. [0039] Between IMC composition injections, control apparatus 60 uses transfer pump 66 to circulate IMC composition through the system. The pin on second injector 32 remains in its closed position thereby preventing any IMC composition from entering mold cavity 16. One purpose of circulating the IMC composition between cycles is to prevent any particular portion of the coating from becoming undesirably heated due to its proximity to heating mechanisms on molding apparatus 10. Such heating could detrimentally impact the material properties of the IMC composition or could block the IMC fluid lines by solidifying the IMC composition therein. [0040] Controls 76 and keypad 78 of control apparatus 60 enable an operator to adjust and/or set certain operating parameters of control apparatus 60. For example, the controls can be manipulated to increase or decrease the amount of IMC composition to be filled in metering cylinder 64 by allowing the valve that controls communication between metering cylinder 64 and receiving container 62 to remain open for a longer duration. Additionally, the controls can be manipulated to adjust the elapsed time from T₀ that metering cylinder 64 is filled by transfer pump 66 and/or the amount of time elapsed from T₀ that cylinder 64 is emptied by the hydraulic means. This time may be adjusted to more closely approximate TIM_C-

[0041] The sensor can be a pressure transducer mounted adjacent mold cavity 16 and adapted to record a pressure in mold cavity 16. Here, the timer of control apparatus 60 can be eliminated. Rather than using the elapsed time from the start of the mold process, control apparatus 60 injects IMC composition into mold cavity 16 based on the pressure recorded in mold cavity 16 by the pressure transducer sensor. The IMC composition desirably is injected into mold cavity 16 at the same point in the molding process, TI_MC, irrespective of what type of sensor is used. [0042] The pressure in mold cavity 16 will initially rise while the resin fills mold cavity 16. The pressure will rise further as mold cavity 16 is packed. Finally, the pressure in mold cavity 16 will begin to decrease as the molded article cools and begins to solidify. At a predetermined pressure during the cooling phase that corresponds with T_IM_C, the IMC composition is preferably injected into mold cavity 16. The predetermined pressure is generally based on the specific type of resin used and may also be based on the specific type of IMC composition used. [0043] Based on the pressure measurements taken by the pressure transducer sensor, the series of functions performed by control apparatus 60 also can be dependent on the pressure measured in mold cavity 16. Thus, each of the functions will occur at a predetermined pressure in mold cavity 16 so that the IMC composition can be injected into mold cavity 16 at the desired point in the molding process. Injecting IMC composition into a mold cavity 16 and onto the surface of a molded article based on the pressure measured in mold cavity 16 is described in U.S. Patent No. 6,617,033. [0044] The pressure transducer alternatively can be a plurality of pressure transducers positioned at varying locations around mold cavity 16. In this arrangement, control apparatus 60 performs its functions, including injecting the IMC composition based on a plurality of pressure measurements. For example, control apparatus 60 can perform its functions based on predetermined pressure averages of the plurality of pressure measurements taken by the plurality of pressure sensors. This arrangement may be desirable because a plurality of pressure transducers may be able to better determine the actual pressure observed in mold cavity 16. [0045] Some conventional injection molding machines and molds already are equipped with one or more transducers adapted to measure pressure in mold cavity 16. These machines often are capable of sending a signal representative of the measured pressure or pressures to associated equipment such as control apparatus 60 through conventional data transfer means. In this case, the need for a remote pressure transducer sensor is eliminated. Control apparatus 60 need only be suitably connected to injection molding machine 10 to receive the signal representative of the pressure measurement(s) taken from mold cavity 16. [0046] The sensor can be a thermocouple mounted adjacent mold cavity 16 and adapted to record a temperature in mold cavity 16. In this embodiment, the timer of control apparatus 60 can also be eliminated. Further, control apparatus 60 injects IMC composition into the mold cavity 16 based on the temperature recorded in mold cavity 16 by the thermocouple sensor. The IMC composition is desirably injected into mold cavity 16 at the same point in the molding process, TI_MC, as the previous sensors. The main difference is injection of the IMC composition is temperature dependent.

[0047] Control apparatus 60 can be equipped with and/or connected to a data collection means. The data collection means can be an on-board hard drive or other recording medium capable of recording the operating parameters set on control apparatus 60 for one or a series of molded articles. Other alternate arrangements are possible, such as, for example, connecting the apparatus to a network and recording operating parameters at a remote location. In any case, the data collection means can record the predetermined elapsed time settings from T_o that the various control apparatus functions are set to use and/or the actual elapsed time intervals when the various functions occur. [0048] For example, for each injection of IMC composition, the data collection means can record the time from T₀ that transfer pump 66 fills metering cylinder 64, the time from T₀ that the pin of second injector 32 opens, the time from T₀ that the hydraulic means evacuates metering cylinder 64 and second injector 32 injects the IMC composition into mold cavity 16 and/or the time from T₀ that the pin of second injector 32 closes. Other functions also can be recorded including without limitation the number of SMC composition injections for a specific amount of IMC composition, the hydraulic pressure used to evacuate metering cylinder 64, etc.

[0049] If one or more pressure transducers are used in place of the rocker switch (a time dependent sensor), the data collection means can be used to record related measurements therewith. For example, the data collection means can record the specific measured pressures at which time the various functions of control apparatus 60 occur. Likewise, if the sensor is a thermocouple, the temperature measurements taken thereby can be recorded. [0050] In any case, the data or information recorded by the data collection means can be used for quality control purposes. For example, a coated part can be examined upon being ejected from mold cavity 16 and compared against the data collected on the specific injection of IMC composition associated with that part. If the part does not meet certain quality control requirements, such as lack of adhesion between the coating and the thermoplastic, lack of scratch resistance, surface imperfections, lack of adequate coating coverage, etc., the present parameters (whether time dependent, pressure dependent, temperature dependent or otherwise), can be adjusted to improve the coating characteristics of future coated parts.

[0051] Control apparatus 60 also can be equipped with a means for transferring collected data. This can be through any conventional means including providing a disk drive or the like that allows the data to be recorded to a mobile storage medium, providing a data link that is connectable to a local computer, an intranet, the internet, other network, etc. Such means for transferring data can allow remote analysis of the collected data in real-time. [0052] Control apparatus 60 also can include a conventional package code reader (not shown) such as a bar code reader. The reader can be used to scan a code on a particular container of IMC composition placed in receiving cylinder 62 and injected onto a plurality of molded parts. Used in conjunction with the data collection means described above, the code for a particular container of IMC composition can be associated with data recorded for all injections of IMC composition from the particular container. Further, the code of the IMC container can be associated with a finished parts bin or collection means that receives finished parts with a coating thereon from molding apparatus 10. Recording and storing such information allows particular finished parts to be analyzed and easily compared against the data recorded thereabout and the particular IMC composition used.

[0053] Control apparatus 60 can be provided with a user interface that allows a user to simply select a part icon that represents a series of parts to be molded and coated. Selection of a specific part icon on the user interface presets the control parameters on control apparatus 60 whether they are time-based, cavity pressure-based, or otherwise. The user interface eliminates the need for an operator to set the control parameters individually each time a new part series is to be run through the molding and coating process. [0054] Control apparatus 60 can be provided with a display means such as a monitor (not shown). Display means can display, in real time, any of the data or information being sensed and/or recorded by control apparatus 60. Further, control apparatus 60 can be configured to only allow a specific number of injections per container of IMC composition. Alternatively, or additionally, control apparatus 60, when used with the code reader, could be set to operate only with a specific type of IMC composition.

[0055] Returning now to the molding system that works in conjunction with control apparatus 60, during an injection fill stage, the first composition in a melted or softened state is initially injected into mold cavity 16 by first injector 30 at a first or filling pressure for a first predetermined period of time. This first filling pressure ranges generally from about 5 to about 17.5 MPa (1000 to 2500 psi), preferably from about 8 to about 15 MPa (1200 to 2000 psi), and more preferably from about 10 to about 12 MPa (1500 to 1800 psi). During the injection fill stage, generally from about 70 to about 100%, preferably from about 80 to about 99%, and more preferably from about 88 to about 95% of the total volume of mold cavity 16 is filled with the first composition. The injection fill stage generally has a duration of from about 1 to about 20 sec, preferably from about 1.5 to about 10 sec. [0056] After the injection fill stage, an injection pack pressure stage occurs for a second predetermined period of time wherein first injector 30 substantially fills the remainder of the capacity of mold cavity 16 with the first composition under a second or packing pressure that is reduced or relatively lower when compared to the filling pressure of the injection fill stage. During the injection pack pressure stage, generally from about 0.001 to about 30%, preferably from about 1 to about 20%, and more preferably from about 5 to about 12% of the mold cavity volume, i.e., the volume of the mold cavity which was not filled during the injection fill stage, is filled by the first composition. [0057] The packing pressure of the packing stage can be a single constant pressure or a number of different pressures, all less than the filling pressure exerted during the injection fill stage. The packing pressure ranges generally from about 1.75 to about 15 MPa (250 to 2000 psi), preferably from about 2 to about 13 (300 to 1875 psi), and more preferably from about 3 to about 7 MPa (400 to 1000 psi). A two-pressure, step-down drop can be used during the packing stage. For example, a 4 MPa (600 psi) pressure can be used for a portion of the packing stage before being stepped down to 3 MPa (400 psi) for the remainder thereof. After the packing stage, the injected first composition substantially fills mold cavity 16 and conforms to the shape of mold cavity 16, thereby beginning to form a molded article. [0058] A subsequent holding stage occurs for a third predetermined period of time wherein the injection pressure of the first composition is reduced to a third or holding pressure, which is less than the packing pressure of the packing stage. The holding pressure ranges generally to about 3 MPa (400 psi), preferably from about 7 KPa to about 2 MPa (1 to 300 psi), and more preferably from about 1 to about 1.75 MPa (150 to 250 psi). In the holding stage, substantially stalling screw 46 and allowing the molded article to sufficiently cool can be desirable. The molded article is sufficiently cool when it begins to "skin over" and acquires a modulus or hardness sufficient enough to withstand a subsequent pressure exerted by first nozzle 30 to physically reposition the molded article within mold cavity 16 as described in more detail below. The holding stage pressure can be maintained for any desired time period but typically ranges from about 2 to about 20 sec, preferably from about 4 to about 16 sec, and more preferably from about 6 to about 12 sec.

[0059] Subsequent to the holding stage, a molded article positioning stage is initiated. At a time prior to and optionally during injection of the IMC composition from control apparatus 60, first injector 30 places an increased pressure relative to the holding pressure on at least a portion of the molded article. Preferably, the increased pressure, also referred to herein as a fourth pressure or a positioning pressure, is applied substantially immediately after the molded article has attained the modulus sufficient to resist the injection pressure and be positioned in molding cavity 16 by the positioning pressure. The positioning pressure can be exerted on a) a sprue, if the mold cavity has a sprue forming a mold runner, b) a bushing, or c) the area adjacent to, around, or in front of a gate pin or like mold shut off device. Thus, during the molded article positioning stage, first injector 30 is utilized to place a pressure on the molded article that is greater than the holding pressure exerted during the hold stage to position or reposition the molded article in mold cavity 16. [0060] During solidification of the molded article, cooling takes place, which is believed to cause at least a slight shrinkage of the molded article in mold cavity 16. Shrinkage within mold cavity 16 may or may not be visually noticeable to the unaided eye and may not result in the molded article separating from walls of mold cavity 16. In the positioning stage, first injector 30 places a sufficient amount of pressure on the molded article to position it so that an IMC composition can be applied with relatively less pressure than would be required without positioning the molded article and promote flow of the IMC composition. During the part positioning stage, the fourth pressure exerted by first injector 30 is limited only by the upper limits producable thereby and ranges generally from about 0.7 to about 20 MPa (100 to 3000 psi), preferably from about 1.4 to about 10 MPa (200 to

1500 psi), and more preferably from about 2.75 to about 5.5 MPa (400 to 800 psi). [0061] The pressure applied during the positioning stage urges or forces the molded article away from first injector orifice 38 of first injector 30. As shown in FIG. 2, the molded article would be urged, forced or otherwise moved toward surface 34 thereby providing less resistance to IMC composition flow between the molded article and surface 36. The lowered resistance can be maintained during the entire coating process. When the IMC composition is injected through second orifice 40, as described below, the coating composition can flow with less resistance than it otherwise would without the part positioning pressure from the first injector. By positioning the molded article in mold cavity 16 prior to coating, the injection pressure at which the IMC composition is injected may be reduced. This reduces stresses or pressure exerted in the molded article during coating. More- over, surface characteristics of the coated article also may be improved.

[0062] After the surface of the molded article to be coated has cooled below the melt point or otherwise reached a temperature or modulus sufficient to accept or support an IMC composition, a predetermined amount of the IMC composition can be injected through second orifice 40 into mold cavity 16 and onto the molded article. If the IMC composition is cured by heat, it desirably is injected before the surface of the molded article has cooled so much that curing is inhibited. This point in the molding process can occur during or after the positioning stage. In either case, the hydraulic means is actuated to evacuate a predetermined amount of the IMC composition from metering cylinder 64 and inject the evacuated comp- osition into molding cavity 16. The IMC composition can continue to be injected into mold cavity 16 even after the positioning stage ends, i.e., in a post-positioning stage that occurs after part positioning pressure is reduced to zero. [0063] The mold is not opened or undamped before the IMC composition is applied. That is, mold halves 12,14 maintain parting line 22 and generally remain substantially fixed relative to each other while both the first and second compositions are injected into mold cavity 16. Thus, the substantially fixed volume of mold cavity 16 is maintained throughout the molding and coating steps. When injected, the IMC composition spreads from the mold surface and coats a predetermined portion or area of at least one surface of the molded article. Immediately or very shortly after the IMC composition is fully injected into mold cavity 16, apparatus 60 allows the valve of second injector 32 to return to its closed position, thereby preventing further injection of IMC composition into mold cavity 16. [0064] After a predetermined amount of IMC composition is injected into mold cavity 16 and covers or coats the predetermined area of the article or substrate, the coated article can be removed from the mold. However, before the mold halves are parted, the coating is cured by components present within the IMC composition. The cure is optionally heat activated, from sources including the substrate or mold halves which are at or above the curing temperature of the IMC composition. Cure temperature varies depending on the IMC composition utilized. As mentioned above, the IMC composition, if its curing is heat activated, preferably is injected before the molded article has cooled to the point below where proper curing of the coating can be achieved easily. These types of IMC compositions require a minimum temperature to activate the catalyst and/or initiator present therein which causes a crosslinking reaction to occur, thereby curing and bonding the coating to the molded article. [0065] FIG. 4 shows pressure versus time curves for molding apparatus 10 as well as control apparatus 60. Filling, packing, holding, positioning, and post- positioning stages are shown. As explained above, the fill stage pressure is relatively higher than the packing stage pressure. The packing stage is shown having two different pressures, but one or more than two pressures also can be utilized during the packing stage. During the holding stage, the pressure from first composition injector 30 decreases when compared to the packing stage to a negligible level in part to allow the molded article to achieve a suitable modulus for repositioning in the subsequent stage. Next, first composition injector 30 again exerts a pressure during the positioning stage greater than the holding stage pressure. The positioning stage can begin at about approximately the same time as the IMC composition starts to be injected into mold cavity 16.

[0066] As shown in FIG. 4, the IMC composition continues to be injected during the part positioning stage. As also illustrated, the IMC composition injection can continue after the positioning stage has been completed, terminating in the post-positioning stage. Alternatively, the IMC composition can be injected into mold cavity 16 after the positioning stage has been completed and thus begin and end in a post-positioning stage.

Claims

CLAIMS We claim:

1. A method for providing a coated molded article, comprising: a) injecting at a first pressure a first composition into a mold cavity (16); b) continuing to inject into said mold cavity (16) said first composition but at a second pressure, said second pressure being less than said first pressure; c) when injection of said first composition into said mold cavity (16) is complete, applying to the injected first composition a third pressure that is less than said second pressure and allowing said first composition to form a molded article; d) to said molded article, applying a fourth pressure, said fourth pressure being greater than said third pressure and acting to position said molded article within said mold cavity (16) after the molded article; and e) after said molded article has cooled sufficiently so as to attain a modulus capable of receiving and supporting a coating, injecting into said mold cavity (16) and onto at least one surface of said molded article a second composition, thereby providing said coated molded article.

2. The method of claim 1 wherein at least one of the following is true: (i) said mold cavity (16) has a volume that remains substantially constant throughout said method, and (ii) said mold cavity (16) is defined by mold members (12,14) that generally remain a substantially fixed distance relative to one another throughout said method.

3. The method of any of claims 1 to 2 wherein said second pressure comprises a plurality of varying pressures all of which are less than said first pressure.

4. The method of any of claims 1 to 3 wherein step (c) occurs after said first composition substantially completely fills said mold cavity (16).

5. The method of any of claims 1 to 4 wherein said first pressure is from 5 to 17.5 MPa and said second pressure is from 1.75 to 15 MPa.

6. The method of any of claims 1 to 5 wherein said third pressure is up to 3 MPa and said fourth pressure is from 0.7 to 20 MPa.

7. The method of any of claims 1 to 6 wherein said fourth pressure is exerted on at least one of a sprue, a bushing, and an area adjacent to, around, or in front of a mold shut-off device.

8. The method of any of claims 1 to 7 wherein step (e) begins during and continues beyond step (d).

9. The method of any of claims 1 to 8 wherein said fourth pressure urges said molded article toward a surface (34) of mold cavity (16), thereby allowing said second composition to be injected between said molded article and another surface (36) of mold cavity (16) with less resistance.

10. The method of any of claims 1 to 9 wherein both of steps (d) and (e) begin, relative to step (c), at approximately the same time.