Abstract:
A process of molding a component on a substrate utilizes a substrate having a peripheral flange that projects into a parting line between mold segments defining a mold cavity, wherein the flange has a projecting, continuous circuitous ridge that forms a seal between the substrate and an upper mold segment. The process allows a substantially flash free molded component to be formed directly on a substrate, thus eliminating the need for a separate flash removal step.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to injection molding processes, and more particularly to molding on a substrate.  
         BACKGROUND OF THE INVENTION  
         [0002]    Reaction injection molding (RIM) is a process for molding polymeric parts by injecting low molecular weight, reactive, low viscosity liquids at high pressure into a mixing chamber and then into a mold cavity. The liquid reactants polymerize in the mold to form a molded article. Molds used for reaction injection molding, like many molds, comprise at least two segments, which in a mold-closed position, come together to define a mold cavity into which the reactants are injected. The mold segments have complimentary shaped faces which come together when the mold is closed to define a parting line. Unfortunately, there is usually some degree of mismatch between the faces. This mismatch of the mold segments results in the formation of small gaps between the mating faces at the parting line. Such gaps allow liquid mixture injected into the mold cavity to invade the parting line at its edges and produce protrusions, known as “flash”, on the finish article.  
           [0003]    A particular application for reaction injection molding of a component directly on a substrate is in the production of acoustic barrier systems for motor vehicles. It is common practice in the motor vehicle industry to employ a double wall acoustic barrier arrangement to reduce noise from the engine compartment to the passenger compartment of a motor vehicle. The acoustic barrier system typically includes a metal wall separating the engine compartment from the passenger compartment, and a dash barrier spaced away from the passenger compartment side of the metal wall. A foam (i.e., an expanded thermoplastic material) or fiber sound absorbing or damping material is typically disposed in the space defined between the steel wall and the dash barrier. The dash barrier is typically a panel made of self-supporting, relatively dense, resilient or flexible synthetic plastic material, and the sound absorbing or damping material, also referred to as a decoupler, is typically in the form of a foam sheet or panel, or a fibrous mat. Often, the decoupler panel or mat is attached to the barrier panel prior to installation of the acoustic barrier and decoupler into a vehicle so that the barrier and decoupler are installed as a unit into a vehicle.  
           [0004]    A premium process for producing high quality acoustic barrier systems comprising an acoustic barrier panel secured to a foam panel includes steps of injection molding an acoustic barrier panel, and foaming the foam panel in a mold cavity directly against a surface of the barrier panel using a reaction injection molding (RIM) technique. Heretofore, it has not been possible to produce a foam RIM part without unwanted thin protrusions (flash) at the edges of the part which were located at the parting line of the mold segments. In order to meet the rigid dimensional and quality requirements common in the automotive industry, the finished parts must generally be free of flash.  
           [0005]    Attempts to eliminate flash from RIM parts have generally focused on removing the flash after the molding process has been completed. Various mechanical flash removal apparatuses, cryogenic flash removal methods, and handwork processes have been devised to remove flash from RIM parts. However, these apparatuses and processes have achieved very limited success. Mechanical flash removal apparatuses have generally failed to consistently remove all of the flash material from a RIM part and/or have removed surface material from the RIM part resulting in destruction of texturing or other surface features of the part in the area of the mold seam. Similarly, cryogenic processing and/or handwork processing have not provided consistent satisfactory results due to incomplete removal of all flash material and/or damage to surface features of the RIM part. Further, handwork processes are very time consuming and labor intensive, with as much as about 40% of the total production cost for certain RIM parts being attributable to hand removal of flash material.  
           [0006]    A flash-proof RIM mold and method are allegedly disclosed in U.S. Pat. No. 5,543,159. The method involves use of an interlayer film of thermosetting resin disposed on an edge of a parting line at one of a pair of mold segments. The interlayer film acts as a seal between the mating faces of the mold segments to fill any gaps between the mating faces and prevent intrusion of liquid reactants into the parting line during the RIM process. In order to cause the interlayer film to adhere firmly to the face of one mold segment and be readily separable from the face of the other mold segment, the face of a first mold segment is roughened to provide a multiplicity of anchoring sites for the film, and the face of a second mold segment is preferably polished to provide a smooth surface which will facilitate easy separation of the face of the second mold segment from the film. It is desirable to apply a mold release agent to the face of the second mold segment between each molding cycle to ensure release of the second mold segment from the interlayer film sealing the parting line gaps. The interlayer film is installed by depositing a strip or bead of thermosetting resin to the roughened surface of the first mold segment, closing the mold to allow the resin to flow and fill any gaps along the parting line, partially curing the resin while the mold is closed so as to form a material that is sufficiently hard to retain any formed contours after the mold is open, opening the mold, trimming away any material that has exuded into the mold cavity, and completing curing of the resin. It is alleged that the seal may be used to mold as many as about 5,000 parts before repair (i.e., replacement) of the seal is required.  
           [0007]    Disadvantages with this process and apparatus include the requirement for modification of the mold segments, the need for applying mold release agents between each molding cycle, and the necessity for periodic removal of the film seal and fabrication of a new seal. Further, it is not evident how the process and apparatus may be adapted or modified for forming a RIM component directly on a thermoplastic substrate located in the mold cavity adjacent cavity surfaces of one of the mold segments.  
           [0008]    Accordingly, there is a need for improved processes of reaction injection molding a component on a substrate while preventing or reducing formation of flash.  
         SUMMARY OF THE INVENTION  
         [0009]    The process of the invention allows a substantially flash free molded component to be formed directly on a substrate. The process eliminates the need for a separate flash removal step, allowing the resulting product to be ready for use directly out of the mold without any intervening steps.  
           [0010]    In accordance with an aspect of this invention, an improved process of molding a component on a substrate is achieved by providing the substrate with an integral seal that prevents materials introduced into a mold cavity during molding from exuding from the mold cavity and along the parting line between mating faces of first and second mold segments defining a mold cavity. By providing a seal on the substrate upon which the component is formed, a new seal is provided during each molding cycle. This eliminates the need for specially treating mating surfaces on the mold segments (i.e., roughening of one mating surface and polishing of another). The process also eliminates, or at least reduces, the need for treating the mating surface of at least one of the mold segments with a release agent. Further, the process of the invention substantially reduces or eliminates flash formation during molding without requiring frequent monitoring and replacement of a multiple use seal anchored to one of the mold segments. The process of this invention is inherently adapted for molding a component on a substrate.  
           [0011]    In accordance with a particular aspect of the invention, there is provided a process of molding a component on a substrate by providing first and second mating mold segments that, when in a closed position, define a mold cavity for receiving a liquid mixture of reactants; providing a substrate having a contoured surface which conforms with mold cavity defining surfaces of the first mold segment, the substrate having a peripheral flange conforming with the complementary shaped faces of the mold segments, the peripheral flange including at least one continuous circuitous ridge that projects from a surface of the flange; positioning the substrate it the first mold segment, closing the mold; introducing moldable material into a mold cavity defined by the closed mold; allowing the moldable material to solidify and form a molded component; opening the mold; and removing an article including the substrate and an integral molded component which is substantially free of flash.  
           [0012]    These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross-sectional view of a molding apparatus suitable for use in practicing the invention.  
         [0014]    [0014]FIG. 2 is an expanded, partial cross-sectional view of the apparatus of FIG. 1, showing details at the mold parting line when the mold is open.  
         [0015]    [0015]FIG. 3 is an expanded, partial cross-sectional view of the apparatus of FIG. 1, showing details at the mold parting line when the mold is closed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    In FIG. 1, there is shown a cross-sectional view of a mold  10  comprising a mold segment  12 , and a mold segment  14 . Mold segments  12  and  14  are hinged together with a precision open/close mechanism  16 . When the mold  10  is closed, as shown in FIG. 1, mold segment  12  and mold segment  14  together define a mold cavity in which an injection molded thermoplastic substrate  18  is disposed, and in which a mixture of liquid reactants is injected and reacted to form a molded component  20  which conforms with the remaining shape of the mold cavity that is not occupied by substrate  18 . Mold segments  12  and  14  have complementary shaped faces  22  and  24  that mate with each other at a parting line  26 .  
         [0017]    Substrate  18  has a contoured surface which conforms with mold cavity defining surfaces of mold segment  12 . In the illustrated embodiment, substrate  18  is a substantially flat panel or sheet, and mold segment  12  has a substantially flat surface conforming with the shape of substrate  18 . Substrate  18  also has a peripheral flange  28  which has a shape conforming with the complementary shaped mating faces  22  and  24  of mold segments  14  and  12 , respectively. Mating faces  22  and  24  define a parting line or plane that extends circumferentially around the mold cavity defined by mold segments  12  and  14 . Peripheral flange  28  extends continuously in a circumferential loop into a small gap defined between mating faces  22  and  24 .  
         [0018]    As shown in greater detail in FIGS. 3 and 4, peripheral flange  28  includes two continuous circuitous lips or ridges  30  and  32  that project from an upwardly facing surface  34  of substrate  18 . Ridges  30  and  32  are integrally formed features of substrate  18 . Ridges  30  and  32  define concentric continuous protuberances which circumscribe the mold cavity, and which are disposed within the small gap between mating faces  22  and  24  of mold segments  14  and  12 , respectively. As shown in the Figures, ridges  30  and  32  have a continuously curved transverse profile, and more particularly, a semi-circular transverse profile. Upon closing of mold  10 , as illustrated in FIG. 3, mating face  24  of upper mold segment  12  engages ridges  30  and  32 , causing ridges  30  and  32  to become slightly deformed, i.e., compressed and flattened at the apex thereof, whereby two concentric peripheral seals are developed between mold segment  14  and ridges  30  and  32 . This sealing mechanism redefines a sealed mold cavity between substrate  18  and mold segment  14 .  
         [0019]    In order to provide a suitable seal for preventing the reactant mixture injected into the mold cavity during the RIM process, substrate  18 , and therefore integral ridges  30  and  32 , is made of a material that exhibits suitable compressibility and deformability to provide a sealing function. Examples of suitable substrate materials that are capable of performing the required sealing function include various thermoplastic or elastomeric materials, such as thermoplastic olefins, rubber modified polypropylene, elastomer-modified polyurethanes, elastomer-modified polyamides, etc. The substrate materials may contain fillers and/or reinforcing materials such as fibers, along with other conventional additives.  
         [0020]    Desirably, substrate  18  is a part having very precise dimensions to insure precise engagement with the mold segments and excellent sealing with the mold segments. While it is conceivable that other techniques may be employed for fabricating substrate  18 , injection molding provides a suitable technique for economically forming a substrate  18  having the required precise dimensions.  
         [0021]    In order to precisely locate substrate  18  within the mold cavity defined between mold segments  12  and  14 , substrate  18  is desirably formed with one or more locator features  36  which come into registry with a slot or recess  38  defined on the mold cavity defining surface of upper mold segment  12 .  
         [0022]    Molded component  20  may be formed using generally any combination of liquid reactants suitable for reaction injection molding technique. The resulting component  20  may either be comprised of a substantially continuous solid material, or blowing agents may be introduced into the mold cavity along with the liquid reactants to form an expanded plastic material or foam having either open or closed cells containing a gas.  
         [0023]    During conventional RIM processes a relatively precise quantity of liquid reactants is introduced into the mold cavity, with a small overage escaping along the parting line to form flash. In accordance with the principles of this invention, flash is prevented or significantly reduced by the sealing action of ridges  30  and/or  32 . Accordingly, any excess liquid reactant injected into the mold cavity could result in high pressures that are sufficient to damage the mold. Therefore, it is desirable to provide lower mold segment  14  with a pressure relief valve  40  that will prevent unacceptably high pressures from building up within the mold cavity.  
         [0024]    Molded component  20  may be secured to substrate  18  during the RIM process by development of adhesion between substrate  18  and component  20  during the RIM process and/or by physical entrapment of protruding anchor features (not shown) integrally formed, or attached to, substrate  18 .  
         [0025]    In the illustrated embodiment, substrate  18  represents an acoustic barrier that is, for example, injection molded from a filled thermoplastic material having elastomeric properties, and component  20  represents a plastic foam sound absorbing or decoupling material, such as a polyurethane foam material. The resulting combination of acoustic barrier substrate  18  secured to foam material  20  is useful as an acoustic barrier system that may be installed as a unit on the passenger side of a metal wall separating an engine compartment from a passenger compartment of a motor vehicle. The invention allows foam component  20  to be formed on and secured to barrier substrate  18  without requiring any separate steps for attaching foam component  20  to barrier substrate  18 , and without requiring any steps for removing flash subsequent to reaction injection molding of component  20 . However, the illustrated embodiment only represents a particular useful application for the invention. Other advantageous applications of the invention will be readily apparent to those skilled in the art.  
         [0026]    The process of reaction injection molding a component on a substrate in accordance with the principles of this invention involves first positioning the substrate in the lower segment  14  such that the contoured surfaces of substrate  18  and the mold cavity defining surfaces of mold segment  14  are in conforming registry, and with the peripheral flanges of substrate  18  engaging the mating face  22  of mold segment  14 . Thereafter, mold  10  is closed by pivoting mold segment  12  around open/close hinge mechanism  16  into the closed position shown in FIG. 1. This causes peripheral flange  28 , including ridges  30  and  32 , to become compressed. More specifically, engagement between mating face  24  of mold segment  12  causes ridges  30  and  32  to become compressed and deform, whereby a sealing engagement is achieved between mating face  24  of mold segment  12  and ridges  30  and  32 . After the mold cavity has been sealed by engagement between mating face  22  and ridges  30  and  32 , a mixture of liquid reactants is injected into the mold cavity and allowed to polymerize to form molded component  20  which conforms with the shape of the mold cavity. The mold is then opened and the composite article comprising the molded component  20  and substrate  18  is removed.  
         [0027]    While the invention is particularly well suited for reaction injection molding processes, the processes of this invention may be employed in other applications in which a component is molded (shaped in a mold cavity) on a substrate.  
         [0028]    The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.