Abstract:
A method of manufacturing an automotive reflector comprising a series of steps. A thin plastic film having a backing material is thermoformed into the rough shape of the reflector. The thermoformed film is called a pre-form. The pre-form has a concave surface and a convex surface. The backing material forms the convex surface. The pre-form is placed within an injection molding press with the concave surface juxtaposed a mold core. Molten reinforced plastic material is injected into the mold adjacent to the backing material. The plastic material heats and fuses to the backing material to form a reflector. After the plastic material has cooled, the reflector is removed from the injection mold as a finished reflector.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a method of manufacturing an automotive reflector. More specifically, the invention is directed to manufacturing an automotive reflector from a thermoformed film having a highly reflective material that is integrally molded into a reflector. 
     2. Description of the Related Arts 
     Most automotive reflector assemblies are made from a reflector and a lens. The reflector is injection molded to have a curved shape. The interior of the reflector is metalized to provide a highly reflective coating. The metalized surface is produced in several ways including vacuum deposition, sputter coatings or ion coatings. These coating methods generally require that the reflector be pre-molded and placed within a metalizing chamber. Most chambers are operated under a vacuum and require removing some or all of the air within the chamber. A significant percentage of the metal used in the metalization process falls outside of the reflector. This generally requires the use of protective masks that are fitted over the reflectors to prevent metalization of these outside areas. The method thus described is a batch process that requires loading and unloading the reflectors into a chamber for metalization. 
     The conventional metalization process is described in U.S. Pat. No. 4,085,248. The interior surface of the reflector requires a highly polished or smooth finish to receive the metalization. This is achieved by either finely polishing the molds or by applying a base coat to the interior surface of the reflector. The metal is deposited on the interior surface of the reflector usually by vacuum deposition. The metal most commonly used in vacuum deposition is aluminum. Because the aluminum surface is subject to oxidation, a protective outer coating is deposited atop the aluminum to maintain the reflectivity of the aluminum coating. It is desirable to produce a reflector without these metalization and coating steps. 
     It is also desirable to manufacture reflectors from plastic materials that withstand the high temperatures created by the lamp. Currently, most high quality thermoplastic reflectors are made from unfilled-engineered plastic materials such as polycarbonate. These materials are able to both provide the desired high temperature resistance and smooth finish for an optical surface, but they are more expensive than other plastic materials. Plastic materials filled with reinforcing fibers or particles are also known to be able to withstand the higher temperatures, and cost substantially less than the unfilled polycarbonate, but the filler material, usually glass, talc, or mica, causes surface irregularities that degrade the optical performance of the reflector. These materials require a base coat between the plastic reflector and the metalized coating to provide a smooth surface. This additional step may negate the cost savings from the materials selection. 
     It is also desirable to separate the metalization step from the molding step. The metalization chambers required to produce an optical-quality surface are very expensive. The equipment needed to injection mold the reflector is much more affordable. Rather than shipping bulky metalized reflectors to assembly facilities, it is desirable to manufacture a lightweight pre-form that contains the metalized coating reflective surface. This enables the manufacture of the finished reflector at the final assembly location and permits the greater utilization of the more expensive metalization chambers. 
     U.S. Pat. No. 5,833,889, teaches a method of making an automotive reflector by first thermoforming a polymeric film to have the shape of the reflector and then injection molding a rigid backing to the film. The backing may include glass reinforcement material that in the absence of the film would degrade the optical coating. The film provides a smooth surface to receive the metalization. The method described in the U.S. Pat. No. 5,822,899 patent still requires a separate metalization step that is avoided by the present process. By incorporating the reflective material into the film prior to forming, the expensive and complicated metalization process is avoided. It is much simpler and less costly to form a flat film to have a reflective surface than applying metal to a curved reflector. 
     In an unrelated art area, it is known to apply decorative films or appliqués to the exterior surface of molded articles. U.S. Pat. Nos. 5,266,377 and 5,223,315 teach the manufacture of a container having a printed label. The label is placed within the cavity of the mold and then the container is molded within the label. Applying films to the exterior surface of an article is understood because as the article is formed within the mold, it pushes outwardly, stretching the film within the mold. It is not known to manufacture articles having a smooth film surface laminated to the surface of the part. Manufacturing an article having a smooth laminated interior film is more complex because as the article is molded, it tends to collapse the film within the mold. The collapsed film often causes wrinkles, pleats or other unwanted blemishes. 
     The films used to produce thermoformed pre-forms are generally placed within a rigid frame. The frame retains two or more sides of the film while the film is heated. The film and frame are then placed above or below the mold for thermoforming. A process using frames to thermoform films is described in UK Patent Application No. 6B2187132A and is incorporated herein by reference. The use of frames is again a batch process where the frame receives a length of film. The frame is needed to provide tension to the film as it is thermoformed. It is desirable to provide a method for manufacturing thermoformed films that does not require the use of a frame to retain the film or to provide tension to the film during thermoforming. It is also desirable to provide a method of precisely indexing the film without the need for a frame. 
     After the film is thermoformed, it produces a pre-form having an offal portion surrounding the pre-form. The offal portion is trimmed in a separate trimming operation and removed from the pre-form. It is desirable to provide a thermoforming process that simultaneously thermoforms and trims the pre-form while retaining the offal portion on a film roll. This enables a continuous thermoforming and trimming process that does not require the separate handling of the offal portion. 
     These deficiencies and problems are overcome by the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method of manufacturing an automotive reflector comprising a series of steps. A thin plastic film having a backing material is thermoformed into the rough shape of the reflector. The thermoformed film is called a pre-form. The pre-form has a concave surface and a convex surface. The backing material forms the convex surface. It is preferable that the film be formed to have a highly reflective surface. This may be achieved by depositing a metal coating to the film using conventional metalization equipment or by incorporating material, either polymeric or metallic, into the film that produces a reflective surface on the film. 
     The pre-form is placed within an injection molding press with the concave reflector surface juxtaposed a mold core. Molten plastic material is injected into the mold adjacent to the backing material. The plastic material heats and fuses to the backing material to form a reflector. After the plastic material has cooled, the reflector is removed from the injection mold as a finished reflector. 
     In an alternative embodiment of the present invention, the thermoforming operation may simultaneously form and trim the film. This is especially useful when using films that have a reflective surface and the offal portion is not needed as a mask. In this alternative embodiment, the film is retailed between rollers and thermoformed in the desired shape. The thermoforming press includes cutting blades that trim the film to the desired shape when the mold is moved to a closed position. 
     This alternative embodiment enables the manufacture of a reflector without the need for a separate metalization step. The film has a highly reflective material that provides the reflectivity necessary for automotive reflectors. It is thermoformed into the rough shape of the finished reflector and integrally molded with plastic material in a process described as insert molding. 
     Utilizing a coiled film stock further enhances the manufacturing method. The film stock is indexed using a sprocketed roller. The film is thermoformed into a pre-form while the sprockets retain the film perimeter. The thermoforming step simultaneously forms the film into a pre-form and trims and or severs the perimeter of the pre-form from the remainder of the film. The pre-form is removed from the film leaving blanks. The film surrounding the blanks constitutes the offal portion of the film and is taken up by a take-up spool. 
     The process eliminates the need for a frame to retain the film. The process also eliminates separately collecting the offal portion from the trimmed pre-form. 
     These and other objects, features, and advantages of the present invention will become more readily apparent when viewed in connection with the accompanying drawings wherein like reference numbers correspond to like components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the thermoforming and trimming apparatus used in the present invention. 
     FIG. 2 is a cross-sectional view of the thermoforming station illustrated in FIG. 1 taken along the lines  2 — 2 . 
     FIG. 3 is a perspective view of a film loading station. 
     FIG. 4 is a cross-sectional exploded view of the injection mold apparatus illustrated in FIG. 3 taken along the lines  4 — 4 . 
     FIG. 5 is the injection mold apparatus illustrated in FIG. 4 in the closed position. 
     FIG. 6 is a cross-sectional view of the reflector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described through a series of drawings, which illustrate the thermoforming and injection molding operation claimed. The drawings describe a thermoforming station that operates without the need of a separate frame; however, the design may also be used with a conventional thermoforming apparatus. The invention will also be described as a method of manufacturing a headlamp reflector, however other reflectors may also be manufactured using the same or similar process, technique and equipment, and are included within the invention described herein. 
     The following items are a word list of the items described in the drawings and are reproduced to aid in understanding the invention; 
       10  thermoforming and trimming apparatus 
       12 ,  14 ,  16  thermoforming stations 
       18  film roll 
       20 ,  22  sprocketed rollers 
       24  teeth 
       26  film 
       28 ,  30  sprocketed rollers 
       32  take-up spool 
       34  mold 
       36  closure member 
       38  reflective surface 
       40  backing material 
       42  vacuum line 
       44  positive pressure lines 
       46  knife edge 
       48  pre-form 
       50  offal portion 
       52  blank 
       54  perforated edge portion 
       56  loading machine 
       58  injection molding machine 
       60  core 
       62  cavity 
       64  concave surface 
       66  convex surface 
       68  gates 
       70  plastic material 
       72  reflector 
     Illustrated in FIG. 1 is a perspective view of a thermoforming and trimming apparatus  10 . The apparatus  10  utilizes a film having a highly reflective surface. The apparatus  10  comprises three thermoforming and trimming stations  12 ,  14  and  16 . While the apparatus  10  is illustrated with three thermoforming stations, one station is sufficient. Multiple thermoforming stations reduced the cycle time and increase the throughput of the apparatus  10 . The apparatus  10  receives a film roll  18 . As will be described in more detail below, the film roll  18  includes a reflective surface and a backing material. The leading edge of the film roll  18  is fed between sprocketed rollers  20 ,  22 . Teeth  24  on the rollers  20 ,  22  pierce the peripheral portion of a film  26 . This first set of rollers  20 ,  22  serve to index the film  26  through the apparatus  10 . At this initial juncture, the thermoforming stations  12 ,  14  and  16  are not operating. The film  26  is fed through a second series of sprocketed rollers  28 ,  30 . The film  26  is retained tautly between the first set of rollers  20 ,  22  and the second set of rollers  28 ,  30 . A take-up spool  32  serves to coil the film  26  after having passed through the thermoforming stations  12 ,  14  and  16 . 
     The first set of rollers  20 ,  22  are heated and render the film  26  pliable. Other methods of heating the film  26  are also possible such as convection, radiant, dielectric or microwave heating. The pliable film  26  is indexed to thermoforming station  12 . The thermoforming station  12  includes a mold  34  having a curved shape that corresponds to the desired concave surface of the finished reflector. The thermoforming station  12  is raised in the direction A until the mold  34  contacts the reflective surface of the film  26 . The closure member  36  is moved in the downward direction B. The mold  34  and the closure member  36  meet as shown at thermoforming station  14 . 
     Illustrated in FIG. 2 is an enlarged cross-sectional view of the thermoforming station  14  taken along lines  2 — 2  in FIG.  1 . The film  26  includes a reflective surface  38  and a backing material  40 . The reflective surface  38  may be made integrally formed to be reflective, as an applied coating, or the surface may be a separate layer bonded to or deposited on the film  26 . The reflective surface  38  may be made from a variety of materials including deposited metals such as aluminum, nickel, tin or chrome. It is also possible to coat the film  26  with a non-metallic coating and render it highly reflective—or to include these reflective materials within the film  26 . The backing material  40  is made from a thermoplastic polymer that fuses to the molten plastic as will be described below. A large variety of films and materials may be used to produce the film  26  including those taught in U.S. Pat. Nos. 4,446,055, 4,446,172, 4,385,804, and 4,906,084, all of which are incorporated herein by reference. 
     The thermoforming station  14  contacts the mold  34  with the pliable film  26 . The film  26  is trapped between the thermoforming station  14  and the closure member  36 . A vacuum is applied through vacuum lines  42  to draw the film  26  tightly against the mold  34 . Optionally, positive pressure lines  44  apply a positive pressure within the closure member  36  to force the film  26  against the mold  34 . A knife-edge  46  around the perimeter of the closure member  36  trims the film  26  into the desired shape. 
     The thermoforming stations  12 ,  14  and  16  are identical and rotate between the three positions illustrated. Multiple stations are used to reduce the cycle time and increase the throughput of the apparatus  10 . The thermoforming station  14  transforms the film  26  into a pre-form  48  by thermoforming it into the desired shape and trimming the offal portion  50  as shown in FIG.  1 . The pre-form  48  requires a period of residency on the mold  34 . The thermoforming station  14  moves in the direction C at the same speed as the film  26 . The thermoforming station  14  and the film  26  are indexed until they reach the thermoforming station  16 . The thermoforming station  14  becomes the thermoforming station  16 . The time required to index from thermoforming station  14  to thermoforming station  16  is sufficient to thermoform the pre-form  48  into its final shape. The closure member  36  is moved upwardly and the thermoforming station  16  is moved downwardly. The pre-form  48  remains on the mold  34  until an operator removes it. The thermoforming station  16  cycles in the direction D until it reaches the thermoforming station  12  again. 
     The trimming operation leaves a series of blanks  52  corresponding to the area of the pre-form  48 . The offal portion  50  surrounds the blank  52 . Because the perforated edge portion  54  is continuous, the offal portion  50  is coiled by the take-up spool  32 . 
     The apparatus  10  illustrated in FIGS. 1 and 2 does not require a frame to retain the film  26 . The film  26  is retained tautly between rollers  20 ,  22  and  28 ,  30 . The process of thermoforming and trimming the pre-form  48  operates continuously. 
     After the thermoforming step shown in FIGS. 1 and 2, the pre-forms  48  are stacked as illustrated in FIGS. 4 and 5. A robotically controlled loading machine  56  transfers the pre-forms  48  into an injection molding machine  58 . The construction and operation of the loading machine  56  is described in commonly assigned U.S. patent application Ser. No. 08/903,523, filed Jul. 30, 1997 and incorporated herein by reference. The injection molding machine  58  includes a lower mold having a core  60  and an upper mold having a cavity  62 . The pre-form  48  is formed to have a concave surface  64  and a convex surface  66 . The concave surface  64  includes the reflective surface  38 . The convex surface  66  includes the backing material  40 . The pre-form  48  is placed within the injection molding machine  58  with the concave surface  64  juxtaposed the core  60 . The injection molding machine  58  is moved to a closed position as illustrated in FIG.  5 . 
     The pre-form  48  is sized to be snugly fit atop the core  60 . It is preferable that there is little or no space between the pre-form  48  and the core  60 . It may be desirable to form the pre-form  48  slightly smaller than the core  60  so that during the injection molding step, the pre-form  48  is stretched over the core  60 . Molten plastic material  70  is injected through gates  68  and urges the pre-form  48  against the core  60 . The molten plastic material  70  causes the backing material  40  to heat and soften. The softened backing material  40  fuses to the plastic material  70  to form the finished reflector  72  as illustrated in FIG.  6 . The molten plastic material  70  is allowed to cool and the core  60  and cavity  62  are moved to an open position and the reflector  72  is removed. 
     While a wide variety of materials may be used for the molten plastic material, it is preferable to utilize a filled thermoplastic material such as polycarbonate. Filled polycarbonate is low cost and resistant to high temperatures. Common fillers for plastic resins include glass, talc, carbon, mica and wood. Unfortunately, it forms a coarse surface. The coarse surface does not produce a reflector of high quality. The coarse nature of the filled plastic material does not degrade the performance of the reflector because the film reflective surface retains its smooth appearance after the molding operation. 
     The invention has been illustrated as a method of manufacturing an automotive headlamp assembly. Other reflectors may be manufactured using the same process and equipment. The invention has also been described using an integrated thermoforming and trimming apparatus that does not require the use of a separate frame to retain the film. Traditional thermoforming devices may be utilized to manufacture the pre-form. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.