Abstract:
A device for producing a plastic part that has a plurality of components includes a closing unit for receiving at least one mold in which a thermoplastic molded body can be shaped or positioned, and at least one polyurethane unit for introducing a polyurethane material into a larger cavity comprising the thermoplastic molded body. At least one additional polyurethane unit is provided for introducing an additional polyurethane material having different product properties into a same or a different, larger cavity. As an alternative, the at least one polyurethane unit can be adapted for an additional polyurethane material having different product properties for introduction into the same or a different, larger cavity.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of prior filed copending PCT International application no. PCT/EP2007/050734, filed Jan. 25, 2007, which designated the United States and has been published but not in English as International Publication No. WO 2007/101747 and on which priority is claimed under 35 U.S.C. §120, and which claims the priority of German Patent Application, Serial No. 10 2006 010 310.6, filed Mar. 7, 2006, pursuant to 35 U.S.C. 119(a)-(d), the contents of which are incorporated herein by reference in its entirety as if fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a device and a method for producing multicomponent plastic parts. 
         [0003]    Nothing in the following discussion of the state of the art is to be construed as an admission of prior art. 
         [0004]    Molded parts, in particular molded plastic parts, can be coated with a polyurethane material. The molded part is hereby inserted into an enlarged cavity, thereby forming a free space between the cavity wall and the inserted molded part. A polyurethane material for coating the inserted plastic part is filled into this space. After the polyurethane material has cross-linked and hardened, the mold forming the enlarged cavity can be opened and the coated product can be removed. 
         [0005]    It is an object of the present invention to provide an integrated system that can be used to coat a thermoplastic molded part with at least two different polyurethane materials. 
       SUMMARY OF THE INVENTION 
       [0006]    Two alternative concepts are pursued with the device. According to a first embodiment, two entirely separate polyurethane units are associated with a clamping unit, which each can fill the provided reactive material into their own, separate mold cavities which are formed by the clamping unit. According to an alternative embodiment, a mold cavity is formed by the clamping unit, wherein polyurethane material with different material properties can be filled into different partial cavities. The required structure will be described in more detail below. 
         [0007]    Depending if the two polyurethane units are formed completely separately or use various components of the plant jointly, two mixing heads can be supplied via a switching unit from a single metering machine. For example, one component can be gassed “in-line” to attain a foaming effect. “In-line gassing” may be performed with CO 2  gas. For example, the lower section of the inner door module of a motor vehicle can be formed with thin walls and compact in a first color, whereas the upper elbow region can be formed foamed and soft in another color. If only a single PUR unit is used, then the foaming agent can be separately supplied for each charge. 
         [0008]    According to another advantageous feature of the present invention, a plasticizing and injection unit may be associated with the clamping unit for introducing the thermoplastic melt into a corresponding mold. In this case, the thermoplastic molded part can be formed in a first cycle step, wherein the thermoplastic molded part is then coated in the following steps with at least two polyurethane materials having different material properties. Alternatively, a system could be realized that uses two or more plasticizing and injection devices. 
         [0009]    A clamping unit which is particularly suitable for this method includes a rotatable turning plate which cooperates with at least two platens. Molds are arranged between the platens and the interposed turning plate. It will be understood that three, four or more platens may be arranged about the turning plate, whereby the turning plate needs to have a corresponding number of surfaces for receiving the respective mold parts 
         [0010]    According to another advantageous feature of the present invention, an additional mold is arranged opposite the mold for the plasticizing and injection unit, so that the clamping unit can close both molds similar to a sandwich process. 
         [0011]    If the turning plate is implemented as a cube, then identical mold halves can be arranged on all four sides, wherein at least two of these mold halves cooperate with the mold halves disposed on the platens. With this approach, the enlarged cavity or cavities would be produced in a following rotation step by clamping with another mold half disposed on a platen. 
         [0012]    As an alternative to rotating the—possibly already partially coated—thermoplastic molded part, this part can be introduced into an enlarged cavity which has either two separate partial cavities, or wherein different partial cavities can be sequentially formed by pulling out an insert or a core puller. With this approach, too, the plasticizing and injection unit can advantageously already be integrated in the system. It would also be feasible to use a turning plate clamping unit. 
         [0013]    If a separation unit is provided for separating different partial cavities, then this separation unit can preferably be retractable. The separation unit may possibly be retracted even when the mold is already closed. It would then be possible, especially in the latter case, to completely fill a partial cavity, so that no empty space previously occupied by the separation device remains after the mold is opened. Particularly advantageously, a single polyurethane unit capable of sequentially supplying at least two polyurethane materials having different properties can be employed when using several partial cavities. This requires switching mechanisms which supply, for example, different additives (e.g., different dyes and/or gas supply to the components, such as CO 2 ) depending on the selected charge. If only a single polyurethane unit is used to introduce the corresponding material into a cavity or into partial cavities, then devices for changing the flow direction should be implemented. These devices may include a system of channels in the mold, whereby the flow direction in relation to the different partial cavities can be switched. Alternatively, the one polyurethane unit can be connected to different sprues. 
         [0014]    If in addition to the aforementioned switching options a separation device is provided, then the separation device can be configured for realizing the switchable flow paths into the different cavity spaces. 
         [0015]    Alternatively or in addition, the clamping unit can also have a rotary table, a sliding table or an indexing plate assembly. The individual components are known in the art and will therefore not be described in detail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0016]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0017]      FIG. 1  shows a schematic diagram of a first embodiment of a system according to the present invention, 
           [0018]      FIG. 2  shows a schematic diagram of a second embodiment of a system according to the present invention, and 
           [0019]      FIG. 3  is a cross-section, one an enlarged scale, of a mold with switchable flow path. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0021]    Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic top view of a first embodiment of a system according to the present invention. A central clamping unit  10  is provided, of which in the present example only the platens  12 ,  14  and  16  and a turning plate  18  configured for rotation about a vertical axis are shown. The elements that transmit the pulling forces, such as the rods or drives for opening and closing the clamping unit as well as for applying a clamping pressure, are not illustrated. These elements are, however, known in the art and can thus be considered understood in the context of the present invention. 
         [0022]    The turning plate  18  is herein configured fixed in the linear direction and only enabled for rotation. The platens  12 ,  14  and  16 , on the other hand, are configured for linear motion toward the turning plate  18  and in the opposite direction. 
         [0023]    A mold  20 ,  22  and  24  is disposed between each platen  12 ,  14  and  16  and the turning plate  18 . Each of these molds consists of two mold halves  20 ′,  20 ″, and  22 ′,  22 ′″, and  24 ′,  24 ″, of which the mold halves  20 ′,  22 ′ and  24 ′ are affixed to the turning plate and the mold halves  20 ″,  22 ″ and  24 ″ are affixed to the platens  12 ,  14  and  16 . The mold halves  20 ′,  22 ′,  24 ′ and  25 ′ are configured identically. Corresponding cavity spaces, which will be described hereinafter, are formed by the cooperation between the mold halves arranged on the turning plate  18  with the mold halves arranged on the platens  12 ,  14  and  16 . 
         [0024]    In the embodiment according to  FIG. 1 , a plasticizing and injection unit  26  (only shown schematically), which receives thermoplastic starting material via a feed hopper  30 , is associated with the platen  12 . The plasticizing and injection unit  26  is driven by a drive  28 , whereby the starting material is melted and injected into the cavity of the mold  20  in a conventional manner.  FIG. 1  shows the plasticizing and injection unit  26  in a retracted state. During injection, the plasticizing and injection device  26  is moved forward, so that its injection nozzle connects with the sprue of the mold to introduce the melt. 
         [0025]    A first polyurethane unit  32 , which includes a mixing head  34  with a outlet pipe, is associated with the platen  16 . The mixing head  34  can be moved toward the platen  16  and away from the platen  16  in two opposing directions, as indicated by the double arrow. The outlet pipe of the mixing head can thereby be coupled to a sprue region of the mold  24 . 
         [0026]    The mixing head  34  is connected by way of component supply lines  46  and  48  with two containers  38  and  40  containing the two polyurethane components isocyanate and polyol. These two components are supplied to the mixing head  34  by pumps under high-pressure. The mixing head  34  is also connected via a supply line  52  with a dye container  50 , from which a first dye material is supplied to the mixing head  34 . The polyurethane components and the dye material are intermixed in the mixing head and discharged via the outlet pipe. The various metering systems and polyurethane partial units are illustrated only schematically in  FIG. 1 . In practice, the systems are somewhat more complex, which is known to a person skilled in the art. 
         [0027]    A second polyurethane unit  32 ′, which also includes a mixing head, is associated with the platen  14 . The mixing head is also movable towards the platen  14  and in the opposite direction, as indicated by the double arrow. The associated drive and the mimic panel are again not illustrated. The outlet pipe of the mixing head  36  can also connect with a sprue of the mold  22  for transferring the polyurethane mixture into the mold cavity of mold  22 . 
         [0028]    The mixing head  36  is again coupled with the containers  38  and  40  via the components supply lines  42  and  44  and receives from the containers the isocyanate and polyol components via pumps. Of course, separate containers may also be provided. The mixing head  36  is again connected via a supply line  56  with a container  54  for a second dye component. 
         [0029]    The system which is schematically depicted in  FIG. 1  operates as follows: 
         [0030]    Initially, in a first cycle step, a plastic melt is produced with the plasticizing and injection unit  26  and injected into the cavity of the mold  20 . After the thermoplastic maternal has hardened, the platen  12  is retracted form the turning plate  12 , whereby the turning plate can be rotated counterclockwise by 90° ( FIG. 1 ) after the other platens  14  and  16  have opened. The thermoplastic product produced in the preceding step is retained in the mold half  20 ′ and carried along accordingly. 
         [0031]    The platens  12 ,  14  and  16  are now closed again and locked, wherein an enlarged cavity is formed due to a corresponding shaping of the mold  22 . An unobstructed space is then formed between the cavity wall of the mold half  22 ″ and the product, into which polyurethane material is injected by the backed-up mixing head  36 . 
         [0032]    After the polyurethane material has at least partially hardened (cross-linked), the mixing head  36  and also the platen  14 —as well as the other platens  12  and  16 —are again moved in the opposite direction away from the turning plate  18 , so that the turning plate  18  can rotate freely counterclockwise by 90°. After the platens  12 ,  14  and  16  have once more closed, a yet again large cavity is formed in the mold  24  conforming with a shape of the mold half  24 ″, into which after the mixing head  34  is again backed up, additional polyurethane material with an other material property, e.g., a different color, can be injected. 
         [0033]    Depending on the design of the different cavities in the molds  22  and  24 , a thermoplastic part coated with different polyurethane materials can be produced. If the turning plate  18  is once more rotated by 90° after opening the platens  12 ,  14  and  16 , then the finished product—shown as the image in of FIG.  1 —can be removed. 
         [0034]    All the aforementioned method steps can be performed cyclically in synchronism; in other words, corresponding materials can be introduced at the same time into the cavities of the molds  20 ,  22  and  24  and at least partially hardened in the cavities, so that the turning plate  18  can be further rotated after the platens  12 ,  14  and  16  have been opened. 
         [0035]    It will be understood that other devices can be added to the system illustrated in  FIG. 1 . For example, spraying devices for introducing a parting agent on the cavity surface of the molds  22 ″ and  24 ″ can be associated with the two molds  22  and  24 . Moreover, robotics for removing or inserting a part can be provided. 
         [0036]      FIG. 2  shows an embodiment of a system of the invention which is somewhat different from the embodiment depicted in  FIG. 1 . Compared to  FIG. 1 , the platen  14  as well as the second polyurethane unit  32 ′ have been omitted. The mixing head  34 ′ is also implemented differently. The mixing head  34 ′ is now configured for switching the supply of a reagent or an additive which can be added to the polyurethane components polyol and isocyanate. 
         [0037]    The mixing head  34 ′ is connected via a supply line  56 ′ with a container  54 ′, from which the second dye can be supplied to the mixing head  34 ′. Depending on the charge, the mixing head  34 ′ admixes either the first dye component or the second dye component to the two reaction components polyol and isocyanate and injects this different mixture into partial cavities of the enlarged cavity in the mold  24 . 
         [0038]    To this end, the material to be filled in must be introduced into a specific partial cavity. A suitable embodiment is shown in  FIG. 3 .  FIG. 3  shows in detail schematically a cross-section of a mold, which may be the mold  24  incorporated in  FIG. 2 . The mold in  FIG. 3  includes a first mold half  60 ′ and a second mold half  60 ″. The first mold half  60 ′ can be attached to the turning plate, whereas the second mold plate  60 ″ can be attached to the movable platen  16 . 
         [0039]    A cavity is formed between the two mold halves  60 ′ and  60 ″, in which a thermoplastic molded part  68  is already disposed. A cavity with two partial cavities  66 ′ and  66 ″ is formed in an enlarged cavity between the thermoplastic part  68  and the cavity wall of the mold half  60 ″. The two partial cavities  66 ′ and  66 ″ are divided by a divider plate  70 , so that they are not connected to each other. The divider plate  70  is affixed to the mold half  60 ″ and sealingly extends to the thermoplastic molded part  68  when the mold is closed. 
         [0040]    A channel system is formed in the mold half  60 ″, wherein—starting at the sprue  62 —a main channel extends to a branch point where it splits into two partial channels  62 ′ and  62 ″. These partial channels terminate in the partial cavities  66 ′ and  66 ″. A switching device in form of a swing valve  64  is shown at the branch point, which can be switched by a switching mechanism into a desired position  64 ′,  64 ″. The switching operation is indicated by the double arrow. Depending on the position of the switch, the flow path extends either from the sprue  62  to the partial cavity  66 ′, or from the sprue  62  to the partial cavity  66 ″. In combination with the mixing head  34 ′ and depending on the operation of the mixing head, a first polyurethane material with a first material property can be filled into the partial cavity  66 ′. The swing valve is then switched and a polyurethane material with a second material property is filled into the second partial cavity. After the polyurethane materials are at least partially cross-linked and hardened, the mold  60 ′ can be opened and the finished part can be removed. 
         [0041]    Several other procedures for filling different partial cavities are known in the art. For example, different partial cavities can have separate flow channels, wherein the mixing head must then be rotated from one sprue to another sprue. Alternatively, core pullers or sliders can be employed which are retracted after a partial cavity is filled and then form an additional partial cavity, wherein in a subsequent step an additional polyurethane material with a different material property is filled into the newly created partial cavity. 
         [0042]    The material properties of the additives can be changed for altering the haptic properties of the material, such as the softness or hardness, so that different structures can be produced. Moreover, to allow an even greater combination of materials, not only two, but several separate polyurethane units, or alternatively polyurethane units (mixing heads) with several switching processes and variations can be implemented. 
         [0043]    In summary, with the present invention, a thermoplastic material or in general an insert can be versatilely coated with at least two or more polyurethane materials having different material properties. 
         [0044]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
         [0045]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: