Abstract:
The present invention relates to a method and to an apparatus for producing plastic products with an integrated reinforcing structure. To do so, a flexible fabric is first placed onto a surface of a cavity of a mold and is successively coated with plastic on the various sides.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2009/061562, filed Sep. 7, 2009, which designated the United States and has been published as International Publication No. WO 2010/031710 and which claims the priority of German Patent Application, Serial No. 10 2008 047 564.5, filed Sep. 16, 2008, pursuant to 35 U.S.C. 119(a)-(d). 
     The present invention relates to a method and an apparatus for producing plastic products with integrated reinforcing structure. 
     BACKGROUND OF THE INVENTION 
     It is amply known to reinforce plastic products using fibers to meet particular mechanical or physical demands. Plastic products that are especially under stress can be provided with additional reinforcing structures. These reinforcements or functional components become increasingly important, given the continuous trend to provide plastic products of increasingly thinner wall thickness or system plastic products. This trend is based in particular on material-saving needs because material contributes substantially to the production price of a product as costs for raw material rise. 
     It was already known heretofore to provide certain products with ribs or similar external elements for mechanical reinforcement. It is further known to compression-mold or to shape soaked or impregnated plastic mats with a plastic material and then to subject it to back injection molding. 
     Furthermore, there is the trend for some time now to use injection molding or extrusion machines to incorporate fibers, especially glass fibers, into the plastic melt in order to enhance the mechanical properties of the entire product. The fiber orientation is oftentimes dependent on the flow behavior in such fiber-laden plastics so that the effective direction cannot be easily predefined. Moreover, the mostly short fiber elements are oftentimes amorphous and randomly arranged in their direction. Therefore, it is not possible to provide reinforcements in particular stress directions. Moreover, injection molding and extrusion applications permit heretofore only the production of limited fiber lengths because the fibers are broken, trimmed, or otherwise cut in the plasticizing device. 
     Plastic is increasingly used in many high-tech areas that encounter stress peaks only in certain regions or aligned high stress peaks. These products do not necessarily require the presence of reinforcements across the entire product; rather, these parts could be reinforced in some areas only so that the regions that are especially under stress are able to withstand the particular mechanical or physical demands. Still, the reinforcing measures should normally not be visible. Rather, it mostly desired to provide the respective products with same optic and haptic properties across the entire surface. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention, to provide a method and an apparatus for producing plastic products with integrated reinforcing structure to obviate the afore-stated drawbacks and to attain the desired properties. 
     According to one aspect of the invention, the object is attained by a method for producing plastic products with integrated reinforcing structure, using an apparatus, comprised of a multi-cavity clamping unit as well as at least two devices for feeding impregnating material, resin material, or plastic material into a cavity of a mold, to carry out the following steps: depositing and securing a flexible fabric element of fibers or filaments upon a mold surface of a first half-mold of a mold, associating a second half-mold of a mold to the first half-mold and closing the thus-established first mold to define a first cavity; introducing a first plastic or impregnating material into the first cavity to form a first layer, opening the first mold after the first layer has at least cured in part, with the fabric element forming a first intermediate product, which is coated with plastic or impregnated, staying on the first half-mold of the mold associating a third half-mold of a mold to the first half-mold of a mold and closing the thus-established second mold to define a cavity which in relation to the fabric is positioned in opposition to the layer applied first, introducing a further plastic material into this cavity to form a second layer, opening the second mold after the second layer has at least cured in part, and removing the thus-produced product. 
     According to another aspect of the invention, the object is attained by an apparatus having at least three half-molds for establishing at least two molds with different cavities, a clamping unit for receiving, for changing association of the various half-molds, and for applying a clamping force for each mold, at least two devices for introducing plastic, resin, or impregnating materials into the cavities, and a depositing device for placing a flexible fabric onto the cavity surface of a half-mold. 
     Accordingly, it is a core idea of the present invention to apply initially a flexible fabric (generally textile) onto the cavity surface of a mold. Subsequently, various combinations of the half-molds and formation of molds result in the realization of layers, especially plastic layers, on both sides of this fabric. Overall, a cost-efficient and rapid production of a plastic product with sandwich construction can be realized in a simple manner with a single apparatus in which a fabric (especially textile fabric) is embedded in at least two layers and which ensures a respective reinforcement. 
     According to a particularly preferred embodiment, an impregnating agent can be introduced as first material to fully permeate the textile reinforcing structure and to ensure an entire impregnation. Further layers are then applied incrementally on the thus-produced (intermediate) product. When applying two further plastic layers on both sides of the thus impregnated reinforcing textile, a sandwich product is realized having a fully impregnated reinforcing textile in one operating step. To date, it was required to produce in a first separate step a product provided with a respective impregnation of matrix, and then to place the product in a second separate operating step—if necessary after a shaping step—in an injection molding machine and to mold around it. 
     According to a further advantageous embodiment, it is moreover possible to coat a plastic layer or the impregnation layer in a further process step with a surface layer, resin layer, or varnish layer so as to realize a thin coating or finish. 
     Preferably, a plastic material for a layer is made and introduced by means of an extrusion or injection molding process; According to the invention, this is implemented on the same apparatus which may optionally be configured as sliding table, rotary table, or reversing plate machine. 
     As an alternative, the plastic material may also be made or introduced by a reaction injection molding process, for example with polyurethane or another thermoset. 
     When depositing the fabric structure, only particular regions of the plastic product may also be selected. As a result, the formation of reinforcing structures in some areas is possible. When providing an impregnation in a first coating step, such a local reinforcement renders possible the impregnation of the fabric surfaces only. Overall, reinforcing zones of higher, smaller or even no reinforcing zones at all may be formed within the plastic product. 
     Prior to each application of a layer, functional elements may be applied onto the (intermediate) product formed beforehand. After application of at least the last layer, these functional elements are then integrated in the plastic product. 
     In this way, separate devices such as sensors, lamps, actuators, can be used or other functional elements can be configured integrally with the reinforcing structure. For example, metallic filaments can be incorporated into the reinforcing structure to attain a conducting function in dependence on physical conditions and to detect a crack or fracture for example or also to sense another load—such as a strain. 
     Further advantages and features are set forth in the patent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Various exemplary embodiments of the present invention will now be described in greater detail with reference to the attached drawings. The drawings show in 
         FIG. 1  a schematic illustration of a concrete embodiment of a machine according to the invention for carrying out the method according to the invention, 
         FIG. 1   a  a schematic illustration of one variation of the machine of  FIG. 1  equipped with a vacuum means to hold a flexible fabric on a cavity surface, 
         FIG. 1   b  a schematic illustration of another variation of the machine of  FIG. 1  with adhesive applied to hold a flexible fabric on a cavity surface, 
         FIG. 2  a schematic illustration like  FIG. 1  but in a second opened process state of the machine, 
         FIG. 3  a schematic illustration like  FIG. 1  but in a third process state of the machine, 
         FIG. 4  a schematic illustration like  FIG. 1  but in a fourth process state of the machine, 
         FIG. 5  a schematic illustration like  FIG. 1  but in a fifth process state of the machine, 
         FIG. 6  a schematic illustration like  FIG. 1  but in a sixth process state of the machine, 
         FIG. 7  a schematic illustration like  FIG. 1  but in a seventh process state of the machine, 
         FIG. 8  a schematic illustration like  FIG. 1  but in a eighth process state of the machine, and 
         FIG. 9  a schematic illustration like  FIG. 1  but in a ninth process state of the machine, 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A concrete embodiment of an apparatus according to the invention for carrying out the method according to the invention will now be described with reference to  FIGS. 1 to 9 . A clamping unit  10  can be seen which has a fixed platen  12  and a moving platen  14  (mobility see double arrow) which are connected to one another via tie bars  11 . An approximately cubic reversing plate  16  is arranged on a turntable (not shown) between both platens  12  and  14  and is movable jointly with the not shown turntable also in the direction of the moving platen and in addition rotatably arranged (cf. arrows). 
     The fixed platen  12  and the moving platen  14  have arranged thereon half-molds  17  and  20 , respectively which—as will be disclosed hereinafter—differ as far as their cavity space is concerned. Moreover, further half-molds  18  and  19  are mounted on opposite sides of the reversing plate  16 . Also these half-molds are differently configured. The half-mold  17  can hereby define with the half-molds  18  and  19 , respectively, a mold (first and second molds). Moreover, the half-mold  20  may also define with the half-mold  19  a mold (third mold). As an alternative, the clamping unit may, of course, also be designed as sliding table clamping unit or rotary table clamping unit for example. Important is only that three or more cavities can be established. 
     Plasticizing and injection units  28  and  29  (shown only schematically) are arranged in the area of the fixed and moving platens  12  and  14  and can be docked to the respective molds via respective funnels. A further plasticizing and injection unit  30  is additionally provided which is arranged as so-called “bolt-on-unit” to the side (also above as an alternative) of the clamping unit and—at least in one position can be docked directly to the reversing plate  16  from where the melt can be routed via respective channels via one of the half-molds into a cavity. As an alternative, it is also possible to configure the clamping unit, provided as “bolt-on-unit” for docking directly to a half-mold (e.g. half-mold  19 ). 
     In a manner known per se, the plasticizing and injection units  28  to  30  can be used to inject plastic melt into the cavity of a pertaining mold. 
     As an alternative, it is also possible to provide, instead of a plasticizing and injection unit, another feed unit for a plastic, resin, impregnating agent, varnish, thermoplastic material or thermoset, as will be clear hereinafter. 
       FIGS. 1 to 9  further show the presence of a device  50  for introduction of a flexible fabric (generally textile) into the clamping unit. This device  50  includes a robotic arm having an arm end for arrangement of a pick-up unit for grabbing the flexible fabric (textile). The robotic arm is able to grab a flexible fabric (textile) and to place it on the cavity surface of a half-mold (here half-mold  18 ), when the clamping unit is open. 
     The mode of operation of the afore-described embodiment is as follows: 
     At the beginning of the process cycle described here, the clamping unit  10  of the injection molding machine is open, as shown in  FIG. 1 , the half-mold  18  is associated to the half-mold  17 , and the half-mold  19  is associated to the half-mold  20 . The respective plasticizing and injection units  28  to  30  are withdrawn from the molds. 
     The robotic arm  50  picks up a flexible fabric (textile)  23  which may involve a fabric, non-woven, knitted fabric, interlaced fabric, weaved fabric, or like textile composites formed there from, and places it on the cavity surface of the mold  18 . For that, means are provided to hold the flexible fabric (textile)  23  on the cavity surface of the half-mold  18 . This may be vacuum means for example, as indicated in  FIG. 1   a . As an alternative, the flexible fabric (textile)  23  may be held by an adhesive or boding agent on the cavity surface of the half-mold  18 , as indicated in  FIG. 1   b . The cavity surface may optionally also be wetted with bonding agent or provided with suitable mechanical receiving elements in order to secure the flexible fabric (textile). 
     After introduction of the flexible fabric (textile), the robotic arm  50  is retracted from the clamping unit, in particular from the space between the two half-molds  17  and  18 —as depicted in  FIG. 2 , and the clamping unit  10  is closed (cf.  FIG. 3 ). As a result, the half-molds  17  and  18  form a first mold in which a cavity is established which is configured essentially on the side of the mold  17  in relation to the flexible fabric (textile)  23 . 
     The plasticizing and injection unit  28  is docked onto the first mold and a first plastic material is injected into the cavity. This first plastic material  24  substantially covers the flexible fabric (textile)  23  on one side—or in other words, the flexible fabric (textile)  23  bears upon a surface of the thus-produced product. It is, of course, possible to arrange the flexible fabric (textile)  23  on selected sites only so that the surface of the thus produced product is provided with the fabric textile only in some areas. 
     Subsequently, the clamping unit is opened again, as shown in  FIG. 4 , with the intermediate product of the fabric (textile)  23  made in the first step (no longer flexible now) and the first plastic material  24  staying on the half-mold  17 . 
     Subsequently—as also hinted in FIG.  4 —the reversing plate  16  is turned by 180° to associate the half-mold  19  to the half-mold  17 . Then, the clamping unit is closed again (cf.  FIG. 5 ), thereby establishing a cavity with regard to the previously produced intermediate product on the side of the half-mold  19 . The plasticizing and injection unit  30  injects into this cavity a second plastic material which is conducted via the reversing plate  16  and the half-mold  19 . As an alternative, the plasticizing and injection unit  30  could also be docked directly onto the half-mold  19 . 
     After the second plastic material  25  has cured at least in part, the clamping unit  10  is opened again, with the thus produced intermediate product remaining on the half-mold  19 . As a result, a plastic product is created in which the fabric  23  is sandwiched between the layers formed by the first plastic material  24  and the second plastic material  25 . The illustration of  FIG. 6  should be considered only very schematically as the fabric (textile) can no longer be recognized in the product. Rather, it is fully enveloped by the different layers. The fabric (textile) may hereby be embedded substantially across the entire surface or only integrated in part, depending on the desires of the user or on the demands to be met by the product. The first and second plastic materials may be identical or also different. 
     According to a simplified embodiment, the production may be concluded at this point and the product transferred for further processing. 
     In the present embodiment however, the reversing plate  16  is turned again so that the currently produced intermediate product, comprised of the layers  23  to  25 , is associated together with the half-mold  19  to the half-mold  20  (cf.  FIG. 7 ) After closing the clamping unit  10 , the half-molds  19  and  20  form a third mold having a cavity which is arranged on the side of the mold  20  adjacent to the intermediate product. Docking the plasticizing and injection unit  29  and introducing a third plastic material forms a coat (cf. reference numeral  26  in  FIG. 9 ) having defined surface properties. 
     After undergoing at least partial curing and opening, the finished product can then be removed. 
     Further alternatives are realized through slight modifications of the embodiment illustrated in  FIGS. 1 to 9  within the scope of the invention. 
     According to a particularly preferred variation, the plasticizing and injection unit  28  is replaced for example by an injection device for an impregnating agent. When injecting a highly viscous plastic material in a first step, it is conceivable that the fabric material (reinforcing textile) has not fully permeated the material and still has a flexible core. The reinforcement effect is thus impaired. In order to realize a complete permeation, a first step may involve impregnation in which essentially the flexible fabric material (reinforcing textile)  23  is fully impregnated in the respectively small cavity of the first mold—comprised of the half-molds  17  and  18 . Subsequently, the following steps involve, as described above, the application of two further plastic materials so that the thus-produced product has now an impregnated fabric (textile) sandwiched between two plastic layers. This results in a superior reinforcement (in all areas or some areas). 
     Further, instead of one or more plasticizing and injection units  28  to  30 , polyurethane mixing heads may be provided so that a thermoset, instead of a thermoplastic, is introduced into the cavity. This is especially of interest when a surface coating (e.g. the layer  26 ) is demanded with specially desired properties (haptic, light-fastness, etc.). 
     It is also possible to provide a varnish as surface material so as to remove a varnished product (varnish layer would then also be the layer  26 ). 
     Especially when the first layer is configured as impregnation, as described further above, it may be desirable as a departure from the embodiment in  FIGS. 1 to 9 , to be able to form a fourth mold in order to realize also a varnishing in addition to a first impregnation layer, a second plastic layer, and a third plastic layer. As can be seen, there is a wide range of applications of the present invention. 
     Besides the fabric material (reinforcing textile), each process step may involve the application of further functional elements such as sensors or the like on a surface of the intermediate product. These functional elements are then cast in a following process step so as to form an integral part of the product. Also the fabric, knitted fabric or non-woven (generally reinforcing textile) may have areas with metal filaments or similar element which later can be operated (used) as actuator or sensor. 
     Of course, a number of further processing devices may be provided to implement coatings, layers, treatments etc. in the various process sections. 
     The present invention permits the introduction of the reinforcing structures in plastic products in numerous design variations so as to be able to provide thin components or components that are under great stress in particular with the desired mechanical, thermal, physical or other properties. Also, respective functional elements can be integrated which may be necessary in the area of the reinforcing structure.