Abstract:
In a method of making plastic articles with embossed pattern, a plastic material is injection-molded in a cavity of a clamping unit of an injection molding machine to form an injection-molded plastic article. A pattern is embossed from a foil strip onto a previously injection-molded plastic article to form a finished plastic product with embossed pattern, whereby the embossing step is decoupled from the injection molding step and carried out separately from a clamping step of the clamping unit.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is a continuation of prior filed copending PCT International application no. PCT/EP00/03702, filed Apr. 26, 2000. 
   This application claims the priority of German Patent Application Serial No. 199 20 941.3, filed May 7, 1999, the subject matter of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a method of and apparatus for making plastic articles with embossed pattern. 
   A typical field of application of plastic articles with embossed pattern is the fabrication of injection-molded circuit boards, such as 3-D Molded Interconnected Devices (3-D MID) through hot stamping a pattern of conductor paths from a foil strip onto an injection-molded substrate. MIDs are formed parts with integrated conductive pathways and, compared to conventional circuit boards, afford enormous technical and rationalization potentials while substantially being more environmentally compatible. Through the provision of MIDs, electric and mechanical components can be integrated in circuit boards of almost any shape. MIDs enable completely different functions and contribute to a miniaturization of products. By saving mechanical components, the assembly is simplified while reliability in operation is enhanced. 
   Heretofore, plastic articles with a pattern that has been stamped under hot conditions have been made through several separate steps in a same way as the afore-mentioned 3-D MIDs. Reference is made, e.g., to German Pat. No. DE 197 32 353 A1. Plastic articles are initially made by using a conventional injection molding machine. Subsequently, the injection-molded plastic articles are subject to a stamping process in which the pattern is transferred from a foil strip onto the plastic articles under hot conditions. In order to realize a clean embossing operation, the plastic articles should be fat-free and dirt-free and pre-heated to a different temperature depending on the plastic material being used. In the event of intermediate storage, the plastic articles must therefore be preheated, cleaned and, possibly, degreased, before the embossing operation can be applied. Moreover, the plastic articles must be accurately positioned before placing the plastic foil strip in the stamping press. As currently the placement of the foil strip is done manually, an added error source must be accepted, when fabricating MIDs. 
   European Pat. No. EP 0 671 251 A1 describes an injection molding machine which has several processing stations, in particular when making multi-components injection-molded parts, whereby the actual injection steps and the other processing steps, such as cooling, ejecting, spraying and shaping of the injection-molded articles, are carried out in separate stations. By subdividing the overall production process in as many small units as possible, the cycle time should be shortened. This, however, significantly complicates the structure of the injection molding machine. 
   German Pat. No. 195 04 332 A1 describes the simultaneous fabrication and assembly of individual products through injection molding. The injection molding machine has cavities for molding plastic articles, wherein each injection-molding operation produces simultaneously in the respective cavities several different injection-molded articles which are then put together in the assembly spaces to a finished plastic product. A closing of the mold results in a closing of the cavities as well as of the assembly spaces, which remain closed during the injection process. During this time, the assembly spaces are inaccessible. This type of molding machine is not suitable for supply of foil strip material and transfer of patterns from the foil strip onto the injection-molded articles. 
   It would therefore be desirable and advantageous to provide an improved method and apparatus for making plastic articles that obviates prior art shortcomings and allows fabrication of plastic articles with an embossed pattern in a clean, rapid and precise manner, while still experiencing as little waste as possible. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a method of making plastic articles with embossed pattern, includes the steps of injection molding plastic material in a cavity of a clamping unit of an injection molding machine to form an injection-molded plastic article; and embossing a pattern from a foil strip onto a previously injection-molded plastic article to form a finished plastic product with embossed pattern, whereby the embossing step is decoupled from the injection molding step and carried out separately from a clamping step of the clamping unit. 
   The present invention resolves prior art problems by using a single machine, that is an injection molding machine, to injection-mold the plastic articles and immediately thereafter to transfer in an embossing step the pattern from the foil strip onto the plastic articles. Thus, the plastic articles are already at the required temperature before undergoing the embossing operation, by suitably controlling the cooling time of the molded articles. Error sources, as experienced during manual placement of pre-fabricated plastic articles in stamping presses, are now eliminated. In order to reduce the overall number of work stations to a minimum and thus to shorten the production time for a finished product, the embossing operation of one workpiece can be carried out at a same time as the injection-molding operation of another workpiece or possible other processing steps such as ejection of finished products and/or placement of cores, i.e. while the mold is closed. This is possible because, unlike the prior art, closing of the injection mold initiates solely the injection molding operation which is then executed when the mold is closed, while the embossing operation is carried out through a separate motion, divorced from the closing operation, but still spatially integrated in the injection molding machine. As a result, the overall cycle time for fabricating a finished product with embossed pattern is reduced to the duration of the actual injection-molding operation. 
   According to another aspect of the present invention, an injection molding machine for making plastic articles, includes an injection-molding unit; a clamping unit having a fixed mold mounting plate and a moving mold mounting plate; at least one injection molding station having an injection mold which includes a fixed mold half attached to the fixed mounting plate, and a moving mold half attached to the moving mounting plate; at least one embossing station disposed between the fixed and moving mounting plates, wherein the embossing station includes a stamping plunger, movable between the mounting plates and having attached thereon stamping tools, and a reservoir of a foil strip; and a transfer unit for interaction with the injection molding and embossing stations. 
   An injection molding machine according to the present invention can be made simple in structure because the manufacturing process is not split into a multiplicity of steps, such as injection molding, cooling, ejection etc., carried out in separate stations. 
   Suitably, the mounting plate that is operatively connected to the stamping plunger is provided with a bore for passage of the stamping plunger. In this way, a great plunger stroke can be provided and sufficient clearance is still afforded in the embossing station to allow easy execution of other processing steps, such as insertion of cores and/or ejection of the finished plastic article with embossed pattern, at a same time as the injection-molding operation while the injection mold is closed. Opening of the injection molding machine is only required to a degree that allows further advance of the injection-molded plastic article to undergo the next processing operation. 
   According to another feature of the present invention, an auxiliary element may be provided on the fixed mounting plate or moving mounting plate, for supporting the attached half of the injection mold, wherein the stamping plunger is movably guided in the auxiliary element. In this way, all components of the injection molding machine can be exposed to a substantially even load, despite the eccentric arrangement of the injection molding position, on the one hand, and the large clearance in the embossing station, on the other hand. Tilting moments encountered during eccentric injection molding operation can thus be compensated. 
   According to another feature of the present invention, an injection molding machine may include only a single injection station and a single embossing station, wherein the moving mold half is made of two identical tools. In this way, existing tools can be used for injection molding as well as for the embossing operation. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Other features and advantages of the present invention will be more readily apparent upon reading the following description of a preferred exemplified embodiment of the invention with reference to the accompanying drawing, in which: 
       FIG. 1  is a longitudinal section of a clamping unit of an injection molding machine according to the present invention; 
       FIG. 2  is a sectional view of the clamping unit, taken along the line II—II in  FIG. 1 ; and 
       FIG. 3  is a sectional view of the clamping unit, taken along the line III—III in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
   Turning now to the drawing, and in particular to  FIG. 1 , there is shown a longitudinal section of a clamping unit of an injection molding machine according to the present invention. It is to be understood by persons skilled in the art that the term “injection molding machine” is used here in a generic sense and may include a horizontal injection molding machine as well as a vertical injection molding machine. 
   The clamping unit includes a fixed mold mounting plate  1  and a moving mold mounting plate  2  in opposite relationship, with the mounting plate  2  traveling on rods  23 , shown in  FIG. 3 , along the center line C. A rotary table  3  is mounted on the mounting plate  2 , e.g., via braces, and supports a base plate  4 . Mounted onto the base plate  4  is a mold half, generally designated by reference numeral  5  and forming part of a molding station with an injection mold comprised of the mold half  5  and a mold half  6 . The mold half  5  thus represents the moving component of the mold while the mold half  6  represents the fixed component of the injection mold. In the non-limiting example of  FIG. 1 , the mold half  5  is comprised of two identical tools  5   a ,  5   b . Of course, the mold half  5  may also have a single piece configuration. When the mold halves  5 ,  6  of the injection mold are closed, cavities  7  are demarcated for receiving plastic material  8  injected via a sprue bushing  9  with elbowed pathway, and a hot runner  10 , for subsequent formation of plastic articles  11  during phase-1 of the fabrication precess. The sprue bushing  9  and the hot runner  10  are integrated in an auxiliary element in the form of a retainer block  12  which is secured to the fixed mounting plate  1  via an interposed backing plate  13 . The retainer block  12  has a throughbore for passage of a stamping plunger  14  that forms part of an embossing station. In a clamping direction of the clamping unit, the retainer block  12  has a length L P  in the embossing station, i.e. area of the stamping plunger  14 , which length L P  is equal to the sum of the length L W  of the mold half  6  and the length L H  of the retainer block  12  In the molding station, i.e. L P =L W +L H , to establish a symmetric force flow during clamping operation. 
   The retainer block  12  has a throughbore for passage of a stamping plunger  14  that forms part of the embossing station. The stamping plunger  14  is movably guided hydraulically and/or pneumatically in a guide bushing  15  which is suitably secured in the throughbore of the retainer block  12 . For ease of illustration, the hydraulic and/or pneumatic components for moving the stamping plunger  14  have not been shown in the drawings. In the area of the stamping plunger  14 , the fixed mounting plate  1  has a suitably sized bore in alignment with the throughbore in the retainer block  12  for passage of the stamping plunger  14  to allow provision of a suitably great stamping stroke and thus formation of a sufficient clearance  16 . The provision of such clearance  16  permits the execution of further operations, such as ejection or removal of the finished products and, possibly, placement of cores to be encapsulated by injection molding, in addition to the embossing operation. 
   As shown in  FIG. 1 , the stamping plunger  14  has a clearance-proximal head portion  17  which has attached thereon a heatable stamping die  19  at interposition of a thermally insulating plate  18 , and a roll-off device, generally designated by reference numeral  20  and shown in more detail in  FIG. 2 . The roll-off device  20  supplies a foil strip  21  which carries a pattern to be transferred onto the injection molded articles  11  and travels underneath the stamping die  19 , as indicated in  FIG. 3  by dashdot line. Examples of patterns may include an electric conductor path structure or a design structure for aesthetic reasons. 
     FIG. 1  shows the situation in which the mold halves  5 ,  6  of the injection mold are closed and the stamping plunger  14  occupies the retracted position, whereas  FIG. 2  shows the situation in which the stamping plunger  14  is moved into the clearance  16  to press in phase-2 the advanced foil strip  21  against the plastic articles  11  that have been previously injection molded in phase-1 and transferred by the rotary table  3  to the embossing station. As the foil strip  21  is pressed against the plastic articles  11 , the foil strip  21  is transferred in accordance with the pattern on the stamping die  19  onto the plastic articles  11 . For ease of understanding, the roll-off device  20  is shown in  FIG. 2  also by way of dashdot line to depict the disposition when the stamping plunger  14  occupies the retracted position, shown in  FIG. 1 . 
   Disposed behind the cavities  7  and the plastic articles  11  are ejectors  22  for knocking out the plastic articles  11  from the injection mold, after the plastic articles  11  have undergone the embossing operation and transfer of the pattern onto the plastic articles  11 . 
   The injection mold operates as follows: In phase-1, plastic material is injected through hot runner  10  into the cavities  7  to mold the plastic articles  11 , while at the same time previously injection-molded plastic articles  11  undergo the embossing operation in phase-2. A cycle of the injection machine is as follows: 
   Phase-1: 
   As soon as the clamping unit is closed and the injection mold is clamped, plasticated material is injected into the cavities, which may, optionally, have cores incorporated therein. At the conclusion of the injection operation, the injection machine applies after-pressure and subsequently the cooling time commences. 
   Phase-2: 
   At the same time parallel to phase-1, the embossing operation is implemented by stamping the desired pattern upon the plastic articles  11  previously injection molded in phase-1. During the embossing operation, the stamping plunger  14  is moved at a predetermined speed from the initial retracted position to the stamping position to press the foil strip  21 , supplied and kept under tension by the roll-off device  20 , against the plastic articles  11 . Travel and pressure of the stamping plunger  14  are suitably controlled by a proportional valve, not shown. The force as well as the speed of the stamping plunger  14  are adjustable as profile. Control of parameters and input of desired values is implemented through machine control. After being held in position for the necessary retention time to transfer the pattern onto the plastic articles  11 , the stamping plunger  14  returns to the initial position and the foil strip  21  is indexed ahead. Subsequently, the finished plastic products provided with the pattern are ejected or removed by a robot, not shown. The empty cavities in phase-2 portion of the injection machine may now receive, optionally, cores to be molded around. 
   After termination of the cooling period, the injection mold is opened, and the moving half  5  is rotated by 180° by the rotary table  3  so that the plastic articles  11  molded in phase-1 are transferred from the injection station to the embossing station, and the empty cavities with or without cores from phase-2 are transferred from the embossing station to the injection station. The next cycle can now begin. 
   Persons skilled in the art will understand that the injection molding machine may run more than two phases, e.g., when multi-component injection molding is desired before the embossing operation. In this case, the rotary table is subdivided in a respective number of stations. If need be, an embossing station may also be provided with several stamping plungers with foil strip, in the event the number and arrangement of the plastic articles requires such a configuration. It will also be understood by persons skilled in the art that is certainly possible to so configure the clamping unit as to secure the rotary table  3  to the moving mounting plate  2  and the stamping plunger  14  to the fixed mounting plate  1 , and such configuration is also considered to be covered by this disclosure. Although the foregoing drawing shows the arrangement of the roll-off device  20  at the stamping plunger  14 , is, of course, also conceivable to secure the roll-off device to a fixed component, e.g. the fixed mounting plate or the retainer block, without departing from the spirit of the present invention. 
   While the invention has been illustrated and described as embodied in a method of making plastic articles having embossed pattern, and apparatus for carrying out the method, 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. 
   What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: