Abstract:
Device to produce polyurethane articles ( 37 ) covered by a film ( 19 ), including a mold ( 30 ) comprising a female part ( 13 ) and a male part ( 12 ) defining a molding cavity ( 18 ) inside which polyurethane material ( 24 ) is able to be injected. The device also comprises, in association with the perimeter edge of said female part ( 13 ), means able to exert a connection function in substantial cooperation with the zone of discontinuity between said female part ( 13 ) and said male part ( 12 ). The means comprise a movable annular ring-nut ( 22 ) including a first position ( 22   a ) to load a segment of said film ( 19 ) in order to insert said segment inside the mold, and a second position ( 22   b ) at least partly overlapping on the perimeter of said female part ( 13 ) in order to cooperate with said female part ( 13 ) during the molding of said polyurethane material ( 24 ).

Description:
FIELD OF THE INVENTION 
     The invention concerns a device to make polyurethane articles, covered with a decorative film, which consists of a molding apparatus equipped with means able to perform the function of a perimeter undercut of the article. 
     The invention also concerns a method to produce polyurethane articles, wherein the steps of thermoforming the covering film and injecting/molding the polyurethane material are carried out in a single piece of apparatus and substantially in a single step, allowing to eliminate the subsequent, laborious operations of filling, sanding and painting in order to obtain the finished product. 
     The invention also allows to accelerate and automate both the steps of loading the film into the mold and also those of moving and discharging the covered polyurethane articles at the end of the forming/molding process. 
     The invention also concerns the polyurethane articles, covered with a decorative film, obtained with this method and this device. The invention is applied in the field of molding polyurethane articles, such as small articles of furniture, furniture wings, panels for automatic distributing machines or domestic appliances, containers, etc. 
     The invention reduces to a minimum the number of working stages needed to complete the production process, reducing the relative times and spaces, and allows to obtain finished products of high quality and surface finish, with substantially any desired shape. 
     BACKGROUND OF THE INVENTION 
     There are various methods, in the state of the art, to produce polyurethane articles, which are finding more and more varied applications in many fields of use. 
     Such articles are obtained, at present, essentially by means of two production processes. 
     A first process provides to paint the surface of the article after it has been removed from the mold. This process requires complex operations on the article which has been removed from the mold, such as trimming, filling, sanding and painting. These operations are not only very laborious, but also they do not give satisfactory results which can be repeated with acceptable levels of standardisation. Moreover, they require considerable manpower and long production times. 
     Furthermore, these operations considerably limit the possibility of automating the production process. 
     A second process provides to apply a covering, protective film at least on the visible face of the polyurethane article. 
     In this case, the state of the art provides to thermoform a covering film in a first mold, to insert it into another mold, and then to inject the polyurethane inside this second mold. By means of this film, the polyurethane articles are ensured the necessary surface resistance and the desired aesthetic quality. 
     However, this technique, using pre-formed films, also has some disadvantages, including the surface quality of the product, which is never regular due to the plays in elasticity of the products which are heated at different times, and to the adaptation of the thermoformed film to the mold because of the injection of the polyurethane. A further problem is the absence of a constant quality. 
     Moreover, this technique requires large work surfaces, both to move the material and also to perform the various steps described above. 
     The present Applicant, in the patent application PCT/IBOO/01084, proposed an innovative method to produce covered polyurethane articles, by means of thermoforming the covering film in a mold and injecting polyurethane material into the same mold, wherein most of the disadvantages listed above are eliminated. 
     The articles obtained with the method described above emerge from the mold substantially finished, and only require the perimeter trimming of the film. 
     Document WO 00/12282 describes a method to mold objects made of plastic material wherein a covering sheet is made to adhere, by means of jets of compressed air, against the wall of the upper part of the mold, and then the plastic material is injected from below in order to form the covered article. 
     Document WO 96/03267 describes a method to produce covered thermoplastic articles wherein a covering film is arranged inside the cavity of the mold, and then the thermoplastic material is injected to thrust the film against the wall of the mold. This method provides that the edges of the film can be released during the injection process to allow the film to move into contact with the wall of the mold while the injected material fills the cavity thereof. 
     Document DE-A-4033297 shows a method to produce covered thermoplastic articles substantially identical to the previous ones. 
     In these prior art documents a first problem concerns the correct finishing of the visible surface of the covered polyurethane article, which must not have any visible signs or marks deriving from the forming and injection process. 
     Another problem concerns the possibility of moving and discharging, in an easy and rapid fashion, the finished covered article at the end of the molding process. 
     A further problem concerns the possibility of achieving covered polyurethane articles with particular shapes and contours, for example with undercuts which may be different from each other on each occasion. 
     The Applicant has devised and embodied this invention to solve these and other problems, and to obtain further advantages as will be shown hereafter. 
     SUMMARY OF THE INVENTION 
     The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the main embodiment. 
     The purpose of the invention is to achieve a method and a device suitable to supply, in a single molding step and with a single apparatus, a substantially finished polyurethane article characterized by high surface quality, even when there are perimeter undercuts present. 
     Another purpose is to achieve a molding device equipped with means able to cooperate with the perimeter edge of the article when the mold is closed, such means allowing to form a perimeter undercut and preventing the creation of an imperfect and/or damaged edge in correspondence with the discontinuity created between the coupled surfaces of the male and female parts of said mold. 
     A further purpose is to achieve a production method wherein the steps can be largely automated and allow the automatic loading of the film in correspondence with the mold, and also the molding, removal and discharge of substantially finished articles, which require only a perimeter trimming of the covering film present. 
     Another purpose of the invention is to achieve a device wherein the shape, and in particular the perimeter edge, of the article can be changed quickly, without requiring complex operations to dis-assemble and re-assemble parts, or the particular use of the labor force. 
     The molding device according to the invention comprises a molding apparatus consisting, in a substantially conventional fashion, of a female part, or matrix, suitable for the conformation of the visible face of the article, and a male part, or punch, suitable for the conformation of the non-visible face. 
     The male part is associated with press means able to move it from an open position to a closed position and incorporates the means to inject the polyurethane material when the mold is closed. The male and female parts of the mold have heating means which can be activated on command, for example, but not only, consisting of heated water circulating in the inner volume of the two elements, or of electric resistances, radiating elements, hot air, or other means. 
     In one embodiment of the invention, the heating means of the male and female part of the mold are autonomous and independent with respect to each other. 
     According to one characteristic of the invention, in association with the perimeter edge of the female part of the mold there are means able to perform a function of continuity and connection in correspondence with the zone of discontinuity between the male and female parts of the mold. 
     Said means are removable and replaceable and comprise, in a preferential embodiment, an annular ring-nut or frame which extends outside, and partly overlapping, the perimeter of the female part, so as to constitute substantially an auxiliary element, or counter-matrix, of the female part. 
     The annular ring-nut has at least one perimeter edge protruding forwards, in the direction of the molding cavity, which is shaped so as to cooperate with said discontinuity between the two parts of the mold, so that it is possible to form a perimeter undercut. 
     In this way the annular ring-nut allows to form a perimeter edge of the article without imperfections or irregularities, so that the only operative step required after the article has been removed from the mold is the perimeter trimming of the possible excess film. 
     According to another characteristic of the invention, the annular ring-nut is associated with movement means which allow it to make at least the following displacements: 
     to be positioned in a position outside the molding apparatus in order to lay, cut and clamp, on part of its perimeter, a segment of the covering film, 
     to be translated towards the molding apparatus in order to insert the film into the mold, 
     to be lowered into substantial co-operation with the perimeter edge of the female part of the mold, 
     to be raised with respect to the female part, once the forming and molding step is completed, taking the molded article with it, and finally 
     to be translated laterally with respect to the molding apparatus, in order to allow the article to be removed and discharged, exploiting the excess parts of the film protruding from the figure of the article. 
     In order to perform the operation of loading the film into the mold, the annular ring-nut includes first vacuum means able to retain the film at least temporarily against the upper surface of the ring-nut. 
     In one embodiment of the invention, the annular ring-nut also has second vacuum means able to locally create a vacuum in order to achieve the thermoforming of the covering film, said means including external suction holes and slits outside the figure of the molded article. 
     In a further embodiment, the annular ring-nut has heating means, which can be selectively activated during the forming step of the film. 
     The heating means, according to a variant of the invention, are autonomous and independent with respect to the heating means of the components of the mold, so as to allow a selectively differentiated heating according to specific requirements. 
     In a preferential embodiment of the invention, the molding apparatus comprises pressure means, adjustable in pressure, suitable to cooperate with the surface of said annular ring-nut so as to define a sealing outer perimeter which retains the film mechanically during its thermoforming step. 
     According to a variant, said pressure means and said annular ring-nut have respective means, mating and cooperating, which prevent the formation of wrinkles and creases in the film during the thermoforming step and the subsequent injection of the polyurethane. 
     In another variant, in the case when the molding apparatus is of the type suitable for the simultaneous formation of two or three figures, there are cutting means provided suitable to cut the film in correspondence with a zone of separation between the two figures, in order to allow the two articles to be removed separately. 
     In a preferential embodiment, the annular ring-nut is of the interchangeable type, to allow to define perimeter edges, and the relative undercuts, of a different shape according to the specific application. 
     According to another variant, the molding apparatus comprises auxiliary heating means able to locally determine different temperatures with respect to the rest of the figure. 
     According to a further variant, the molding apparatus comprises means to deliver compressed air, able to be selectively activated, to collaborate in the operation of forming the film and its adhesion to the inner surface of the female part of the mold. 
     There are many advantages to the invention, apart from the fact that it obtains a covered article, finished in every part, in a single step. 
     The complete thermoforming and definitive union of the film and the polyurethane are obtained using heat and pressure generated by the polymerization reaction of the polyurethane itself. This ensures that the quality is constant, that the whole visible surface of the article is perfect and that the results can be repeated; this cannot be obtained with known techniques. 
     The method eliminates all those steps subsequent to molding, such as filling, sanding and painting, thus bringing considerable advantages in terms of economy, safety (for example, the emission of solvents, waste disposal, fire risks, etc.) and ecology. Moreover, by eliminating these steps it is possible to automate a large part of the operations of the whole production process. 
     Using a removable and interchangeable ring-nut allows to achieve the desired perimeter undercuts in the article, and therefore allows, substantially in a single step, to produce articles with a complex and elaborate shape. 
     Moreover, thanks to the removable ring-nut, it is possible to automate the steps to load the film into the mold and to discharge the finished polyurethane article. 
     In order to obtain higher productivity, a further embodiment provides several molds in line, operating in sequence and having the same characteristics as those described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These characteristics and advantages of the invention will become clear from the following description of the preferential form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: 
     FIG. 1 shows a section of a form of embodiment of the molding apparatus to produce covered polyurethane articles according to the invention; 
     FIGS. 2 a - 2   h  show in sequence the cycle of loading, thermoforming, molding and discharge of the polyurethane article using the device according to the invention; 
     FIG. 3 shows an enlarged detail of the apparatus in FIG. 1; 
     FIG. 4 shows a variant of FIG. 3 in the case of a molding apparatus to make two separate figures. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to the attached Figures, the reference number  10  denotes in its entirety a molding device to produce polyurethane articles according to the invention. 
     The device  10  comprises a molding apparatus  30  consisting of a female part  13 , or matrix, associated with a fixed support  14 , and a male part  12 , or punch, associated with a press element  11  driven to open/close by means of movement actuators which are not shown here. 
     Both the male part  12  and the female part  13  have heating means, of a conventional type and not shown here (for example internal conduits with heated water circulating). 
     The male part  12 , in this case in a substantially central position, has an injection channel  17 , associated with an injection head  117 , through which the foamy polyurethane  24  is injected, when the mold is closed, into the molding cavity  18  defined between the male part  12  and the female part  13 . 
     It is obvious that, within the field of the invention, the injection channel  17  could be located in a non-central position, or there could be two or more injection channels, possibly usable in alternation. 
     In this case, the molding device  10  comprises means  20  able to feed a thermoformable covering film  19  which is first inserted into the mold  30  and then made to adhere through thermoforming, as will be explained better hereafter, to the inner wall of the female part  13 . 
     The film  19  is between 0.2 and 1.4 mm thick, preferably between 0.4 and 0.8 mm. 
     In the embodiment shown here, and as can be seen in greater detail in FIG. 1, in cooperation with the perimeter of the female part  13  of the mold there is an annular ring-nut  22  of the removable type with a front perimeter edge  23  facing towards the molding cavity  18 . The front edge  23  is suitable to perform a function of continuity, substantially in correspondence with the zone of separation which is formed, when the mold is closed, between the female part  13  and the male part  12  of the mold. 
     The front edge  23  preferentially has at least part of its perimeter shaped and rounded so as to connect the parts of the mold and so as to allow to form an edge of the article, with its relative perimeter undercut, in correspondence with said position of discontinuity. 
     In this way, the article can be discharged from the mold already substantially finished, and requires only the perimeter trimming of the possible excess film  19 . 
     In the preferential embodiment, the annular ring-nut  22  has heating means  33 , for example hot water circulating inside. 
     The heating means  33  are advantageously independent and autonomous with respect to the heating means associated with the matrix  13  and the punch  12 , so as to be able to determine a differentiated heating in the various zones of the film  19  and/or of the injected polyurethane. 
     The annular ring-nut  22  according to the invention is able to be moved so that first the film  19  is inserted into the mold  30  and then the finished polyurethane article is discharged from the said mold  30 . 
     The cycle to move the ring-nut  22  to perform the molding of a polyurethane article is shown in FIGS. 2 a - 2   h.    
     In FIG. 2 a , the ring-nut  22  is in a position  22   a  outside the mold  30  and near the means  20  to feed the film  19 . 
     Gripper means  31 , able to translate on a substantially horizontal plane, are arranged to grip the end of the film  19 , unroll a segment of a defined length and lay said segment above the ring-nut  22 . When the film  19  has been arranged above the ring-nut  22 , cutting means  32  are activated to cut the segment from the reel  20 . 
     In this step, first vacuum means  26  are activated, arranged inside and on the perimeter of the ring-nut  22 , which are able to be selectively activated to retain the film in co-operation, in this case, with the two short sides of the ring-nut  22 . 
     The ring-nut  22  is then translated on a substantially horizontal plane (FIG. 2 b ) to be taken to a position  22   b  substantially inside the mold  30 , in an intermediate position between the matrix  13  and the punch  12 . Then, the ring-nut  22  is lowered substantially to rest on and couple with the perimeter of the matrix  13 , with the film  19  held taut above the molding cavity  18  (FIG. 2 c ). 
     At this point, the punch  12  is lowered into contact with the film to heat it, and pressure means  21  are activated to mechanically clamp the film  19  in position on the upper edge of the ring-nut  22  (FIG. 2 d ). 
     In the embodiment shown here, the action of the pressure means  21  is advantageously adjustable in intensity; in cooperation with relative segments of the upper surface of the annular ring-nut  22 , the pressure means  21  define the housing for perimeter vacuum sealing means, such as O-rings  27 . 
     In the case shown here, the pressure means  21  have a tooth  25  suitable to cooperate with a mating cavity  28  made on the perimeter of the annular ring-nut  22 , in order to prevent the formation of folds and wrinkles in the film  19  during thermoforming. 
     The first vacuum means  26  are then de-activated, while the heating means  33  inside the ring-nut  22  are activated and also second vacuum means  126 , able to determine the thermoforming of the film  19  and its adhesion to the inner surface of the matrix  13 . 
     During the thermoforming step, according to the variant shown in FIG. 1, means to deliver compressed air  34  associated with the punch  12  are activated to cooperate with said heating means  33  and said second vacuum means  126  in order to complete the thermoforming operation of the film  19 . 
     It should be noted that both the first vacuum means  26  and especially the second vacuum means  126  which are activated during the thermoforming of the film  19  have their relative suction holes arranged outside the figure of the polyurethane article; as a result, when they are activated they do not cause signs, prints or other marks of any type on the visible face of the finished product after molding, which ensures a high surface quality of the visible face. 
     In this step, it is also possible to activate auxiliary heating means  38  to determine differentiated and localized heating in specific zones of the film  19 . 
     When the thermoforming is complete, the punch  12  is closed on the matrix  13  and the injection of the foam polyurethane  24  is begun through the injection head  117  and the injection channel  17  (FIG. 2 e ). 
     The heat and pressure generated during polymerization of the polyurethane  24  cause the thermoforming of the film  19  to be completed, and the film  19  is definitively and stably attached to the outer surface of the article. 
     When molding is complete, the mold is opened (FIG. 2 f ) and the annular ring-nut  22  is first raised and then translated laterally, to allow the article  37  to be removed. The article  37  thus achieved remains resting on the annular ring-nut  22  due to the presence of the perimeter edge of the excess film  19 . 
     Finally, the ring-nut  22  is returned to its initial position  22   a  (FIG. 2 g ) to allow the expulsion means  35  to be activated, which allow to discharge the polyurethane article  37  which falls into an underlying collection tray  36 . 
     From the tray  36 , the finished article is sent to a station for the perimeter trimming of the excess film  19 , in order to complete the process and to obtain the finished piece. 
     In the event that the mold is used to simultaneously make two or more adjacent figures (FIG.  4 ), cutting means  29  are provided to separate the film  19  in correspondence with an intermediate position of said two figures, allowing to remove and discharge individually the two articles thus obtained. 
     It comes within the field of the invention to provide systems able to apply two films  19 , one for each side of the article. 
     It also comes within the field of the invention to provide that a single press comprises not only two or more figures, but also two or more molds driven simultaneously. 
     Additions and/or modifications can be made to the method and device as described heretofore without departing from the spirit and scope thereof. 
     It is also obvious that, although the invention has been described with reference to specific examples, a person skilled in the art shall certainly be able to achieve many other equivalent solutions, all of which shall come within the field and scope of the invention.