FR2884173A1 - Rotational molding setting for plastic molding, comprises preheating a zone to be colored, depositing a dosette on the zone, fusing the dosette, controlling the fusion, heating and cooling the mold - Google Patents

Abstract

The process further comprises obtaining the end product after inspection (6) of the mold, by depositing the dose product and closing the mold. The dosette and dose are made of plastic material. The setting of zones is limited by projecting relieves in hollow combined with stencil.

Description

The invention relates to a method of rotomolding decorations.

  The present invention relates more particularly to the field of rotational molding, whose technique is applicable to the production, using molds, of parts made of fusible material. More particularly, this technology is used for molding plastics, especially polyethylenes, polypropylenes, crosslinked polyethylenes, polycarbonates, and PVC.

  In this connection, such a rotomolding method usually comprises a sequence of operations combining, in this order: the filling of the empty mold with the raw material (in the form of powder, or liquid, or paste, in the case of plastics), - the closure of the mold, - the conjugation of a specific molding-specific temperature cycle (depending on the combination of the raw material, the material and the shape of the mold, and the desired characteristics for molding, in particular thickness and appearance), and rotational cycles of the mold according to different axes of rotation, also specific to the molding produced and the know-how of the rotomould, - the opening of the mold, - the demolding of the finished piece.

  Note that the parts obtained by rotational molding are generally monochrome, because it is difficult to make decorations in one or more colors different from the basic shade.

  This issue of decoration is important, especially when the completed piece must include a functional or aesthetic, or identification.

  Certain materials such as polyethylene, commonly used in rotomolding, have non-stick properties such as decorations made with paints, inks, or varnishes, do not adhere permanently to the external surface, and there are defects of delamination, fluffing, or peeling. If functional decorations are necessary, for such products, they must be made on ancillary supports, which must be reported, on the molded products, by mechanical methods such as screwing, riveting, or similar. Some glues allow the adhesion of decorations reported on substantially flat surfaces, but their behavior to bad weather leaves much to be desired.

  The use of a reported decoration, when it is possible (which is not always the case, according to the morphology of the products produced), has the disadvantage of a vulnerability to tearing, to degradation, and to wear.

  The behavior of a decor reported against external agents: bad weather, ultraviolet, temperature differences, is different from that of the basic product. This may have additional disadvantages, particularly with regard to the expansion behavior.

  Various attempts have been made to modify the coloration of the product after the end of its molding cycle: for example, a method for modifying the color by heating or acid attack is known. Or a color turning process by exposing a polymeric plastic product, containing organic dyestuffs, to electron beams.

  Such methods may alter the product already molded, and do not allow the free choice of colors or decor locations, while being difficult and expensive to implement.

  It is still known, through the document WO 02/094 557, a decorating method using a multilayer decal: adhesive / dye-wax mixture / adhesive. This decal is applied to the inner face of the rotational mold at a temperature close to the demolding temperature, a pressure is applied to this decal so as to transfer the contents to the selected surface, the support of the decal is then removed, and the normal rotational molding cycle is then continued. Such a method requires the preparation of an expensive multilayer decal: cost of the tooling for making the decals, plus unit cost of each decal. In the case of plastics, the number of suppliers in the world is extremely small. The high unit cost generally limits the launch to the strict amount of parts to produce, which does not allow any error during installation. The application of pressure on this decal preferably requires the use of a form tool, the profile of the area on which is applied this decal. It should be noted that such a decal can only be properly applied on a flat or slightly curved surface. This method is poorly applied to the decoration of areas with significant relief. And the colored zone is moreover constituted of a mixture of composition substantially different from that of the rest of the molded product.

  In short, there is no known method for making a decor in the same material as the rest of the molded product, with a choice of colors among all the pigments available on the market for the material in question, in a simple operating mode and not not requiring complex tools, and able to achieve this scenery in areas of any relief.

  In the end, the present invention attempts to remedy the aforementioned problems through a solution using the usual rotomolding installations, and ensuring the realization of a decor in at least a portion of the thickness of the molded product itself , and this in an area of any relief (the only limitation of the relief being related solely to the demolding stresses of the molded product).

  - Thus, the invention relates to a rotomolding decorating process comprising the combination of a cycle of climbs and descents temperature and a cycle of rotation of the mold relative to the various axes of the rotational molding system, characterized by the that the operating sequence is composed, in this order, for each zone and for each color, of the following operations: - optional preheating of the area to be colored deposit in the mold of a first quantity of colored material called pod in the zone intended to be colored fusion of said pod - control of the melting of said pod optional local heater of the mold realizing if necessary the complete melting of said pod taking over the control of the melting of said pod and repetition of the previous operation until complete melting control cooling and, by the fact that after verification that all the decorations required in the mold are carried out, the end of the operating sequence for obtaining the final product is composed of the following operations: - deposit, in the mold, of the quantity of product called dose corresponding to the complete elaboration of the product - closure of the mold normal cycle rotational molding, itself comprising an appropriate combination of temperature cycles and rotational cycles, cooling, mold opening and demolding of the finished part.

  The obtaining of decorations in several zones results from the successive fusion, or combined according to their arrangement in space, of several first pods, each corresponding to the realization of a decoration in the outermost layer of the product, in a zone determined. It is only after the fusion of all these first pods in position that the dose corresponding to the remainder of the raw material needed to produce the finished product is incorporated in the mold, before the closure of the latter, and the start of the cycle. normal rotational molding.

  According to the same inventive concept, the same method is applicable for obtaining a multi-layered decoration: after the fusion, in a given zone, of the first pod, is deposited, superimposed on this first molten pod, the material first of a second pod in another color. The local heating of the area concerned allows the fusion of the second pod. After cooling of the latter, other colored layers can be applied in the same way, by depositing, melting and cooling other pods.

  In a preferred application, pods and doses are made of plastics.

  Thus, it is possible to produce a multicolored product, which may especially comprise identification markings, traceability, barcodes, or any other type of identifier, in particular an individual identifier.

  The decor being realized within the product, and in the same material, offers the same behavior vis-a-vis the external physical agents, in particular the dilation, the resistance in front of the ultra-violet rays and bad weather.

  The decor is indestructible, unalterable, can not be torn or degraded. Products thus decorated are particularly suitable for all street and street furniture applications.

  According to an advantageous embodiment, the limitation of the areas of decorations can be obtained by arranging the mold, in particular by protruding reliefs and / or recesses, possibly in combination with the use of stencils.

  Other objects and advantages of the present invention will become apparent from the following description relating to an exemplary embodiment given by way of indication and not limitation.

  The understanding of this description will be facilitated with reference to the accompanying drawing, wherein: the single figure is a process flow diagram.

  As shown in the figure of the attached drawing, the present invention relates to the field of decoration products obtained by rotational molding.

  The rotational molding process is applicable to a wide variety of fusible materials, including plastics.

  A rotomoulding installation comprises a mold support for rotating the mold around one or more axes of rotation, and means for heating and cooling the same mold. This mold is removable so as to extract the finished product, which may advantageously be in the form of a seamless hollow body. The sequence of operations combines, in this order: the filling of the empty mold with the raw material (in the form of powder in the case of plastics), the closing of the mold, the conjugation of a molding-specific temperature cycle carried out (depending on the combination of the raw material, the material and the shape of the mold, and the characteristics desired for the molding, in particular thickness and appearance), and cycles of rotation of the mold according to different axes of rotation, they also specific to the molding carried out and the know-how of the company implementing the rotational molding, - the opening of the mold, the demolding of the finished part.

  Such a sequence can be long for large plastic products, such as tanks, tanks, bins, cowlings, street or street furniture.

  To facilitate the understanding of the description which follows, it has been identified in the attached drawing, the various operations constituting the sequence of the method according to the invention.

  The rotomolding decoration method, according to the invention, consists, in the case of a single decoration, in a single color and in a single zone, of the following operations: - preheating 1 of the zone to be colored deposit 2 in the mold of a first quantity of colored material called pod in the area to be colored test 3 of verification of the complete fusion of the pod o in the alternative of a report of incomplete fusion of the pod at the end of the test 3, execution of a local heating 4 of the mold carrying out the complete melting of said pod, and resumption of the verification test 3 at the end of the local heating 4 o in the alternative of a statement of complete merger of the pod at the end of the test 3, performing a cooling 5 - test 6 to search for another decor to perform: other area to decorate, and / or additional decoration superimposed on a decor already made o in case of need to pose another dec after test 6, repeat steps 1 to 6 included for the new decor, in the area considered, and with the adapted pod o in the absence of other decorations to perform, move to the next step deposit 7, in the mold filled with the pod or melts in position, the amount of product called dose corresponding to the complete development of the product - closure 8 of the mold normal rotomoulding cycle 9, comprising: o cycles 10 rise and lowering the temperature of the mold 11, the cycles 10 and 11 being combined according to the know-how of the firm. cooling the opening of the mold and demolding the finished product.

  Preferably, the preheat 1, as the local heating 4 is performed from the face of the mold opposite to the molded product, so as to obtain the melting of the material of the first pod.

  The preheating phase 1 may be omitted, particularly if the mold is already at a temperature close to the melting temperature of the raw material, or if it facilitates the introduction of the content of the pod.

  Local heating 4 is only intended to complete the complete melting of the pod, in the case where preheating 1 has proved insufficient.

  But, in any case, the conduct of at least one of two heating operations: preheating 1, or local heating 4, is essential to the implementation of the method according to the invention.

  The obtaining of decorations in several zones results from the repetition of the operations of preheating 1, deposition of dosette 2, melting, complete melting verification test 3, local heating 4, cooling 5. Thus is carried out the successive fusion, or combined according to their arrangement in space, several first pods, each corresponding to the realization of a decor in a given color, each in a specific area.

  Obtaining a multi-layered decoration is done in the following way: after having done the installation of a scene according to the operations of sequence 1 to 5, by using a first pod, one carries out, in superposition on this first fondue, a similar cycle consisting of operations 1 to 5, using a second pod in another color. After cooling of the latter, other colored layers can be applied in the same way, by repeating the cycle, using as many pods as superimposed colors.

  The verification test 6 to search for another decoration to be made: another zone to be decorated, or / and additional decoration superimposed on a decoration already made, makes it possible to verify that all the decorations have been arranged in all the desired zones, and in the overlays required. If this is the case, the deposit 7 is made in the mold, the dose corresponding to the remainder of the raw material needed to produce the finished product, before the closure 8 of the mold, and the start of the normal rotational molding cycle 9.

  The limitation of the decoration areas can be obtained by a mold layout, including protruding reliefs and / or recesses, possibly in combination with the use of stencils.

  As can be seen from the foregoing description, the solution according to the invention avoids the use of ancillary devices and expensive tools.

  It also has the advantage of allowing the implementation of the stages of decoration, prior to the closure of the mold, outside the rotomolding installation itself. Thus a mold can, especially in the case of a bulky piece and long cycle, be prepared with the incorporation of the decor pods, masked time, even before it is mounted on the rotational molding machine.

  In short, as can be seen from the foregoing, the present invention does not only respond to a problem of feasibility, in particular in the case of the decoration of plastics such as polyethylene, but also to the problem of the decor of any shape, and the cost of this décor.

  Although the invention has been described with respect to a particular embodiment, it is understood that it is in no way limited and that various modifications of shapes, materials and combinations thereof can be made. various elements without departing from the scope and spirit of the invention.

Claims (3)

  1. Rotational molding decorating method comprising the combination of a cycle of climbs and descents in temperature and a cycle of rotation of the mold with respect to the various axes of the rotomoulding installation, characterized in that the operating sequence is composed, in this order, for each zone and for each color, of the following operations: - optional preheating (1) of the area to be colored - deposit (2) in the mold of a first quantity of colored material called a pod in the zone intended to be colored - melting of said control pod (3) of the fusion of said pod - optional local heating (4) of the mold realizing if necessary the complete melting of said pod - resumption of control of the fusion of said pod and Repetition of the above operation until complete cooling control (5) and, after verification (6), that all the decorations required in the mold are carried out, the end of the operating sequence for obtaining the final product is composed of the following operations: - deposit (7), in the mold, of the quantity of product called dose corresponding to the complete elaboration of the product - closure ( 8) of the mold - normal rotational molding cycle (9), itself comprising an appropriate combination of temperature cycles (10) and rotation cycles (11), cooling (12), opening of the mold and demolding (13) of the finished piece.   2. rotomolding decorating method according to claim 1, characterized in that the pods and the dose consist of plastics.   3. rotomoulding decorating method according to one of the preceding claims, characterized in that the limitation of the decorating areas is obtained by a mold arrangement, in particular by protruding reliefs and / or hollow, in combination optionally with the use of stencils.