Description

Field of the art

The present invention regards the field of injection molding of thermoplastic materials. More in detail, the method subject of the present patent application regards a double- or multi- injection molding, for obtaining mechanically constrained multi-material components, avoiding gluing.

Prior art

The market needs, in particular in the automotive industry, are getting increasingly specific and demanding both in terms of the aesthetic appearance of each component and as concerns the technical performance which are specifically regulated according to safety criteria and rules.

Most of the plastic components of a vehicle are currently obtained by means of injection molding of thermoplastic polymers.

Various molding techniques have been developed over the years. In particular, techniques regarding the present invention are the multi -injection techniques which reveal numerous advantages, including reducing the production steps and the ensuing optimization of times and costs.

The double-injection technique is characterised by the injection of two different materials into the same cavity, but through two different nozzles. In case of injection of more than two materials, then we have multi -injection.

Besides this technique, which is commonly used for obtaining two-coloured or multi- coloured components or components consisting of aesthetically different material, there is also the rotary table molding. This over-molding technique uses a rotatable hydraulic or electrical plate. One half of the mold is fixed on this plate, mounted on the movable plane of the pressing machine in vertical position. After injecting the first material, by means of the main injection unit, the rotary plate displaces the mold and positions it so as to allow the injection of the second material.

At the current state of the art, internal door uprights of vehicles are especially the components obtained by means of double-injection with rotary table, when the project provides for that these components be made with two different colors.

Aerodynamic spoilers are also commonly manufactured in this manner.

The criticalities arising from this technique above all regard the cohesion between the two components and some international patents have the specific object of overcoming these problems.

It is clear that a similar problem could entail considerable gravity should the lack of cohesion occur, for example, on a spoiler which could become extremely dangerous for other road users should it break.

An example of the patents dedicated to solving this problem is the United States patent number US 2014 212621 which described a method for the multiple injection of thermoplastic materials having different hardness. The object of the aforementioned patent is to make the two components adhere to each other hermetically. Such object is attained by means of a step subsequent to molding consisting in a welding externally covered by a decorative film which guarantees a pleasant aesthetic appearance of the piece thus made.

It is clear that such patent, just like all other patents and other techniques in use in the double- or multi-injection molding sector, do not overcome the identified technical problem neither effectively nor economically.

Thus, an object of the present invention is to offer perfect adhesion between the various parts of the same component of the vehicle, obtained by means of double- or multi-injection molding, thanks to solutions that are directly applied inside the mold, without requiring subsequent machining steps, including gluing. Description of the invention

According to the present invention, herein described is a mold, a method for multi-injection molding and the product thus obtained which allow to effectively overcome the problems outlined above.

Said mold is a common mold for double-injection or multi -injection molding, possibly with rotary or translating table, provided with at least two nozzles or a plurality of nozzles suitable to introduce into said mold at least one pair of thermoplastic materials for obtaining a product consisting of a first material and at least one second material.

These molds are characterised by at least one retractable projection that can take on a first extended configuration suitable to project into the interspace of the mold. This retractable projection can also advantageously take on a second retracted configuration, which does not project into the interspace, letting the injected thermoplastic material to spread to all available spaces.

Preferably present in the mold are a plurality of retractable projections.

These may possibly be characterised by different diameter and lengths.

Advantageously, said retractable projections are positioned at the superimposition zone provided between the various materials that will form the end product. Even more advantageously, in order to solve mechanical strength problems in case of an explosion, said retractable projections are organized according to a plurality of axes comprised between 3 and 10 axes, preferably 4-5 axes.

By so doing, the mechanical stress that the finished product, which obviously has its weak point at the superimposition zone between the materials, is subjected to, will be distributed along several directrices, obtaining a highly resistant product in which the materials are constrained mechanically.

The method for obtaining said products uses the mold described previously and follows the steps of:

- first injection of the first material into the interspace of the mold while the retractable projections are in said extended configuration. Hence, at said projections, housings will be created in said first material having diameter and depth corresponding to the diameter and length of the retractable projections;

- waiting for the time necessary for cooling and for the at least partial solidification of said first material;

- receding said retractable projections in said second retracted configuration;

- second injection of the second material into the interspace of the mold. Said second material, penetrating into said housings, forms at least one nail head should the retractable projection in the mold be one. Thus, a plurality of nail heads that will determine the mechanical constraint between the two materials will be created in the preferred embodiment.

- waiting for the time necessary for cooling said second material and removing the finished product from the mold.

Should the mold be of the rotary table type, the method will comprise a step of rotating said rotary table before proceeding to said step of second injection.

Should the mold be of the translating table type, the method will comprise a step of translating said translating table before proceeding to said step of second injection.

The previously described method and mold may be advantageously used for obtaining products consisting of more than two materials, with suitable technological solutions. In this case, during the step of second injection, at least one second group of retractable projections is suitable to take on said first extended configuration at a second superimposition zone provided between the second material and a further material. Subsequently there is a step of receding the second group of retractable projections and a step of third injection in which said further material is injected into the mold, penetrating into the housings created in said second material and thus forming the provided nail heads suitable to mechanically constrain the second material and the further material.

Thus, the obtained product will have at least one superimposition zone between at least one pair of materials, possibly with different colors. Said superimposition zone, which will have a surface area comprised between 2% and 20% of the surface area occupied by each material, will comprise said nail heads consisting of the extension of the second material into the special houses provided in the first material.

Possibly, provided for in the method may be a step for heating the superimposition zone between the two materials so as to chemically activate it and facilitate adhesion.

The components of the vehicle, with which the present invention seems to perfectly fit, are the two-coloured or multi-coloured aesthetic components of the interior of the vehicle, preferably the upright of the front door and the aerodynamic spoilers.

The advantages provided by the present invention will be clear in light of the description outlined up to now. Furthermore, they will be more apparent due to the attached figures and relative detailed description.

Description of the figures

The invention will be described hereinafter in at least one preferred embodiment, provided by way of non-limiting example, with reference to the attached figures, wherein:

- FIGURE 1 shows an interior door upright of a vehicle 10 shown in which are the first material 11 and the second material 12 and the superimposition zone 13 between the two with the dashed line.

- FIGURE 2 illustrates the rear of the door upright 10 of the previous FIG. 1 in which the nail heads 14 that follow a plurality of alignments can be seen in the superimposition zone 13.

- FIGURE 3 shows a cross-sectional view of the nail head 14 which mechanically constrains the first material 11 with the second material 12 in the superimposition zone 13 between the two.

- FIGURE 4 shows the sole component consisting of the second material 12 of an aerodynamic spoiler, in which the nail heads 14 are shown.

- FIGURE 5 shows the sole component consisting of the first material 11 of the same aerodynamic spoiler of FIG. 4. Detailed description of the invention

Now, the present invention will be illustrated purely by way of non-limiting or non-binding example, with reference to the figures illustrating some embodiments regarding the present inventive concept.

With reference to FIG. 3 shows is a significant section of the product 10 obtained using the mold subject of the present invention with the method associated thereto.

In a preferred embodiment, the product 10 is an internal upright of the door of a motor vehicle, consisting, for aesthetic purposes, of two colors, and thus two different thermoplastic materials.

The section shows the first material 11 which has the housings that are occupied by the second material 12, forming nail heads 14. All the nail heads 14 are arranged in a superimposition zone 13 with surface area equivalent to about 10% of the surface area occupied by said first and second material 11-12.

As observable in FIG. 2, which represents the rear face, i.e. the face that cannot be seen from within the vehicle, of the upright thus obtained, it is clear that the nail heads 14 are organized according to 4 different axes.

In this manner, the mechanical constraint that is created between the first and the second material 11-12 is much more effective than the sole chemical constraint that could be obtained by gluing at the superimposition zone 13 between the materials.

A second type of product 10 obtained according to the teachings of the present invention is an aerodynamic spoiler whose components are represented in Figs. 4 and 5. Assuming to be able to separate the two components resulting from the two injections that lead to obtaining the spoiler (an impossible task considering the strong mechanical adhesion between the two injected parts). Fig. 5 illustrates the result of the first injection and Fig. 4 shows the product of the second injection.

It should be observed that Fig. 3 could be a significant section for both represented products 10 (door upright and spoiler).

The mold used for obtaining said products 10 is a common double-injection mold in which retractable projections were arranged at the position desired for said nail heads 14.

More in detail, the retractable projections are suitable to reversibly take on a first extended configuration and a second retracted configuration.

In the first extended configuration they project into the interspace of the mold, while in the second retracted configuration they leave the entire space vacant, receding into the matrix of the mould.

As previously illustrated, the positioning of the retractable projections must coincide with the position of the nail heads 14, thus they must be in the provided superimposition zone 13 of the two materials 11-12, organized along 4 different axes, so as to distribute the mechanical stress to the utmost.

The method consists of the following steps:

- first injection of the first material 11 into the interspace of said mold while the retractable projections are in said extended configuration to create said housings.

- waiting for the time necessary for cooling and for the at least partial solidification of said first material 11;

- receding said retractable projections in said second retracted configuration;

- second injection of said second material 12 into the interspace of the mold forming said nail heads 14;

- waiting for the time necessary for cooling said second material 12 and removing the finished product 10.

Lastly, it is clear that the invention described up to now may be subjected to modifications, additions or variants obvious to a man skilled in the art, without departing from the scope of protection outlined by the attached claims.