FR2889100A1 - Manufacturing procedure for rigid support with foam layer consists of injecting plastic for support into mould containing foam layer - Google Patents

Abstract

The rigid support with a foam covering layer, e.g. for motor vehicle interior trim, is made by placing a layer of a thermoplastic foam material (18) against the inner surface of an open mould section (10), closing the mould with another section (14) to leave a cavity between it and the foam layer, and injecting a non-cellular plastic material into the cavity to form the rigid support (20). During the injection process the two mould sections are moved apart while the cavity remains sealed, so that the thickness of the foam layer does not differ by more than 10 per cent from its original thickness before the mould was closed.

Description

2889100 1

  The present invention relates to a method of manufacturing a part comprising a layer of thermoplastic foam material supported by a support, as well as the part obtained.

  Although the invention applies to the manufacture of parts having a relatively rigid support and a thermoplastic foam layer disposed on the support, such a part generally comprises an additional layer on the face of the foam opposite that which is at contact of the support, this additional layer having elastomeric properties. Whether or not such an outer layer is present, the foam layer is intended to give damping properties which depend on the flexibility of the foam layer, and therefore on various properties such as its porosity.

  It is already known from US 6 576 332 to make such pieces by a method in which a skin is placed against a first mold part, a support is placed against another mold part, and a material capable of foam is injected between the skin and the support. After or during this injection, the two mold parts are spaced relative to each other so that the intermediate layer forms a foam. This step of spacing is sometimes delayed so that the injected material has undergone partial cooling. The injection step of the foam-forming material can also be carried out as the mold parts gradually move apart, and the formation of the foam is achieved by continuing this separation. In these known methods, the foam is formed after the production of the support.

  It is also known to produce such parts in a process in several operations. In a first operation, a foam layer or a skin-foam complex is produced at a first station, then the foam layer or the complex is placed on a first mold part, the mold is closed, and the plastic material intended for forming the support is injected into a cavity left between the foam layer and the other mold part. This method has a disadvantage because the non-cellular plastic material of the support is injected against the foam which is therefore subjected to the injection pressure of the plastic material of the support. In such a process, the foam layer always has some crushing. It is not uncommon for the thickness of the foam layer to be halved. It is conceivable that such a foam layer has properties of flexibility and damping that are not as good as those of the initial layer.

  For the production of parts having damping properties determined by the latter method, it is therefore necessary to initially use a foam layer having damping properties much greater than the desired properties, so that after the compression performed in the mold, the foam layer still retains the desired damping properties. The development of such techniques is very delicate, and requires new studies with each change of shape or material.

  It is an object of the invention to overcome the disadvantage of the second method by combining therein features of the first method. This combination of known means gives an unexpected result, different from the results obtained by each of the two aforementioned methods.

  More specifically, in the processes of the aforementioned first type, the foam layer can have substantially constant properties throughout its thickness. In the second method, because of the injection of the warm, non-cellular thermoplastic material against one side of the foam, this foam face tends to experience greater heating and to create a porosity gradient such as porosity. is the lowest on the support side. According to the invention, in a method of this second type, an additional step of separating the two mold parts is added during or, preferably, after the injection of the non-cellular plastic material of the support. It is found that the parts obtained then have a porosity which is the largest on the side of the support.

  More specifically, the invention relates to a method for manufacturing a part comprising a layer of thermoplastic foam supported by a support, of the type which comprises the provision of a layer of thermoplastic foam on a surface of a mold portion, while the mold is open, closing the mold to define a cavity between the foam layer and another mold portion, and injecting into the cavity a non-cellular plastic material for to form the support; according to the invention, the method comprises, after the end of the injection of the plastic material intended to form the support, a step of progressive spacing at a predetermined speed of the two mold parts, in a direction having a component in the direction the thickness of the foam layer, with preservation of the sealing of the molding cavity.

  Preferably, the method further comprises a waiting step between the end of the injection step of the non-cellular plastic material and the step of progressive separation.

  Preferably, the step of progressive separation is carried out over a distance such that, in the finished part, the layer of foam has a thickness of between 0.5 and 1.5 times the thickness of the foam in the state free before closing the mold, and advantageously such that, in the finished part, the foam layer has a thickness that does not differ by more than 10% of the thickness of the foam in the free state before the closure of the mold .

  Preferably, the step of progressively separating the two mold parts is carried out at a speed of between 0.1 and 10 mm / s.

  The invention also relates to a damping piece having a layer of flexible thermoplastic foam disposed on a substantially rigid support; according to the invention, the foam layer has a porosity gradient between the face adjacent to the support and the opposite face, the gradient is such that the porosity decreases from the face adjacent to the support towards the opposite face.

  Preferably, the decrease in porosity corresponds to an increase in the pore size.

  Preferably, the thermoplastic material of the foam is chosen from polyolefins and polyvinyl chloride, especially polyethylene.

  Preferably, the thermoplastic foam layer has a thickness of less than 23 mm.

  Preferably, the foam further comprises a surface layer, on the opposite side of the support, and the surface layer advantageously has elastomeric properties.

  Preferably, the non-cellular plastic material of the support and the thermoplastic material of the foam layer are of the same chemical nature.

  Other features and advantages of the invention will be better understood on reading the description which follows, with reference to the appended drawing in which: FIG. 1 is a diagrammatic section illustrating the stage of the process in which the mold is closed, but the non-cellular plastic material has not yet been injected; Figure 2 is a schematic section corresponding to Figure 1, but in which the non-cellular plastic material for forming the support has been injected; and Figure 3 illustrates the next step of the method in which the two mold parts have been discarded, in the characteristic step of the invention.

  Figures 1 to 3 are very schematic views illustrating the principle of the method according to the invention, in very exaggerated form. The mold used essentially comprises a die 10 having a cavity 12, and a punch 14 having an injection channel 16. There is shown a layer 18 of foam or skin-foam complex with its normal expanded form.

  The state shown in FIG. 1 is obtained by separating the two mold parts 10, 14, by placing the foam 18, then by introducing the punch 14 into the position marked inside the matrix 10.

  FIG. 2 illustrates the step of injecting the non-cellular plastic material to form a support 20. The injected plastic material exerts a pressure which reduces the thickness of the foam 18. In the state shown in FIG. 2, the injection has just been interrupted, and the foam 18 has been compressed by injecting the non-cellular material so that its thickness has greatly decreased.

  Figure 3 illustrates the essential step of the method of the invention. The porosity of the foam 18, and therefore its damping properties, have been reduced in the step of FIG. 2, with respect to the foam introduced into the cavity of the matrix 10. In the step illustrated in FIG. , the matrix 10 is spaced from the punch 14 (or vice versa) by a distance marked with the reference 22, preferably when the injection of the non-cellular material is complete, and that this material has passed to an at least partially solidified state.

  This spacing causes an increase in thickness of the foam layer 18 in the spacing direction, that is to say horizontally in FIG. 3. According to the invention, the spacing distance is selected so that the The foam layer has a final thickness of between 0.5 and 1.5 times its initial thickness, and preferably between 0.9 times and 1 times its initial thickness, as illustrated in FIG.

  When the non-cellular plastic material is introduced for the formation of the support 20, the injected material is hot and transfers heat to the foam 18, preferably near the injected material.

  A temperature gradient is thus created between the hot plastic material of the support 20 and the mass of the mold. Accordingly, as the foam expands due to the spacing of the two mold parts shown in FIG. 3, the hottest foam portion tends to exhibit greater expansion than the less hot portion. As a result, the foam portion closest to the support 20 exhibits greater expansion and thus greater porosity than the remote foam portion of this support.

  In the conventional method in which the cooling is carried out from the state shown in FIG. 2, the part closest to the plastics material of the support 20 has undergone the greatest heating and, since it does not have the opportunity to expand later, it has the greatest compression and therefore the largest reduction in porosity. Consequently, in the molded part obtained after the step of FIG. 2, the porosity gradient of the foam layer 18 is such that the porosity increases from the support towards the surface opposite to the support. On the contrary, during the implementation of the method of the invention, this effect is at least compensated and, more often, more than compensated, that is to say reversed, so that the piece obtained has a gradient. of porosity such that the porosity is greatest near the support 20.

  As the foam layer 18 has returned to a thickness similar to that which it originally had, its damping properties are similar. It is therefore not necessary to empirically determine, for each piece shape, which type of foam to use initially to achieve the desired end properties. According to the invention, the final properties obtained with the foam layer are practically those that can be expected from the use of the initial foam.

  Shown in Figures 1 to 3, in schematic and exaggerated form, the principle of the invention. There are thus shown marginal portions of foam which undergo compression during the injection of the plastic material of the support, and which do not undergo expansion when the two mold parts are moved apart, since the thickness direction of the these foam parts is perpendicular to the direction of separation. These parts can be avoided if necessary by using a mold of suitable shape. Thus, the molds generally have relatively elaborate and complex forms, and the process of the invention is carried out in such a way that the foam resumes its original properties in substantially the regions in which these properties are present. the most important.

  It is necessary, for the implementation of the method of the invention, that the foam used is formed of a thermoplastic material, so that it can have the necessary expansion or expansion in the spacer phase. It may be polyvinyl chloride, a polyolefin, and in particular polyethylene which is well suited to this kind of this process. It is furthermore advantageous if the plastics material of the support is of a chemical nature compatible with that of the foam, and, in an ideal case, is made of the same plastic material.

  The spacing distance marked by reference 22 corresponds to the thickness recovery that is desired to give to the foam. Other parameters of the method of the invention are the moment at which the step of separating the two mold parts begins, and the spacing speed.

  It is desirable that the spacing step begins only after the end of the injection of the plastic material of the support. In the opposite case, the plastic material of the support could be introduced in excessive quantity.

  In addition, it is desirable that there is a waiting time between the end of the injection of the plastic material of the support and the start of the spacing step so that the heat of the injected plastic material is transmitted. to deeper layers of the foam and that the expanded thickness is greater.

  Finally, in order for the foam 18 to fill the gap created by the spacing step of the two mold parts, it may be desirable to use a die portion 10 having suction channels, so that the foam remains well pressed against the surface of the cavity of the die part.

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Claims (10)

  A method of manufacturing a part comprising a layer of foam (18) of thermoplastic material supported by a support (20), of the type which comprises: - the provision of a layer of foam (18) of thermoplastic material on a surface of a mold part (10), while the mold is open, - closure of the mold so that it delimits a cavity (12) between the foam layer (18) and another mold part (14) and injecting into the cavity (12) a non-cellular plastic material intended to form the support (20), characterized in that it comprises, after the end of the injection of the plastic material intended to form the carrier (20), a step of progressively moving away from the two mold parts (10, 14) in a direction having a component in the direction of the thickness of the foam layer (18), with retention sealing the molding cavity (12).   2. Method according to claim 1, characterized in that it further comprises a waiting step between the end of the injection step of the non-cellular plastic material and the step of progressive separation.   3. Method according to one of claims 1 and 2,   characterized in that the step of progressively spacing is performed over a distance (22) such that, in the finished part, the foam layer has a thickness of between 0.5 and 1.5 times the thickness of the foam in the free state before closing the mold.   4. Method according to claim 3, characterized in that the step of progressive separation is performed over a distance (22) such that, in the finished part, the foam layer has a thickness which does not differ by more than 10. % of the thickness of the foam in the free state before the closure of the mold.   5. Method according to one of the preceding claims, characterized in that the progressive step 2889100 9 of the two mold parts (10, 14) is performed at a speed of between 0.1 and 10 mm / s .   Damping member having a layer of flexible thermoplastic foam (18) disposed on a substantially rigid support (20), characterized in that the foam layer (18) has a porosity gradient between the face adjacent to the support ( 20) and the opposite face, and the gradient is such that the porosity decreases from the adjacent surface of the support (20) to the opposite face.   7. Part according to claim 6, characterized in that the decrease in porosity corresponds to an increase in the pore size.   8. Part according to one of claims 6 and 7, characterized in that the thermoplastic material of the foam (18) is selected from polyolefins and polyvinyl chloride.   9. Part according to any one of claims 6 to 8, characterized in that it further comprises a surface layer on the opposite side of the support (20).   10. Part according to any one of claims 6 to 9, characterized in that the non-cellular plastic material of the support (20) and the thermoplastic material of the foam layer (18) are of the same chemical nature.