Method for producing fiber-reinforced plastic parts, and fixing by means of a double-sided adhesive layer

Abstract

In a method for producing fiber-reinforced plastic parts in a mold and an adhesive layer for carrying out the method, the adhesive layer adhesive force on the mold is greater than the adhesive layer adhesive force on the segment, so that, after a first segment is removed, the adhesive layer remains completely in the mold and after the temperature of the adhesive layer is increased through contact with a melted plastic matrix, the remaining adhesive force is sufficient to adhere at least a second segment. The adhesive layer, introduced into the mold relatively expensively, and removed from the mold and disposed of at further expense, is used repeatedly, not just for a single adhesion operation. The expense for procuring the adhesive layer, its introduction into the mold, removal and disposal remains but through its division over numerous production operations, the total expenditure proportion for each operation decreases dramatically.

Claims

1. A method for producing fiber-reinforced plastic parts in a mold, the method comprising: fixing a first segment of a first flexible strip made of fiber-plastic composite material to a surface of the mold using an adhesive layer between the first segment and the mold, wherein the adhesive layer is spaced apart from all peripheral edges of the first segment and the adhesive force of the adhesive layer on the mold is greater than the adhesive force of the adhesive layer on the first segment, lifting the first segment off the mold, the adhesive layer remaining completely in the mold after the first segment has been lifted off, heating the adhesive layer by contact of the first segment with a melted plastic matrix, and after the heating of the adhesive layer, adhering at least a second segment of a second flexible strip made of fiber-plastic composite material to the surface of the mold using the remaining adhesive force of the adhesive layer.

2. The method according to claim 1, further comprising: locating the adhesive layer on a carrier foil and introducing the adhesive layer on the carrier foil into the mold, wherein the adhesive layer on the carrier foil has an adhesive power low enough for the carrier foil to act as a mechanical carrier for the adhesive layer during introduction of the adhesive layer on the carrier foil into the mold, and pulling the carrier foil off the adhesive layer, the adhesive layer hereby remaining at least for the most part in the mold.

3. The method according to claim 1, further comprising locating the adhesive layer on the first segment and introducing the adhesive layer on the first segment into the mold.

4. The method according to claim 3, wherein the adhesive layer is covered by a protective foil prior to introduction of the adhesive layer on the first segment into the mold.

5. The method according to claim 1, wherein the adhesive layer covers only part of the area of the first segment.

6. The method according to claim 1, wherein, after the first segment has been lifted off, a cleaning compound is injected into the mold, wherein the adhesive layer builds an adhesive force to the cleaning compound that is higher than the adhesive force between the adhesive layer and the mold.

Description

(1) Further details and features of the invention are explained in more detail below on the basis of an exemplary embodiment. This intends merely to explain, not to restrict, the invention. The following is shown in schematic representation:

(2) FIG. 1 a section of an injection mold with segments, glued therein, of a flexible strip made of fiber-plastic composite material

(3) FIG. 2 a curved segment with adhesive layer and protective foil

(4) FIG. 1 shows, as a perspective view, the corner part of an injection mold 2 that serves to produce a molded part F, shown by a dotted line. At the shown corner, said molded part F is provided with a short support column F1, extending horizontally and to the left, which support column is molded in the recess 21 of the injection mold 2. From the recess 21, the concave transition to the rear wall of the injection mold 2 is shown by hatching in FIG. 1.

(5) If forces that are oriented transverse to the longitudinal axis act on the end of the support column F1 shown far left, the support column F1 is particularly stressed at its transition points to the remaining region of the molded part F. In this exemplary embodiment, to avoid tearing of the plastic material in this critical connection zone of the support column F1 to the rest of the molded part F, five segments 1 of a flexible strip made of fiber-plastic composite material are also molded-in.

(6) Of these, the two segments 1 that can be seen on the left are drawn in section, so that the fibers extending therein more or less in the longitudinal direction of the segment 1 become visible. The respective adhesive layers 3, which fix the two segments 1 on the inner surface of the injection mold 2, are also drawn in section.

(7) In FIG. 1, it is easy to comprehend that, before the molded part F is molded, the segments 1 must be fixed with sufficient adhesive force on the inner surface of the injection mold 2. The adhesive force must not only be sufficient to ensure that the segments 1 remain in the required position with the required accuracy, but also that they adhere to the surface of the injection mold 2 over as large an area as possible, in particular in the curved regions, so that they withstand the surge from the wave of the injected liquid plastic for the molded part F.

(8) To this end, adhesive layers 3 ensure the adhesion of the segments 1 to the injection mold 2. They are shown in FIG. 1 with a very great material thickness, so that they can be recognized. In practice, however, they will merely be a film that is so thin that it is hardly identifiable as a separate layer, and thus also does not leave behind any notch in the surface of the molded part F. Both adhesive layers 3 consist of permanently sticky hot-melt adhesives with differing adhesive forces, wherein the adhesive layer facing the segment 1 has a lower adhesive force than the adhesive layer facing the injection mold 2. The former is, for example, an adhesive layer on the basis of thermoplastic rubber, the latter is an adhesive made of synthetic rubber. The configuration of the material of the adhesive layers required for this is carried out, according to the current prior art, on the basis of catalogs and technical data from the adhesive manufacturers, depending on the materials of the injection mold, the plastic of the fiber-reinforced segment as well as under consideration of the selected maximum temperature for the processing operation.

(9) In FIG. 1, it is clear to see that the segments 1 can be fixed on flat parts of the injection mold 2 just as well as on curved parts. In particular, the flexible segments 1 can also be arranged in a twisted manner. Through the application of multiple adjacent segments 1, larger reinforcements of the molded part F can be formed.

(10) FIG. 2 shows a segment 1 that is already curved to the extent required for application onto a convex curvature of the injection mold 2. On its side facing the injection mold 2, said segment is provided with an adhesive layer 3. Said adhesive layer is covered with a protective foil 4 to prevent it from being touched prior to the adhesion, and thus becoming unusable. FIG. 2 shows the state shortly before introduction of the segment 1 into the injection mold 2, wherein the protective foil 4 has started to be pulled off.

(11) For practical trials, a matrix of polypropylene with a material thickness of 0.2 mm was introduced into an injection mold made of tool steel with a synthetic rubber coating of the surface as an adhesive layer. A segment of a plastic strip made of PP, which was reinforced with numerous fibers made of carbon, was fixed in the injection mold on the adhesive layer and injected into the surface of a molded part made of fiberglass-reinforced polypropylene. Before the first injection operation, the adhesive force between the adhesive layer and the surface of the injection mold was 1.4 times greater than the adhesive force between the adhesive layer and the segment. After the first injection molding at a temperature of 235 degrees and the removal of the finished molded part together with the segment molded thereon, the adhesive layer remained completely in the injection mold. The adhesive force between the adhesive layer and the injection mold subsequently fell, but was still 1.2 times greater than the adhesive force between the adhesive layer and the next segment glued into the injection mold.

(12) With every further injection molding and every further new segment of the strip made of fiber-plastic composite material glued into the injection mold, the absolute values for the adhesive forces fell by 2 percent, but the respective adhesive force between the injection mold and the adhesive layer was still greater than the adhesive force between the adhesive layer and the segment. Herein, the latter adhesive force was sufficient not just to hold each new segment in the mold prior to injection molding for a total of 75 injection operations, but also to prevent the respective segment from slipping during injection molding. For the 24 next injection molding operations, the stuck-on segment was in each case displaced only by up to 1 mm, i.e. around 8 percent of the width of the strip.

(13) After up to 400 injection molding operations, the adhesive force of the adhesive layer was no longer sufficient to glue a further segment into the mold and hold it there in a defined manner during the injection molding. The adhesive layer then had to be removed from the mold.

LIST OF REFERENCE SIGNS

(14) F Molded part is reinforced by the molding-in of segments 1 in the injection mold 2 F1 Support column on molded part F 1 Segment of a flexible strip of fiber-plastic composite material 2 Injection mold for molded part F 21 Recess in the injection mold 2 for shaping the support column F1 3 Adhesive layer between injection mold 2 and segment 1 4 Protective foil 4 on adhesive layer 3