DE102007009384B4 - Process for back-molding a film - Google Patents

Abstract

Method for back-injection with grain embossing of a film, in particular a foam film, comprising the steps: a) heating the film to the forming and grain temperature; b) placing the film between a first and a second tool half of an open tool, the second tool half having a grain at least in a partial area of its surface; c) Targeted cooling of the film in its rear area facing away from the grain, so that a temperature gradient running from the rear to the front is generated in the film, the film remaining at the grain temperature on its front; d) preforming the film by at least partially closing the tool, a contour-matched core being inserted into the first tool half for preforming the film, which core is removed after the preforming; e) suction of the film to the surface of the second tool half by applying negative pressure in the area between the surface of the second tool half and the film; f) Injecting an injection molding compound in the area between the surface of the first mold half and the film.

Description

The invention relates to a method for back-molding a film, in particular a compact film or foam film.

Interior trim parts of motor vehicles are generally produced in multiple layers in order to combine materials with good mechanical properties with materials with good optical and haptic properties. In order to connect the various layers to one another, it is known to use lamination processes. It is also known to back-inject layers with a further material.

In particular, it is known to back-inject foam sheets with a thermoplastic material. It is also known to provide the film with a grain during the back injection.

The pamphlet EP 1 284 182 A2 discloses a method and apparatus for molding parts with a molded surface structure.

The pamphlet DE 10 2004 025 571 A1 discloses such a method for producing a plastic composite molded part by back-molding a foam film. First, a foam sheet is preheated to the embossing temperature. The heated film is arranged between the tool halves of an open injection molding tool and is preformed by closing the tool and applying compressed air and then pressed against the surface of one of the tool halves. The forming of the film can be supported by applying negative pressure on the side against which the film is to be pressed. Thereafter, the foam film is back-injected with a thermoplastic material. The surface of the mold half against which the film is pressed has a grain that is transferred to the foam film when the foam film is pressed against it.

The problem, however, is that the foam film can collapse to a greater or lesser extent when the injection molding compound is back-injected due to the pressure and in particular the high temperature of the injection molding compound. This adversely affects the visual and haptic properties of the foam film and thus of the composite part.

The object of the invention is therefore to create a method for back-molding a film in which, in particular, such a collapse of a foam film is at least reduced.

This object is achieved by a method according to the independent claim.

Advantageous developments are described in the dependent claims.

The method according to the invention for back-molding a film with grain embossing comprises the steps: a) heating the film to the forming and grain temperature; b) placing the film between a first and a second tool half of an open tool, the second tool half having a grain at least in a partial area of its surface; c) Targeted cooling of the film in its rear area facing away from the grain, so that a temperature gradient running from the rear to the front is generated in the film, the film remaining at the grain temperature on its front; d) preforming the film by at least partially closing the tool; e) suction of the film to the surface of the second tool half by applying negative pressure in the area between the surface of the second tool half and the film; f) Injecting an injection molding compound in the area between the surface of the first mold half and the film.

The sequence according to the invention can in principle be used for several types of film. Single-phase foils (“compact foils”) can be used and in particular “foam foils”, that is to say in particular foils which are provided with an additional foam layer. The following statements (up to the end of this document are made using the example of foam films, but they also apply accordingly to other films, e.g. compact films.

The fact that the film is cooled from the rear and a temperature gradient running from the rear to the front is generated means that the effects of the pressure and the temperature of the injection molding compound on the foam film can be better withstood during the injection of the foam film, which at least reduces the collapse of the foam film . The fact that the front side of the foam film remains at the grain temperature ensures that a grain is formed in the foam film despite the cooling.

When partially crystalline materials are heated, the foil should be heated above the crystallite melting temperature and must not cool down below the recrystallization temperature before the tool is turned. This varies slightly from material to material and can be determined using a DSC. It is advisable to heat the compact layer to a higher temperature (approx. 200-220 ° C), as the viscosity of the film decreases as the temperature rises, thus increasing the graining capacity (the film flows better into the grain of the tool).

Amorphous materials should be heated and cooled above the melt temperature.

The step from cooling the rear area of the foam sheet to pressing the front side onto the at least partially grained surface of the second tool half is preferably carried out very quickly in order to be able to build up a high temperature difference between the front and rear side of the foam sheet and until the sheet is grained to obtain.

A TPO (thermoplastic polyolefin), PVC (polyvinyl chloride) or TPU (thermoplastic polyurethane) foam sheet is particularly suitable as the foam sheet. The grain temperatures for these films are preferably in the range of 175-220 ° C.

The foam sheets preferably have a thickness of 0.25 to 5 mm.

Thermoplastic polymers, for example PP (polypropylene) or a blend such as PC / ABS (polycarbonate / acrylonitrile-butadiene-styrene copolymer), which may contain additives such as fibers and minerals, are suitable as injection molding compounds.

In the case of ABS or ABS + PC, the decor can be protected against the higher injection pressure and the higher melt temperature compared to PP by a suitable barrier. This must allow clawing or a melt connection with the ABS or ABS + PC melt. Can be used here e.g. a needle felt or a knitted fabric made of PES or a thin ABS or ABS + PC film. The barrier is laminated onto the foam sheet before the process.

An advantageous development of the invention provides that, in order to cool the rear area of the foam film, the foam film is brought into contact with the surface of the first tool half, which is suitably tempered.

The fact that the film is cooled flat on the rear side through contact with the tempered first tool half means that the outlay on equipment remains limited. In principle, however, it is also possible to use an extra cooling element to cool the back of the foam sheet.

An advantageous development of the invention provides that the back cooling of the foam film takes place in the course of the preforming.

This makes it possible to keep the period between sufficient cooling of the rear side of the foam sheet and the introduction of the grain very short, as a result of which a relatively high temperature difference can be generated and maintained between the front and rear side of the foam sheet.

An advantageous development of the invention provides that the second tool half is tempered in such a way that the foam film is further cooled on contact with the tool half.

An advantageous development of the invention provides that the cooling of the foam film is maintained by controlling the temperature of the second mold half during the injection of the plastic melt.

An advantageous further development of the invention provides that the first tool half is heated to a temperature of at most 80 ° C., preferably at most -5 ° C., on its surface at the time at which it is brought into contact with the back of the foam film.

An advantageous development of the invention provides that the second tool half at the point in time at which it is brought into contact with the foam sheet is heated on its surface to a temperature of at most 60 ° C, preferably at most 20 ° C, and the temperature control during During injection, the plastic melt does not exceed a temperature of 100 ° C., preferably 240 ° C. (for polypropylene melts).

An advantageous further development of the invention provides that the preforming of the foam film is supported by compressed air applied to the back of the foam film and / or a slide movement of the first tool half.

In this context, a stamping movement is to be understood as the forward and backward movement of the first tool half.

Furthermore, it is provided according to the invention that a contour-matched core is inserted into the first tool half for preforming the foam film and is removed after the preforming.

Such a core enables the foam sheet to be almost completely preformed into its final shape simply by the closing movement of the tool. The core is removed after preforming.

An advantageous development of the invention provides that the plastic melt takes place in the open, in the opening, in the closing or in the closed tool.

The invention will now be explained in more detail using an exemplary embodiment.

In the exemplary embodiment described here, a composite part is produced by back-molding a foam film.

First, the foam film, here a TPO foam film with a thickness of 4 mm, is heated to a temperature of 210 ° C. by means of infrared radiation.

The heated film is arranged between a first and a second tool half of an open tool. By means of a clamping frame, the foam film is pressed all the way along its edge to the second tool half and is held in this way. Alternatively, however, it is also possible to hold it so that the foam film can slide afterwards during the subsequent preforming.

By closing the mold, the foam sheet is brought into contact with the first mold half and is preformed by the closing movement. The first half of the tool is heated to a core temperature of around 30 ° C at the time it is brought into contact with the foam film. In the course of the preforming, the foam film is thus specifically cooled in its rear region, as a result of which a temperature gradient running from the rear to the front is generated in the foam film.

The second tool half contains a shell insert which has a grain in one area. In this exemplary embodiment, the shell insert is an electroform made of nickel; the grain was produced as part of the electroforming process.

The shell insert is perforated over the entire area. A negative pressure is applied via the perforation, with which the preforming of the foam sheet is supported and the foam sheet is finally pressed against the surface of the shell insert.

In addition, it is possible to support the preforming by means of overpressure, which is applied to the back of the foam film. For example, suitable valves can be provided in the first tool half, via which compressed air can be passed in the area between the surface of the first tool half and the back of the foam sheet.

Furthermore, it is possible for the first tool half to be designed in such a way that it can execute a slide movement in order to reinforce the preforming of the foam film by its movement.

In this exemplary embodiment, the period between the contact of the first tool half with the foam sheet and the complete contact of the foam sheet with the second tool half is less than 5 s.

The shell insert of the second half of the tool is also tempered. At the point in time when the foam sheet is in contact with its surface, it has a temperature of around -5 ° C. The foam sheet is thus cooled further over its front side. Because the foam sheet is at the graining temperature directly before it comes into contact with the surface of the shell insert, the grained area of the shell insert is reflected in the front side of the foam sheet.

When the tool is closed and the foam sheet is attached, a cavity remains between the back of the foam sheet and the surface of the first tool half, which cavity corresponds to the desired shape of the carrier layer to be formed below for the foam sheet. An injection molding compound, here a PP with a proportion of reinforcing fibers, is injected into this cavity using conventional hot runner technology in the first mold half.

Alternatively, it is possible to inject the injection molding compound into an opening, a closing or an open tool.

During the injection, the temperature of the shell insert is continuously controlled so that the foam sheet is kept below the temperature at which both the compact layer can be adversely affected by the injection pressure and the melt temperature at the injection point (shine, sink marks) and the foam could collapse locally as a result. The foam or compact film can be protected against collapse locally at the injection point by means of platelets attached to the rear. This also works with conventional back injection / back injection embossing of foam films, not only with in-mold graining.

When moving with compressed air, a seal on the stenter frame should be used for sealing.

After completion of the injection process and sufficient cooling of the injection molding compound, the composite part is removed after opening the mold.

According to the invention, a core which is adapted to the shape of the desired deformation of the foam film is inserted into the first tool half and is removed after the preforming.

As an alternative to foam films, compact films can also be back-injected and grained in a similar manner.

Of course, shell inserts made of other materials, for example steel or aluminum, can also be used, or a shell insert can be dispensed with, i.e. the second tool half is directly shaped and grained. The introduction of a grain can alternatively take place, for example, by etching, eroding or mechanical processing.

Composite parts produced in this way can be used, for example, as interior trim parts of motor vehicles.

Claims (11)

Method for back-injection with grain embossing of a film, in particular a foam film, comprising the steps: a) heating the film to the forming and grain temperature; b) placing the film between a first and a second tool half of an open tool, the second tool half having a grain at least in a partial area of its surface; c) Targeted cooling of the film in its rear area facing away from the grain, so that a temperature gradient running from the rear to the front is generated in the film, the film remaining at the grain temperature on its front; d) preforming the film by at least partially closing the tool, a contour-matched core being inserted into the first tool half for preforming the film, which core is removed after the preforming; e) suction of the film to the surface of the second tool half by applying negative pressure in the area between the surface of the second tool half and the film; f) Injecting an injection molding compound in the area between the surface of the first mold half and the film. Procedure according to Claim 1 , characterized in that, in order to cool the rear region of the film, the film is brought into contact with the surface of the first tool half, which is suitably tempered. Method according to one of the preceding claims, characterized in that the back cooling of the film takes place in the course of the preforming. Method according to one of the preceding claims, characterized in that the second tool half is tempered so that the film is further cooled on contact with the tool half. Procedure according to Claim 4 , characterized in that the cooling is maintained during the injection of the injection molding compound. Method according to one of the preceding claims, characterized in that the first tool half at the time at which it is brought into contact with the rear side of the film is heated on its surface to a temperature of at most 60 ° C, preferably at most 20 ° C. Method according to one of the preceding claims, characterized in that the second tool half at the time at which it is brought into contact with the film is heated on its surface to a temperature of at most 80 ° C, preferably at most -5 ° C, and that the injection molding compound does not exceed a temperature of 240 ° C., preferably 190 ° C., during the injection. Method according to one of the preceding claims, characterized in that the preforming of the film is supported by compressed air applied to the rear side of the film and / or a slide movement of the first tool half. Method according to one of the preceding claims, characterized in that the injection molding compound takes place in the open, in the opening, in the closing or in the closed tool. Method according to one of the preceding claims, characterized in that the film has a thickness of 0.25 to 5 mm. Method according to one of the preceding claims, characterized in that the film is a compact film or a foam film, the foam film in particular being a TPO, PVC or TPU foam film.