WO2025017216A1

WO2025017216A1 - Method of manufacturing a composite part comprising a core and a skin region

Info

Publication number: WO2025017216A1
Application number: PCT/EP2024/070785
Authority: WO
Original assignee: Mitsubishi Chemical Advanced Materials GmbH; MCPP Innovation LLC
Current assignee: Mitsubishi Chemical Advanced Materials GmbH; MCPP Innovation LLC
Priority date: 2023-07-20
Filing date: 2024-07-22
Publication date: 2025-01-23
Anticipated expiration: 2026-01-20

Abstract

A method of manufacturing a composite part (2) comprising a core (4) and a skin region (6) formed of a skin polymer attached thereto, comprises the following steps: a) providing a core element (8) having a surface with at least one upper contacting region having a plurality of anchoring sites (10); b) applying onto the contacting region a layer (12) of the skin polymer in granular form, whereby skin polymer granules contact and embed the anchoring sites; c) applying a heating step whereby the skin polymer granules are molten to form a molten skin polymer matrix (18); d) applying a pressing and cooling step, whereby the skin polymer matrix solidifies to form a skin region (6) mechanically engaged into the anchoring sites of the core element forming the core.

Description

Method of manufacturinq a

a core and a skin reqion

Field of the Invention

The present invention relates to a novel method of manufacturing a composite part comprising a core and a skin region formed of a skin thermoplastic polymer attached thereto.

Background of the Invention

A notorious challenge arising in the manufacture of plastics containing composite parts is to properly join adjacent layers of different materials. Evidently, such adjacent layers can be neighboring layers within a composite part, also called "core layers", or they can be a surface layer, also called "skin layer", adjacent to a core layer. By "properly join" it is meant that the involved layers shall be joined in a reliable manner, i.e. without subsequent tendency to delaminate, and without adversely influencing the inherent properties of the involved materials. A further requirement for any such manufacturing processes is that they should be as simple and energy efficient as possible.

One important type of composite parts are automotive interior parts comprising a comparably stiff core, acting as a rigid carrier, provided with a comparably flexible and/or soft skin. An example for this are vehicle trim panels, door panels, dashboards, instrument panels, etc. as discussed, e.g., in WO 2017/046166 A1 and in references cited therein. Such parts are generally not planar, but rather have a stiff core with a three-dimensionally shaped surface. To achieve a contact across the entire surface, it is necessary that an adjacent skin layer has a corresponding three-dimensional shape.

A method and an apparatus for manufacturing thin-walled hollow shells for parts such automotive door panels, controls and instrument panels is slush molding. An alternative to slush molding includes deep drawing of a flexible foil or sheet into the desired shape. A useful material for the skins of high-end soft-touch car interior surfaces is polyvinyl chloride (PVC), which is directly available in powder form for use in slush molding. A possible alternative to PVC would be a styrenic block copolymer based thermoplastic elastomer (TPE-S), which, however, has to be cryogrinded into powder form.

An early patent relating to a method and an apparatus for manufacturing thinwalled hollow shells by slush molding is US 4,562,025. As summarized in WO 2017/046166 A1 , one starts with a box filled with a particulate PVC compound positioned beneath and locked to a heated mould , which will supply powder to the mould. The mould is repeatedly inverted to melt powder onto the hot mould surface and sintering of the particles is induced by heat. After the PVC particles have sintered together, a sheet of plasticized PVC is formed, the sheet or skin is cooled and removed from the mould.

Presently, a process for manufacturing interior parts is based on a three-step process of polyurethane (PU) backfoaming, which involves injection molding of carrier, i.e. core slush (rotational) molding of PVC powder to form a skin joining skin and carrier with a PU foam layer.

An alternative three-step process based on laminating involves injection molding of carrier, i.e. core separate production of skin as a preformed foil joining skin and carrier by gluing, namely with spray glue.

While the above methods have been proven to work, they have certain disadvantages.

In the case of PU backfoaming, the used PU material is impossible to recycle, poses health and safety problems and involves a complicated technology. The slush molding step is energetically very intensive, as it involves a 50 - 240 - 50 ^QC temperature cycle. The necessary equipment comprises: an injection molding machine and related tools a slush molding machine and related tools a PU backfoaming machine and related tools

Moreover, there is only a limited adhesion between PU foam and skin. This may cause ballooning during high temperature airbag deployment.

In the case of lamination, the use of spray glue also poses health and safety problems related to the formation of VOC and odor. The necessary equipment comprises: an injection molding machine and related tools a lamination equipment to apply spray glue and skin.

It would thus be desirable to provide an improved method of manufacturing composite parts comprising a mechanically performant core and at least one skin region made of a thermoplastic polymer attached to a face region of the core.

In particular, it would be desirable to eliminate the use of spray glue or polyurethane foaming from the process reduce the number of production equipment components and required tooling thus providing investment advantages eliminate the injection molding step eliminate the PU mixing unit, high pressure mixing chamber and related tooling eliminate the slush molding step ln comparison with slush molding, it should be possible to implement a more favorable temperature cycle, basically using a a 50 - 190 - 50 ^QC temperature cycle instead of a 50 - 240 - 50 ^QC. Most desirably, it should be possible to produce a part combining structural rigidity with a high-quality surface finish in one processing step.

Summary of the Invention

The present invention reduces the above-mentioned disadvantages and provides the above-mentioned desirable advantages. It also provides further advantages as mentioned further below.

According to the invention, there is provided a method of manufacturing a composite part comprising a core and at least one skin region formed of a skin polymer attached thereto, the method comprising the following steps: a) providing a core element having a surface with at least one upper contacting region having a plurality of anchoring sites; b) applying onto the contacting region a layer of the skin polymer in granular form, whereby skin polymer granules contact and embed the anchoring sites; c) applying a heating step whereby the skin polymer granules are molten to form a molten skin polymer matrix; d) applying a pressing and cooling step, whereby the skin polymer matrix solidifies to form a skin region mechanically engaged into the anchoring sites of the core element forming the core; wherein either

(i) the core element is provided as a blank of a thermoplastic fleece with reinforcement fibers that are predominantly oriented in an orientation direction z perpendicular to the core element surface; or else

(ii) the core element is provided as a continuous sheet of a thermoplastic fleece with reinforcement fibers, wherein the heating step c) and the pressing and cooling step d) are carried out continuously in a double band press; wherein the thermoplastic fleece consists of a core thermoplastic polymer, and wherein cavernous surface structures of the thermoplastic fleece and/or surface portions of the reinforcement fibers act as said anchoring sites, the heating step c) also causing melting of the core thermoplastic polymer, whereby the core element is formed to the core.

A further advantage of the above method is a weight saving without loss of stiffness.

The method of the present invention is advantageously implemented according to either one of following three principal embodiments.

According to a first embodiment (claim 2), the core element is provided as a blank of a thermoplastic fleece with reinforcement fibers that are predominantly oriented in an orientation direction z perpendicular to the core element surface, and wherein the pressing and cooling step is carried out in a tool in a press. The term "blank" shall be understood as piece or section of the respective material, e.g. a substantially rectangular plate. The heating step c) can be carried out e.g. in an infrared heater, but preferably a contact heater is used in which the above-mentioned blank covered with a layer of skin polymer in granular form is placed on a heater plate. Thereafter, the heated blank is transferred into a press provided with a pressing tool where step d) is carried out. As will be understood, the tool can be configured with planar faces for production of planar, "2D" composite parts, or it can have appropriately configured faces for production of non-planar, "3D" composite parts. The press with tool are configured in such manner that a pre-selected thickness of the pressed composite part is obtained. The term "pre-selected thickness" refers either to the constant thickness of a 2D composite part or to the variable thickness of a 3D composite part.

Inventors have found that by virtue of using predominantly z-oriented reinforcement fibers, a favorable counter-force is exerted by the core element against the compressive force applied during the pressing step, which leads to an improved contact between the skin and the core.

According to a second embodiment (claim 3) and to a third embodiment (claim 4), the core element is provided as a continuous sheet of a thermoplastic fleece with reinforcement fibers, wherein the heating step c) and the pressing and cooling step d) are carried out continuously in a double band press. An appropriate double band press, which has a first pressing stage which is heated followed by a second pressing stage which is cooled, has been described e.g. in US 8540830 B2. In the present case, a layer of skin polymer in granular form is applied onto the continuous sheet of a thermoplastic fleece with reinforcement fibers before entry into the double band press.

According to the second embodiment, the composite part is then obtained by cutting sections of a continuous pressed sheet obtained in said pressing and cooling step d). In other words, the desired, "final" composite part is directly taken after the pressing and cooling step performed in the double band press. This embodiment has the advantages of simplicity and substantially uninterrupted operability. However, it will be understood that only 2D composite parts can be formed in this manner. The degree of consolidation of the core element can be defined within a certain range by appropriately setting the distance between pressing elements in the second stage of the double band press.

In contrast, according to the third embodiment, the composite part is obtained by a sequence of steps carried out after exiting from the double band press. Specifically, this comprises

(1 ) cutting sections of a continuous pressed sheet obtained in said pressing and cooling step d),

(2) optionally storing said sections,

(3) subjecting said sections to a further heating step whereby the skin polymer matrix and said core thermoplastic polymer are molten, (4) applying a further pressing and cooling step in a tool in a press, thereby forming said composite part.

As will be understood, this third embodiment combines some of the features of the first and second embodiments. In simple words, the double band pressing method of the second embodiment is used to form sections of pressed preforms of the desired composite part. Either in a direct next step or after temporary storage, the preforms are then subjected to a further heating followed by a further pressing and cooling step in a tool in a press. This latter step offers the above-mentioned possibilities of 2D- and 3D-forming.

Advantageously (claim 5), in step b), the layer of skin polymer in granular form is applied with a predefined distribution of grain size, starting with comparatively small sized granules near the upper contacting region of the core element and ending with comparatively large sized granules or even with a foil of skin polymer further away from the upper contacting region. For example, the small sized granules may have an average diameter of about 150 pm and the large sized granules may have an average diameter of about 300 pm.

According to another embodiment (claim 6), the method further comprises an embossing step carried out on the skin region.

The core thermoplastic polymer can be selected from a variety of known polymers such as e.g. polyamide (PA), polypropylene (PP), polyphenylene sulfide (PPS), polyetherimide (PEI) and polyetheretherketone (PEEK), but also acrylonitrile styrene acrylate (ASA) and acrylonitrile butadiene styrene (ABS). The melting temperature of the core thermoplastic polymer should be sufficiently low so that the press heating, which is conducted at a temperature adapted to the skin polymer, leads to melting of the core thermoplastic polymer. For example, if using PVC or TPE-S as skin polymer, suitable core polymers appear to be PP or else ASA or ABS.

The actual choice of skin polymer and core polymer will depend on the application. For airplane interiors, a preferable core polymer would be PPS whereas for automotive interiors this could be PP. For aerospace applications, the use of PEI- PEEK combinations or PPS-PEI combinations is preferable.

In certain embodiments using UHMWPE as skin polymer, the suitable core polymers notably include PP.

According to one embodiment (claim 7), the core thermoplastic polymer is polypropylene, preferably a polypropylene with a melt flow index MFI (230°C, 2.16kg) of 1 to 1000, preferably of 10 to 300 g/10min.

As also known in the field of fiber reinforced thermoplastics, the reinforcement fibers can be selected from a large variety, including but not limited to glass fibers, carbon fibers, aramid fibers and basalt fibers. Alternatively, the reinforcement fibers may be made of a high-melting thermoplastic, i.e. from a material that does not melt at the processing temperatures of the heat pressing step. According to an advantageous embodiment (claim 8), the reinforcement fibers are glass fibers, carbon fibers or recycled carbon fibers.

As also known from the field of fiber reinforced thermoplastics, the core element formed of a thermoplastic fleece with reinforcement fibers may comprise structural reinforcement elements. Therefore, according to one embodiment, the core element further comprises at least one reinforcement layer. In certain embodiments, the reinforcement layer is selected from a fabric, a multiaxial stitch or unidirectional reinforcement.

Selection of the skin polymer depends on the intended application. According to one embodiment (claim 9), the skin polymer is ultra-high molecular weight polyethylene (UHMWPE). Due to its comparatively rigid structure, UHMWPE as skin polymer is mainly useful for manufacturing flooring panels, panels for use in wet environments and for certain panels in recreational vehicles.

According to another embodiment (claim 10), the skin polymer is polyvinyl chloride (PVC). This material is readily available in powder or granular form for use in slush molding. In certain embodiments, customized PVC granules having a diameter in the range of 50 to 250 pm which are coated with one or more of a stabilizer package, a mould release agent, pigments, and a drying agent and/or which contain a plasticizer are used.

According to a further embodiment (claim 11 ), the skin polymer is a styrenic block copolymer based thermoplastic elastomer (TPE-S). TPE-S is typically a soft elastomeric material, consisting of SBS/SEBS block copolymers, mineral oils, polyolefins, and stabilizers. The styrenic blocks build rigid domains which provide the required mechanical properties, whereas the ethylene-butadiene blocks make up the elastomeric core. They are melt processable along similar conditions as polyolefins. TPE-S materials typically show rubbery properties, are resistant to high and low temperatures, easy to color, provide good adhesion to polyolefins, and are easy to recycle.

According to certain embodiments (claim 12), the skin polymer granules contain a blowing agent. The use of blowing agents as tear promoters in thermoplastic skin layers produced by slush molding is basically known, e.g. from WO 2017/046166 A1 and in references cited therein. In the context of the present invention, the inclusion of a blowing agent into the skin polymer granules leads to an expansion of the skin during the heating step, thereby reducing the skin density and providing a light-weight, soft-touch solution. According to certain embodiments (claim 13), the method further comprises a step of forming a texture onto an exposed face region of the skin surface. By "exposed face region" is meant a face region of the skin surface directed away from the core.

According to yet another embodiment (claim 14), the composite part is a vehicle interior component, particularly a dashboard, instrument panel, trim panel, or door panel.

Brief description of the drawings

The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 shows an installation for carrying out a first embodiment of the present invention, in a schematic, perspective view;

Fig. 2 shows a core element with a molten skin polymer matrix, after heating step c), in an enlarged schematic perspective view;

Fig. 3 shows an installation for carrying out a second embodiment of the present invention, in a schematic, perspective view; and

Fig. 4 shows an additional installation for carrying out a third embodiment of the present invention, in a schematic, perspective view.

Detailed description of the invention

It will be understood that the figures are not necessarily drawn to scale. In some instances, relative dimensions are substantially distorted for ease of visualization. Identical or corresponding features in the various figures will generally be denoted with the same reference numerals.

A first embodiment of the invention is illustrated in Figs. 1 and 2. The production of a composite part 2 comprising a core 4 and a skin region 6 formed of a skin polymer attached thereto starts by providing a core element 8 having a surface with an upper contacting region that has a plurality of anchoring sites 10. In the example shown here, the core element 8 is a blank of a thermoplastic fleece with reinforcement fibers that are predominantly oriented in an orientation direction z perpendicular to the core element surface. For simplicity, the anchoring sites are depicted as simple protrusions of the core element's upper surface. A layer 12 of the skin polymer in granular form is then applied onto this contacting region by means of a dispenser 14, whereby skin polymer granules contact and embed the anchoring sites 10.

The skin polymer loaded core element 8 is subsequently transferred into a heater device 16, which in this example is a contact heater with a pair of hot plates. A heating step is then carried out whereby the skin polymer granules are molten to form a molten skin polymer matrix 18.

The composite object thus formed is transferred to a press 20 equipped with a suitable tool 22. Here, a pressing and cooling step is carried out, whereby the skin polymer matrix solidifies to form skin region 6 mechanically engaged into the anchoring sites of the core element 8 now forming the core 4.

In the example shown in Figs. 1 and 2, the core element 8 is a blank of a thermoplastic fleece f with reinforcement fibers r that are predominantly oriented in an orientation direction z perpendicular to the core element surface.

The second and third embodiments are illustrated in Figs. 3 and 4. In this case, the core element is provided as a continuous sheet 24 of a thermoplastic fleece with reinforcement fibers. A heating step and a following step of pressing and cooling are carried out continuously in a double band press 26. Before entering the double band press, a layer 12 of the skin polymer in granular form is applied onto the sheet 24 by means of a dispenser 14, whereby skin polymer granules contact and embed the anchoring sites 10.

According to the second embodiment, the composite part 2 is obtained by cutting sections 28 of a continuous pressed sheet 30 obtained in the pressing and cooling by the double band press.

In the example shown in Fig. 3, an embossing step can be applied to the sheet 30 exiting from the double band press 26 by means of an embossing roll 32.

According to the third embodiment, the composite part 2 is obtained by a sequence of steps carried out after exiting from the double band press 26. As in the second embodiment, this comprises cutting sections 28 of the continuous pressed sheet 30. After optional storage, the sections 28 are subjected to a further heating step in an oven 16 whereby the skin polymer matrix and the core thermoplastic polymer are molten. A further pressing and cooling step is then carried out in a tool 22 of press 20, thereby forming the composite part 2.

In all of the above-described embodiments, the thermoplastic fleece consists of a core thermoplastic polymer, wherein cavernous surface structures of the thermoplastic fleece and/or surface portions of the reinforcement fibers act as anchoring sites. The heating step also causes melting of the core thermoplastic polymer, whereby the core element 8 is transformed into the core 4.

Claims

1 . A method of manufacturing a composite part (2) comprising a core (4) and a skin region (6) formed of a skin polymer attached thereto, the method comprising the following steps: a) providing a core element (8) having a surface with at least one upper contacting region having a plurality of anchoring sites (10); b) applying onto the contacting region a layer (12) of the skin polymer in granular form, whereby skin polymer granules contact and embed the anchoring sites; c) applying a heating step whereby the skin polymer granules are molten to form a molten skin polymer matrix (18); d) applying a pressing and cooling step, whereby the skin polymer matrix solidifies to form a skin region (6) mechanically engaged into the anchoring sites of the core element forming the core; wherein either

(i) the core element (8) is provided as a blank of a thermoplastic fleece (f) with reinforcement fibers (r) that are predominantly oriented in an orientation direction (z) perpendicular to the core element surface; or else

(ii) the core element is provided as a continuous sheet (24) of a thermoplastic fleece with reinforcement fibers, wherein the heating step c) and the pressing and cooling step d) are carried out continuously in a double band press (26); wherein the thermoplastic fleece consists of a core thermoplastic polymer, and wherein cavernous surface structures of the thermoplastic fleece and/or surface portions of the reinforcement fibers act as said anchoring sites, the heating step c) also causing melting of the core thermoplastic polymer, whereby the core element is formed to the core.

2. The method according to claim 1 , wherein the core element is provided as a blank of a thermoplastic fleece (f) with reinforcement fibers (r) that are predominantly oriented in an orientation direction (z) perpendicular to the core element surface, and wherein the pressing and cooling step is carried out in a tool (22) in a press (20).

3. The method according to claim 1 , wherein the core element is provided as a continuous sheet (24) of a thermoplastic fleece with reinforcement fibers, wherein the heating step c) and the pressing and cooling step d) are carried out continuously in said double band press (26), wherein said composite part

(2) is obtained by cutting sections (28) of a continuous pressed sheet obtained in said pressing and cooling step d).

4. The method according to claim 1 , wherein the core element is provided as a continuous sheet (20) of a thermoplastic fleece with reinforcement fibers, wherein the heating step c) and the pressing and cooling step d) are carried out continuously in said double band press (26), wherein said composite part is obtained by

(1 ) cutting sections (28) of a continuous pressed sheet obtained in said pressing and cooling step d),

(2) optionally storing said sections (28),

(3) subjecting said sections (28) to a further heating step whereby the skin polymer matrix and said core thermoplastic polymer are molten,

(4) applying a further pressing and cooling step in a tool (22) in a press (20), thereby forming said composite part (2).

5. The method according to one of claims 1 to 4, wherein, in step b), the layer (12) of skin polymer in granular form is applied with a predefined distribution of grain size, starting with comparatively small sized granules near the upper contacting region and ending with comparatively large sized granules away from the upper contacting region.

6. The method according to one of claims 1 to 5, further comprising an embossing step carried out on the skin region (6).

7. The method according to one of claims 1 to 6, wherein the core thermoplastic polymer is selected from polypropylene, PEI, and PPS.

8. The method according to one of claims 1 to 7, wherein the reinforcement fibers are glass fibers, carbon fibers or recycled carbon fibers.

9. The method according to one of claims 1 to 8, wherein the skin polymer is ultra-high molecular weight polyethylene (UHMWPE).

10. The method according to one of claims 1 to 8, wherein the skin polymer is PVC.

11 . The method according to one of claims 1 to 8, wherein the skin polymer is TPE-S.

12. The method according to claim 10 or 11 , wherein said skin polymer granules contain a blowing agent.

13. The method according to one of claims 10 to 12, further comprising a step of forming a texture onto an exposed face region of the skin surface.

14. The method according to one of claims 1 to 13, wherein the composite part is a vehicle interior component.