WO2015071155A1

WO2015071155A1 - One-shot manufacturing of composites

Info

Publication number: WO2015071155A1
Application number: PCT/EP2014/073876
Authority: WO
Inventors: Rainer Zimmermann
Original assignee: Evonik Industries Ag; ZIMMERMANN, Cornelia
Priority date: 2013-11-15
Filing date: 2014-11-06
Publication date: 2015-05-21
Also published as: DE102013223353A1; TW201533109A

Abstract

The invention relates to a method for manufacturing composites with a poly(meth)acrylimide (P(M)I), more particularly polymethacrylimide (PMI), foam core. The method is characterised in that the foam material is first heated in an apparatus using near-IR radiation, and is transferred to a press having heatable two-shell tools where it is joined to two prepregs.

Description

One-shot production of composites

FIELD OF THE INVENTION The invention relates to a process for the production of composites with a

Poly (meth) acrylimide (P (M) I), especially a polymethacrylimide (PMI) foam core. The method is characterized in that the

Foamed material is first heated in a device by means of near infrared radiation, transferred to a press with heatable clamshell tools and is connected there with two prepregs.

PRIOR ART Various processes for the production of fiber-reinforced plastics with a rigid foam or for the shaping of hard materials are known in the art

Foamed materials in general. In the context of this invention, rigid foams are understood as meaning foams which can not be mechanically deformed with low forces, such as commercially available PU or polystyrene foams, and then reset again. Examples of rigid foams are, in particular, PP, PMMA or highly crosslinked PU foams. A particularly strong resilient hard foam material is poly (meth) acrylimide (PMI), as sold Zürn example from Evonik under the name ROHACELL ^®.

A well-known method for producing described

Composite materials is the shaping of the cover layers with subsequent filling of the foam raw material and its final foaming. Such a method is described for example in US 4,933,131. A disadvantage of this method is that the foaming is usually very uneven. This is especially true for materials such as PMI, which can be added as granules at best. Another disadvantage of such a method is that for

Shaping a pure foam material that removes cover layers again would have to be. In the case of composite components, in turn, the adhesion between the outer layers and the foam core is often not sufficient for mechanically stressed components.

In Passaro et al., Polymer Composites, 25 (3), 2004, p. 307ff a method is described in which a PP foam core material is combined with a fiber-reinforced plastic in a pressing tool and thereby the foam core material by means of the tool targeted only at the surface is heated to allow a good bond to the cover material. In Grefenstein et al., International SAMPE Symposium and Exhibition, 35 (1, Adv. Materials: Challenge Next Decade), 1990, p.234-44 is an analogous process for producing sandwich materials with a honeycomb core material or a PMI foam core described. A shaping is not possible with these two methods, but only the production of sandwich materials in sheet form.

WO 02/098637 describes a process in which a thermoplastic cover material is melt-applied to the surface of a foam core material, then molded together with the foam core into a composite molding by means of a twin-sheet process, and then the thermoplastic is cooled in such a way. that the cover material solidifies in the mold. However, only a limited number of materials can be combined with this process. For example, fiber-reinforced cover materials can not be produced. Also, the method for the mere shaping of a foam workpiece is without

Cover materials not applicable. Furthermore, the selection of the

Foam materials limited to elastically deformable materials at low temperatures. A hard foam would be without such a procedure

uniform heating of the foam material structurally too damaged.

Very similar is the method described in EP 0 272 359. Here is in

Foam core blank first cut into shape and placed in a tool.

Subsequently, the melt of the thermoplastic material is injected onto the surface. By raising the temperature, the foamed core blank is foamed thereon, which results in pressing on the surface of the covering material. Although it can be achieved with this method better adhesion to the cover material. For this is the method with the additional step of first shaping consuming and much more limited in terms of realizable forms.

In W. Pip, Kunststoffe, 78 (3), 1988, p.201 -5 a process for the production of molded composites with fiber-reinforced cover layers and a PMI foam core in a press tool is described. In this method, the merging of the individual layers takes place in a heated pressing tool, wherein a slight shaping is carried out by compressing the uppermost layers in the locally heated foam material. At the same time, a method is described in which a mold can be formed by re-foaming within the tool. The disadvantages of such a method have already been discussed previously. As a third variant, a method is disclosed in which an elastic compression of the material during the pressing of a preheated

Foam material takes place. The preheating takes place in an oven. Disadvantage of this method, however, is that very high temperatures are required for thermoelastic deformation for many foam materials. For example, temperatures of at least 185 ° C are required for PMI foams. Furthermore, the core material must be heated over the entire material area accordingly, in order to avoid material fractures. However, at such temperatures, especially as they are possible in the uniform distribution only with a longer heating time of several minutes, many covering materials, such as e.g. PP, so damaged that the process is not feasible.

U. Breuer, Polymer Composites, 1998, 19 (3), pp. 275-9 discloses a slightly modified process of the previously discussed third variant of Pip for PMI foam cores. Here, the heating of the PMI foam core and the fiber-reinforced cover materials takes place by means of an IR heat lamp. Such IR radiant heaters, which radiate mainly light with wavelengths in the range between 3 and 50 μιτι (IR-C, or MIR radiation) are particularly well suited for rapid heating of the substrate. However, the energy input - if desired - is very high, which at the same time leads to the damage of many cover materials, such as the PP example. Thus, in Breuer et al. also only polyamide 12 (PA12) as a possible matrix material for the

Cover layers disclosed. PA 12 can be easily heated to over 200 ° C without damaging the plastic. A simultaneous Shaping the foam core is not possible in this procedure, since the heat radiation of the IR radiation range does not penetrate into the foam matrix and thus no thermoplastic moldable state is achieved.

task

Against the background of the prior art discussed, it was therefore an object of the present invention to provide a novel process by means of which composite materials with a P (M) I foam core can be produced easily and with high throughput speed without structural damage to the foam core.

In particular, it was an object of the present invention to provide a method for

At the same time, the choice of the surface material is relatively freely selectable, without this being damaged during processing.

Furthermore, independent of the individual tasks

Embodiments with the novel method fast cycle times of significantly less than 10 min to be feasible.

Other, not explicitly discussed at this point, may be further from the prior art, the description, the claims or

Embodiments result. solution

In addition, the term poly (meth) acrylimide means polymethacrylimides, polyacrylimides or mixtures thereof. The same applies to the corresponding monomers such as (meth) acrylimide or (meth) acrylic acid. Thus, for example, the term (meth) acrylic acid is understood to mean both methacrylic acid and acrylic acid and mixtures of these two.

The objects are achieved by a novel process for the production of composite materials with a foam core of a hard foam, in particular with a foam core of P (MI), preferably with a foam core of PMI.

Particularly preferably, it is in the foam material of the

Foam core around a PMI foam in a density range of 25 to 220 kg / m ³ .

In addition to P (M) I can also rigid foams made of polypropylene (PP) or highly crosslinked polyurethane (PU) to foam cores in

Composite materials are processed.

PP foams are known above all as insulation material, in transport containers and as sandwich material. PP foams can contain fillers and are usually commercially available in a density range between 20 and 200 kg / m ³ . PU rigid foams in turn are distinguished from PU flexible foams by a more closed pore structure and a higher degree of crosslinking. PU rigid foams may additionally contain larger amounts of inorganic fillers.

The inventive method for producing composite materials with two outer layers and a foam core lying between them is characterized in particular by the following process steps: a) heating the foam core in a heating station with near infrared radiation (NIR radiation), b) transferring the heated foam core into a press by means of a transport device with a travel frame, c) closing the press, wherein the press has a two-shell mold and both tool shells are each covered with a fiber matrix or prepreg cover layer composed of a fiber material and a resin, d) heating the tool shells to the curing temperature of the

Resin, e) cooling the tool shells to a demolding temperature and f) opening the press, moving out the travel frame and removing the composite material.

In process step a), the foam cores are inserted into the machine-side effective range of the heating fields of the heating station. With regard to process step a), in particular NIR radiation with a wavelength between 0.78 and 1.40 μm is suitable. It proves to be particularly favorable if the foam core is already clamped in the transport device during the heating process.

The radiation intensity and duration are dependent on various factors and can be optimized for the skilled person with a few experiments. Thus, these heating parameters are dependent on the softening temperature of the foam material used, the pore size or material density, the material thickness and the distance of the radiation sources to the foam core. The radiation intensity usually has to be increased with stronger materials, a higher material density, a larger material thickness and a greater distance to the radiation sources. Furthermore, the radiation intensity can be varied depending on the degree of transformation to be achieved. The radiation intensity is usually adjusted so that in the middle of the foam core, a temperature between 170 and 250 ° C is achieved. Preferably, the heating station has a plurality of NIR light sources, so that the

Surface of the foam core is heated evenly. In this way, the foam core is heated to the plasticizing temperature of the foam material.

Surprisingly, it has been found that by the gentle heating of the material in process step a) a plastic deformability by a uniform

Heat input can be brought about without at the same time causing damage to the material. In particular, the e.g. Damage to the hard foam surface observed upon heating in an oven is maintained

appropriate implementation of the present proceedings. The thermal radiation of the NIR spectral range used penetrates the gas phase of the

Foam cells without absorption and causes a direct heating of the cell wall matrix. Particularly surprisingly, it was found that a particularly uniform heat distribution can be achieved in thicker foam cores by such heating with NIR radiation. The transfer of the heated foam core in a press in process step b) by means of a transport device with travel frame. As a rule, this transport device is provided with a linear motor drive. Preferably, the foam core is already entering the heating station in one with the

Tray frame connected clamping frame clamped. In particular, care must be taken that the foam core remains completely above the plasticization temperature during this transport. This can be achieved by a short path between the heating station and the press or additionally by a correspondingly high ambient temperature on this route, e.g. within an enclosure or by additional NIR radiation sources. Before the press is closed in process step c), it is optionally possible to

Preform the heated foam core by means of compressed air. This can lead to even better results, especially for composite components with a strong curvature.

In process step c) followed by the closing of the press, wherein the press has a two-shell tool and both tool shells each with a

Prepreg or fiber matrix cover layer composed of a fibrous material and a resin, are occupied. In this case, the two-shell tool has a shape that acts predeterminably on the composite component during the pressing.

In a first variant of the present invention, the material of the cover layers is prepregs. Prepregs consist at least of a resin and a fiber material, wherein the fiber material again consist of long fibers, which are usually in the form of a fabric, knitted fabric, scrim or as an unidirectional (non-directional) layer. With such materials, particularly good mechanical strengths can be achieved.

Furthermore, prepregs are characterized by the fact that, although they are in a storable and processable form, they have not yet hardened. Only after the molding, or in the case of the present invention after the

Forming and the simultaneous connection with the foam core, the prepregs - usually by heat - hardened.

In a second variant of the present invention, as an alternative to the prepregs, sheet-molding compounds (SMC) can also be used as the material of the cover layer. These SMCs are characterized by the fact that they consist of at least one resin, short fibers and mineral fillers. The short fibers are distributed freely in the resin. Such SMCs are more variable to form than prepregs and easier to manufacture. Regardless of whether prepregs or SMCs are used, the resin used may be, in particular, vinyl ester resins, epoxy resins, isocyanate resins or acrylate resins. Prepregs are usually based on epoxy resins, while SMC contain predominantly vinyl ester resins.

The fibers may in particular be coal, glass, polymer or

Aramid fibers act. Most SMC uses short glass fibers.

In addition, adhesion promoters can be used to improve adhesion between the foam core material and cover layers. These adhesion promoters can be contained in the matrix material of the cover layers. Alternatively, the adhesion promoters also be applied to the surface of the outer layers or the foam core before merging. Alternatively, suitable adhesives may be used in this procedure. In particular, polyamides or poly (meth) acrylates have proven to be suitable as adhesion promoters. However, it is also possible to use low molecular weight compounds which are known to the person skilled in the art from the preparation of composite materials, in particular as a function of the matrix material used for the covering layer.

Preferably, the cover sheet forming prepreg or SMC material is positioned in a tenter between the tool halves. Alternatively, the material is fixed in the device by means of a hold-down frame to prevent slippage. For this purpose, the material to be processed is e.g. a few inches above the edge of the tool and is in this area by means of the mentioned

Press down pressed down frame.

In process step d) takes place as after closing the press and thereby taking place shaping a heating of the tool shells on the

Curing temperature of the resin. Due to the direct contact between the

Tool shells and the cover material can be done very fast curing of the resin. The temperature used to cure the resin will depend on the particular resin used and will be readily apparent to those skilled in the art. As a rule, such temperatures are between 100 and 300 ° C. This is

especially preferred for the foaming of the foam core

Temperatures between 170 and 250 ° C suitable for most resin systems. For the less preferred case of a higher required temperature, the curing of the resin may be carried out in another heating station. In process step e) there is a cooling of the tool shells on a

Demolding temperature instead. This can be done, for example, in that the tool shells in the interior or on the side facing away from the workpiece with tubes for a cooling liquid, e.g. are equipped for water. The

Demolding temperature is material-dependent and easy to determine for the expert. It depends on the one hand on the plasticity of the foam core and primarily on the surface properties of the cover material. This should be at the Deformation be firm and have the least possible stickiness to the surface of the tool shells. A suitable

For example, demolding temperature may already be below 80 ° C.

By applying a demolding aid between outer layers and tool shells, this temperature can be additionally increased to improve the cycle times. As demolding aids, for example

Silicone oils or aliphatic oils come to the rescue.

Finally, in process step f), the opening of the press, the retraction of the travel frame and the removal of the product take place. Alternatively, it is also possible first to remove the composite material and then to move back the process frame in order to be replaced.

The inventive method has the particular advantage that it can be carried out with very low cycle times and thus can be used very well in a series production. The process is preferably carried out with a cycle time of at most 10 minutes, preferably less than 6 minutes.

For the entire process according to the invention are to be selected

Process parameters according to the system used in each case and their

Design, as well as the materials used. You can by few

Preliminary tests are easily determined for the expert.

In an alternative embodiment, the inventive method can also by means of a twin-sheet method under vacuum or under reduced pressure

be performed. The twin-sheet device is designed such that it can be used as a press molding machine. The twin-sheet process is basically characterized by the fact that two or more workpieces in a single step in the vacuum or under reduced pressure deformed and thereby without additives such as adhesives, welding aids or

Solvents are welded together. This process step is to be carried out in short cycle times, economically and environmentally friendly. As part of the The present invention has surprisingly been found that this method by the additional process step of preheating the workpieces by irradiation with NIR radiation having a wavelength between 0.78 and 1, 40 μιτι in

Process step b) also for the processing of the above

Hard foam materials that seemed to be unsuitable according to the prior art, can be used. Due to the relatively fast feasible heating with said radiation a stress-free, uniform heat distribution throughout the workpiece is achieved. The intensity of the radiation can be varied depending on the used foam material in said range. With additional use of cover materials, the temperature of the heating fields and their intensity are modified so that even with different

Processing and molding temperatures Foam core and cover materials are molded and bonded together. Such adjustments are easily feasible for the skilled person with a few attempts.

A great advantage of the method according to the invention is that it can be carried out in an environmentally friendly manner and in very short cycle times while at the same time

Summary of several steps in a process.

Surprisingly, the choice of the cover material is relatively free. These may be, for example, pure thermoplastics, woven or knitted fabrics or composites thereof, e.g. so-called organo sheets or plastic-coated textile carrier webs such as e.g. Imitation leather act. The cover material is preferably a fiber-reinforced plastic. The fibers may in turn be, for example, aramid, glass, carbon, polymer or textile fibers. The plastic, in turn, may preferably be PP, polyethylene

(PE), polycarbonate (PC), polyvinyl chloride (PVC), an epoxy resin, an isocyanate resin, an acrylate resin, a polyester or a polyamide.

A preferred material for the foam core is P (M) I, in particular PMI. Such P (M) I foams are also referred to as rigid foams and are characterized by a particular strength. The P (M) I foams become normally produced in a two-stage process: a) production of a cast polymer and b) foaming of this cast polymer.

To prepare the cast polymer, monomer mixtures which contain (meth) acrylic acid and (meth) acrylonitrile, preferably in a molar ratio of between 2: 3 and 3: 2, as main constituents, are first prepared. In addition, other comonomers may be used, such as e.g. Esters of acrylic or methacrylic acid, styrene, maleic acid or itaconic acid or their anhydrides or vinylpyrrolidone. However, the proportion of the comonomers should not be more than 30% by weight. Small amounts of crosslinking monomers, e.g. Allyl acrylate, can also be used. However, the amounts should preferably be at most 0.05% by weight to 2.0% by weight.

The mixture for the copolymerization further contains blowing agents which are in

Temperatures of about 150 to 250 ° C either decompose or evaporate and thereby form a gas phase. The polymerization takes place below this temperature, so that the cast polymer contains a latent blowing agent. The polymerization suitably takes place in block form between two glass plates.

In a second step, the temperature then takes place at a corresponding temperature

Foaming the cast polymer. The preparation of such PMI foams is basically known to the person skilled in the art and can be read, for example, in EP 1 444 293, EP 1 678 244 or WO 201 1/138060. As PMI foams in particular ROHACELL ^® types of the company Evonik Industries AG may be mentioned.

With regard to production and processing, acrylimide foams are to be regarded as analogues for the PMI foams. For toxicological reasons, however, these are much less preferred than other foam materials. The required foam parts can be produced by a suitable choice of the glass plates or by a production by means of an in-mold-foaming. Alternatively, the production of foamed foam plates by cutting, sawing or milling. In this case, preferably several foam parts can be cut from a plate. The density of the rigid foam material is relatively freely selectable. For example, PMI foams can be used in a density range of 25 to 220 kg / m ³ .

Sawn, cut or milled foam core pieces have the advantage over in-mold foaming produced that they have open pores on the surface. When contacted with the resin impregnated fibers, a portion of the uncured resin penetrates into these open pores at the

Foam core surface. This has the advantage that after curing a particularly strong adhesion at the interface between the foam core and

Jacket material is obtained.

In addition to the method described are also by means of the method

producible composite materials part of the present invention. These

Composite materials comprise a hard foam core of foamed PP, P (M) I or highly crosslinked PU and two outer layers of at least one cured resin and a fiber material. Compared to the state of the art, these composite materials differ in that the cover layers consist of a cured prepreg or SMC material and have no connecting elements such as seams, bolts or other force introduction elements. In addition, the composite materials according to the invention may differ in that they need not have an adhesive layer between foam core and cover materials.

Basically, the workpieces of the invention are made of a rigid foam as a core material very widely used.

Composite materials prepared according to the invention can in particular

Application in mass production e.g. for body shop or for

Interior linings in the automotive industry, interior parts in rail vehicles or shipbuilding, in the aerospace industry, in mechanical engineering, in the automotive industry

Find furniture or in the construction of wind turbines. Lettering of the drawing

Fig. 1: Schematic representation of the production of composite components according to the invention

A: heating-up phase; B: shaping (1) IR heaters

(2) cup tools of the press

(3) foam core

(4) Prepregs in the tenter

(5) Composite material of foam core and two cured prepregs

embodiments

In the following, general descriptions are shown for some particular embodiments of the invention. They also contain examples.

Corresponding experiments were successfully carried out.

Example: Production of fiber-reinforced plastics with foam core

(Composite components)

The process is carried out on a twin-sheet forming machine such as model T8 from Geiss AG. The machine was equipped in the following configuration:

Heating fields with flash emitters (NIR, 0.78-1, 40 μηη)

Adjustable workspace window

Height-adjustable upper heating Pressing force 30 to (min.), Motorized drives Heating and cooling forming tool

To illustrate this embodiment, reference is made to FIG.

It is used a PMI foam of the type ROHACELL ^® IG in the density of 71 Kg / m ³ and the thickness of 12.7 mm.

In general, the process parameters to be selected depend on the design of the system used in each case. They must be determined by preliminary tests. Thus, the guide temperature T _F depends on the T _g (S) of the PMI foam matrix, after the forming temperature of the cover layers, after the

Height adjustment of the upper heater T _g (S) <T _F (temperature of the upper heater). It is important that the temperature of the upper heater is set higher, the greater the distance to the foam matrix. Depending on the degree of deformation (U _g ) of the partial

Component areas, the radiator field intensity (I) can be varied. Near the edge of the hold-down, the radiator field intensity I near 100% is chosen to be a

Ensuring the flow of material and at the same time maintaining the clamping of the material.

Circulation of the cover layers: It is possible, e.g. drapeable fabric / scrim or made of different fiber types or fiber blends composite materials are used, which are equipped with thermo-plastic phases. This can optionally be done using a melt adhesive film or web as

Bonding agents take place. In concrete example, an 800 μm thick layer of organo-sheet from Bond Laminates (Tepex® Dynalite 102-RG600) was used at the top and bottom. In another example, polycarbonate film Lexan in the thickness 1500 μιτι was used on both sides The reshaped foam core is heated in the heating station by means of IR radiation to an internal temperature of 220 ° C and then moved into the press tool. On the two inner surfaces of the pressing tool said cover sheet blanks are placed. Subsequently, the pressing tool is closed and heated to a temperature of 180 ° C. After about 3 to 4 minutes, the tool is cooled to below 80 ° C and the component is removed. After a reheating of the tool, the production of the next composite component can begin.

Claims

claims

1 . A process for producing composite materials having two outer layers and an intermediate foam core, characterized in that the foam material of the foam core is highly cross-linked PU, PP or P (M) I, and the process is as follows

Process steps comprises: a) heating the foam core in a heating station with near infrared radiation (NIR radiation), b) transferring the heated foam core in a press by means of a transport device with travel frame, c) closing the press, wherein the press comprises a two-shell tool and both tool shells are each covered with a fiber matrix or prepreg cover layer composed of a fiber material and a resin, d) heating the tool shells to the curing temperature of the

Resin, e) cooling the tool shells to a demolding temperature and f) opening the press and removing the composite material.

2. The method according to claim 1, characterized in that the NIR radiation has a wavelength between 0.78 and 1, 40 μιτι,

3. The method according to any one of claims 1 or 2, characterized in that it is the foam material is a PMI foam in a density range of 25 to 220 kg / m ³ .

4. The method according to any one of claims 1 to 3, characterized

in that directly before or directly after process step c)

Preform the heated foam core by means of compressed air.

5. The method according to any one of claims 1 to 4, characterized in that it is the cover layer is a prepreg, which consists of at least a resin, and a fiber material.

6. The method according to claim 5, characterized in that the fibers in the form of a fabric, knitted fabric, scrim or as an unidirectional layer.

7. The method according to any one of claims 1 to 4, characterized

characterized in that the cover layer is a sheet-molding compound (SMC) consisting of at least one resin, short fibers and mineral fillers.

8. The method according to any one of claims 5 to 7, characterized in that it is the resin to a vinyl ester resin, an epoxy resin, a

Isocyanate resin or an acrylate resin.

9. The method according to any one of claims 5 to 7, characterized in that the fibers are carbon, glass, polymer or aramid fibers.

10. The method according to any one of claims 1 to 9, characterized

characterized in that the method is performed with a cycle time of at most 10 minutes.

1 1. Composite material comprising a rigid foam core made of foamed PP, P (M) I or highly cross-linked PU and two outer layers of at least one cured resin and a fiber material, characterized

in that it can be produced by means of a method according to at least one of claims 1 to 10, and that the composite material does not have any connecting elements such as seams, bolts or others

Having force introduction elements.

12. Composite material according to claim 1 1, characterized in that

this has no adhesive layer between the foam core and cover layers.