TW201533109A - One-shot production of composites - Google Patents

Abstract

The invention relates to a process for the production of composites with a foam core of poly(meth)acrylimide (P(M)I), in particular of polymethacrylimide (PMI). A feature of this process is that the foam material is first heated in an apparatus by means of near IR radiation, is transferred to a press with heatable double-shell moulds, and is bonded there to two prepregs.

Description

One-time completion method of composite

The present invention relates to a process for the manufacture of a composite having a foam core of poly(meth)acrylonitrile imine (P(M)I), especially polymethacrylimide (PMI). The method is characterized in that the foam material is first heated in a device using near-infrared light (IR) radiation, transferred to a press having a heatable double-shell mold, and bonded to the two prepregs herein. .

The prior art has generally described various methods for the manufacture of fiber reinforced plastics having rigid foams or for the formation of rigid foam materials. In the present invention, the rigid foam means: a foam which is not subjected to mechanical deformation due to a small force and which is subsequently recovered, for example, is not a commercially available PU foam or a commercially available polystyrene foam. body. The rigid foam is, for example, in particular a PP foam, a PMMA foam or a highly crosslinked PU foam. Rigid foam material can withstand extremely high loading of the poly (meth) Bing Xixi imine (PMI), for example it is being marketed by the name ROHACELL ^® by Evonik.

A conventional method for producing the composite material is the formation of an outer layer, which is then charged with the raw material for the foam and finally foamed. A method of this type is exemplified in US 4,933,131. The disadvantage of this method is that the foaming is carried out in a very uneven manner. This is especially true for materials that can be added in particulate form at best, such as PMI. Another disadvantage of this type of method is that in order to shape a material made entirely of foam, it may be necessary to remove the outer layer again. In the case of composite components, the bond between the outer layer and the core of the foam is therefore often unsuitable for components that are subject to mechanical loads.

Passaro et al., in Polymer Composites, 25(3), 2004, pp. 307ff, describes a method in which a PP foam core material is combined with a fiber reinforced plastic in a stamper and the foam core material is This is particularly heated by the mold only on the surface to allow good bonding to the outer layer material. Grefenstein et al., in International SAMPE Symposium and Exhibition, 35 (1, Adv. Materials; Challenge Next Decade), 1990, pp. 234-44, describe a similar fabrication of sandwich materials using a honeycomb core material or a PMI foam core. method. However, these two methods do not provide any forming, but merely provide for the manufacture of sheet-shaped sandwich materials.

WO 02/098637 describes a process in which a thermoplastic outer layer material in the form of a melt is guided onto the surface of a foam core material and then molded together with the foam core by a two-piece process to obtain a composite molding, and then The thermoplastic is cooled to cure the outer layer of material. However, this method can only be combined with a limited number of materials. For example, it is impossible to manufacture warp fibers Dimensional strengthening of the outer layer material. This method is also not suitable for simple forming of a foamed workpiece without an outer layer material. In addition, the choice of the foam material is limited to materials that are elastically deformable at low temperatures. Rigid Foam In this type of process there is excessive structural damage under the foam material without uniform heating.

The method described in EP 0 272 359 is very similar. Here, the foam core preform is first cut into shape and placed in a mold. The thermoplastic melt is then injected onto the surface. The foam core preform is then foamed by increasing the temperature, and this foaming creates a pressure on the surface of the outer layer material. What is true is that this method allows the surface to achieve better adhesion to the outer layer of material. However, this method is relatively complicated with the otherwise initial forming operation and is generally significantly more limited in the achievable shape.

W. Pip, Kunststoffe, 78 (3), 1988, pp. 201-5 describes a process for producing a molded composite having a fiber-reinforced outer layer and having a PMI foam core in a stamper. In a heated stamper, the method is combined with individual layers wherein some micro-forming is achieved in the locally heated foam material via compaction of the uppermost layer. The shape of the method also described can be formed by post-foaming in the mold. The disadvantages of this type of method have been discussed above. The elastic compression of the material in the method disclosed as the third variation is carried out during compression of the preheated foam material. This preheating is carried out in a furnace. Then, the disadvantage of this method is that many foam materials require extremely high temperatures for the deformation process of the thermoplastic. For example, a PMI foam requires a temperature of at least 185 °C. In addition, the core material must have been properly heated over the entire area of the material to avoid breakage in the material. crack. However, it is only possible to achieve this type of temperature by heating for many minutes, especially with a uniformly distributed temperature, and many outer layer materials such as PP are damaged to such an extent that the method does not work.

U. Breuer, Polymer Composites, 1998, 19(3), pp. 275-9 discloses a third variant of the method that is slightly modified by Pip for the PMI foam core. Here, the PMI foam core and the fiber-reinforced outer layer material are heated by an IR heating lamp. These IR radiant heaters in particular emit light having a range of from 3 to 50 microns (IR-C radiation or MIR radiation) and are particularly suitable for rapid heating of the substrate. However, the energy introduced here (desirably) is extremely high and at the same time causes damage to many outer layers of material, such as PP. Breuer et al. therefore again reveal that only nylon-12 (PA12) is a possible matrix material for the outer layer. The PA 12 can be easily heated to above 200 ° C without any damage to the plastic. It is not possible in this procedure to simultaneously shape the foam core because the heat radiated by the IR radiation zone does not penetrate into the foam matrix and thus does not reach the thermoplastic moldable state.

In view of the prior art discussed, it is therefore an object of the present invention to provide a novel method which can easily and at a high throughput rate to produce a composite having a P(M)I foam core without The core of the bubble has structural damage.

In particular, it is an object of the present invention to provide a method for manufacturing the composite by forming while relatively freely selecting the surface material Material, and does not cause any damage during processing.

Another intent is that the novel method is capable of achieving fast cycle times well below 10 minutes, regardless of the individual specific examples listed for the purpose.

Other objects not explicitly discussed at this point may be derived from the prior art, the description, the patented scope or examples.

Achieving the purpose

The term poly(meth) acrylimide in the following refers to polymethacrylimide, polypropylene quinone, and mixtures thereof. Corresponding considerations apply to the corresponding monomers such as (meth) acrylimide and (meth)acrylic acid. For example, the term (meth)acrylic refers not only to methacrylic acid, but also to acrylic acid and mixtures of the two.

These objects utilize a foam core having a rigid foam (especially a foam core made of P(MI), preferably a foam core made of PMI). A novel manufacturing method for composite materials is achieved. Particularly preferred is that the foam material of the foam core is a PMI foam having a density in the range of 25 to 220 kg/m 3 . The method of the present invention can process not only P(M)I, but also rigid foam made of polypropylene (PP) or made of highly crosslinked polyurethane (PU) for compounding. A foam core is produced in the material.

PP foams are especially known as insulating materials, in transport containers and as interlayer materials. The PP foam may comprise a filler and is commercially available with a density in the range of from 20 to 200 kg/m3.

Compared with the flexible PU foam, the rigid PU foam is characterized by a more closed pore structure and a higher degree of crosslinking. Rigid PU foams may also contain a relatively large amount of inorganic filler.

The method for producing a composite material having a second outer layer and a foam core disposed between the two layers is characterized in particular by the following steps: a) heating the foam with near-infrared light radiation (NIR radiation) in a heating unit a core, b) transferring the heated foam core to a press using a conveyor having a moving frame, c) closing the press, wherein the press comprises a double shell mold and each of the mold shells has been Covered by a fibrous substrate or a prepreg cover composed of a fiber material or a resin, d) heating the mold shells to a curing temperature of the resin, and e) cooling the mold shells to a mold release temperature and f The press is opened and removed from the composite.

In step a), the foam core is inserted into the active portion of the heating field of the heating unit of the machine. NIR radiation having a wavelength of 0.78 to 1.40 microns is particularly suitable for step a). In procedures which have proven to be particularly suitable for this, the foam core has been clamped in the delivery device during this heating.

The intensity and time of the radiation are here dependent on different factors and can be optimized in some experiments by those skilled in the art. These heating parameters depend on the softening point of the foam material used, the pore size or density of the material, the thickness of the material, and the distance of the source of radiation from the core of the foam. One The factors that generally increase the radiation intensity are: increased material robustness, higher material density, greater material thickness, and greater distance of the source of radiation from the core of the foam. The intensity of the radiation can be varied as the desired shape changes. In this connection, the radiant intensity is generally adjusted to reach a temperature of 170 to 250 ° C in the center of the foam core.

Preferably, the heating unit has a plurality of NIR light sources such that the surface of the foam core is uniformly heated. The foam core is thus heated to the plasticizing temperature of the foam material. Surprisingly, it has been found that the non-invasive heating of step a) allows the plastic to be deformed via uniform heat introduction without any incidental damage to the material. Properly performing the method does not particularly cause damage to the surface of the rigid foam, which can be observed, for example, during heating in the furnace. The heat radiated in the NIR spectral region used passes through the gas phase of the chamber without absorption and direct heating of the chamber wall matrix occurs. Particularly surprisingly, it has been found here that this type of NIR radiant heating achieves a particularly uniform heat distribution even in relatively thick foam cores.

In step b), the heated bulb core is transferred to the press for transfer using a conveyor having a moving frame. The delivery device typically has a linear motor drive. Preferably, when the foam core is moved into the heating unit, it has been clamped in a holding frame that connects the movable frame. In particular, it must be noted that during this delivery the foam core as a whole is still above the plasticizing temperature. This can be achieved by using a short distance between the heating unit and the press or/and by using a moderately high ambient temperature in this zone (for example in a hood) or by using another NIR radiation source. .

In step c), the preforming of the heated foam core may optionally be carried out using compressed air prior to closing the press. This can lead to even better results, especially in the case of composite components with high curvature.

In step c), the press is then closed, and the press has a double-shell mold, and the two mold shells each have a prepreg transparent sheet or a fiber-matrix sheet composed of a fiber material and a resin, respectively. cover. The shape of the double-shell mold here influences the composite component during the pressing process.

In a first variant of the invention, the prepreg constitutes the material of the outer layer. The prepreg system consists of at least one resin and one fibrous material, wherein the fibrous material is in turn composed of long fibers, usually in the form of a woven, knitted or laid roving or in the form of a non-oriented layer.

Particularly good mechanical strength values can be obtained with materials of those types.

Another feature of the prepreg is that although it is suitable for storage and processing, it has not yet been hardened. Only after the forming method, or in the case of the present invention, the prepreg is hardened (usually by introducing heat) after the forming method and while joining the foam core.

In a second variant of the invention, it is also possible to use a sheet molding compound (SMC) instead of the prepreg as an outer layer material. These SMCs are characterized in that they are composed of at least one resin, short fibers, and inorganic fillers. The short fibers are freely dispersed in the resin here. These SMCs are more functional and easier to manufacture in the molding process than prepregs.

Whether using prepreg or SMC, the special resin that can be used is B. Ester resin, epoxy resin, isocyanate resin and acrylate resin. The prepreg is usually made of epoxy resin as the substrate, but the SMC mainly contains a vinyl ester resin.

The fibers may in particular be carbon fibers, glass fibers, polymer resins or polyarsenamide fibers. SMC mainly uses short glass fibers here.

It is also possible to use an adhesion promoter to improve the adhesion between the foamed new material and the outer layer. The adhesion promoter may be present in the matrix material of the outer layer. In an alternative possibility, the adhesion promoter is applied to the surface of the outer layer or to the surface of the foam core prior to bonding of the materials. It is also possible to use a suitable adhesive in this procedure. Special adhesion promoters which have proven to be suitable are polyamines and poly(meth)acrylates. However, it is also possible to use low molecular weight compounds known to those skilled in the art of composite manufacturing, especially those required for the matrix materials used in the outer layer.

Preferably, the prepreg or SMC material forming the transparent sheet is positioned between the two mold halves in the clamping frame. In an alternative form, the material is secured in the device using a stacked fastener frame to avoid slippage. To this end, the material to be treated, for example, protrudes by more than a few centimeters of the edge of the die, and in this zone the material is driven downwards by means of the stacked fastener frame.

In step d), after the press has been closed and after the resulting forming process has been carried out, the shells are heated to the curing temperature of the resin. Due to the direct contact between the mould shells and the outer layer material, it is possible here to achieve an extremely rapid hardening of the resin. The temperature used to cure the hardening of the resin It depends on the particular resin used and can be readily determined by those skilled in the art. These temperatures are usually from 100 to 300 °C. In particular, the preferred temperature (170 to 250 ° C) for foaming of the foam core is also suitable for most resin systems. In the less preferred case of higher necessary temperatures, the curing of the resin can be achieved in another heating unit.

In step e), the form is then cooled to a demold temperature. In an example of a method for achieving this cooling, the form has a tube for a cooling liquid (for example for water) inside or on a face facing away from the workpiece. The demolding temperature is herein material dependent and can be readily determined by those skilled in the art. He first depends on the plasticity of the core of the foam and depends primarily on the surface properties of the outer layer of material. At the demolding temperature, the material should be strong and exhibit minimal adhesion to the surface of the mold. Suitable release temperatures can be, for example, generally higher than 80 °C. In order to improve the cycle time, this temperature can be additionally increased by applying a release aid between the outer layer and the form. For example, polyoxyphthalic oils or aliphatic oils can be used as the release aid.

Finally, in step f), the press is opened, the moving frame is withdrawn and the product removed. In another alternative possibility, the composite is first removed and the moving frame is then withdrawn for insertion of new material.

The method according to the invention has in particular the main advantages that it can be carried out in very short cycle times and can therefore be used in mass production with excellent results. Preferably, the process is carried out with a cycle time of up to 10 minutes, preferably less than 6 minutes.

The method parameters selected for the overall method of the present invention will depend on the system used in the individual case and its design, and will also depend on the materials used. Those skilled in the art can easily decide with some preliminary experiments.

In an alternate embodiment, the process of the invention can also be carried out in a vacuum or at subatmospheric pressure using a twin-sheet method. The design of the two-piece device is here to make it a compression molding machine.

An essential feature of the two-piece process is that two or more workpieces are molded in a vacuum or under subatmospheric pressure in one step and thus fused to one another without the addition of additives such as adhesives, auxiliary fused materials or solvents. This step can be done in a cost-effective and environmentally friendly manner with short cycle times. Surprisingly, it has been found that for the purposes of the present invention, this method can also be used for the above rigid foaming due to the additional step of preheating the workpiece via irradiation of NIR radiation having a wavelength of 0.78 to 1.40 micrometers in step b). The treatment of the bulk material, which is clearly unsuitable in accordance with the prior art. Due to the relatively rapid heating by the use of said radiation, a uniform stress-free heat distribution is achieved throughout the workpiece. The intensity of the radiation varies within the stated range depending on the requirements of the foam material used. When the outer layer material is additionally used, the temperature of the heating field and its strength are improved so that the foam core and the outer layer material are jointly subjected to foaming and bonding treatment even at different processing temperatures and molding temperature conditions. Suitable modifications of this type can be readily accomplished by some experimentation by those skilled in the art.

A great advantage of the method of the invention is that it can be carried out in an environmentally friendly manner and in a very short cycle time, while combining multiple operations into one method.

Surprisingly, the outer layer material can be selected relatively freely. Here, for example, the material may simply be a thermoplastic, or a woven or knitted fabric or a composite of these, examples being known as organic panels or plastic coated textile carrier webs, such as synthetic leather. Preferably, the outer layer material is a fiber reinforced plastic. The fibers may, for example, be polyarylene fibers, glass fibers, carbon fibers, polymer fibers or textile fibers. The plastic may preferably be in the form of PP, polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), epoxy resin, isocyanate resin, acrylate resin, polyester or polyamide.

P(M)I, especially PMI, is here a preferred material for the core of the foam. These P(M)I foams are also referred to as rigid foams and are characterized by particular robustness. The P(M)I foam is generally produced in a two-stage process: a) the manufacture of a cast polymer and b) the foaming of the cast polymer.

The casting polymer is produced starting from a monomer mixture comprising (meth)acrylic acid and (meth)acrylonitrile (preferably a molar ratio of 2:3 to 3:2) as a main component. It is also possible to use other co-monomers such as esters of acrylic or methacrylic acid, styrene, maleic acid or itaconic acid, or anhydrides thereof, or vinylpyrrolidone. However, the ratio of such comonomers should not be more than 30% by weight here. It is also possible to use a small amount of crosslinking monomer, such as allyl acrylate. However, the amount should preferably be at most from 0.05% by weight to 2.0% by weight.

The copolymerization mixture also contains a blowing agent which decomposes or evaporates at a temperature of from about 150 to 250 ° C and thus forms a gas phase. The polymerization is below this Occurs at temperatures and the cast polymer thus contains a potential blowing agent. This polymerization is advantageously carried out in a block mould between two glass sheets.

In the second step, the foaming of the cast polymer is then carried out at a suitable temperature. The production of these PMI foams is known in principle from the person skilled in the art and can be found, for example, in EP 1 444 293, EP 1 678 244 or WO 2011/138060. Special mention may be made of PMI foam is available from Evonik Industries AG level of ROHACELL ^®. The acrylonitrile imide foam can be considered to be similar to the PMI foam in terms of production and handling. However, for toxicological reasons, acrylonitrile imide foams are significantly less preferred than other foam materials.

The desired foam portion can be produced by a suitable selection using a glass plate or by a manufacturing method using in-mold foaming. In an alternative, the products are made from a foamed sheet by a cutting, sawing or grinding process. It is more likely here to cut a plurality of bubble portions from one piece.

The density of the rigid foam material can be selected relatively freely. For example, a PMI foam having a density in the range of 25 to 200 kg/m 3 can be used.

The advantage of sawn, cut or ground foam core fragments compared to fragments made by in-mold foaming is that they have openings on the surface. When the material is brought into contact with the resin-impregnated fiber, some of the resin which has not yet hardened penetrates into the opening in the surface of the core of the foam. This has the advantage that the hardening produces a particularly strong bond on the boundary between the foam and the sheathing material.

The present invention not only provides the method described, but also provides a method by which the method can be Made of composite materials. These composite materials have a rigid foam core made of foamed PP, P(M)I or highly crosslinked PU and two outer layers made of at least one hardened resin and one fibrous material. In contrast to this prior art, these composite materials differ in that they are composed of a hardened prepreg material or a hardened SMC material and do not contain connecting elements such as seams, bolts or other guiding forces. The components. The composite material of the present invention may also differ in that it is not required to have a binder layer between the foam core and the outer layer material.

The workpiece of the invention made of a rigid foam as a core material is in principle diverse.

The composite material produced in accordance with the invention is particularly useful, for example, in the following mass production: body construction or interior in the automotive industry, in railway vehicles or ship construction, aerospace industry, mechanical engineering, furniture construction or wind turbines. Internal parts.

A‧‧‧heating period

B‧‧‧forming

(1)‧‧‧IR heating system

(2) ‧ ‧ shell mold in the press

(3) ‧ ‧ foam core

(4) ‧‧‧Prepreg in the clamping frame

(5) ‧‧‧Composites made of foam core and two hardened prepregs

Figure 1: Manufacturing diagram of the composite component of the present invention.

Some specific examples of the invention are provided below. These also contain examples. The corresponding experimental system was successfully completed.

Example: Fabrication of fiber-reinforced plastic (composite components) with a foam core

The process is carried out in a machine for a two-piece forming process, an example being T8 from Geiss AG. Here, the machine is configured as follows: a heating field with a flash source (NIR; 0.78 to 1.40 microns)

Adjustable operating room window

Adjustable height above heating system

Compressive force 30 metric tons (minutes), motor driven

Heatable and cooled forming die

Figure 1 is cited to illustrate this specific example.

A ROHACELL ^® IG PMI foam having a density of 71 kg/m 3 and a thickness of 12.7 mm was used.

The method parameters to be selected depend on the system design used in any particular case. He must decide by using preliminary experiments. The guiding temperature T _F depends on the T _g (S) of the PMI foam matrix, the temperature of the outer layer in the forming method, and the height adjustment of the upper heating system T _g (S) ≦ T _F (the upper heating system temperature) And set. The rule here is that the temperature of the upper heating system must be adjusted upward as the difference from the temperature of the foam matrix increases. It is also possible to vary the source field strength (I) in relation to the degree of formation (U _g ) of a partial location of the component. In the edge location near the overlapped fastener, the selected source field strength is close to 100% in order to ensure continuous flow of the material while holding the material.

Outer layer: For example, it is possible to use a drapable knit/laying gauze or a composite material which has been manufactured from a very wide variety of fiber types or fiber mixtures and which already contains a thermoplastic phase. This can optionally use a hot melt adhesive film or a corresponding non-woven fabric as an adhesion promoter. In this particular example, on A layer of organic panels (Tepex® Dynalite 102-RG600) from Bond Laminates having a thickness of 800 microns was used below. In another example, a Lexan polycarbonate film having a thickness of 1500 microns was used on both sides.

The foam core to be subjected to the molding method is heated in the heating unit to an internal temperature of 220 ° C by IR radiation, and then moved into the stamper. The outer layer preform has been placed on the inner region of the stamper. The stamper was then closed and heated to a temperature of 180 °C.

After about 3 to 4 minutes, the mold was cooled to below 80 ° C and the assembly was removed. Once the mold has been reheated, the next composite assembly can be fabricated.

(1)‧‧‧IR heating system

(2) ‧ ‧ shell mold in the press

(3) ‧ ‧ foam core

(4) ‧‧‧Prepreg in the clamping frame

(5) ‧‧‧Composites made of foam core and two hardened prepregs

Claims (12)

A method for producing a composite material having two outer layers and a foam core disposed between the outer layers, wherein the foam material of the foam core is a highly crosslinked PU, PP or P ( M) I, and the method has the steps of: a) heating the foam core with near-infrared radiation (NIR radiation) in a heating unit, b) foaming the heated foam by means of a conveyor having a moving frame Transferring the core to the press, c) closing the press, wherein the press comprises a double-shell mold and each of the two mold shells has been covered by a fibrous substrate or a prepreg cover each composed of a fibrous material or a resin Covering, d) heating the mold shells to the curing temperature of the resin, e) cooling the mold shells to a demolding temperature, and f) opening the mold and removing the composite material. The method of claim 1, wherein the wavelength of the NIR radiation is from 0.78 to 1.40 microns. The method of claim 1, wherein the foam material is a PMI foam having a density ranging from 25 to 220 kg/m 3 . The method of claim 1, wherein the pre-molding of the heated foam core is carried out using compressed air immediately before or after step c). The method of claim 1, wherein the outer layer is a prepreg composed of at least one resin and one fibrous material. The method of claim 5, wherein the fiber is in the form of a knit, a knit or a laid scrim or in the form of a non-oriented layer. The method of claim 1, wherein the outer layer is a sheet molding compound (SMC) composed of at least one resin, short fibers, and a mineral filler. The method of claim 5, wherein the resin is a vinyl ester resin, an epoxy resin, an isocyanate resin or an acrylate resin. The method of claim 5, wherein the fiber is carbon fiber, glass fiber, polymer fiber or polyamine fiber. The method of any one of claims 1 to 7, wherein the method is carried out with a cycle time of up to 10 minutes. A composite material having a rigid foam core made of foamed PP, P(M)I or a highly crosslinked PU, and a second made of at least one hardened resin and a fibrous material An outer layer, characterized in that it can be manufactured by a method as claimed in at least one of claims 1 to 10, and the composite material does not have a connecting member such as a seam, a bolt or other force introducing element. A composite material according to claim 11 which has no adhesive layer between the core of the foam and the outer layer.