EP2470351A1

EP2470351A1 - Fibre-reinforced polyurethane moulded part comprising three-dimensional raised structures

Info

Publication number: EP2470351A1
Application number: EP10751805A
Authority: EP
Inventors: Stephan Schleiermacher; Roger Scholz; Hans-Guido Wirtz; Klaus Franken
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2009-08-26
Filing date: 2010-08-17
Publication date: 2012-07-04
Also published as: WO2011023322A1; JP2013503211A; RU2012111120A; CN102574335A; KR20120089840A; US20120148803A1; CA2769884A1; BR112012004110A2; MX2012002237A

Abstract

The invention relates to a fibre-reinforced polyurethane moulded part which has structures such as ribs, struts or domes, said structures being likewise fibre-reinforced.

Description

FIBER-REINFORCED POLYURETHANE FORMAT WITH THREE-DIMENSIONAL LEVERAGE

STRUCTURES

The present invention is a fiber-reinforced polyurethane molding having structures such as ribs, ridges or domes, wherein these structures are fiber-reinforced.

The fiber reinforcement of different polymers is widespread. The combination of a fiber and a polymer matrix results in a material which has the low density of the polymer but at the same time has a high specific rigidity and strength. This makes such composites particularly interesting for lightweight applications. It is mainly made of flat structures, in which the fibers can be evenly distributed.

The use of fibers in polymer structures is known, for example, from US-A-3,824,201. Mats, nonwovens, long fibers or continuous fibers are wetted by polyester-polyurethane compounds described there and then cut before they cure.

In addition to the use of natural fibers, the use of glass fibers has become established for reinforcing polymer moldings. For mechanical applications, the glass fibers are usually present as roving, nonwoven or as tissue. Glass fibers have high strength and rigidity.

The high strength of the glass fiber is based on the size influence. The elongation at break of a single fiber can be up to 5%. The tensile and compressive strength of the glass fiber ensures a special stiffening of the plastic while maintaining a certain flexibility. The modulus of elasticity of glass fibers differs only slightly from that of a compact volume of glass material. The glass fiber has an amorphous structure, the molecular orientation is random. The glass fiber has isotropic mechanical properties. Glass fibers behave ideally linear elastic until breakage. They have only a very small material damping on ng. The stiffness of a component made of glass fiber reinforced plastic results from the modulus of elasticity, direction and volume fraction of the glass fibers and to a small extent from the properties of the matrix material, since usually a much softer plastic is used.

Fiberglass-reinforced plastics are of great importance today, for example in the aerospace or automotive industries, including automobiles, transport machines, construction machines, mobile homes, agricultural machines, trucks, semi-trailers, but also housing parts for stationary machines or non-self-propelled machines and truck boxes. In aviation and aerospace, composite structures with long fibers are used to build predominantly load-bearing structures. In the automotive industry, long fibers made of glass or natural fibers are currently being used to stiffen thermoplastic components (eg cladding).

If one mixes long glass fibers in a polymeric mixture, they do not arrange themselves regularly; they are rather randomly distributed. Long glass fibers in a random arrangement in the polymeric structure are known, for example, from US-A-4,791,019. However, methods are also known by which the glass fibers are aligned in a particular direction. This is described for example in CN 101 314 931 A.

Furthermore, methods are known in which a sheet-like element is coated with a fiber-reinforced polyurethane layer. This coating increases the stability of the actual product. One such method is For example, in WO 2007/075535 A2 and DE 10 2006 046 130 Al described.

DE 196 149 56 A1 and DE 10 2006 022 846 A1 disclose fiber-reinforced molded parts. In addition to glass fibers, mats are used here to reinforce the polymeric structure. Such mats, woven or knitted fabric may also be made of glass fiber.

In the production of a fiber-reinforced polyurethane molding in the RIM (Reaction Injection Molding) process, usually a mixture of polyurethane and the fibers in the lower part of an open tool is distributed by a robot surface. By closing the mold with the upper part, the punch, the mixture is pressed into the desired shape. The pressure also releases air bubbles trapped in the mixture. The shape of the product obtained is determined by the shape of the tool. On the surface of the end product structures are visible even after pressing, which are caused by the glass fibers. In order to achieve a more uniform surface, it is possible to use different lengths of glass fibers. Thus, JP 59086636 A describes a glass fiber reinforced resin composition, wherein the glass fibers have different lengths. Also in WO 00/40650 long and short fibers are used to reinforce polyurethane compounds. The short fibers are 0.635 cm (1/4 inch) or less in length; the long fibers are 0.635 cm (1/4 inch) long or larger. Here, the PUR and long and short fibers are mixed in a fixed mass ratio. The total fiber content in a rib is therefore always lower than in the area, if the long fibers do not penetrate into the rib.

DE 101 20 912 A1 describes a composite component made of polyurethane and its use in exterior body parts. The corresponding composite components are composed of two layers, one layer full-surface short fiber reinforced polyurethane with a paintable surface contains. The second layer contains long fiber reinforced polyurethane. The use of short fibers leads to a smooth, so paintable, surface. However, this layer has other particular mechanical properties than the long fiber reinforced layer.

From DE 10 2005 034 916 Al a method for producing a foaming member is known. Such a foaming part consists for example of fiber-reinforced polyurethanes. Here carrier materials are temporarily incorporated into the structure. However, these do not connect to the plastic, so that the corresponding carrier material can be removed after curing. The obtained foam part then has a structure on the surface.

The production of such fiber-reinforced polyurethanes is often carried out by spraying. A method describes, for example, DE 10 2005 048 874 A1.

The preparation of such materials usually takes place in such a way that the long fibers used for the reinforcement, preferably compressed air, are guided laterally into the spray jet of a polyurethane reactive mixture via a funnel-shaped applicator rigidly connected to the polyurethane (PUR) spray mixing head. Also available on the market are devices in which the polyurethane mixture is produced around a central tube. In the tube long fibers are transported by air flow. At the end of the tube, the "liquid tube" of freshly mixed polyurethane components wets the fiber / air flow In the case of materials reinforced with long fibers, the starting material is usually rovings, that is, bundles of endless, untwisted, stretched fibers. which first pass through a cutting unit also attached to the PUR spray mixing head before the cut fibers are wetted with the polyurethane. In spray processes of this type, the most uniform possible distribution of the fiber PUR reaction mixture, usually over several layers, sought. In applications with a high reproducibility claim, the spray mixing heads and the chute are therefore guided by robots.

It is ideal that the long fibers are wetted substantially on all sides with polyurethane reactive mixture. Such PU-wetted fibers do not have a uniform structure. Rather, there are air pockets between the irregularly arranged long fibers. To produce a molded part, the PU-wetted long fibers are correspondingly introduced into an open mold. The loosely accumulated fibers are forced into the final position by closing the tool under pressure with possibly elevated temperature. Even air pockets are pressed out in this process. By such a method, it is possible different components, such as instrument panel, door trim, seat back trim, hat racks, horizontal and vertical outer trim parts such. Engine hoods, roof modules, side paneling parts manufacture.

For stiffening corresponding components often contain ribs, webs, domes or similar three-dimensional raised structures. These are needed, for example, for later attachment, for glands and inserts. Such structures are obtained by grooves and / or conical recesses in the upper tool, the punch. Frequently, the gap width or the diameter / cross section of these recesses is so small that long fibers with the intumescent PU can not penetrate into the cavities. Only those long fibers can foam into the cavities, which lie in their orientation to match the cavities. However, most of the long fibers are tilted, so that mainly PUR, but no or very few fibers penetrate. So it can not ensure that later ribs, webs and / or domes are fiber-reinforced.

It follows that such structures, which have no or a smaller proportion of fibers, have different properties as the actual shaped body. Thus, the coefficient of thermal expansion is greater when there are fewer fibers. These differences in the linear expansion coefficient then lead to a bending of the actual molded body under thermal stress.

The protruding structures also have a lower bending modulus. The dome, ribs and / or webs are not sufficiently reinforced accordingly. Thus, only lower loads can be held over them as force introduction points, as would be possible with a completely fiber-reinforced polyurethane molded part. Also possibly introduced screws do not grasp here so well.

In the following, a simple model will be described to estimate the likelihood that a fiber (such as glass fiber) applied to a tool half in a spray process may penetrate into a slender component structure, such as a rib.

The following assumptions are made for this:

The single fiber is considered slim and rigid (fiber length>>

Fiber thickness)

The fibers initially settle in the tool level before being transported with the ascending matrix material into areas oriented perpendicular to the tool plane (for example ribs) (2-dimensional view)

As a criterion of whether a fiber can penetrate into a rib, only the fiber orientation and the fiber length is used.

Thus, the probability of penetration of those fibers is estimated which are immediately "below" a corresponding one Component structure like a rib located. Mutual obstruction of the fibers is excluded for simplicity.

A fiber can penetrate into a rib if and only if the in

Rib width projected fiber length is less than twice the

Rib width (see Fig. 1)

In the distribution of the fiber orientations (fiber angle) it is assumed that all orientations are equally probable, ie there is no preferred direction of the fiber orientation

The probability of an event (here: the application of a fiber in a certain angle range 0 <α _FaS er <α _gre nz) is defined as:

P = -S- m

With

P = probability (value between 0 and 1)

g = number of favorable cases

m = number of possible cases

The number of possible cases m corresponds to the number of applied fibers n. Favorable cases are all those fiber orientations lying between 0 ° and cxgrenz, ie

360 °

Thus, there is a probability of the occurrence of fiber orientation within the above-mentioned angle range

p _ ^α border

360 °

With a complete 360 ° turn of a fiber, however, a favorable angle range for penetration into the rib does not occur only once, but four times. These are the angular _ranges (0 <α _FaSe r <oL _limit ), (180 ° - αgrenz <α _FaS er <180 °), (180 ° <α _FaS er <180 ° + α _gre nz) and (360 ° - ⁽ Xgrenz <α _FaS er <360 °). Thus, there is a likelihood of penetration of a fiber in the rib (P _R).

.2 B,

α arcsin ()

limit Δ-

PR = H

360 ° 360 °

for 2 B

1

For ratios of rib width to fiber length greater than 0.5, P _R by definition becomes 1 (see assumptions) because then fiber orientation no longer plays any role.

Figure 2 shows the probability of fiber penetration into a rib (P _R ) as a function of fiber length for four different rib thicknesses.

Fig. 1 illustrates the relationship between fiber orientation, length and rib width. The assumption is that a fiber that is at most twice as long as the rib width can always enter the rib (regardless of the fiber angle). The idea is that the fiber only touches one edge of the rib and can then be "tucked" into the rib just when the point of contact of the fiber and the rib edge is the fiber center, and longer fibers can only enter the rib when their angle α _FaSe r is less than a _critical angle α _gre nz, otherwise the fiber rests against both edges of the rib, and if the fiber rests on only one edge of the rib and the center of the fiber is outside the rib, it will slip away assuming that this fiber can not enter the rib, the assumptions made here will lead to a higher likelihood of fiber entry into the rib, since in reality the fibers will certainly interfere with each other in their mobility.

The object of the present invention is therefore to provide a fiber-reinforced polyurethane molding, which raised Having three-dimensional structures, wherein the molded body itself and these structures are reinforced with fibers.

In a first embodiment, the object is achieved by a long-fiber-reinforced polyurethane molded body, with three-dimensional raised structures, in particular ribs, webs and / or domes, which is characterized in that it also contains short fibers in addition to the long fibers, wherein the weight ratio between short Fibers and / or platelet-shaped fillers to the fiber-free polyurethane matrix in a volume of ribs, webs and / or domes is greater than the weight ratio of short fibers and / or platelet-shaped fillers to the fiber-free polyurethane matrix in areas outside the raised structures.

As long fibers, natural or synthetic fibers can be used. In addition to glass fibers and basalt fibers

also find carbon fibers, aramid fibers, natural fibers, for example

Hemp fibers (sisal, flax) application. Preferably, glass fibers are used.

These long fibers preferably come from a roving and are cut in a corresponding existing cutting tool, so that the fibers in the molded part, for example, a length of 1 to 30 cm, preferably from 2.5 to 10 cm.

According to the invention, the three-dimensional raised structures, ie ribs, webs and / or domes, contain short-fiber-reinforced polyurethane. According to the invention, the term "short fibers" also includes platelet-shaped fillers, for example phyllosilicates, in particular mica. As short fibers, natural or synthetic fibers are used. The short fibers may be, for example, ground glass fibers, basalt fibers or carbon fibers. But it can also wollastonite, for example, are available under the brand name used Tremin ^® or a similar mineral. The fibrous, needle-like crystals of Tremin ^® are inventively preferred.

The size of the short fibers / platelet fillers is defined by their length / diameter. In particular, the length of short fibers / diameter of platelet-shaped fillers is: between 1 μm to 800 μm, preferably 4 μm to 600 μm, particularly preferably 100 μm to 500 μm

According to the invention, the mixture of polyurethane reactive mixture and long fibers is introduced into an open mold, as shown in FIG. Subsequently, polyurethane is applied locally to the corresponding points of the raised structures together with short fibers. The polyurethane reactive mixture containing short fibers is applied in particular at the locations where the cavities for the ribs, webs and / or domes are located in the die and flows after closing the tool unhindered in these cavities.

If the cavities for ribs, webs and / or domes are in the lower part of the tool, the polyurethane reactive mixture containing the short fibers can be introduced into the cavities and then the polyurethane reactive mixture containing long fibers can be applied in a planar manner.

The short fibers thus have a length that is short enough so that they can flow freely into the cavities for the ribs, webs and / or domes. They therefore flow with the optionally foaming PUR into the cavities, while long fibers tilt and can not or hardly penetrate into the cavities with the PUR.

FIG. 4 describes a corresponding method without the use of short fibers or platelet-shaped fillers, in which the raised areas remain unfilled.

Preferably, a polyurethane molded body according to the invention also has an additional outer skin, which adjoins the side which has no three-dimensional structures. Such an outer skin consists in particular of a thermoformed film which in particular comprises acrylonitrile-butadiene-styrene (ABS), polymethyl methacrylate (PMMA), acrylonitrile-styrene-acrylate (ASA), polycarbonate (PC), thermoplastic polyurethane, polypropylene (PP), polyethylene (PE) and / or polyvinyl chloride (PVC).

As an alternative to the aforementioned outer skins, these may also comprise so-called in-mold coating coatings or gel coat coatings. In-mold coating is a process by which the coating of a plastic molded part is already carried out in the mold. For this purpose, a highly reactive 2-component paint is brought into the mold by means of suitable painting technology. Thereafter, according to the invention, the long-fiber-reinforced polyurethane layer is applied to the open mold. Subsequently, the short fiber-reinforced polyurethane component is applied locally and the tool is closed here.

In a further embodiment, the present invention is achieved by a method for producing a fiber-reinforced polyurethane molding. Such a process comprises wetting long glass fibers with a polyurethane reactive mixture, introducing this mixture into the open mold, topping with short fiber reinforced PUR, and closing the mold. For this purpose, a method is particularly preferred in which the gas stream containing solids or the gas streams containing solids are not metered into the already dispersed spray jet of the reaction mixture, but are introduced into the mixing chamber of the mixing head in the still liquid, non-dispersed jet.

A "liquid jet of a PUR reaction mixture" is understood according to the invention as meaning a fluid jet of a PUR material, in particular in the region of a mixing chamber for mixing the reaction components in liquid form, which is not yet in the form of fine reaction mixture droplets dispersed in a gas stream , ie in particular in a liquid viscous phase.

The prior art processes essentially use a gas stream or nozzle to atomize a PUR reaction mixture and meter a solid-containing gas stream into such an atomized PUR spray. For each spray, as in this case, the distance between adjacent spray particles orthogonal to the main spray direction of a jet increases with increasing distance to the spray nozzle. Inevitably, the likelihood of the solid particles colliding with polyurethane droplets or already wetted filler particles and becoming wetted rapidly decreases rapidly. The conditions change when, according to the method according to the invention, the mixing of fillers and polyurethane takes place in a mixing chamber.

The device is characterized in that solids are passed through a conveying gas stream into a mixing chamber and there encounter a liquid jet of a PUR reaction mixture. The gas streams with solids are allowed to meet in the mixing chamber by entering two or more points in the mixing chamber. Here, adjacent spray jets can enclose large angles with each other and stand perpendicular to a circular peripheral line of the cylindrical mixing chamber. They then collide in the imaginary central axis of the mixing chamber. But they can also be introduced tangentially and form a vortex, which describes a circle which is orthogonal to the main flow direction in the mixing chamber. In the method according to the invention, the particles can not dodge each other or move away from each other because they are prevented by the walls of the mixing chamber. Therefore, in the process according to the invention, solids are forcibly wetted with the PUR reaction mixture inside the mixing chamber without loss and become part of a homogeneous gas / solid / PUR material mixture.

It is preferred to further increase the mixing quality of the resulting gas / solid / PUR material mixture in the mixing chamber by additional air swirls. The air swirls are generated by air from tangential air nozzles. The circular surfaces enclosed by them form a right angle with the axis of the main flow direction in the mixing chamber.

According to the invention, one and the same PUR can be used to use or increase the content of the short fibers; Common methods provide the short fibers in the polyol formulation so that the concentration is fixed throughout the production process.

The upper part of the mold has cavities into which the foaming PUR reactive mixture can then penetrate. In particular, the short-fiber-reinforced reactive mixture penetrates here.

A polyurethane molded body produced by such an inventive method not only has a high stability in the actual body. By foaming the short fiber-reinforced polyurethane component in the cavities of the upper tool and the later dome, ribs and / or webs are fiber-reinforced. As a result, a higher stability of these structures is achieved. LIST OF REFERENCES:

1 freshly mixed polyurethane

2 long fibers

3 upper half form

4 recess for rib

5 lower half form

6 freshly mixed polyurethane with short fibers

7 Component with flat pressed long glass fibers

8 rib of a component filled with unreinforced polyurethane

9 rib of a component filled with polyurethane reinforced with short fibers

Claims

claims

1. Long-fiber-reinforced polyurethane molded body, with three-dimensional raised structures, in particular ribs, webs and / or domes, characterized in that it further contains short fibers in addition to the long fibers, wherein the weight ratio between short fibers and / or platelet-shaped fillers to the fiber-free polyurethane matrix in a volume of ribs, webs and / or domes is greater than the weight ratio of short fibers and / or platelet-shaped fillers to the fiber-free polyurethane matrix in flat areas outside the raised structures.

2. Polyurethane shaped body according to claim 1, characterized in that the long fibers comprise glass fibers.

3. Polyurethane shaped body according to claim 1, characterized in that the long fibers have a length of 1 to 30 cm, in particular from 2.5 to 10 cm.

4. polyurethane molding according to claim 1, characterized in that short fibers have a length / diameter of 1 to 800 .mu.m, in particular from 4 to 600 microns.

5. Polyurethane shaped body according to claim 4, characterized in that the short fibers comprise ground glass fibers.

6. Polyurethane molded article according to claim 5, characterized in that the short fibers comprise wollastonite fibers.

7. polyurethane molding according to one of claims 1 to 6, characterized in that the long fiber-reinforced side further comprises an outer skin.

8. Polyurethane molded body according to claim 7, characterized in that the outer skin of a deep-drawn film, in particular of acrylonitrile-butadiene-styrene (ABS), polymethyl methacrylate (PMMA), acrylonitrile-styrene acrylic ester (ASA), polycarbonate (PC), thermoplastic Polyurethane, polypropylene (PP), polyethylene (PE) and / or polyvinyl chloride (PVC).

9. polyurethane molding according to claim 7, characterized in that the outer skin comprises a two-layer film.

10. Polyurethane shaped body according to claim 7, characterized in that the outer skin comprises a metal foil, in particular an aluminum foil or a steel foil.

11. Polyurethane shaped body according to claim 7, characterized in that the outer skin comprises an in-mold coating and / or gel coat coating.

12. A process for producing a polyurethane molding according to any one of claims 1 to 11, characterized in that

(a) long fibers are wetted with a PUR reactive mixture, these are introduced into an open mold,

(B) locally distributed with short fibers reinforced PUR reactive mixture applied and

(c) then the mold is closed with the upper part.

13. The method according to claim 12, characterized in that the steps (a) and (b) are reversed.

14. The method of claim 12 or 13, wherein i) introduces a gas stream containing short fibers in a liquid stream of a polyurethane reactive mixture, wherein the polyurethane fibers containing the short fibers is sprayed, ii) optionally introduces a gas stream containing long fibers in this spray, iii) spraying the short fibers and optionally the long fibers containing PUR spray into an open mold or onto a substrate carrier, iv) optionally increasing the amount of the short fibers below (i), if no gas stream containing the long fibers is introduced simultaneously.

15. The method according to any one of claims 12 to 14, characterized in that one uses an upper part or a lower part of the tool with cavities for ribs, webs and / or domes.

16. The method according to any one of claims 12 to 15, characterized in that in the open tool first an outer skin is inserted, then the PUR wetted long fibers are introduced, then additionally applied locally distributed short-fiber reinforced PUR reactive mixture and then the mold with the Upper part is closed.