Thermoplast reinforced with thermoplastic fibre mats

The invention relates to thermoplastics reinforced with mats made from thermoplastic fibers and to molded parts made therefrom.

Fiber-reinforced thermoplastic sheets or thermoplastic sheets, as they are known, for example, from EP 300237 B or EP 345463 B, are high-quality construction materials which are usually finished in a hot pressing process in heated compression molding presses under pressure to give the desired molded parts. They are mainly used in machine and apparatus construction, in the automotive and aircraft industries, as well as for sports and household appliances.

In particular for the production of complex parts, in which the material has to cover large flow distances in a short time during the pressing process in the mold, whereby not only matrix polymer, but also fibers have to be transported into the most distant parts of the mold, the fiber is preferred in the form of Cut fiber mats are used.

Glass fibers are mainly used as reinforcing fibers. For areas of application in which particularly high rigidity and low weight are required, carbon fibers or aramid fibers, for example, are also suitable. In comparison to unreinforced thermoplastics, the fiber reinforcement achieves above all a higher strength and a higher rigidity (increase in the modulus of elasticity), but at the same time a reduction in the elongation at break occurs. However, this reduced elongation at break represents a decisive disadvantage for various applications, for example for components or panels in motor vehicles that are prone to impact or stone chipping.

The object of the present invention was therefore primarily to find materials which do not have these disadvantages and in particular have higher elongations at break, but which should nevertheless achieve higher strengths than with unreinforced thermoplastics.

Such materials with good strengths and at the same time high elongation at break could be obtained according to the invention by using fiber mats made of thermoplastics as reinforcing fibers for the matrix thermoplastics.

The invention accordingly relates to a fiber mat-reinforced thermoplastic in which the reinforcing fibers are thermoplastic fibers whose melting point is at least 20 ° C, preferably at least 40 ° C higher than the melting point of the matrix thermoplastic and whose elongation at break in the tensile test (according to ISO 527) is at least 10% can be used alone or optionally in combination with other reinforcing fibers. The elongation at break of the fibers is preferably at least 12%.

All thermoplastically processable polymers can be used as matrix polymers. Preference is given to using polyolefins, such as, for example, polyethylene or polypropylene, polyamides (for example, polyamide 6), polyesters, for example polybutylene terephthalate, both homopolymers and copolymers being possible. Polypropylene homo- or copolymers are particularly preferred. The MFI (measured in accordance with DIN 53735 at 230 ° C. and 2.16 kg) is advantageously at least 100 g / 10 min, even better at least 250 g / 10 min, when polypropylenes are used.

All thermoplastics that can be processed into fibers, such as polyolefins, polyamides, polyesters, polycarbonates, polyurethanes, polyphenylene oxide, polyphenylene sulfide, polysulfones, polypropylenes, polyamides, for example polyamide 66 or polyamide 46, and polyesters, for example polyethylene terephthalate, can be used for the fiber mats. The fiber lengths are usually from 30 to 150 mm, preferably from 50 to 100 mm. The fiber titer is preferably about 3 to 150 dtex, particularly preferably 17 to 70 dtex. Depending on the polymer used and on the process conditions during fiber production, the elongation at break of the fibers is between 10% and approximately 100%, the upper limit of the elongation at break preferably being a maximum of 60%.

The fibers can be formed into mats on conventional web-forming systems, such as cards with panels or pneumatic web-formers. The mat weight is preferably 100 to 1000 g / m 2², particularly preferably at 300 to 600 g / m 2².

The fiber mat-reinforced thermoplastics according to the invention are produced, for example, by melting the matrix polymer, optionally together with customary additives, such as stabilizers, pigments, fillers (e.g. talc, mica, chalk), lubricants,

AT 407 251 B

Nucleating agents, flame retardants, etc. in an extruder, extrusion through one or more slot dies, bringing together in the still liquid state with one or more fiber mats, as well as subsequent pressing and cooling, preferably continuously between the belts of a double belt press. The composite panels obtained can be pressed into high-quality molded parts with uniform fiber distribution and good surface quality.

The proportion of reinforcing fibers in the finished composite is approximately in the range from 10 to 40% by weight, preferably from 20 to 30% by weight. It is also possible to use mats with different reinforcing fibers. Depending on the special requirements placed on the profile of properties of the finished composites, it may also be possible to use the thermoplastic reinforcing fibers in combination with other reinforcing fibers, such as glass, carbon or aramid fibers.

With the present invention, it has now unexpectedly succeeded in incorporating thermoplastic fibers into thermoplastic matrix polymers and also processing the resulting composite into finished parts, with the mechanical properties of the fibers being retained to such an extent that composite components with only a moderately reduced modulus of elasticity compared to glass fiber reinforcement significantly increased elongation at break can be obtained. Values ​​for the elongation at break (measured according to ISO 527 in the tensile test) are, for example, in the case of polypropylene as the matrix polymer in the range of about 40%, the tensile strength (ISO 527) in the range of about 44 MPa and the tensile modulus of elasticity (ISO 527 ) in the range of around 2500 MPa. The comparable values ​​for glass fiber reinforced polypropylene are in the range of about 1.8% for the elongation at break, of about 60 MPa for the tensile strength and of about 4500 MPa for the tensile modulus of elasticity. For unreinforced polypropylene, the corresponding values ​​(Daplen BE 60, MFI (230 ° C / 2.16 kg) 0.3, from PCD polymers) are around 500% for elongation at break, 40 MPa for tensile strength and 1200 MPa for the modulus of elasticity. As an additional advantage, the fiber mat reinforced thermoplastics according to the invention have a lower density than glass fiber reinforced thermoplastics. For example, with 25% by weight of polyester fiber in a polypropylene matrix, the density is approx. 1 g / cm³, compared to about 1.08 g / cm³ with glass mat reinforced polypropylene with the same fiber content.

The fiber mat-reinforced thermoplastics according to the invention are preferably used for the production of molded parts, the heated thermoplastics being compressed in appropriate compression molding machines. The invention accordingly also relates to molded parts which are produced from fiber mat-reinforced thermoplastics according to the invention. The most homogeneous possible fiber distribution in the pressed part is essential, especially when the material has to cover longer distances in the mold during the pressing process. In this case in particular, there is the risk of segregation, ie the risk that the fibers are not transported to the same extent as the melted matrix. In the extreme case, the matrix is ​​pressed out of the insert and forms the flow front alone. In the finished pressed part (pressed part), zones with reduced fiber content, in extreme cases completely fiber-free zones, then arise, particularly in the areas of the pressed part that are farthest away from the insert or areas of the pressed part that are difficult to reach from the flow process (e.g. ribs). Surprisingly, this problem does not occur with the thermoplastics according to the invention reinforced with thermoplastic fiber mats. Due to the good fiber transport during pressing, the pressed parts obtained have a very good and even fiber distribution. The fiber transport is so good that, for example when pressing a heated insert placed on one side in a rectangular flat mold, the flow front of which during pressing has to cover a distance that corresponds at least to the distance from the molding press to the original edge of the insert, the fiber content of the resulting pressed part, measured in samples that are no more than 3 Represent% by weight of the compact and a total surface area of ​​at least 85 cm² own, is at least 80% of the fiber content of the insert. The invention accordingly also relates to molded parts made from thermoplastics reinforced with fiber mats according to the invention, their fiber content, measured in samples which represent at most 3% by weight of the compact and a total surface area of ​​at least 85 cm² have at least 80% of the fiber content of the thermoplastic used.

AT 407 251 B

Example 1: Production of the fiber mat-reinforced thermoplastics

A polyester staple fiber made of polyethylene terephthalate (17 dtex, 60 mm cut length, melting point 255 ° C, elongation at break in accordance with ISO 527: 50%) was processed on a needle felting line consisting of carding machine, täfler, pre- and main needle machine and winder to form fiber mats of 500 g / m² processed. A layer of polymer melt of 3000 g / m 2 was applied to a mat² made of Daplen PP XS 80 (MFI 2.16 / 230 250 g / 10 min, melting point 169 ° C) extruded by means of a slot die and a second fiber mat (500 g / m²) placed on top. The mat - melt - mat system was fed to a double belt press at a speed of 1 m / min and pressed in this with a pressure of 150 N / cm 3 at 200 ° C. and a dwell time of 6 min. A polyester mat-reinforced PP with a thickness of 4 mm, a fiber content of 25% by weight and a density of 0.99 g / cm was obtained³, an elongation at break in the tensile test of 40%, a tensile strength of 44 MPa and a tensile modulus of elasticity of 2500 MPa.

Example 2: Production of a pressed part

Blanks of the semifinished product obtained according to Example 1 with dimensions of 240 x 166 x 3.7 mm each were heated to 200 ° C. in a contact furnace, stacked one on top of the other, placed on one side in the cavity of a plate-shaped plunge edge tool with dimensions 590 mm x 250 mm and pressed with a pressing force of 2000 kN. During the pressing process, the present composite (PP matrix and polyester fiber reinforcement) completely filled the cavity.

The pressed board was 2 mm thick and was cut into strips of 15 mm x 250 mm. When determining the fiber distribution, all of them showed 37.5 cm² large stripes (corresponding to a total surface of 85.6 cm²) a fiber content of over 20% by weight, corresponding to over 80% of the originally used fiber content of 25% by weight.