Moulded Product for Automotive Panels

Abstract

Composite molded product comprising of at least one polyamide-reinforcement layer consisting of a polyamide matrix and reinforcement fibers, characterised in that the polyamide-reinforcement layer is porous due to the consolidation using a pressurised steam process.

Claims

1. A method of producing a porous molded product, comprising: randomly disposing polyamide-binding material, and a plurality of reinforcement fibers to form a web, the polyamide-binding material including at least one of fibers, flakes, and powder; and treating the web with pressurized saturated steam to consolidate the web.

2. The method of claim 1, wherein the pressurized saturated steam has a pressure in a range of 9 to 20 bars.

3. The method of claim 1, wherein the web is treated in a pressure resistant mold having at least one steam permeable surface forming the molded product.

4. The method of claim 1, wherein the web is pre-bonded before steam treatment.

5. A method for producing a porous molded product, comprising: blending reinforcing fibers with a matrix; placing the blend of reinforcing fibers and matrix into a mold such that a web is formed in the mold; heating the web with saturated steam at a pressure of about 9-20 bars, the saturated steam being of a first temperature lower that the melting temperature of the matrix; and melting the matrix as it is exposed to the first temperature.

6. The method of claim 5, wherein the matrix is comprised of at least one of polyamide fibers, powder of flakes.

7. The method of claim 5, wherein the web is formed by air lay, wet lay, or carding.

8. The method of claim 5, wherein the reinforcing fibers are comprised of a polymer having a melting temperature higher than that of the matrix.

9. The method of claim 5, wherein at least some of the plurality of reinforcing fibers cross each other to form at least one crossing point, and wherein the matrix only binds the at least one crossing points.

10. The method of claim 5, further comprising pre-binding the matrix and reinforcing fibers before the web is exposed to saturated steam.

11. The method of claim 5, wherein the matrix and reinforcing fibers are randomly disposed in the web.

12. The method of claim 5, wherein the reinforcing fibers is comprised of at least one of glass fibers and polyethylene terephthalate (PET) fibers.

13. The method of claim 5, wherein the reinforcing fibers is comprised of polyethylene terephthalate (PET) fibers, wherein the melting point of the reinforcing fibers is similar to the melting point of the matrix, and wherein the reinforcing fibers remains in a fibrous state when exposed to saturated steam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 Graph of the dynamic young modulus of different samples.

[0037] FIG. 2 Graph of the loss factor of the same samples.

[0038] FIG. 3 Comparison of the acoustic absorption of a web consolidated using hot molding plates or the steam process according to the invention.

[0039] FIG. 4 Comparison of the thermal conductivity of a web consolidated using hot molding plates or the steam process according to the invention.

DETAILED DESCRIPTION

[0040] For the composites, according to the invention, matrix-forming binder fibers were mixed with reinforcement fibers and carded to form a web. Webs were pre-bonded using needling for handling purposes. (But any kind of pre-bonding processes can be used.) To prevent the composite samples from sticking or solidification to the mold particularly at release of the steam pressure from the tool, a thin nonwoven as surface cover can be used. The nonwoven used does have a neglectable influence on the main features like thickness, acoustic behaviour or stiffness of the final product. The webs for the polyamide-reinforcement layer according to the invention were consolidated using saturated steam as specified.

[0041] State of the art samples were compared with polyamide reinforcement layers according to the invention. The state of the art composites were bought according to the availability on the market.

[0042] Composite 1 A state of the art composite based on polypropylene as the binder and glass fibers as the reinforcement material, having a density of 881 kg/m.sup.3 known in the market as Symalite.

[0043] Composite 2 A state of the art felt based material made of bicomponent PET as the binder material and cotton as the reinforcement material having a density of 314 kg/m.sup.3.

[0044] Composite 3 A composite according to the invention made of 45% PA binder fibers and 55% of glass fibers as the reinforcement fibers. Starting weight of the web was 1000 gram per m.sup.2. The composite was molded according to the invention using 11 bars absolute of saturated steam for 9 sec. The final density of the formed polyamide reinforcement layer is 384 kg/m.sup.3.

[0045] Composite 4 A composite according to the invention made of 55% PA binder fibers and 45% of glass fibers as the reinforcement fibers. Starting weight of the web was 1000 gram per m.sup.2. The composite was molded according to the invention using 11 bars absolute of saturated steam for 9 sec. The final density of the formed polyamide reinforcement layer is 303 kg/m.sup.3.

[0046] The dynamic young modulus over a temperature range was measured, and from this the tensile loss factor was calculated according to ISO 6721-4. The measurements and calculations were done using a 0.1 dB Metravib Viscoanalyser Type VA 2000. See FIGS. 1 and 2 for the results on all composites

[0047] For composite parts used in the automotive industry heat stability requirements are increasing. Particularly in the engine bay directly due to new motor generations generating more heat, as well as due to the option to keep the heat inside using isolation to optimise the overall use of fuel, leads to higher heat stability requirements. Normally the test for engine bay material is a long-term heat stability test at 120 C. or at 150 C. However, the actual temperature can rise easily to 180-190 C. for a short time. This temperature range can occur close or around hot engine sides, like exhaust line, manifold or compressors.

[0048] One requirement of the heat stability test is to know if the composite product keeps its form and shape during the exposure to heat. For instance, a parcel shelf placed under a sunny window should not sag after a while. An engine bay cover should keep its stiffness. The tensile loss factor over this temperature range is important for the stiffness retention of the product, when in use.

[0049] FIG. 1 shows the dynamic young modulus. Composite 1 the state of the art product based on a PP matrix and Glass fibers as reinforcement shows in absolute terms a higher modulus than composite 3 and 4 according to the invention. This is mainly due to the higher overall density. However, the trend is to obtain the same or better stiffness performance at a lower density saving weight in the car. More important however is that the state of the art composite 1 shows a significant loss of dynamic young modulus over the temperature range measured. Therefore, products made of combinations with PP tend to get softer at higher temperature. Composite 2 is a combination of CoPET/PET bicomponent binding fibers and cotton as the reinforcement material showing an overall too low dynamic young modulus to be self-supporting.

[0050] The composites per the invention show a much better behaviour over the temperature range measured. It was found that the dynamic young modulus of the polyamide reinforcement layer does not change more than 20% over a temperature range of 150 C. to 210 C. Rendering an overall more heat stable product.

[0051] FIG. 2 shows the tensile loss factor over the temperature range measured on the composite products. Composites 1 is state of the art based on polypropylene (PP) as matrix binder fiber produced with a molding method without steam. Although the products have a good loss factor up till 160 C., it rapidly loses its heat stability due to melting.

[0052] Composite 2 is a combination of CoPET/PET bicomponent binding fibers together with cotton as the reinforcement fibers. Therefore the bad loss factor over the measured temperature range is basically due to the CoPET, already softening at 80 C. and above 110 C. starting to melt. Although this is dependent on the CoPET used. Higher melting CoPET has other disadvantages including an increase in cost. In an absolute way, a composite material using PET alone would give a product with a good heat stability, it is not known today how this can be achieved, without heat damaging the reinforcement fibers due to the very high melting T needed.

[0053] Composite 3 and 4 are combinations of PA binder with glass fiber reinforcement fibers consolidated using steam according to the invention. Both have a stable tensile loss factor () of less than 0.15 over a temperature range of 60-210 C.

[0054] The polyamide reinforcement product can be compressed fully or partially to obtain a formed product. Due to the consolidation process using saturated steam according to the invention it is possible to obtain a product with a lower density and still obtain the wanted stiffness. Because the heating process using saturated steam melts the polyamide binder fibers at a much lower temperature than the thermoplastic reinforcement fibers, and all across the thickness at a nearly same time, the resilience on web structure of the reinforcement fibers can be kept. By reducing the amount of matrix forming polyamide to such a level that the overall product is just fully bonded, a porous reinforcement layer can be obtained with a density that is only 5 to 80% of the bulk density of the materials of the composite. However preferably a range from 5 to 60%, even more preferably 5 to 25% is obtainable and more advantages due to the lower costs of the overall part. Therefore, it is possible to obtain a product that is not solid but stays porous, rendering in a better acoustic absorber (see FIG. 3) due to the porosity of the material as well as a better thermal conductivity (see FIG. 4). By adjusting the density either by more compacting or by increasing the amount of PA matrix it is possible to adjust both the acoustic properties as well as the thermal conductivity.

[0055] Sample A and B were produced using the same web material of 65% Glass fibers and 35% PA binder fibers. Composite A was consolidated using the saturated steam according to the invention and Composite B was consolidated using compression between hot plates. Both were treated such that a fully bonded product was achieved.

[0056] The acoustic absorption properties of the composites formed were measured using an impedance-tube, according to the ASTM (E-1050) and ISO (10534-1/2) standards for impedance tube measurements (measurement between 200 and 3400 Hz). The thermal conductivity was measured using a guarded hot plate according to ISO8301.

[0057] The acoustic absorption and the thermal conductivity were found to be better in the steam treated product than in the hot plate treated product. This is partly due to the necessity to use more compression during the heating process using hot plates to obtain a fully bonded product. Therefore, obtaining a denser product B in the first place, hence a less porous product, showing a decrease in both thermal conductivity and acoustic property.