METHOD FOR PRODUCING A FIBER MATRIX SEMI-FINISHED PRODUCT

Abstract

The present invention relates to a process, especially impregnation process, for producing a semifinished fiber matrix product using micropellets.

Claims

1. A process for producing a semifinished fiber matrix product, the process comprising: applying a polymer composition in the form of a micropelletized material to a fiber material, subjecting the fiber material with the applied polymer to a temperature and pressure, and period of time sufficient to impregnate the polymer composition into the fiber material and consolidate the polymer composition with the fiber material to produce a composite, and cooling the composite to obtain a semifinished fiber matrix product.

2. The process as claimed in claim 1, wherein: the temperature is equal to or greater than the melting temperature of the polymer composition, the pressure is 2 to 100 bar; and the fiber material comprises a semifinished fiber product or a nonwoven structure.

3. The process as claimed in claim 2, wherein the fiber material is a semifinished fiber product and is selected from the group consisting of weaves, laid scrims including multiaxial laid scrims, knits, braids, nonwovens, felts, mats or unidirectional fiber strands, a mixture of two or more of these materials, and combinations thereof.

4. The process as claimed in claim 1, wherein the polymer composition comprises at least one thermoplastic selected from the group consist of polyamide (PA), polycarbonate (PC), thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polylactic acids (PLA), acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), polyether ether ketone (PEEK), polyether imide (PEI), polyether sulfone (PES), polymethylmethacrylate (PMMA), polyoxymethylene (POM), and polystyrene (PS), and derivatives and blends thereof.

5. The process as claimed in claim 1, wherein the polymer composition comprises at least one addition or additive.

6. The process as claimed in claim 5, wherein the additives comprise ultraviolet light stabilizers, flame retardants, leveling-promoting additives, lubricants, antistats, colorants, nucleators, crystallization promoters, fillers, or other processing auxiliaries, or mixtures thereof.

7. The process as claimed in claim 1, wherein the micropelletized material has a mean grain size of 0.01 to 3 mm, determined by means of dry sieve analysis according to DIN 53477.

8. The process as claimed in claim 1, wherein the micropellets are round, ellipsoidal, cubic or cylindrical.

9. The process as claimed in claim 1, wherein the micropelletized material has a bulk density of 200 to 1800 g/L, determined according to EN ISO 60.

10. The process as claimed in claim 1, wherein the micropellets have a residual moisture content of not more than 0.3% by weight, based on the total weight of the micropellets.

11. The process as claimed in claim 1, wherein the micropellets have a Shore A hardness of more than 90, and have a Shore D hardness of more than 60, where the Shore hardness is determined according to DIN 43505 with test instrument A or test instrument D.

12. The process as claimed in claim 1, further comprising applying multiple layers of the micropelletized material to the fiber material.

13. The process as claimed in claim 1, further comprising applying the micropelletized material to the fiber material in an amount sufficient to result in a semifinished fiber matrix product having 25% to 80% fiber material as defined according to DIN 1310.

14. The process as claimed in claim 1, wherein the semifinished fiber matrix product is a single-layer semifinished fiber matrix product.

15. A method for producing a semifinished fiber matrix product, the method comprising impregnating and bonding two or more layers of a fiber material with a polymer composition in the form of micropellets.

16. A single-layer semifinished fiber matrix product comprising at least one fiber material impregnated and consolidated with a polymer composition in the form of a micropelletized material at a temperature and pressure sufficient to impregnate and consolidate the polymer composition into and with the fiber material.

17. The single-layer semifinished fiber matrix product as claimed in claim 16, wherein: fiber matrix product has 25 vol % to 65 vol % fiber material as defined according to DIN 1310 the fiber matrix product has a fiber distribution gradient from the surface to the middle, and the distribution gradient differs by at most 5% from the surface to the middle; the fiber matrix product has a gas cavity content of less than 10 vol % based on the overall volume of the product; the fiber material comprises 1 to 100 semifinished fiber laminas comprising endless fibers, the laminas each having a basis weight of 5 g/m.sup.2 to 3000 g/m.sup.2 and being selected from the group consisting of weaves, laid scrims including multiaxial laid scrims, knits, braids, nonwovens, felts, mats or unidirectional fiber strands, a mixture of two or more of these materials, and combinations thereof; the polymer composition has a melt volume flow rate MVR to ISO 1133 of 50 cm.sup.3/10 min to 500 cm.sup.3/10 min at a load of 5 kg and a temperature of 260 C., and comprises at least one thermoplastic selected from the group consisting of polyamide (PA), polycarbonate (PC), thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polylactic acids (PLA), acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), polyether ether ketone (PEEK), polyether imide (PEI), polyether sulfone (PES), polymethylmethacrylate (PMMA), polyoxymethylene (POM), and polystyrene (PS), and derivatives and blends thereof; and the micropelletized material has a mean grain size of 0.01 to 3 mm.

18. The single-layer semifinished fiber matrix product as claimed in claim 17, wherein: the fiber matrix product has 40 vol % to 50 vol % fiber material as defined according to DIN 1310; the fiber distribution gradient differs by at most 3% from the surface to the middle; the gas cavity content is less than 5 vol % based on the overall volume of the product; the melt volume flow rate is 100 cm.sup.3/10 min to 200 cm.sup.3/10 min; the polymer composition comprises at least one thermoplastic from the group consisting of polypropylene (PP), polyamide (PA), polycarbonate (PC), polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), and derivatives and blends thereof; the fibers are glass fibers and/or carbon fibers; and the single-layer semifinished fiber matrix product is produced by a process comprising: applying the polymer composition in the form of the micropelletized material to the fiber material in an amount sufficient to result in a semifinished fiber matrix product having 25% to 65% fiber material as defined according to DIN 1310, subjecting the fiber material with the applied polymer to the temperature and pressure sufficient to impregnate and consolidate the polymer composition into the fiber material to produce a composite, and cooling the composite to obtain the semifinished fiber matrix product.

19. The process as claimed in claim 1, wherein: the temperature is equal to or greater than the melting temperature of the polymer composition; the pressure is 2 to 100 bar; the fiber material is a semifinished fiber product comprising 2 or more layers of the fiber materials, wherein the fiber materials comprise at least one of carbon fibers and glass fibers, and the materials are selected from the group consisting of weaves, laid scrims including multiaxial laid scrims, knits, braids, nonwovens, felts, mats or unidirectional fiber strands, a mixture of two or more of these materials, and combinations thereof; the polymer composition comprises at least one thermoplastic selected from the group consisting of polyamide (PA), polycarbonate (PC), thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polylactic acids (PLA), acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), polyether ether ketone (PEEK), polyether imide (PEI), polyether sulfone (PES), polymethylmethacrylate (PMMA), polyoxymethylene (POM), and polystyrene (PS), and derivatives and blends thereof; and the micropelletized material has a mean grain size of 0.01 to 3 mm.

20. The process as claimed in claim 19, wherein: the temperature is at least 20 C. greater than the melting temperature of the polymer composition, and the pressure is 10 to 40 bar; the polymer composition comprises at least one addition or additive selected from the group consisting of ultraviolet light stabilizers, flame retardants, leveling-promoting additives, lubricants, antistats, colorants, nucleators, crystallization promoters, fillers, and other processing auxiliaries, or mixtures thereof; the micropellets are round, ellipsoidal, cubic or cylindrical, and have: a bulk density of 200 to 1800 g/L, determined according to EN ISO 60; a residual moisture content of not more than 0.3% by weight based on the total weight of the micropellets; a Shore A hardness of more than 90 determined according to DIN 43505 with test instrument A; and a Shore D hardness of more than 60 determined according to DIN 43505 with test instrument D; the micropelletized material is applied to the fiber materials by at least one of scattering, tricking, printing, spraying, irrigating, thermal spraying, flame spraying, and fluidized bed coating processes; and the process further comprises, after application of the micropelletized polymer to the fiber material, scintering the micropeletized polymer, optionally under pressure, at a temperature below the melting temperature of the polymer.

Description

EXAMPLES

[0154] Using process steps a) to e) described, a semifinished fiber matrix product was produced, once with use in process step c) of ground polymer composition (comparative test) and once with use of polymer composition in the form of micropelletized material (inventive example).

[0155] The semifinished fiber product used was a 2/2 twill weave made of filament glass with silane size and a basis weight of 290 g/m.sup.2.

[0156] The micropelletized material or the ground polymer composition was applied to the fiber materials in such amounts as to result in a proportion by volume of fiber materials in the semifinished fiber matrix product, defined according to DIN 1310, of 45%.

[0157] The semifinished fiber matrix products were produced by hot-pressing fiber material and thermoplastic matrix at temperatures in the range from 290-C to 320 C. [0158] A) Powder (cryogenically ground) of a polymer composition based on polyamide with a mean grain size of 0.7 mm. [0159] B) Micropelletized material (cylindrical form and ellipsoidal form) of a polymer composition based on polyamide with a mean grain size of 0.7 mm.

TABLE-US-00001 TABLE 1 Comparison of the results from powder application and micropelletized material application A B (comparative example) (inventive example) Purity of the polymer + composition (powder had impurities after (micropelletized material had the grinding) no impurities) Energy expenditure for + production of the semifinished (relatively high energy (relatively low energy fiber matrix product expenditure resulting from expenditure in production of grinding operation and in the semifinished fiber matrix production of the semifinished product from micropelletized fiber matrix product) material) Evolution of dust in production + of the semifinished fiber matrix (visible evolution of dust) (no visible evolution of dust) product Absorption of moisture by the + polymer composition (grinding material had a (micropelletized material had a relatively high moisture level) relatively low moisture level) Surface quality of the + semifinished fiber matrix (inhomogeneities apparent on (fewer inhomogeneities product the surface) apparent on the surface) Tensile strength of the + semifinished fiber matrix (elevated tensile strength product compared to comparative example)

Delamination Test

[0160] To demonstrate that an inventive single-layer semifinished fiber matrix product has a lesser tendency to delaminate than a multilayer composite according to the prior art, test specimens were subjected to a mechanical test and this was used to determine the composite strength using tensile tests according to EN ISO 527 for determination of ultimate tensile stress, elongation at break and modulus of elasticity at a defined temperature. EN ISO 527-1 (latest edition of April 1996, current ISO version February 2012) is a European standard for a is for determination of tensile properties which are determined by a tensile test with a tensile tester. For this purpose, a specially designed test specimen holder was used, which enabled simple pushing-in and fixing of the cross-tension sample used as test specimen under tensile stress.

[0161] The testing was conducted on a Zwick UTS 50 tensile tester from Zwick GmbH & Co. KG, Ulm, with introduction of force by means of a mechanical clamping head. Each test specimen, referred to hereinafter as cross-tension sample, consisted of a semifinished fiber matrix product strip (55402 mm.sup.3) onto which a fin (40404 mm.sup.3) of nylon-6 had been injection-molded.

Feedstocks

Thermoplastic Matrix 1: Nylon-6 (PA6)

Nylon-6:

[0162] Injection molding type, free-flowing, finely crystalline and very rapidly processible (BASF Ultramid B3s), with a density of 1.13 g/cm.sup.3 and a melt flow index MVR of 160 cm.sup.3/10 min [test conditions: ISO1133, 5 kg, 275 C.] or a relative viscosity number (0.5% in 96% H.sub.2SO.sub.4, ISO 307, 1157, 1628) of 145 cm.sup.3/g.

Thermoplastic Matrix 2: Nylon-6 (PA6)

Nylon-6:

[0163] Film type, unreinforced, moderately free-flowing (BASF Ultramid B33 L), with a density of 1.14 g/cm.sup.3 and a relative viscosity number (0.5% in 96% H.sub.2SO.sub.4, ISO 307, 1157, 1628) of 187-203 cm.sup.3/g.

Semifinished Fiber Product

[0164] Balanced roving glass weaves (YPC ROF RE600) consisting of 1200 tax warp and waft filaments in a 2/2 twill weave with a thread density of 2.5 threads/cm. Total basis weight 600 g/m.sup.2, with 50% in warp direction and 50% in weft direction. Weave width 1265 mm, roll length 150 lfm. Modification of the weft threads with specific size adapted to the polymer system (polyamide in the examples section).

Semifinished Composite Product 1

[0165] Semifinished composite product 1 was produced in a static hotplate press. Semifinished composite product 1 with an edge length of 420 mm420 mm consisted of 4 laminas of semifinished fiber product and an amount of polymer composed exclusively of thermoplastic matrix 1, which was applied and distributed homogeneously over the fiber laminas and resulted in a fiber volume content of 47% or in a thickness of 2.0 mm. For consolidation and impregnation, a surface pressure of 24 bar and a temperature of 300 C. were applied for 240 s. Subsequent cooling to room temperature was effected over 300 s at constant pressure. The semifinished fiber product laminas were thus homogeneously embedded in the resultant semifinished composite product 1 in sheet form; no material/phase boundaries formed within the matrix owing to the homogeneous single-layer matrix system; no physical distinction was possible between the inner embedding composition and surface.

Semifinished Composite Product 2

[0166] Semifinished composite product 2, as an example of a multilayer construct according to the prior art, was likewise produced in a static hotplate press. The semifinished product intended for the multilayer construct with an edge length of 420 mm420 mm consisted of 4 laminas of semifinished fiber product and an amount of polymer composed exclusively of thermoplastic matrix 1, which was applied and distributed homogeneously over the fiber laminas and resulted in a fiber volume content of 49% or in a thickness of 1.9 mm. For consolidation and impregnation, a surface pressure of 24 bar and a temperature of 300 C. were applied for 240 s. Subsequent cooling to room temperature was effected over 300 s at constant pressure.

[0167] In order to produce a layered construct, a 50 m-thick film of thermoplastic matrix 2 was applied to each side of this semifinished product in a subsequent processing step. This again was effected in a static hotplate press at a temperature of 260 C. and a surface pressure of 9 bar that was maintained for 120 seconds. The cooling to room temperature within 60 s was effected at a surface pressure of 7.5 bar. Because of the different viscosities of the thermoplastic matrices 1 and 2, the structure of the composite material was inhomogeneous. Within the semifinished composite product 2 in sheet form that was produced in this way, the semifinished fiber laminas were embedded homogeneously in the matrix 1, whereas exclusively matrix 2 was present at the two surfaces, analogously to the semifinished products according to WO 2012/132 399 A1 and WO 2010/132 335 A1.

Testing

[0168] The test specimen used for the mechanical testing of the composite adhesion between the semifinished composite product and thermoplastic that had been molded-on by injection molding was what is called a cross-tension sample. Each of these cross-tension test specimens consisted of a semifinished composite product strip (55402 mm.sup.3) onto which a fin (40404 mm.sup.3) of nylon-6 had been injection-molded. With regard to cross-tension samples see also W. Siebenpfeiffer, Leichtbau-Technologien im Automobilbau [Lightweight Construction Technologies in Automaking], Springer-Vieweg, 2014, pages 118-120. In the cross-tension test, the cross-tension sample is then clamped in a holder and subjected to a tensile force from one side. The tensile test is illustrated in a stress-strain diagram (modulus of elasticity).

[0169] For each of the cross-tension tests to be conducted in the context of the present invention, an inventive heated, unformed semifinished composite product 1 and also a semifinished composite product 2 of multilayer construction according to the prior art were each back-molded with a total of 22 Identical fins. The respective semifinished composite product 1 or 2 was previously provided with an 8 mm hole at the gate mark, in order that there was no additional resistance to the formation of fins for the polyamide melt to be molded on. After processing, individual sheet sections suitable for testing were cut out at selected positions along the flow pathway using a bandsaw of the System Flott type from Krku GmbH, Groseifen.

[0170] For mechanical testing of the composite strength, indices were determined from tensile tests on the cross-tension samples. In this case, a specially designed test specimen holder was used, which enabled simple pushing-in and fixing of the cross-tension sample under tensile stress. The testing was conducted on a Zwick UTS 50 tensile tester from Zwick GmbH & Co. KG, Ulm, with introduction of force by means of a mechanical clamping head. The parameters employed in the mechanical testing can be found in Table 2.

TABLE-US-00002 TABLE 2 Test parameters in the tensile test Test parameter Value State of the test specimens dry (80 C. vacuum dryer, about 200 h) Testing speed [mm/min] 10 Maximum force absorbed [kN] 50 Initial force [N] 5

[0171] A criterion defined for the composite strength was the maximum force measured that was determined in the tensile test. The first measurable drops in force were caused by the first cracks in the material, detachment processes, deformations or similar effects prior to attainment of the maximum force, and seemed unsuitable as a criterion for composite strength. The maximum force measured was obtained on failure of the cross-tension sample; it is therefore referred to hereinafter as breaking force. In principle, it should be noted that the maximum force may depend not only on the composite bonding and the geometry but always also on the test method and test conditions.

[0172] For every semifinished composite product, 10 fin pull-off tests were conducted in each case in order to enable a statistically reliable conclusion.

Experimental Results

[0173] In the case of the semifinished composite product 1 (inventive), in all cases, there was purely cohesive failure of the thermoplastic matrix 1 directly at the uppermost semifinished fiber product lamina of the semifinished fiber product.

[0174] In the case of the semifinished composite product 2 (noninventive), by contrast, there was always a mixed fracture consisting of cohesive and adhesive failure in the interface layer between thermoplastic matrix 1 and thermoplastic matrix 2. No cohesive failure of thermoplastic matrix 1 was found above the uppermost lamina of semifinished fiber product.

[0175] In the case of the noninventive semifinished composite product 2, the near-surface layer of thermoplastic matrix 2 was thus tom off the substrate consisting of semifinished fiber product and thermoplastic matrix 1, whereas, in the case of the inventive single-layer semifinished composite product 1, no such division was observed within a surface-parallel layer in the thermoplastic matrix 1.

TABLE-US-00003 TABLE 3 Statistical summary of 10 fin pull-off tests Test result for semifinished Test result for semifinished No. composite product 1 composite product 2 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 +

[0176] The results are assessed according to the magnitude of the pull-off force. A + Indicates the higher pull-off force in each case for the two semifinished composite products compared with one another, whereas a indicates the lower force, and a + symbolizes a pull-off force higher by at least 15%.

[0177] The test results show that the maximum force in the comparisons of the two semifinished composite products was always higher for the inventive single-layer semifinished composite product 1 than in the case of the semifinished composite product 2 with a layered construction. The mean value of the individual test results from the test series for the inventive single-layer semifinished composite product 1 was also well above that of the semifinished composite product 2.

[0178] In summary: the fin pull-off strength was distinctly higher for the inventive single-layer semifinished composite product 1 than for the semifinished composite product 2.