PELLETS OF A GLASS FIBER-REINFORCED THERMOPLASTIC POLYMER COMPOSITION, AND METHOD OF THEIR MANUFACTURE

Abstract

Pellets of a glass fiber-reinforced thermoplastic polymer composition include a sheathed continuous multifilament strand having a core that extends in the longitudinal direction and a polymer sheath which intimately surrounds said core, wherein the core includes at least one continuous glass multifilament strand, the polymer sheath has a thermoplastic polymer composition including a polyolefin and having a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of at least 1.0 dg/min and less than 20 dg/min, wherein the length of the glass filaments in the pellets is substantially the same as the pellet length, and is 10 to 55 mm, preferably 10 to 40 mm, more preferably 10 to 30 mm and most preferably from 10 to 20 mm.

Claims

1. Pellets of a glass fiber-reinforced thermoplastic polymer composition comprising a sheathed continuous multifilament strand comprising a core that extends in the longitudinal direction and a polymer sheath which intimately surrounds said core, wherein the core comprises at least one continuous glass multifilament strand, the polymer sheath consists of a thermoplastic polymer composition comprising a polyolefin and having a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of at least 1.0 dg/min and less than 20 dg/min, wherein the length of the glass filaments in the pellets is substantially the same as the pellet length, and is 10 to 55 mm.

2. The pellets according to claim 1, wherein the sheathed continuous multifilament strand comprises a polyethylene wax having a melting point of 50 to 100 C., MW of 5 to 10 kg/mol and a MWD of 5 to 10 in an amount of less than 0.50 wt %, with respect to the sheathed continuous multifilament strand.

3. The pellets according to claim 1, wherein the sheathed continuous multifilament strand comprises a polyethylene wax having MW of at most 10 kg/mol in an amount of less than 0.50 wt %, with respect to the sheathed continuous multifilament strand.

4. The pellets according to claim 1, wherein the polyolefin comprises a propylene-based polymer and/or an elastomer of ethylene and an -olefin comonomer having 4 to 8 carbon atoms, wherein the propylene-based polymer is at least one selected from the group consisting of a propylene homopolymer, a propylene random copolymer and a heterophasic propylene copolymer and mixtures thereof.

5. The pellets according to claim 1, wherein the polyolefin comprises or consists of a propylene homopolymer having a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of 25 to 50 dg/min and a heterophasic propylene copolymer having a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of 0.1 to 5.0 dg/min.

6. The pellets according to claim 1, wherein the amount of the glass filaments is 20 to 70 wt % with respect to the sheathed continuous multifilament strand.

7. A process for preparing pellets of a glass fiber-reinforced thermoplastic polymer composition comprising a sheathed continuous multifilament strand comprising a core that extends in the longitudinal direction and a polymer sheath which intimately surrounds said core, comprising the sequential steps of: b) applying the polymer sheath of a thermoplastic polymer composition comprising a polyolefin around the at least one continuous glass multifilament strand to form a sheathed continuous multifilament strand, wherein the thermoplastic polymer composition has a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of at least 1.0 dg/min and less than 20 dg/min, and c) cutting the sheathed continuous glass multifilament strand to obtain the pellets, wherein the length of the glass filaments in the pellets is substantially the same as the pellet length, and is 10 to 55 mm.

8. A process for preparing an extruded article by melting and extruding the pellets according to claim 1.

9. The process according to claim 8, wherein the article is a hollow article or a sheet.

10. The process according to claim 8, wherein the amount of the glass filaments is 20 to 70 wt % with respect to the extruded article.

11. The process according to claim 8, wherein the extruded article is produced by melting and extruding the pellets without an addition of a further polyolefin.

12. The process according to claim 8, wherein the extruded article is produced by melting and extruding the pellets together with a further propylene-based polymer.

13. The process according to claim 12, wherein the further propylene-based polymer has a melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of less than 20 dg/min.

14. A process for preparing a thermoformed article, comprising the process according to claim 8 to obtain the extruded article, wherein the extruded article is a sheet, and thermoforming the sheet.

15. The process according to claim 14, wherein the thermoformed article is a top cover in an article for covering battery components in an automotive prime-mover battery pack, wherein the top cover has an outer major surface and an inner major surface that is shaped to conform to the battery components.

16. An extruded article comprising or made by melting and extruding the pellets according to claim 1.

17. The extruded article according to claim 16, wherein the article is a multiwall article having a largest dimension of at most 425 mm and a wall thickness of at most 3 mm, wherein the melt flow index as measured according to ISO1133-1:2011 (2.16 kg/230 C.) of the thermoplastic polymer composition of the polymer sheath has the melt flow index of the polymer is 10 to 15 dg/min.

18. A thermoformed article made by thermoforming the extruded article according to claim 16.

19. The thermoformed article according to claim 18, wherein the thermoformed article is a top cover in an article for covering battery components in an automotive prime-mover battery pack, wherein the top cover has an outer major surface and an inner major surface that is shaped to conform to the battery components.

Description

EXAMPLES

[0143] Materials Used [0144] PP1: SABIC PP 595A, propylene homopolymer (Melt flow index of 47 dg/min as measured according to ISO1133 at 230 C./2.16 kg, MW of 165 kg/mol, MWD of 7.6) [0145] PP2: SABIC PP 83MF10, heterophasic propylene copolymer consisting of propylene homopolymer and propylene-ethylene copolymer (Melt flow index of 1.8 dg/min as measured according to ISO1133 at 230 C./2.16 kg; ethylene content (Tc) in heterophasic propylene copolymer of 13.91.1 wt %, MW of 422 kg/mol, MWD of 7.4) [0146] GF: glass multifilament strand having a diameter D of 19 micron and a tex of 3000 containing 2% by mass of sizing aminosilane agent [0147] LDPE: SABIC LDPE 1905U0 Ultra Melt Strength (UMS), Melt Flow Index 5 dg/min at 190 C. and 2.16 kg, measured according to ISO 1133. Density 920 kg/m.sup.3 according to ASTM D1505.

[0148] Impregnating agent: a highly branched polyethylene wax having density: 890-960 kg/m.sup.3, dynamic viscosity: 40-58 mPa.Math.s at 100 C. (ASTM D3236), melting point: 65 C., MW: 400 kg/mol, MWD: 6.8 (Dicera 13082 Paramelt) [0149] Coupling agent: Exxelor P01020 powder (PP-g-MA) from ExxonMobil: density: 900 kg/m.sup.3, melting point: 162 C., MFR: 430 g/10 min at 230 C. and 2.16 kg (testing method: ASTM D1238) [0150] UV stabilizer: Chimasorb 119FL, a hindered amine light stabilizer (HALS) [0151] Thermal stabilizer: Irganox B 225 commercially available from BASF, blend of 50 wt % tris(2,4-ditert-butylphenyl)phosphite and 50 wt % pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate]

[0152] Herein, MW is measured according to ASTM D6474-12.

Examples 1-2

[0153] Preparation of Sheathed Continuous Multifilament Strands (Wire-Coating)

[0154] Sheathed continuous multifilament strands were prepared from the components as given in Table 1 using the wire coating process as described in details in the examples of WO2009/080281A1. After the wire coating process, the strands were cut into pellets having length of 15 mm. In the pellets, the glass multifilament thus had a length L of 15 mm and a diameter D of 19 micron (L/D ratio of 789).

[0155] For pellets B, the wire coating process was performed by [0156] unwinding from a package of a continuous glass multifilament strand containing at most 2% by mass of a sizing composition, [0157] applying 2.6 wt % of an impregnating agent onto the multifilament strand to form an impregnated continuous multifilament strand; [0158] applying a sheath of thermoplastic polymer composition previously mixed in the twin screw extruder around the impregnated continuous multifilament strand to form a sheathed continuous multifilament strand.

[0159] For pellets A, the wire coating process was identical except that the step of applying the impregnating agent was not performed.

TABLE-US-00001 TABLE 1 Ex A Ex B PP1 (MFI 47 dg/min) 43.7 41.97 PP2 (MFI 1.8 dg/min) 24.07 23.5 GF 30.17 30.17 impregnating agent 0 2.6 coupling agent 1.8 1.5 UV stabilizer 0.06 0.06 thermal stabilizer 0.2 0.2 MFI of composition (dg/min)* 17.5 17.2 The amounts are in wt % with respect to the total composition of the pellets. *Melt flow index determined according to ISO1133-1: 2011 at 230 C./2.16 kg of the thermoplastic polymer composition for preparing the sheath.

[0160] Extrusion

[0161] For example 1 and 2 respectively, the pellets obtained by Ex A and B were fed into the hopper of a twin screw extruder (co rotating, L/D=32, D=44 mm), where upon shear in the range of 100-1000 1/s and temperature profile 60 C. (pellet feeding), 4D zone 210 C., 12D zone 235 C., 10D/210 C. and die zone temperature 190 C. the polymer melts and dispersion and breakage of the glass fibers occurs. The melted composition was conveyed into the die where it was shaped and pulled out of the die by a puller.

[0162] It was possible to perform the extrusion without sagging. Upon cooling, the final product was obtained. Throughput of the extruder was 80 kg/h.

Comparative Experiment 3

[0163] Pellets of long glass fiber reinforced polypropylene composition (STAMAX 60YM240) having a sheath made of a thermoplastic polymer composition having an MFI of 47 dg/min as measured according to ISO1133 at 230 C./2.16 kg were melt-mixed and subjected to the same extrusion step as in Example 1 together with PP2 and additives.

[0164] The composition of the extruded article is shown in Table 2.

TABLE-US-00002 TABLE 2 Ex B sheath of STAMAX 60YM240 (MFI 47 dg/min) 41.97 PP2 (MFI 1.8 dg/min) 23.5 GF (core of STAMAX 60YM240) 30.17 impregnating agent 2.6 coupling agent 1.5 UV stabilizer 0.06 thermal stabilizer 0.2 MFI of composition (dg/min)* 17.2 The amounts are in wt % with respect to the total composition of the pellets. *Melt flow index of the mixture of the polymer composition of the sheath and PP2 calculated based on the MFI of the individual components measured according to ISO1133 at 230 C./2.16 kg

[0165] It was possible to perform the extrusion without sagging. Upon cooling, the final product was obtained.

[0166] Properties

[0167] For the extruded articles of Ex 1, 2 and CEx 3, the following properties were measured by cutting of samples in extrusion direction from the extruded article. Results are presented in Table 2.

[0168] E-modulus according to ISO 527-2/1B

[0169] Tensile strength according to ISO 527-2/1B

[0170] Further, the dispersion level of the glass filaments in the extruded article was determined. Samples were cut from the extruded article on multiple locations. The dispersion level was determined using Micro-computed tomography (PCT) and X-ray image analysis.

TABLE-US-00003 TABLE 2 Ex 1 Ex 2 CEx 3 extruded low MFI low MFI high MFI pellets composition pellets pellets and low MFI PP wax no yes yes GF dispersion ++ ++ + E-modulus 1.34 1.24 1 0 [%] Tensile strength 1.34 1.24 1 0 [%] E-modulus 1.78 1 45 [%] Tensile strength 1.60 1 45 [%]

[0171] The addition of a polypropylene with a low MFI allows extrusion, but the glass filament dispersion is not ideal (CEx 3). Pellets having a sheath made of a composition having a low MFI can be extruded into articles with a better glass fiber dispersion and better mechanical properties (E1 and E2).

[0172] The absence of wax in the pellets led to better mechanical properties (Ex 1 vs Ex 2). This is surprising in view of the well-known effects of the impregnating agent to effectively couple the glass fibres to each other and to the polypropylene sheath in the pellet and to provide a sufficient dispersion of the glass fibres in downstream conversion processes.

Comparative Experiment 4

[0173] Comparative experiment 3 was repeated except that 20 wt % of PP2 was replaced by the same amount of LDPE.

[0174] It was possible to perform the extrusion without sagging although the extrudability was reduced compared to Ex 1, 2 and CEx 3. Upon cooling, the final product was obtained.

[0175] Compared to CEx 3, the mechcanial properties of the extruded product were not higher and the GF dispersion was worse, causing white spots.

Comparative Experiment 5

[0176] Pellets of long glass fiber reinforced polypropylene composition (STAMAX 30YM240, 40YM240 and 60YM240) were subjected to the same extrusion step as in Example 1. It was not possible to perform the extrusion due to sagging.

Comparative Experiment 6

[0177] Pellets of glass fiber reinforced polypropylene composition made by a pultrusion process (Verton MV006S) were subjected to the same extrusion step as in Example 1. It was not possible to perform the extrusion due to sagging.

[0178] It can be understood that it is not possible to extrude pellets comprising a composition having a high MFI on their own (CEx 5 and CEx 6) whereas the pellets according to the invention allows extrusion (E1 and E2).