Flame retardant polypropylene composition

Abstract

The present invention relates to a flame retardant polypropylene composition for a conduit, appliance, and/or automotive wire, comprising a flame retardant composition comprising: a) a base resin comprising a heterophasic propylene copolymer which comprises a polypropylene homo- or copolymer matrix and an ethylene propylene rubber dispersed in said matrix, and b) a metal hydroxide or hydrated compound, wherein the heterophasic propylene copolymer has a MFR.sub.2 below 0.8 g/10 min and a xylene cold soluble (XCS) fraction content between 1 and 15 wt % based on the total weight of the heterophasic propylene copolymer.

Claims

1. A flame retardant composition comprising: a) a base resin comprising a heterophasic propylene copolymer which comprises a polypropylene homo- or copolymer matrix and an ethylene propylene rubber dispersed in said matrix, and b) a metal hydroxide, wherein the heterophasic propylene copolymer has a MFR.sub.2 below 0.8 g/10 min and a xylene cold soluble (XCS) fraction content between 1 and 15 wt % based on the total weight of the heterophasic propylene copolymer; and wherein the heterophasic propylene copolymer has a total amount of ethylene between 1 and 8.5 wt %, based on the total weight of the heterophasic propylene copolymer.

2. The composition of claim 1 wherein the MFR.sub.2 of the heterophasic propylene copolymer is below 0.5 g/10 min.

3. The composition according to claim 1 wherein the base resin a) and the metal hydroxide b) make up to 80 wt % of the total composition.

4. The composition according to claim 1 wherein the base resin a) is present in the composition in an amount between 30 and 52 wt % and the metal hydroxide b) in an amount from 47 to 62 wt % based on the total weight of the composition.

5. The composition according to claim 1 wherein the composition comprises 40 to 45 wt % of the heterophasic propylene copolymer and 55 to 60 wt % of the metal hydroxide based on the total weight of the composition.

6. The composition according to claim 1 wherein the base resin further comprises a polar ethylene copolymer.

7. The composition according to claim 6 wherein the polar ethylene copolymer is ethylene butylacrylate (EBA).

8. The composition according to claim 6 wherein the polar ethylene copolymer is present in the composition in an amount between 2 to 30 wt % based on the total weight of the composition.

9. The composition according to claim 1 wherein the base resin further comprises an ethylene copolymer having a density between 0.860 to 0.910 g/cm.sup.3.

10. The composition according to claim 9 wherein the ethylene copolymer is present in the composition in an amount between 2 to 30 wt % based on the total weight of the composition.

11. The composition according to claim 1 wherein metal hydroxide b) comprises magnesium hydroxide.

12. The composition according to claim 1 wherein the heterophasic propylene copolymer has a total amount of ethylene between 1 and 7 wt %, based on the total weight of the heterophasic propylene copolymer.

13. A flame retardant composition comprising: a) a base resin comprising a heterophasic propylene copolymer which comprises a polypropylene homo- or copolymer matrix and an ethylene propylene rubber dispersed in said matrix, and b) a metal hydroxide, wherein the heterophasic propylene copolymer has a MFR.sub.2 below 0.8 g/10 min and a xylene cold soluble (XCS) fraction content between 4 and 13 wt % based on the total weight of the heterophasic propylene copolymer and determined according to ISO 16152; and wherein the heterophasic propylene copolymer has a total amount of ethylene between 1 and 8.5 wt %, based on the total weight of the heterophasic propylene copolymer.

14. The composition according to claim 13 wherein the heterophasic propylene copolymer has a total amount of ethylene between 1 and 7 wt %, based on the total weight of the heterophasic propylene copolymer.

15. The composition of claim 13 wherein the MFR.sub.2 of the heterophasic propylene copolymer is below 0.5 g/10 min.

16. The composition according to claim 13 wherein the base resin a) and the metal hydroxide b) make up to 80 wt % of the total composition.

17. The composition according to claim 13 wherein the base resin a) is present in the composition in an amount between 30 and 52 wt % and the metal hydroxide b) in an amount from 47 to 62 wt % based on the total weight of the composition.

18. The flame retardant composition of claim 1, the heterophasic propylene copolymer has a total amount of ethylene between 1 and 5 wt %, based on the total weight of the heterophasic propylene copolymer.

19. The flame retardant composition of claim 13, the heterophasic propylene copolymer has a total amount of ethylene between 1 and 5 wt %, based on the total weight of the heterophasic propylene copolymer.

Description

1. TEST METHODS

(1) a) Melt Flow Rate

(2) The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.2 of polypropylene is measured at a temperature 230 C. and a load of 2.16 kg.

(3) b) Flame Retardancy

(4) Fame retardancy is measured according to ISO 6722:2006, paragraph 12 (resistance to flame propagation). The purpose of said test method is to determine the resistance to flame propagation for automotive cables. The cable (600 mm) is installed at a 45 deg. angle to the vertical line and a flame produced by a Bunsen burner, fed with an appropriate gas, having a combustion tube of 9 mm internal diameter, and a flame height of 100 mm is applied onto the cable sample at a 90 deg. angle 500 mm from the upper end of the insulation.

(5) The test sample shall be exposed to the tip of the inner blue cone of the flame having a length of 50 mm. For cables having a conductor size of equal or smaller 2.5 mm.sup.2 the flame is applied for 15 seconds. In order to fulfil the test, the flame should extinguish within 70 seconds after the burner flame has been taken away with a minimum of 50 mm of insulation from its top remaining unburned. A wire fulfilling this criterion is marked pass, otherwise it is marked fail.

(6) c) Scrape Abrasion

(7) The abrasion test is performed in full accordance with ISO 6722:2006, paragraph 9.3. The abrasion resistance as reported is based on the testing of a wire sample based on a 0.35 mm.sup.2 18 AWG stranded copper conductor with the nominal layer wall thickness being 0.24 mm (actual 0.4 mm). The needle diameters used are 0.45 mm, the force 7 Newton, and the tested samples are not crosslinked. Results are given in Table 3, and are reported as cycles which the material is able to withstand. For every wire tested, twelve samples are tested and the average and minimum number of strokes are reported. If any of the samples withstand less than 200 strokes it is reported as failure in Table 3.

(8) d) Xylene Cold Soluble (XCS) Fraction Content

(9) The amount of xylene cold soluble fraction is determined according to ISO 16152. The amount of polymer which remains dissolved at 25 C. after cooling is given as the amount of xylene soluble polymer. The content of xylene soluble polymer is herein assumed to follow the mixing rule:
XS.sub.b=w.sub.1XS.sub.1+w.sub.2XS.sub.2

(10) Where XCS is the content of xylene soluble polymer in weight-%, w is the weight fraction of the component in the mixture and subscripts b, 1 and 2 refer to the overall mixture, component 1 (matrix component) and component 2 (elastomeric component) respectively.

(11) e) Ethylene Content Both as Total Amount in the Heterophasic Propylene Copolymer and as Amount in the Sole Elastomeric Phase.

(12) The comonomer content is determined by quantitative Fourier transform infrared spectroscopy (FTIR) after basic assignment calibrated via quantitative .sup.13C nuclear magnetic resonance (NMR) spectroscopy in a manner well known in the art.

(13) Thin films are pressed to a thickness of between 100-500 micrometer and spectra recorded in transmission mode. Specifically, the ethylene content of a polypropylene-co-ethylene copolymer is determined using the baseline corrected peak area of the quantitative bands found at 720-722 and 730-733 cm.sup.1. Specifically, the butene or hexene content of a polypropylene copolymer is determined using the baseline corrected peak area of the quantitative bands found at 1377-1379 cm.sup.1. Quantitative results are obtained based upon reference to the film thickness.

(14) The comonomer content is herein assumed to follow the mixing rule below:
C.sub.b=w.sub.1C.sub.1+w.sub.2C.sub.2
where C is the content of comonomer in weight-%, w is the weight fraction of the component in the mixture and subscripts b, 1 and 2 refer to the overall mixture, component 1 (matrix component) and component 2 (elastomeric component), respectively.

(15) As it is well known to the person skilled in the art the comonomer content in weight basis in a binary copolymer can be converted to the comonomer content in mole basis by using the following equation:

(16) $\mathrm{cm}=\frac{1}{1+\left(\frac{1}{\mathrm{cw}}-1\right)*\frac{\mathrm{MWc}}{\mathrm{MWm}}}$
wherein cm is the mole fraction of comonomer units in the copolymer, cw is the weight fraction of comonomer units in the copolymer, MWc is the molecular weight of the comonomer (such as ethylene) and MWm is the molecular weight of the main monomer (i.e., propylene).
f) Density

(17) Density is measured in accordance with ISO 1183 on compression moulded plaques.

(18) g) Flexural Modulus

(19) The flexural modulus is determined according to ISO 178.

(20) The test specimens having a dimension of 80104.0 mm.sup.3 (lengthwidththickness) are prepared by injection molding according to EN ISO 1873-2. The length of the span between the supports is 64 mm, the test speed is 2 mm/min and the force is 100 N.

(21) h) Charpy Impact Strength Notched

(22) Charpy impact strength notched is determined according to ISO 179-1eA:2000 on V-notched samples of 80104 mm.sup.3 at 23 C., 0 C., and 23 C. as specified in the examples. The test specimens are prepared by injection moulding using an IM V60 TECH machinery in line with EN ISO 1873-2 (80*104 mm.sup.3). The melt temperature is 200 C. and the mould temperature is 40 C.

(23) i) Cold Flexibility (Low-Temperature Winding Test)

(24) Cold flexibility is measured in accordance with ISO6722:2006, paragraph 8. The wire is fixed on a rotable mandrel and put in a freezing chamber at 40 C. for 4 hours. After exposure, the test sample is allowed to return to room temperature and a visual inspection of the insulation is made. If no exposed conductor is visible the 1 kVolt, 1 minute withstand voltage test is performed. In the prior voltage test the sample is immersed in salt water bath for 10 minutes. The sample is marked as pass in Table 3 if neither exposed conductor nor breakdown during the withstand voltage test is observed.

(25) j) Thermal Overload in Wound State

(26) Thermal overload is controlled in accordance with ISO6722:2006, paragraph 10.3. The wire is placed in a heating oven at 175 C. for six hours following by a conditioning of minimum 16 hours at room temperature in accordance with paragraph 10.1.4. Thereafter the wire is put on a mandrel defined in Table 8 of ISO6722:2006. No conductor shall be visible and during the withstand voltage test, breakdown shall not occur.

2. EXAMPLES

(27) In the preparation of the inventive compositions (Ex1-Ex3) heterophasic propylene copolymers BA202E, BA212E, available from Borealis AG and PP-EPR1 are used. PP-EPR1 is prepared as follows:

(28) Catalyst Preparation

(29) First, 0.1 mol of MgCl.sub.23 EtOH is suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution is cooled to the temperature of 15 C. and 300 ml of cold TiCl.sub.4 is added while maintaining the temperature at said level. Then, the temperature of the slurry is increased slowly to 20 C. At this temperature, 0.02 mol of diethylhexylphthalate (DOP) is added to the slurry. After the addition of the phthalate, the temperature is raised to 135 C. during 90 minutes and the slurry is allowed to stand for 60 minutes. Then, another 300 ml of TiCl.sub.4 is added and the temperature is kept at 135 C. for 120 minutes. After this, the catalyst is filtered from the liquid and washed six times with 300 ml heptane at 80 C. Then, the solid catalyst component is filtered and dried. Catalyst and its preparation concept is described in general e.g. in patent publications EP 491 566, EP 591 224 and EP 586 390.

(30) Then triethylaluminium (TEAL), dicyclopentyldimethoxysilane (DCPDMS) as donor (Do), catalyst as produced above and vinylcyclohexane (VCH) is added into oil, like mineral oil, e.g. Technol 68 (kinematic viscosity at 40 C. 62-74 cSt), in amounts so that Al/Ti is 3-4 mol/mol, Al/Do is as well 3-4 mol/mol, and weight ratio of VCH/solid catalyst is 1:1.

(31) The mixture is heated to 60-65 C. and allowed to react until the content of the unreacted vinylcyclohexane in the reaction mixture is less than 1000 ppm. Catalyst concentration in the final oil-catalyst slurry is 10-20 wt %.

(32) Polymerization

(33) In PP-EPR1 the matrix is made of a propylene homopolymer which is prepared in a loop reactor and a gas phase reactor (GPR1). The obtained polymer is stabilized with conventional stabilizer and antioxidant. Further information about the propylene homopolymer constituting the matrix is shown in the table below.

(34) Subsequently, the propylene homopolymer is transferred to a second gas phase reactor (GPR2) where the elastomeric polypropylene is prepared. The obtained polymer is stabilized in a conventional twin screw extruder with conventional stabilizers, i.e. calcium stearate and phenolic antioxidant, in conventional amounts, and pelletized for further testing as given in Table 1.

(35) For the preparation of comparative compositions (CE1-CE4) polypropylenes HA507MO (propylene homopolymer), RA130E (random propylene copolymer) and heterophasic propylene copolymers BA125MO and BA204E, available from Borealis AG, are used.

(36) TABLE-US-00001 TABLE 1 Process parameters HPC1 Catalyst feed (g/h) 5.0 Ti content % 1.9 Donor feed (g/t propylene) 80 Al/Ti ratio (mol/mol) 127 Al/donor ratio (mol/mol) 5.0 Prepolymerisation Temperature ( C.) 40 Hydrogen feed (g/h) 0.5 Loop reactor Temperature ( C.) 85 Pressure (kPa) 5462 H2/C3 ratio (mol/kmol) 0.07 MFR10 (g/10 min) 1.1 Gas phase reactor 1 Temperature ( C.) 95 Pressure (kPa) 2301 H2/C3 ratio (mol/kmol) 214 MFR2 (g/10 min) 0.33 Gas phase reactor 2 Temperature ( C.) 50 Pressure (kPa) 2000 C2/C3 ratio (mol/kmol) 700 H2/C2 ratio (mol/kmol) 14

(37) The properties of all the polymers are listed in Table 2.

(38) TABLE-US-00002 TABLE 2 BA202E BA212E PP-EPR1 BA125MO BA204E HA507MO RA130E MFR.sub.2 (g/10 min) 0.3 0.3 0.3 1.3 0.8 0.8 0.25 Density (Kg/m.sup.3) 900 900 900 905 900 908 905 XCS (wt %) 13 10 4.5 16 13 2.5 7 Total Ethylene (wt %) 8.5 4.4 1.4 10 8.5 0 3.6 Ethylene in EPR (wt %) 65 45 30 60 65 Flexural Modulus (Mpa) 1300 1700 2000 1200 1100 1500 800 Charpy notched 50/5 50/5 29/2 50/7 35/4 6/ 20/2 23 C./23 C. (kJ/m.sup.2)

(39) The polymer compositions of all the examples are produced by compounding together the polymers listed in Table 2 with Magnifin H5HV (Mg(OH).sub.2) from Martinswerke, Germany and with Irganox 1010, Irganox 1024 and Irganox PS 802 (antioxidants).

(40) The amount in wt % of each component for both inventive and comparative examples is given in Table 3.

(41) A Buss Co-kneader type PR46B-11D/H1 is used for the compounding.

(42) TABLE-US-00003 TABLE 3 Ex 1 Ex 2 Ex 3 CE1 CE2 CE3 CE4 BA202E 41.4 BA212E 41.4 PP-EPR1 41.4 BA125MO 38.9 BA204E 41.4 HA507MO 41.4 RA130E 41.4 Magnifin H5HV 57.5 57.5 57.5 60 57.5 57.5 57.5 Irganox 1010 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Irganox 1024 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Irganox PS802 0.5 0.5 0.5 0.5 0.5 0.5 0.5

(43) Automotive wires of 0.35 mm.sup.2 (70.254 mm diameter single wires) are produced from the compositions on a Nokia-Maillefer extruder, 45 mm/28D, with a temperature profile of: 165-185-200-215-220 (Bride)-230 (Flansch)-235 (Bypass)-250 (Head)-250 C. (Pressure die).

(44) The outer diameter of the cable is 1.28 mm and the wall thickness 0.24 mm.

(45) The melt temperature is of 220 C. and a line speed of 100 m/min. The conductor is preheated to a setting temperature of 90 C. The compound is pre-dried for 18 hours at 80 C. prior extrusion.

(46) The properties of the 0.35 mm.sup.2 cables are listed in Table 4. The tests are made according to LV112 and ISO6722 (Jan. 17, 2014).

(47) TABLE-US-00004 TABLE 4 Ex 1 Ex 2 Ex 3 CE1 CE2 CE3 CE4 Flame Pass Pass Pass Pass Fail Pass Fail retardancy Cold flexibility Pass Pass Pass Pass Pass Fail Pass 40 C. Needle abrasion Pass Pass Pass Fail Fail Pass Fail min. 200 cycles Minimum No 200 530 985 16 135 260 49 of cycles Avarage No 270 600 1300 19 250 530 55 of cycles Thermal overload Pass Pass Pass Fail Pass Pass Fail in wound state

(48) From Table 4 it can clearly be seen that for thin wires the required cycles of 200 strokes in the needle abrasion test is only met by the inventive compositions and the comparative composition 3, which, however, shows inferior low temperature properties. The other properties are at best for inventive examples 2 and 3.

(49) It is thereby shown that only specific types of heterophasic copolymers are suitable for automotive, conduit and appliance wires.