FLAME RETARDANT AND FIRE RESISTANT POLYOLEFIN COMPOSITION

Abstract

The present invention is directed to a polyolefin composition which has flame retardant and/or fire resistant properties and is suitable as flame retardant and/or fire resistant layer of a wire or cable. The polyolefin composition of the present invention comprises an polyolefin homo- or copolymer, ground magnesium hydroxide having particle size distribution D.sub.50 of 1.5 to 5.0 m in an amount of 30 to 65 wt % based on the weight of the polyolefin composition, and a silicone fluid or gum in an amount of 0.1 to 20 wt % based on the weight of the polyolefin composition. The present invention is further directed to a wire or cable comprising one or more layers, wherein at least one layer thereof is obtained from the polyolefin composition of the present invention. Finally, the present invention is further directed to the use of a polyolefin composition of the present invention as a flame retardant layer of a wire or cable.

Claims

1. A polyolefin composition comprising: (A) a polyolefin homo- or copolymer, (B) ground magnesium hydroxide having particle size distribution D50 of 1.5 to 5.0 m in an amount of 30 to 65 wt % based on the weight of the polyolefin composition, and (C) a silicone fluid or gum in an amount of 0.1 to 20 wt % based on the weight of the polyolefin composition.

2. The polyolefin composition according to claim 1, said polyolefin composition further comprising: (D) a borate in an amount of 5 to 25 wt % based on the weight of the polyolefin composition.

3. The polyolefin composition according claim 2, wherein said borate (D) is selected from the group consisting of a borate of an alkali metal, a borate of an alkaline earth metal, a borate of a metal of groups 3 to 12 of the periodic table of elements, a borate of aluminium, boric acid, boron phosphate, and mixtures thereof.

4. The polyolefin composition according to claim 3, wherein said borate (D) is selected from the group consisting of sodium borate, calcium borate, zinc borate, and mixtures thereof.

5. The polyolefin composition according to claim 4, wherein said borate (D) comprises calcium borate.

6. The polyolefin composition according to claim 1, wherein said silicone fluid or gum (C) is selected from the group consisting of a polysiloxane, preferably a polydimethylsiloxane, a siloxane containing alkoxy and alkyl functional groups and mixtures thereof.

7. The polyolefin composition according to claim 6, wherein said silicone fluid or gum (C) is an organomodified siloxane.

8. The polyolefin composition according to claim 1, wherein said polyolefin homo- or copolymer (A) is an ethylene copolymer comprising ethylene monomer units and comonomer units comprising a polar group.

9. The polyolefin composition according to claim 8, wherein said ethylene copolymer further comprises comonomer units comprising a crosslinkable silane group, wherein said comonomer units comprising a polar group are different from said comonomer units comprising a crosslinkable silane group.

10. The polyolefin composition according to claim 9, wherein the content of said comonomer units comprising a polar group is 2 to 35 wt %, or the content of said comonomer units comprising a crosslinkable silane group is 0.2 to 4 wt %, or the content of said comonomer units comprising a polar group is 2 to 35 wt % and the content of said comonomer units comprising a crosslinkable silane group is 0.2 to 4 wt %, based on the weight of said ethylene copolymer.

11. The polyolefin composition according to claim 8, wherein said comonomer units comprising a polar group are selected from the group consisting of acrylic acid, methacrylic acid, acrylates, methacrylates, vinyl esters, and mixtures thereof.

12. The polyolefin composition according to claim 1, wherein said ground magnesium hydroxide (B) has particle size distribution D50 of 2.5 to 3.5 m.

13. The polyolefin composition according to claim 1, wherein said ground magnesium hydroxide (B) has BET surface area of 1-20 m.sup.2/g.

14. A wire or cable comprising one or more layers, wherein at least one layer thereof is obtained from a polyolefin composition according to claim 1.

15. Use of a polyolefin composition according to 1, optionally after cross-linking thereof, as a flame retardant layer of a wire or cable.

Description

DETAILED DESCRIPTION OF THE INVENTION

1. Methods

a) Melt Flow Rate

[0073] Melt flow rate (MFR) is measured according to ISO 1133 (Davenport R-1293 from Daventest Ltd). MFR values were measured at two different loads 2.16 kg (MFR2, 16) and 21.6 kg (MFR21). The MFR values were measured at 150 C. for ATH containing formulations. For all polymers and all other compounds the temperature of 190 C. was used.

b) Comonomer Content

[0074] 20 Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymer composition or polymer as given above or below in the context.

[0075] Quantitative 1H NMR spectra was recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 MHz. All spectra were recorded using a standard broad-band inverse 5 mm probehead at 100 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d2 (TCE-d2) using ditertiarybutylhydroxytoluen (BHT) (CAS 128-37-0) as stabiliser. Standard single-pulse excitation was employed utilizing a 30 degree pulse, a relaxation delay of 3 s and no sample rotation. A total of 16 transients were acquired per spectra using 2 dummy scans. A total of 32 k data points were collected per FID with a dwell time of 60 s, which corresponded to a spectral window of approx. 20 ppm. The FID was then zero filled to 64 k data points and an exponential window function applied with 0.3 Hz line-broadening. This setup was chosen primarily for the ability to resolve the quantitative signals resulting from methylacrylate and vinyltrimethylsiloxane copolymerisation when present in the same polymer.

[0076] Quantitative 1H NMR spectra were processed, integrated and quantitative properties determined using custom spectral analysis automation programs. All chemical shifts were internally referenced to the residual protonated solvent signal at 5.95 ppm.

[0077] Characteristic signals resulting from the incorporation of vinylacetate (VA), methyl acrylate (MA), butyl acrylate (BA) and vinyltrimethylsiloxane (VTMS), in various comonomer sequences, were observed (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201). All comonomer contents were calculated with respect to all other monomers present in the polymer.

[0078] The vinylacetate (VA) incorporation was quantified using the integral of the signal at 4.84 ppm assigned to the*VA sites, accounting for the number of reporting nuclei per comonomer and correcting for the overlap of the OH protons from BHT when present:

VA=(I*VA(I.sub.ArBHT)/2)/1

[0079] The methylacrylate (MA) incorporation was quantified using the integral of the signal at 3.65 ppm assigned to the 1MA sites, accounting for the number of reporting nuclei per comonomer:

MA=I.sub.1 MA/3

[0080] The butylacrylate (BA) incorporation was quantified using the integral of the signal at 4.08 ppm assigned to the 4BA sites, accounting for the number of reporting nuclei per comonomer:

BA=I.sub.4 BA/2

[0081] The vinyltrimethylsiloxane incorporation was quantified using the integral of the signal at 3.56 ppm assigned to the 1VTMS sites, accounting for the number of reporting nuclei per comonomer:

VTMS=I.sub.1 VTMS/9

[0082] Characteristic signals resulting from the additional use of BHT as stabilizer were observed. The BHT content was quantified using the integral of the signal at 6.93 ppm assigned to the ArBHT sites, accounting for the number of reporting nuclei per molecule:

BHT=IArBHT/2

[0083] The ethylene comonomer content was quantified using the integral of the bulk aliphatic (bulk) signal between 0.00-3.00 ppm. This integral may include the 1VA (3) and aVA (2) sites from isolated vinylacetate incorporation, *MA and aMA sites from isolated methylacrylate incorporation, 1BA (3), 2BA (2), 3BA (2), *BA (1) and aBA (2) sites from isolated butylacrylate incorporation, the*VTMS and aVTMS sites from isolated vinylsilane incorporation and the aliphatic sites from BHT as well as the sites from polyethylene sequences. The total ethylene comonomer content was calculated based on the bulk integral and compensating for the observed comonomer sequences and BHT:

E=(1/4)*[I.sub.bulk5*VA3*MA10*BA3*VTMS21*BHT]

[0084] It should be noted that half of the a signals in the bulk signal represent ethylene and not comonomer and that an insignificant error is introduced due to the inability to compensate for the two saturated chain ends (S) without associated branch sites.

[0085] The total mole fractions of a given monomer (M) in the polymer was calculated as:

fM=M(E+VA+MA+BA+VTMS)

[0086] The total comonomer incorporation of a given monomer (M) in mole percent was calculated from the mole fractions in the standard manner:

M[mol %]=100*fM

[0087] The total comonomer incorporation of a given monomer (M) in weight percent was calculated from the mole fractions and molecular weight of the monomer (MV) in the standard manner:

M[wt %]=100*(fM*MV)/((fVA*86.09)+(fMA*86.09)+(fBA*128.17)+(fVTMS*148.23)+((1fVAfMAfBAfVTMS)*28.05))

[0088] If characteristic signals from other specific chemical species are observed, the logic of quantification and/or compensation can be extended in a similar manner to that used for the specifically described chemical species, e.g. identification of characteristic signals, quantification by integration of a specific signal or signals, scaling for the number of reported nuclei and compensation in the bulk integral and related calculations. Although this process is specific to the specific chemical species in question, the approach is based on the basic principles of quantitative NMR spectroscopy of polymers and thus can be implemented by a person skilled in the art as needed.

[0089] c) Median Particle Size Distribution D.sub.50 Median particle size of metal hydroxide can be measured by laser diffraction (ISO13320), dynamic light scattering (ISO22412) or sieve analysis (ASTMD1921-06). In the additives used in the examples the determination of median particle size distribution D.sub.50 was measured by laser diffraction according to ISO13320.

d) BET Surface Area

[0090] Overall specific external and internal surface area is determined by measuring the amount of physically adsorbed gas according to the Brunauer, Emmett and Teller (BET) method, performed in accordance with DIN ISO 9277.

e) Compression Moulding

[0091] Plaques were prepared for cone calorimeter, LOI, tensile testing and char strength method with compression moulding (Collin R 1358, edition: 2/060510) according to ISO 29. The dimensions of the various plaques depended on the testing method and can be seen in Table

TABLE-US-00001 TABLE 1 Test plaques Test method Surface area (mm) Thickness (mm) Cone calorimeter 100 100 3 LOI 140 150 3 Tensile testing 90 90 2 Char strength method 50 50 3

[0092] The amount of material used for each plaque was calculated by using the density. The material was placed between two sheets of Mylar film and positioned in a frame. The plaques were pressed at 150 C. for 20 minutes and pressure of 114 bar.

f) Cone Calorimeter

[0093] The cone calorimeter (Dual cone calorimeter from Fire Testing Technology, FTT) method was carried out by following ISO 5660. The plaques prepared as described above were placed in a climate room with relative humidity 505% and temperature 23 C. for at least 24 hours prior to the test. Before initializing the tests, the smoke system, gas analyzers, c-factor value, heat flux and scale were calibrated through software ConeCalc. Drying aid and Balston filter were checked and exchanged if necessary. The sample plaques were weighed and the exact dimensions were determined before the bottom and sides were wrapped in a 0.3 mm thick aluminium foil and placed in a sample holder filled with a fiber blanket and a frame on top. The sample was placed in a horizontal position on a loading cell 60 mm from the cone radiant heater with heat flux 35 kW/m.sup.2 and volume flow rate 24 l/min. An electric spark ignition source was placed above the sample and the starting time, time to ignition and end of test were recorded by pushing a button in ConeCalc 5 as they were observed. The test was performed two times on each formulation and after each test was completed, the formed char was obtained. This method was used for obtaining the values of time to ignition (s), time to flame out (s), PHRR (kW/m.sup.2), total heat release (MJ/m.sup.2) and total smoke (m.sup.2) in the Tables below.

g) Limiting Oxygen Index (LOI)

[0094] LOI (Stanton Redcroft from Rheometric Scientific) was performed by following ASTM D 2863-87 and ISO 4589. The plaques prepared as described above were placed in a climate room with relative humidity 505% and temperature 23 C. for at least 24 hours prior to the test. Ten sample rods having length 135 mm, width 6.5 mm and thickness of 3 mm were punched from a plaque. A single sample rod was placed vertically in a glass chimney with a controlled atmosphere of oxygen and nitrogen that had been flowing through the chimney for at least 30 seconds and then ignited by an external flame on the top. If the sample had a flame present after three minutes or if the flame had burned down more than 50 mm, the test failed. Different oxygen concentrations were tested until a minimum oxygen level was reached were the sample passed the test and the flame was extinguished before three minutes or 50 mm.

h) Tensile Testing

[0095] Tensile testing was executed in accordance with ISO 527-1 and ISO 527-2 using an Alwetron TCT 10 tensile tester. Ten sample rods were punched from a plaque using ISO 527-2/5A specimen and placed in a climate room with relative humidity 505% and temperature 23 C. for at least 16 hours previous to the test. The sample rods were placed vertically between clamps with a distance of 502 mm, extensometer clamps with a distance of 20 mm and a load cell of 1 k N. Before the test was carried out, the exact width and thickness for every sample was measured and recorded. Each sample rod was tensile tested with a constant speed of 50 mm/min until breakage and at least 6 approved parallels were performed. In highly filled systems, there is generally a big variation of the results and therefore the median value was used to extract a single value for elongation at break (%) and tensile strength (MPa).

i) Char Strength

[0096] Preparation of the plaques used for char strength measurements was conducted in metal containers that were put on a coil heater and pre-burned before placing the containers in a furnace oven for 1 hour at 800 C., followed by cooling in room temperature. The char strength test was performed on a compression machine typically used when performing flexural modulus testing with a speed of 1 mm/min. The formed char was placed perpendicular to a penetrating member that consisted of a cylinder with a diameter of 3 mm. The thickness of the sample was measured and the instrument was set on penetrating 50% of the thickness. Three different areas on the surface were tested and the average value of the maximum resistance force was used. The method was not applicable for inspection of porous chars as the machine stopped recording the force when it dropped to zero when reaching a pore. Because of this, also visual inspection of the chars from the cone calorimeter was performed.

j) Inspection of Chars

[0097] The chars generated form the cone calorimeter measurements were inspected visually and tactilely in order to identify cracks, and to get a feeling for hardness and strength of the char. Each char was classified as being cracked or not. The char strength was classified according to a scale including categories very brittle, brittle, hard 1 (h1), hard 2 (h2) and hard 3 (h3). When the char is classified as very brittle, it shows no integrity at all and is destroyed even by an air flow generated by a human's breath. Brittle chars are those destroyed by the slightest touch. Since the very brittle and the brittle chars have such a low strength, it is not possible to measure the char strength by the char strength method described above. The char strength of the hardest chars classified h2 and h3 is measured by the char strength method described above and is between 4-5 N for h2-chars, and between 5-6 N for h3-chars. The chars classified as h1 are porous and for that reason not measurable by the char strength method above. The char strength of these chars is estimated to be between 1-4 N.

k) Density

[0098] Density is measured according to ISO 1183-1method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

2. Materials

[0099] a) PE-ter is a terpolymer of ethylene, 21 wt % methyl acrylate and 1.0 wt % vilnyltrimethoxisilane having MFR.sub.2, 16 of 2 g/10 min.
b) gMDH(3) is ground magnesium hydroxide (Apymag 80S), Mg(OH)2, being modified by stearic acid surface treatment; having a median particle size distribution D50 of 3 m as determined by laser diffraction and BET surface area of 8 m2/g, commercially available from Nabaltec AG Germany.
c) CaB is calcium meta borate (B2 CaO42H2 O) supplied by Sigma-Aldrich (Productnumber 11618), CAS-no. 13701-64-9, having a sieve residue on 200 m mesh size of less than 0.1 wt %.
d) PDMS1 is a pelletized silicone gum formulation (Genioplast Pellet S) with high loading of ultrahigh molecular weight (UHMW) siloxane polymer, commercially available from Wacker Chemie AG.
e) PDMS2 is a masterbatch consisting of 40 wt % ultrahigh molecular weight polydimethyl siloxane polymer available from Dow Corning, and 60 wt % ethylene butylacrylate copolymer having a butylacrylate content of 13 wt % and MFR.sub.2 of 0.3 g/10 min. The master batch is available from Borealis, Austria.
f) OMS is an organomodified siloxane (OMS 11-100), i.e. an alkoxy siloxane, commercially available from Dow Corning Corp.
g) LLDPE is a linear low density polyethylene (LE8706), having a density of 923 kg/m.sup.3 and an MFR.sub.2 (190 C., 2.16 kg) of 0.85 g/10 min, commercially available from Borealis, Austria.
h) VLDPE is very low density polyethylene (Queo 8203), the comonomer being 1-octene, produced in a solution polymerization process using a metallocene catalyst, having a density of 883 kg/m.sup.3 and an MFR.sub.2 (190 C., 2.162 kg) of 3 g/10 min, commercially available from Borealis, Austria.
i) A is octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, commercially available from BASE.

[0100] The compositions of the inventive and comparative examples are indicated in the following Tables 2 by giving the amounts of ingredients in percent by weight.

3. Results

[0101]

TABLE-US-00002 TABLE 2 Composition and properties of flame retardant compositions comprising ground metal hydroxide CE1 IE1 IE2 IE3 IE4 IE5 IE6 PE-ter 36.8 36.8 34.8 24.8 26.1 36.8 34.8 AO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 LLDPE 10.0 VLDPE 8.7 gMDH(3) 63.0 58.0 48.0 48.0 48.0 49.5 47 CaB 12.0 12.0 12.0 12.0 12.0 PDMS1 5 PDMS2 5 5 5 5 OMS 1.5 1 Char visual h-1 h-2 h-3 h-1, h-2, h-2 h-2 cracked cracked Char strength (N) 5 5.5 4.5 LOI (%) 31.5 38.5 42.5 51.5 48 Time to ignition 144 145 282 103 92 104 92 (s) Time to flame out 1010 775 1070 830 770 1040 995 (s) PHRR (kW/m.sup.2) 101 119 85 99 111 99 79 Total heat release 45 39 34 37 40 32 30 (MJ/m.sup.2) Total smoke (m.sup.2) 0.4 0.8 1.1 2.0 1.5 1.6 1.6 MFR.sub.21 (g/10 min) 3.9 13 24 20 14 24 Tensile strength 10.3 7.4 9.6 11.3 11.2 10.2 9.1 (MPa) Elongation 60 61 80 64 89 86 98 at break (%)

[0102] As can be derived from Table 2, addition of silicone gum has a positive effect on the processability of the ground magnesium hydroxide (gMDH) based compositions. The silicone gum has a big positive effect on LOI and the char integrity and reduces the total heat release.

[0103] Further, PHRR and total heat release are reduced when calcium borate is added. The addition of a borate has also a big positive effect on the processability. The influence of the borates on the mechanical performance is positive for the ground magnesium hydroxide (gMDH) based compounds.

[0104] As can be seen in Table 2, the inventive formulations IE1-IE6 gave very high LOI and competitive cone calorimeter results. Further on, mechanical performance is good and processability is particularly improved. In all cases hard chars were generated.

[0105] Especially, formulations based on the terpolymer of ethylene (only) and silicone gum give strong char (IE1), being even stronger when combined with calcium borate (IE2, IE5 and IE6). The char strength and char integrity of these formulations are so good that they might work as protective char layer in an extrudable flame resistant application.

[0106] Further, compositions comprising OMS (IE5 and IE6) exhibited improved flame-retardant properties and very hard chars. OMS may thus be preferred, since it also has advantageous toxicity characteristics.

[0107] Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made without departing from the scope of the invention. It is intended that the detailed description be regarded as illustrative, and that the appended claims including all the equivalents are intended to define the scope of the invention.