Tree resistant cable

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DESCRIPTION

Cable resistant to arborescent discharges.

Technical field

This invention relates to an electrical cable insulated with a polyethylene composition having improved resistance to arborescent discharges in water.

Background information

A typical electrical cable generally comprises one or more conductors in a cable core that is surrounded by several layers of polymeric material including a first semiconductor shield layer, an insulating layer, a second semiconductor shield layer, a wire or tape shield. metal and a shirt.

These insulated cables are known to suffer from shorter life when installed in an environment where the insulation is exposed to water, e.g. eg underground or in high humidity locations. The shorter duration has been attributed to the formation of arborescent discharges in water, which take place when a polymeric organic material is subjected to an electric field for a long period of time in the presence of water in liquid or vapor form. The formation of arborescent discharges in water is believed to be caused by a complex interaction between the AC electric field, humidity, time, and the presence of ions. The net result is a reduction in the dielectric strength of the insulator.

Many solutions have been proposed to increase the resistance of organic insulating materials to degradation by the formation of arborescent discharges in water. One solution involves the addition of polyethylene glycol, as an inhibitor of tree discharge development in water, to a low density polyethylene, as described in US Patents 4,305,849. US Patent 4,440,671 provided an improvement in electrical performance. The combined teachings of these patents, however, led to improvements in processability, e.g. eg, resistance to degradation by heat and exudation.

EP0735545 describes polyethylene-based tree fire resistant cable compositions comprising polyethylene glycol and antioxidants.

Description of the invention

An objective of this invention, therefore, is to provide a polyethylene composition, which exhibits exemplary processability in conversion to cable insulator, in terms of resistance to heat degradation and exudation and provides resistance to tree-resembling discharges. in water and commercially acceptable term aging. Other objectives and advantages will be apparent from now on.

In accordance with the invention, a composition has been discovered which satisfies the above objective.

The composition comprises:

(i) polyethylene, and based on 100 parts by weight of component (i), (ii) 0.3 to 0.6 parts by weight of 4,4'-thiobis (2-methyl-6-t-butylphenol); 4,4'-thiobis (2-t-butyl-5-methylphenol); 2,2'-thiobis (6t-butyl-4-methylphenol); or a mixture of said compounds; and (iii) 0.4 to 1 part by weight of a polyethylene glycol having a molecular weight in the range of 1.00 to 100,000.

The present invention further provides a composition comprising:

(i) an ethylene homopolymer obtained by a high pressure process, having a density of 0.910 to 0.930 grams per cubic centimeter and a melt index of 1 to 5 grams per 10 minutes, and, based on 100 parts by weight of component (i), (ii) 0.3 to 0.6 parts by weight of 4,4'-thiobis (2-methyl-6-t-butylphenol); 4,4'-thiobis (2-t-butyl-5-methylphenol); 2,2'-thiobis (6t-butyl-4-methylphenol); or a mixture of said compounds; and (iii) 0.4 to 1 part by weight of a polyethylene glycol having a molecular weight of 5,000 to 35,000.

Description of the preferred embodiment (s)

Polyethylene, as the term is used herein, is a homopolymer of ethylene or a copolymer of ethylene and a small proportion of one or more alpha-olefins having 3 to 12 carbon atoms, and preferably 4 to 8 carbon atoms, and, optionally, a diene, or a mixture of such homopolymers and copolymers. Mix

ES 2 272 039 T3 can be a mechanical mix or an in situ mix. Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.

Polyethylene can be homogeneous or heterogeneous. Homogeneous polyethylenes usually have a polydispersity (Mw / Mn) in the range of 1.5 to 3.5 and an essentially uniform comonomer distribution, and are characterized by relatively low and unique DSC melting points. Heterogeneous polyethylenes, on the other hand, have a polydispersity (Mw / Mn) greater than 3.5 and do not have a uniform comonomer distribution. Mw is defined as weight average molecular weight and Mn is defined as number average molecular weight. Polyethylenes can have a density in the range of 0.860 to 0.950 grams per cubic centimeter and preferably have a density in the range of 0.870 to 0.930 grams per cubic centimeter. They can also have a melt index in the range of 0.1 to 50 grams per 10 minutes.

Polyethylenes can be produced by high or low pressure processes. They are preferably produced in the gas phase, but can also be produced in the liquid phase in solutions or in suspensions by conventional techniques. Low pressure processes are typically done at pressures below 7 MPa (1,000 psi) while low pressure processes are typically done at pressures above 105 MPa (15,000 psi).

Typical catalyst systems that can be used to prepare these polyethylenes are magnesium / titanium based catalyst systems, which can be exemplified by the catalyst system described in US Patent 4,302,565 (heterogeneous polyethylenes); Vanadium-based catalyst systems such as those described in US Pat. 4,508,842 (heterogeneous polyethylenes) and 5,332,793; 5,342,907; and 5,410,003 (homogeneous polyethylenes); a chromium-based catalyst system such as that described in US Patent 4,101,445; a metallocene catalyst system such as that described in US Patents 4,937,299 and 5,317,036 (homogeneous polyethylenes); or other transition metal catalyst systems. Many of these catalyst systems are often called Ziegler-Natta catalyst systems or Phillips catalyst systems. Catalyst systems using chromium or molybdenum oxides on silica-alumina supports can also be included here. Typical procedures for preparing the polyethylenes are also described in the patents mentioned above. Typical in situ polyethylene blends and processes and catalyst systems to provide them are described in US Patents 5,371,145 and 5,405,901. The various polyethylenes can include high pressure low density ethylene homopolymers (HP-LDPEs), linear low density polyethylenes (LLDPEs), very low density polyethylenes (VLDPEs), medium density polyethylenes (MDPEs), and high-density polyethylene (HDPE) that has a density greater than 0.940 grams per cubic centimeter. The last four polyethylenes are generally obtained by low pressure processes. A conventional high pressure process is described in Introduction to Polymer Chemistry, Stille, Wiley and Sons, New York, 1962, pages 149 to 151. High pressure processes are typically free radical initiated polymerizations carried out in a tubular reactor. or a shaken autoclave. In the stirred autoclave, the pressure is in the range of 70 to 210 MPa (10,000 to 30,000 psi) and the temperature is in the range of 175 to 250 degrees C, and in the tubular reactor, the pressure is in the range of 175 at 315 MPa (25,000 to 45,000 psi) and the temperature is in the range of 200 to 350 degrees C.

The VLDPE can be a copolymer of ethylene and one or more alpha olefins having 3 to 12 carbon atoms and preferably 3 to 8 carbon atoms. The density of the VLDPE can be in the range of 0.870 to 0.915 grams per cubic centimeter. It can be produced, for example, in the presence of (i) a catalyst containing chromium and titanium, (ii) a catalyst containing magnesium, titanium, a halogen and an electronic donor; or (iii) a catalyst containing vanadium, an electronic donor, an alkyl aluminum halide modifier, and a halocarbon promoter. The catalysts and processes for obtaining the VLDPE are described, respectively, in US Patents Nos. 4,101,445; 4,302,565; and 4,508,842. The melt index of the VLDPE may be in the range of 0.1 to 20 grams per 10 minutes, and is preferably in the range of 0.3 to 5 grams per 10 minutes. The portion of the VLDPE attributed to the comonomer (s), other than ethylene, may be in the range of 1 to 49 percent by weight based on the weight of the copolymer and is preferably in the range of 15 to 40 percent by weight. A third comonomer may be included, eg, another alpha-olefin or a diene such as ethylidene-norbornene, butadiene, 1,4-hexadiene, or a dicyclopentadiene. Ethylene / propylene copolymers and ethylene / propylene / diene terpolymers are generally referred to as EPRs and the terpolymer is generally referred to as EPDM. The third comonomer may be present in an amount of 1 to 15 percent by weight based on the weight of the copolymer and is preferably present in an amount of 1 to 10 percent by weight. It is preferred that the copolymer contains two or three comonomers including ethylene.

LLDPE can include VLDPE and MDPE, which are also linear, but generally have a density in the range of 0.916 to 0.925 grams per cubic centimeter. It can be a copolymer of ethylene and one or more alpha-olefins having 3 to 12 carbon atoms, and preferably 3 to 8 carbon atoms. The melt index can be in the range of 1 to 20 grams per 10 minutes, and is preferably in the range of 3 to 8 grams per 10 minutes. The alpha-olefins can be the same as those mentioned above, and the catalysts and procedures are also the same, subject to variations necessary to obtain the necessary densities and melt indices.

As indicated, the definition of polyethylene includes homopolymers of ethylene obtained by a conventional high pressure process. The homopolymer preferably has a density in the range of 0.910 to 0.930 grams per cubic centimeter. The homopolymer can also have a melt index in the range of 1 to 5 grams per 10 minutes and preferably has a melt index in the range of 0.75 to 3 grams per 10 minutes. Melt index is determined under ASTM D-1238-95, Condition E. It is measured at 190 degrees C and 2160 grams.

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Component (ii) is 4,4'-thiobis (2-methyl-6-t-butylphenol); 4,4'-thiobis (2-t-butyl-5-methylphenol); 2,2'-thiobis (6-t-butyl-4-methylphenol); or a mixture of said compounds. The amount of component (ii) that can be in the composition of the invention is in the range of 0.3 to 0.6 parts by weight based on 100 parts by weight of component (i). It should be noted that this amount is the total amount of component (ii) regardless of whether it is a single compound or a mixture of two or more compounds.

Generally, polyethylene glycol is defined by its molecular weight, which may be in the range of 1,000 to 100,000, and preferably is in the range of 5,000 to 35,000. The optimum molecular weight is 20,000 (before processing). Those skilled in the art will understand that processing polyethylene glycol reduces its molecular weight from one third to one half. It will further be understood that polyethylene glycol may be in the form of, for example, a copolymer of ethylene glycol and ethylene or in any other form, compound or polymer, which provides the same functionality as polyethylene glycol. Polyethylene glycol is a polar compound, which can be represented by the formulas HOCH₂(CH2OCH2) nCH₂OH or HO (C₂H₄OR)_nH where, for example, n can be 225 to 680. This translates to a molecular weight in the range of 10,000 to 35,000. The amount of polyethylene glycol that can be in the composition is in the range of 0.4 to 1 part by weight based on 100 parts by weight of component (i).

It will be understood that, if one or more additional resins are introduced into the composition, the amounts of components (ii) and (iii) will be based on 100 parts by weight of the total resins in the composition. These resins can be various polyethylenes or polypropylenes, or other polymeric additives commonly used in wires and cables.

Examples of conventional additives that can be introduced into the polyethylene formulation are antioxidants, coupling agents, ultraviolet absorbers or stabilizers, antistatic agents, pigments, colorants, nucleating agents, reinforcing fillers or polymeric additives, slip agents, plasticizers, processing aids, lubricants, viscosity control agents, tackifiers, antiblocking agents, surfactants, diluent oils, metal deactivators, voltage stabilizers, flame retardant fillers and additives, crosslinking agents, reinforcers and catalysts and smoke suppressants. Fillers and additives can be added in amounts ranging from less than 0.1 to more than 200 parts by weight per 100 parts by weight of the base resin, in this case, polyethylene.

Examples of antioxidants are: hindered phenols such as tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane, bis [(beta- (3,5-di-tert-butyl-4-hydroxybenzyl) -methylcarboxyethyl )] sulfide, and thiodyethylene bis (3,5-di-tert-butyl-4-hydroxy) hydrocinnamate; phosphites and phosphonites such as tris (2,4-di-tert-butylphenyl) phosphite and di-tert-butylphenylphosphonite; thiocompounds such as dilauryl thiodipropionate, dimyristyl thiodipropionate, and distearyl thiodipropionate; various siloxanes; and various amines such as polymerized diphenylamines and 2,2,4-trimethyl-1,2-dihydroquinoline. Antioxidants can be used in amounts of 0.1 to 5 parts by weight per 100 parts by weight of polyethylene.

The resin, i.e. component (i), can be cross-linked by adding a cross-linking agent to the composition or by making the resin hydrolyzable, which is achieved by adding hydrolyzable groups such as -Si (OR)₃, where R is a hydrocarbyl radical, to the resin structure by grafting. It is preferred that the resin is crosslinked and that it is crosslinked with an organic peroxide.

Crosslinking of polymers with free radical initiators such as organic peroxides is well known. Generally, the organic peroxide is incorporated into the polymer by melt blending in a roll mill, a biaxial screw kneader extruder, or a Banbury ™ or Brabender ™ mixer at a temperature below the initial temperature for considerable decomposition of the peroxide. . The decomposition of peroxides is evaluated based on their half-life temperatures as described in Plastic Additives Handbook, Gachter et al, 1985, pages 646 to 649. An alternative method for incorporating organic peroxide into a polymeric compound is to mix liquid peroxide and polymer granules in a mixing device, such as a Henschel ™ mixer or an impregnating device such as a simple mixing drum, which are maintained at temperatures below above the freezing point of organic peroxide and below the decomposition temperature of organic peroxide and the melting temperature of the polymer. Following the incorporation of the organic peroxide, the polymer / organic peroxide mixture is then, for example, fed into an extruder where it is extruded around an electrical conductor at a temperature below the decomposition temperature of the organic peroxide to form a wire. The cable is then exposed to higher temperatures at which the organic peroxide decomposes to provide free radicals, which crosslink the polymer.

Suitable crosslinking agents are organic peroxides such as dicumyl peroxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexane; t-butyl cumyl peroxide; and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane-3. Dicumyl peroxide is preferred.

Hydrolyzable groups can be added, for example, by grafting an ethylenically unsaturated compound having one or more -Si (OR) groups₃ such as vinyltrimethoxysilane, vinyltriethoxysilane and gamma-methacryloxypropyltrimethoxysilane to the homopolymer in the presence of the organic peroxides mentioned above. The hydrolyzable resins are then moisture crosslinked in the presence of a silanol condensation catalyst such as dibutyltin dilaurate, dioctyltin maleate, dibutyltin diacetate, stannous acetate, lead naphthenate, and zinc caprylate. Dibutyltin dilaurate is preferred.

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Examples of hydrolyzable graft copolymers are vinyltrimethoxysilane grafted ethylene homopolymer, .... vinyltriethoxysilane grafted ethylene homopolymer, and vinyltributoxysilane grafted ethylene homopolymer .....

A cable using the composition of the invention can be prepared in various types of extruders, eg, single-screw or twin-screw type. Mixing can be carried out in the extruder or prior to extrusion in a conventional mixer such as a Brabender ™ mixer or a Banbury ™ mixer. A description of a conventional extruder can be found in US Patent 4,857,600. A typical extruder has a hopper at its upstream end and a die at its downstream end. The hopper feeds a cylinder, which contains a screw. At the downstream end, between the end of the screw and the nozzle, there is a screen and a breaker plate. The screw portion of the extruder is considered to be divided into three sections, the feeding section, the compression section and the metering section and two zones, the post heating zone and the front heating zone, the sections and zones operating from upstream to downstream. In the alternative, there may be multiple heating zones (more than two) running along the axis from upstream to downstream. If you have more than one cylinder, the cylinders are connected in series. The length to diameter ratio of each cylinder is in the range of 15: 1 to 30: 1. In wire coatings, where the material is cross-linked with an organic peroxide after extrusion, the head die feeds it directly to a heating zone, and this zone can be kept at a temperature in the range of 130 ° C to 260 ° C, and preferably in the range of 170 ° C to 220 ° C.

The advantages of the invention lie in the improved processability of the composition in the form of a wire in terms of resistance to heat degradation and reduction of bleeding. Furthermore, thermal aging and resistance to tree discharge development are as good or better than commercially available materials.

In certain polyethylene compositions 4,4'-thiobis (2-methyl-6-t-butyl phenol) and 2,2'-thiobis (6t-butyl-4-methylphenol) have been found to cause a color problem, which Despite their heat degradation inhibitor qualities, they may be commercially unacceptable. This problem is solved by adding hydroquinone or a substituted hydroquinone in an amount sufficient to inhibit color formation. Details can be found in a United States patent application filed on the same date as Michael J. Keogh's present patent application for a crosslinkable polyolefin composition with patent number 6,103,374.

The term "surrounded" as applied to a substrate that is surrounded by an insulation composition, wrapping material, jacket material, or other layer of cable, is considered to include extrusion around the substrate; substrate coating; or wrapping the substrate as is well known to those of skill in the art. The substrate may include, for example, a core that includes a conductor or a bundle of conductors or various underlying cable layers, as noted above.

All molecular weights mentioned in this specification are weight average molecular weights, unless otherwise indicated.

The invention is illustrated by the following examples.

Examples 1 to 17

In the examples, the equilibrium of each formulation, in percent by weight, is an ethylene homopolymer having a density of 0.92 grams per cubic centimeter and a melt index of 2 grams per 10 minutes, and is prepared by a procedure at high pressure. All amounts are given in percent by weight based on the weight of the total formulation. PEG = polyethylene glycol having a molecular weight before processing of 20,000. Stabilizer A = 4,4'-thiobis- (2-tert-butyl-5-methyl-phenol. Stabilizer B = 4,4'-thiobis (2-methyl-6-t-butylphenol). Dicumyl peroxide is present in the formulations of Examples 1 to 7 and 15 to 17 in an amount of 1.95 percent by weight It is present in the formulation of Example 14 in an amount of 1.75 percent by weight.

The resistance of insulating compositions to tree discharges in water is determined by the method described in US Patent 4,144,202. This measurement provides a value of the resistance to arborescent discharges in water relative to a standard polyethylene insulation material. The term used for this value is “water tree growth rate” (WTGR). The WTGR is found to be at a commercially acceptable level.

The homopolymer is mixed with PEG in a two-cylinder mill operating at 24 revolutions per minute (rpm) in the front cylinder and 36 rpm in the rear cylinder and a temperature of 125 to 130 degrees C in the two cylinders for approximately 10 minutes. The procedure involves preheating the resin to 70 degrees C in an oven; make the resin flow as fast as possible in the two-roll mill (approximately 3 to 4 minutes); add PEG and 4,4'-thiobis- (2-tert-butyl-5-methyl-phenol) and flow for a further 3 to 4 minutes; and then add the peroxide and make it flow, make it flake and stir slowly until well mixed. Enough dicumyl peroxide is introduced into each composition to provide a reading of 763 kg-m (46 inch-pounds) on an oscillating disk rheometer (5 degree arc at 182.2 degrees C (360 degrees F)).

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Each composition is then removed from the two-roll mill as a crepe and cut and molded into 2.54 cm (one inch) discs having a thickness of 0.64 cm (0.25 inch) into a two-stage press:

pressure MPa (psi) temperature (° C) residence time (minutes) initial stage (2,000) 120 9 final stage

280 (40,000) 175 to 20

Each plate is tested for WTGR and the results are compared to a polyethylene control composition, which is 100 percent WTGR. The variables and results are shown in Table I.

TABLE I

<td>Example</td><td> 1</td><td> 2</td><td> 3</td>

<td>PEG</td><td> 0,4</td><td> 0,6</td><td> 0,8</td>

<td>Stabilizer A</td><td> 0,4</td><td> 0,4</td><td> 0,4</td>

<td>WTGR (%)</td><td> 40</td><td> 25</td><td> 16</td>

The following formulations are prepared in a twin screw laboratory mixer using a melting temperature of the mixture of 200 degrees C, followed by the addition of peroxide to effect crosslinking. The crosslinked material is then compression molded (using the condition described in the WTGR sample preparation) on a laboratory plate from which dog bone shaped samples are prepared as described in ASTM D -638. The elongation property of the samples is tested without aging and after aging for 2 weeks in a circulating air oven at a temperature of 150 degrees C following the ASTM D-638 standard. The criteria for passing this test is to retain more than 75 percent of the elongation properties after this aging protocol. As shown in Table II, the minimum level of 4,4'-thiobis- (2-tert-butyl-5-methyl-phenol) necessary to satisfy this requirement is greater than 0.25 percent by weight. The data shows that 0.375 weight percent 4,4'-thiobis- (2-tert-butyl-5-methylphenol) meets this criterion with 0.4 and 0.6 weight percent PEG. See table II with the variables and results.

TABLE II

Ex. 4 5 6 7

<td>PEG</td><td> 0,4</td><td> 0,4</td><td> 0,6</td><td> 0,6</td>

<td>Stabilizer A</td><td> 0,25</td><td> 0,375</td><td> 0,25</td><td> 0,375</td>

<td>Conserv. of leng. (%) **</td><td> 35</td><td> 95</td><td> 4</td><td> 88</td>

** Preservation of elongation after aging in a circulating air oven at 150 degrees C for 2 weeks.

To measure the resistance to heat degradation (pre-curing during extrusion) of the ethylene homopolymer prepared for Examples 1 to 3, an instrument called a Torque Discless Shear Rheometer (MDR) is used here for illustrative purposes. Moving Die Rheometer) 2000, described in ASTM D-5289, and a Rubber Process Analyzer (RPA) 2000, manufactured by Alpha Technologies. The MDR Mh is the maximum torque that represents the total cure measured in a sample and is directly related to the total amount of active peroxide in polymeric formulations. To make an accurate comparison of heat degradation characteristics, MDR Mh must be comparable. The test conditions used to evaluate the total cure by MDR are: 182 degrees C; 0.5 degree arc; 100 cycles per oscillation per minute; test time 12 minutes. Torque is reported in units of Nm (inch-pounds) ((inch-pounds)). As seen in Table III, the total cure level of Examples 8 and 9 to 13 are approximately comparable. RPA was used to evaluate the material's resistance to heat degradation under the present extrusion conditions. This test is carried out using conditions of 150 degrees C; 2.5 degree arc; 200 cycles per oscillation per minute; test time 30 minutes. The resistance to heat degradation under these similar extrusion conditions is calibrated by RPA's Ts1, which is the time required for the torque to reach 0.113 Nm (1 lb-in) above the minimum torque. Under these test conditions the higher the Ts1 value, the greater the resistance to heat degradation. As can be seen from Table III, formulations with 0.3 percent or more stabilizer A or B result in a significant improvement in resistance to heat degradation of 18 percent or more. The variables and results are collected in Table III.

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TABLE III

<td>Ex.</td><td> 8</td><td> 9</td><td> 10</td><td> 11</td><td> 12</td><td> 13</td>

<td>PEG</td><td> 0</td><td> 0,6</td><td> 0,4</td><td> 0,6</td><td> 0,4</td><td> 0,6</td>

<td>Stabilizer A</td><td> 0,18</td><td> 0,18</td><td> 0,30</td><td> 0,375</td><td> 0</td><td> 0</td>

<td>Stabilizer B</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td><td> 0,30</td><td> 0,375</td>

<td>DCP *</td><td> 1,70</td><td> 1,85</td><td> 1,90</td><td> 1,90</td><td> 2,05</td><td> 2,20</td>

<td>MDR Mh</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>Nm</td><td> 0,35</td><td> 0,37</td><td> 0,38</td><td> 0,33</td><td> 0,35</td><td> 0,325</td>

<td>(lbs-inch)</td><td> (3,12)</td><td> (3,26)</td><td> (3,32)</td><td> (2,96)</td><td> (3,12)</td><td> (2,88)</td>

<td>RPA Ts1 (min)</td><td> 9,48</td><td> 8,19</td><td> 29,49</td><td> 33,86</td><td> 34,28</td><td> 38,79</td>

* DCP = dicumyl peroxide

To test additive exudation (loss of additive molecules from the matrix to the granule surface) that can cause extrusion problems such as leakage loss or diameter variation, a method is used that involves washing 100 grams of granules with 100 millimeters of methanol for 1 minute. The methanol is decanted after filtering through a 1-micron polypropylene filter, and analyzed by high pressure liquid chromatography (HPLC) to see the concentration of 4,4'-thiobis- (2-tert-butyl-5- methylphenol). As shown in the data, the presence of PEG helps to solubilize the 4,4'-thiobis- (2-tert-butyl-5-methyl-phenol) in the ethylene homopolymer, thus reducing its exudation by two orders of magnitude. after conditioning at 50 degrees C for 8 weeks. The variables and results are collected in Table IV.

TABLE IV

<td>Ex.</td><td> 14</td><td> 15</td><td> 16</td><td> 17</td>

<td>PEG</td><td> 0</td><td> 0,4</td><td> 0,6</td><td> 0,8</td>

<td>Stabilizer A</td><td> 0,18</td><td> 0,375</td><td> 0,375</td><td> 0,375</td>

<td>Exudation</td><td>greater than</td><td> 2</td><td> 1</td><td> 1</td>

<td>(ppm) **</td><td> 600</td><td></td><td></td><td></td>

** Stabilizer A concentration bleeding after 50 degrees C for 8 weeks in parts per million (ppm).