JPH0224859B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to crosslinkable polymeric compositions that exhibit moisture and heat resistance and flame retardancy and are useful in making insulated wires, cables, and molded articles. More specifically, the present invention
The present invention relates to cross-linkable ethylene-vinyl acetate copolymer compositions that can pass the test method known as the CSA Varnish Test. One of the most important areas where refractory polymer compositions are used is the electrical sector, where both insulating properties and fire resistance are required. This is especially true in the area of conductor insulation. In the past, extrudable compositions utilized in wire and cable technology used halogenated polymers (e.g., chlorinated polyethylene, polyvinyl chloride, chlorobutadiene, chlorinated paraffin, etc.) together with antimony oxide for fire resistance. Required to be present in significant amounts. Alternatively, coatings of chlorosulfonated polyethylene paints have been applied to flame retardant insulation formulations that require additional manufacturing operations. For certain dry transformers, particularly high voltage transformers, there has been a problem in that electrical losses occur due to surface deformation of the organic insulating components used. This problem was solved by adding hydrated alumina to compositions having butyl rubber, epoxy resins or polyester resins as organic binders. However, these compositions do not have a good balance of extrusion properties, physical and electrical properties, thermal resistance, and flame retardancy. Such compositions are described in U.S. Pat.
No. 2997526, No. 2997527, and No. 2997528. The compositions described therein for such applications have poor tensile strength, elongation and percent elongation after aging. In particular, a flame retardant polymeric composition exhibiting improved moisture and heat resistance comprising at least one cross-linkable polymer comprising as a major component an ethylene-vinyl acetate copolymer; BACKGROUND OF THE INVENTION Compositions of intimate mixtures of one or more silanes and one or more hydrated inorganic fillers have found wide acceptance in the wire and cable art. Such compositions are described in North et al. US Pat. Nos. 3,832,326 and 3,922,442. These polymer compositions exhibit a unique combination or balance of improved physical and electrical properties and a high degree of flame retardancy. These highly desirable results are achieved without the use of halogenated polymers (e.g., polyvinyl chloride and chlorosulfonated polyethylene), thereby eliminating hydrogen chloride fumes;
It is also achieved without carbon black, thereby allowing the use of colored insulation; it is also achieved without the currently required flame retardant coating, thereby making it easier to use when using such compositions. Additional steps such as extruded compound insulation on transformers are eliminated; and also antimony trioxide is achieved, thereby eliminating very expensive formulations. Such compositions have particular application as white (inherent properties) and colored uniform insulating compositions and can be extruded onto metals (e.g. copper or aluminum) to provide single layer insulating and sheathing compositions. Can be done. This insulating and sheathing composition is required by American National Standards to operate at voltages up to 600 volts and at temperatures as high as 90°C and in some cases as high as 125°C. These insulating compositions of Nora et al. require a unique combination of excellent electrical properties combined with resistance to heat and flame degradation, and are characterized by low smoke density and non-corrosive fumes. It has special uses in insulating switchboard wire, equipment wire, and automotive wire. In addition to these three essential ingredients, other ingredients such as pigments, stabilizers, lubricants, and antioxidants can be included in the North et al. composition. Among the antioxidants, polymerized trimethyldihydroquinoline was found by North et al. to provide effective antioxidant protection. In the CSA varnish test, three samples of polymer-insulated wire are (1) heated in an oven, (2) immersed in insulating varnish, (3) heated in an oven for an extended period of time, and (4) Cool and (5) bend onto a small diameter mandrel. When bent over a mandrel,
If cracks to the transformer are observed in the insulation of any of the three samples, the polymer composition fails the test. This CSA is a composition embodying the invention of North et al. that uses polymerized trimethyldihydroquinoline as an antioxidant.
Does not pass varnish test. Many polymers are susceptible to oxidation which impairs their physical properties. This degradation is initiated by heat, light or other energy. In most polymers, oxidation proceeds by a free radical mechanism. These free radicals form in polymers under the influence of internal energy sources. These radicals then react with oxygen to form peroxy radicals, which in turn react with the polymer to form hydroperoxide and another radical, which in turn continues the chain reaction. Antioxidants were developed to prevent the deterioration of polymers. These antioxidants either combine with peroxy radicals rendering these radicals incapable of propagating through the reaction chain, or they also decompose the hydroperoxides so that carbonyl groups and additional free radicals are not formed. Perform one of the following functions. The former are called chain-breaking antioxidants, free radical scavengers, or inhibitors, and are usually sterically hindered phenols, amines, etc. The latter are called peroxide decomposers and are generally sulfur compounds (ie mercaptans, sulfides, disulfides, sulfoxides, sulfones, thiodipropionic acid esters, etc.) or metal complex salts of dithiocarbamates and dithiophosphates. Patented technology discloses a number of antioxidants previously used with olefin resins. U.S. Pat. No. 3,160,680 to Solstrup et al. and U.S. Pat. No. 328,290 to Hagemeyer et al.
Antioxidant combinations of sterically hindered phenols and thiodipropionic acid diesters are described for use in α-olefin hydrocarbon polymers. U.S. Pat. No. 3,033,814 to Solstrup et al. discloses the use of a ternary antioxidant consisting of a sterically hindered phenol, a thiopropionate diester, and a phenyl salicylate in a polymer of _C2 to _C10 alpha-olefin hydrocarbons. It is stated that. U.S. Pat. No. 3,181,971 to Rayner et al. discloses the combination of a phenyl antioxidant and a primary or secondary aromatic or aliphatic amino compound in a propylene homopolymer or a copolymer of propylene and other hydrocarbons. It is stated that it can be used. U.S. Pat. No. 3,242,135 to Bown et al. uses a borate ester together with a sterically hindered phenol and a thiodipropionate diester.
It is described as an antioxidant for homopolymers and copolymers of _C2 - _C3 alpha-olefin hydrocarbons. Murdotsk U.S. Patent No.
No. 3245949 describes the combination of phosphorus-containing polyphenolic compounds and dilauryl or distearyl esters of dithiopropionic acid as antioxidants for homopolymers or copolymers of C2 _{- C3} aliphatic olefinic hydrocarbons or mixtures thereof. is described to be used. None of these patents disclose or suggest that these antioxidant combinations can be usefully incorporated into other than hydrocarbon polymers. That is, there is no suggestion that these antioxidant combinations can be used in polymers containing major amounts of ethylene-vinyl acetate copolymers. It is an object of the present invention to provide a cross-linkable ethylene-vinyl acetate copolymer composition that can pass the CSA varnish test. Another object of the present invention is to produce ethylene-vinyl acetate containing silanized hydrated inorganic fillers which not only exhibit excellent moisture and heat resistance and flame retardancy but also successfully pass the CSA varnish test. An object of the present invention is to provide a copolymer composition. All percentages and parts given in the specification are by weight unless otherwise specified. According to the present invention, an antioxidant consisting of a diester of thiodipropionic acid is added to the ethylene-
When used in place of polymerized trimethyldihydroquinoline antioxidants in vinyl acetate (EVA) compositions, the resulting compositions have substantially the same moisture and heat resistance and flame retardancy as the compositions of North et al. It was discovered that not only does it exhibit anti-oxidant properties, it also unexpectedly passes the CSA varnish test. More particularly, the present invention relates to a cross-linkable polymer composition capable of passing the CSA varnish test, characterized in that it consists of the following components: (a) ethylene and a _C2 - _C6 aliphatic carboxylic acid; (b) 80 to ₄₀₀ parts of a hydrated inorganic per 100 parts _{of said} polymer _component ; a filler, (c) 0.5 to 5 parts alkoxysilane per 100 parts of the hydrated inorganic filler as described above, and (d) at least 25% distearyl in an amount effective to cause the polymer composition to pass the CSA varnish test.
An antioxidant composition comprising 3,3'-thiodipropionate. The invention also relates to a cross-linkable polymer composition capable of passing the CSA varnish test, characterized in that it consists of the following components: (a) ethylene and a vinyl _C2 - _C6 aliphatic carboxylic acid; ( _b ) 80 to ₄₀₀ parts of hydrated inorganic filler per 100 parts of _said polymer _component ; (c) 0.5 to 5 parts aquikoxysilane per 100 parts of the hydrated inorganic filler as described above, and (d) 0.1 to 5 parts of distearyl-3,3'-thiodipro as per 100 parts of the polymer component as described above. Pionate. Furthermore, the present invention provides at least 66% by weight of the following components: (a) a copolymer of ethylene with a vinyl ester of a _C2 - _C6 aliphatic carboxylic acid, a _C1 - _C6 alkyl acrylate, or a _C1 - _C6 alkyl methacrylate; (b) 80 to 400 parts of hydrated inorganic filler per 100 parts of said polymer component, and (c) 0.5 to 5 parts of alkoxysilane per 100 parts of said hydrated inorganic filler. cross-linkable polymer compositions of the above-mentioned type, the improvement comprises adding to the above-described polymer compositions an amount effective to cause the compositions to pass the CSA varnish test.
An antioxidant composition containing at least 25% distearyl-3,3'-thiodipropionate is mixed. Still further, the present invention relates to an electrical conductor coated with a uniform insulating layer of any of the above-described cross-linkable polymer compositions capable of passing the CSA varnish test. The present invention relates to a cross-linkable polymer composition consisting of a copolymer of ethylene and a vinyl ester of an aliphatic carboxylic acid, an alkyl acrylate or an alkyl methacrylate, and a silanized hydrated inorganic filler, which passes the CSA varnish test. . These compositions are particularly useful for wire and cable insulation. In addition to the specific antioxidant composition, the compositions of the present invention include one or more cross-linkable or curable ethylene copolymers, one or more silanes, and one or more silanes. Contains hydrated inorganic fillers. These copolymers,
Silanes and inorganic fillers include those described in North et al., US Pat. Nos. 3,832,326 and 3,922,442. The disclosures of these US patents are incorporated herein by reference. Cross-linkable Copolymer Components In this specification, the terms "cross-linkable" or "cross-linked" are described in their ordinary art-recognized meanings. That is, they refer to the formation of the main valence bonds between polymer molecules. Cross-linking is by any of the well-known methods such as chemical means including peroxide cross-linking;
Irradiation using cobalt-60 accelerators, beta-rays, gamma
- by radiation, electrons, x-rays, etc.; or by thermal cross-linking. The basic methods for cross-linking polymers are very well known in the art and need not be described in detail here. The polymeric component of the compositions of the invention is a copolymer of ethylene and a comonomer (which may be a vinyl ester, acrylate or methacrylate). Vinyl esters are vinyl esters of _C2 - _C6 aliphatic carboxylic acids such as vinyl acetate,
It can be vinyl propionate, vinyl butyrate, vinyl pentanoate, or vinyl hexanoate. Acrylates and methacrylates can be any of the _C1 to _C6 alkyl esters, including, for example, methyl-, ethyl-, propyl-, butyl-, pentyl- or hexyl-acrylates or methacrylates. Preferred copolymers that make up the polymer component of this invention are from about 9 to
An ethylene-vinyl acetate copolymer containing about 90% vinyl acetate, preferably about 9% to about 40%, most preferably about 9% to about 28% vinyl acetate, with the balance being ethylene. Small amounts of other crosslinkable polymers or copolymers can also be included in the compositions of the invention in small proportions, although the gain is slight and some properties are adversely affected. However, the ethylene copolymer, preferably the ethylene-vinyl acetate copolymer, should constitute at least about 66% of the total polymer present, as discussed above. Representative such minor polymer components that may be used in such undesirable embodiments include polyethylene, copolymers of ethylene with propylene, butenes, acrylates and malates, polydimethylsiloxane, and polymethyl fluoride. Examples include enylsiloxane and copolymers of vinyl acetate and acrylates. It goes without saying that mixtures of these minor polymer components may also be used. For example, terpolymers of ethylene and vinyl acetate derived from any of the above monomer components (other than ethylene or vinyl acetate) may also be used. A typical terpolymer is ethylene-
It is a terpolymer of vinyl acetate and vinyl maleate. The ethylene-vinyl acetate copolymers used in this invention preferably have a melt index of about 1.0 to about 2.0. Polyethylene useful in the present invention includes substantially all high density, medium density and low density polyethylenes and mixtures thereof. The most preferred polyethylenes for blending for use as uniform insulation in electrical wires and cables generally range from about 0.9 to
00 to about 0.950 g/cc and a melt index of about 1.0 to about 10.0. More specifically, the compositions of the present invention provide the following excellent and unexpectedly balanced properties: 1. Low temperature brittleness: i.e., the compositions do not readily break down during low temperature exercise. No cracking (ASTM D746). 2. Heat resistance after aging: ie excellent elongation even after long operating times at 90°C and even at 125°C. 3. Shows arcing and tracking resistance even at voltages as high as 5KV. In contrast, porcelain shows surface destruction at 4KV. However, this property is rarely required in favorable environments below 600V. 4 Flame resistance and flame retardancy. 5 Resistance to moisture, ie, low mechanical absorption of water and excellent dielectric constant. 6. Resistance to industrial chemicals. The reasons why the compositions of the present invention exhibit such well-balanced properties are unknown. Although it is possible that some synergistic relationship exists between the ethylene-vinyl acetate copolymer, silane, and hydrated inorganic filler, there is no intention to be bound by such theory. However,
In low voltage environments below 5000 volts, and even especially in environments below 600 volts, the compositions of the present invention are particularly useful for uniform insulation facilities. Uniform insulation is an art-recognized term for insulation that extrudes a layer around a conductor, which serves as electrical insulation and armor, and provides physical and flame protection. The composition of the invention is
It is particularly suited to serve as uniform insulation in the range up to 5000 volts and most especially up to 600 volts where only a single extruded sheath is used and where excellent balanced properties are required. In this environment. Ethylene-
It has further been discovered that vinyl acetate copolymers possess very large amounts of filler and yet provide high flexibility and a high degree of cross-linking. The simultaneous achievement of high filler loading, high flexibility and high degree of cross-linking is quite surprising. That is, a high degree of flexibility and a high degree of cross-linking, as well as a high degree of cross-linking and a high filler loading (which implies a low content of cross-linkable polymers). This was because it was generally believed that they were incompatible. The ethylene-vinyl acetate copolymer further provides excellent flame retardancy to the polymer compositions of the present invention. The ethylene-vinyl acetate copolymers described above can be cross-linked by high-energy electron beam irradiation or by the use of chemical cross-linking additives. In preferred compositions of the invention, chemical cross-linking is preferred. This is especially the case when superior physical strength is required. Chemical cross-linking is accomplished by incorporating a cross-linking agent such as dicumyl peroxide or .alpha.,.alpha.'(t-butylperoxy)diisopropylbenzel into the ethylene-vinyl acetate copolymer. This peroxide is activated during subsequent processing to link the chains of the ethylene-vinyl acetate copolymer to form a three-dimensional network (and a small amount of other cross-linkable polymers, if present). . Chemical cross-linking is performed by methods well known in the art, and variations to the general cross-linking conditions described below will be apparent to those skilled in the art. The invention is further not limited to the use of tertiary organic peroxides for chemical cross-linking, but other well-known materials that decompose to give free radicals can be used. Of course, such cross-linking agents should not degrade during formulation of the composition, but the selection of acceptable cross-linking agents will be apparent to those skilled in the art. Generally, the degree of crosslinking of the polymer increases as the amount of crosslinking agent used increases. Usually less than 10% organic tertiary peroxide (based on the polymer) is used, with 3-6%
is a more typical value. Other cross-linking agents may require different amounts, but this can be easily determined. It is often desirable to avoid very small amounts of cross-linking agents, as some loss of resistance to deformation under sudden or continuous pressure may occur. Cross-linking aids such as triallyl cyanurate and the like can also be included to increase the effectiveness of the cross-linking agent. Tertiary organic peroxides, like most other chemical crosslinkers, are activated by heating above the activation temperature at which decomposition occurs. Activation can be effected using any known method, such as application of high pressure steam to the composition. The technology of radiological cross-linking is so well developed that there is little need to describe such methods. The degree of cross-linking generally increases as higher total doses are used, with total doses of about 5 to 25 megarads being used for preferred cross-linking. Cross-linking is generally performed at superatmospheric pressures, e.g. 200~
It is carried out at superatmospheric pressures of the order of 400 psi, although higher or lower pressures may be used. The pressure is
Used to avoid uncontrolled porosity in the polymer, which is highly undesirable in electrical insulation. Generally, the higher the degree of crosslinking, the greater the resistance of the polymer composition to moisture, chemical agents, etc., and the lower the resistance of the polymer composition to abrasion. At low degrees of cross-linking, there is also some loss in thermal resistance as well as a significant effect on % elongation after ripening. The exact degree of cross-linking may of course vary taking into account the above factors and their effect on the final product.
Although high or low cross-linking can be used for wire and cable insulation, ethylene-
Cross-linking % around 95% for vinyl acetate
(measured by extraction of soluble components in cross-linked polymers) is generally preferred. Silane Component One or more substituted silanes are the second essential component of the polymer compositions of the present invention. Any silane that does not adversely affect the desired balanced properties and that aids in bonding the polymers of the present invention and the inorganic filler may be used in the present invention. However, the silane is not flammable, such as alkoxysilanes and amine silanes, and does not interfere with polymer cross-linking or degrade during polymer processing. Preferred silanes for use in forming the insulating composition are alkoxysilanes such as lower alkyl-, alkenyl-, alkynyl-, and aryl-alkoxysilanes; and lower alkyl-, alkenyl-, alkynyl-, and aryl-alkoxyalkoxy or -aryl It is an oxyalkoxysilane. Specific examples of such silanes are methyltriethoxy, methyltris(2-methoxy), dimethyldiethoxy, alkyltrimethoxy, vinyltris(2-methoxyethoxy), and phenyltris(2-methoxyethoxy). , vinyltrimethoxy- and vinyltriethoxy-silane. For best results it is preferred to use vinylsilanes, and the vinylsilanes listed below are particularly preferred. γ-methacryloxypropyltrimethoxy-
silane Vinyl-tris(2-methoxyethoxy)silane H ₂ C=CHSi(OCH ₂ CH ₂ OCH ₃ ) _Trihydrated inorganic filler component The filler used in the present invention is a hydrated inorganic filler such as hydrated aluminum oxide [Al ₂ O ₃・3H ₂ O
or Al(OH) ₃ ], hydrated magnesia, and hydrated calcium silicate. The most preferred of these compounds is hydrated aluminum oxide. In order to obtain the aforementioned good balance of properties, it is essential to use hydrated inorganic fillers during the formulation of the polymer composition. It must be emphasized that other types of fillers, inert or otherwise, cannot be added to the composition in large proportions and still achieve excellent balanced properties. The water of hydration in the inorganic filler must be released during application of sufficient heat to cause combustion or ignition of the ethylene-vinyl acetate copolymer. The water of hydration chemically bound to the inorganic filler is released endothermically. Hydrated inorganic fillers are far superior to other fillers traditionally used in the art to provide insulation as well as flame retardancy, such as carbon black, clay, and titanium dioxide. It was discovered that it increases scorchability. What is even more surprising is that flame retardancy is combined with excellent electrical insulation properties at the high filler contents used. This is because at such high contents the polymer composition contains a large amount of bound water. The size of the filler should conform to the size used by the prior art. Antioxidant Component The antioxidant composition constitutes the fourth component of the polymer compositions of the present invention, and is the component that unexpectedly allows these polymer compositions to pass the CSA varnish test. A diester of thiodipropionic acid constitutes an essential component of this antioxidant. A preferred diester is distearyl-3,3'-thiodipropionate (DSTDP). Although this material is a well-known antioxidant that acts as a peroxide decomposer, it
Its effect on passing the CSA varnish test is not completely understood. The action of this particular diester is even more surprising. Because the related diester, dilauryl-3,3'-thiodipropionate, is used in antioxidant applications.
Although often used interchangeably with or in conjunction with DSTDP,
This is because its use in place of DSTDP does not result in a polymer composition that can pass the CSA varnish test. Constitutes an essential component of antioxidant compositions
In addition to DSTDP, other antioxidants can be used in combination therewith. It has been discovered that the use of two different types of antioxidants provides effective antioxidant action. That is, a mixture of a chain-breaking antioxidant and an antioxidant that is a peroxide decomposer provides a highly effective antioxidant composition. Therefore, along with DSTDP, a well-known peroxide decomposer, amines or sterically hindered phenols can be effectively used as antioxidant compositions. Among these free radical scavengers, sterically hindered phenols are particularly effective. Useful phenols include alkylated phenols, alkylidene-bis-alkylated phenols and polyphenols.
A specific example is 2,6-ditertiary butyl. para-cresol, octadecyl-3,5-di-t-
butyl-4-hydroxyhydrocinnamate,
2,2'-methylenebis(6-t-butyl-4-methylphenol), 4,4'-butylidenebis(6
-t-butyl-3-methylphenol), 1,3,
5-trimethyl-2,4,6-tris(3,5-
Mention may be made of di-t-butyl-4-hydroxybenzyl)benzene and tetrakis[methylene-(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane, the last being particularly preferred. CSA Varnish Test Developed by the Canadian Standards Association, this test applies to coil conductors (CSA Standard C22.2N.116 Section 6.7) and electrical wires and cables (CSA Standard C22.2 No.
3, Section 4.25) is used to evaluate the insulation properties. The test methods applied to coil conductors, wires and cables are substantially the same. A sample of insulated wire was heated in an air oven at 104-106°C for 1/2 hour;
The samples are then removed from the oven and immediately immersed in insulating varnish for 1 hour at room temperature. The samples removed from the varnish are suspended for one hour at room temperature and then placed in an oven for 20 hours at a temperature of either 149-151°C, 159-161°C or 203-205°C. These temperatures depend on the type of wire. After each sample has cooled for 2 hours at room temperature, it is bent once around a small diameter mandrel. If the insulation of any one of the three samples of wire under test develops a crack that leads to the conductor, the insulated wire fails the test. The compositions of the present invention unexpectedly pass this rigorous test. In contrast, the prior art compositions embodied by North et al. possess properties that make them useful as excellent flame retardant wire and cable insulation;
You cannot pass the CSA varnish test. The compositions of the present invention not only pass the CSA varnish test, but also exhibit the excellent flame retardant, moisture and heat resistance of North's polymeric compositions. Proportions of the Ingredients The polymers and fillers in the compositions of the invention can vary in proportions within a wide range. However, the percentage of silane should be in the range of about 0.5 to 5.0 parts per 100 parts of filler. Amounts below this lower limit are insufficient to provide adequate surface treatment, and amounts above this upper limit have an adverse effect on certain physical properties of the extruded insulation compound after cross-linking, namely elongation. Sometimes. Best results are achieved with 80-400 parts by weight or more (most preferably at least 125-150 parts by weight) of filler, 0.5-5.0 parts by weight of silane and
onto wires and cables, e.g. by extrusion, in the presence of 100 parts by weight of polymer;
Obtained in coating. The antioxidant composition must be used in an amount that provides effective antioxidant protection while providing sufficient DSTDP to cause the polymer composition to pass the CSA varnish test. If DSTDP is the only ingredient in the antioxidant composition, there are no special problems in passing the CSA varnish test. Other antioxidants are DSTDP
When combined with antioxidants, the DSTDP should constitute at least 25% of the antioxidant composition. The antioxidant composition in terms of specific amounts should range from 0.5 to 5.0 parts, preferably from 1.0 to 3.0 parts per 100 parts of polymer. Compositions of the invention can be made in a number of ways. However, in each case it is necessary to bring the filler into intimate contact with the silane. For example, a preferred method of filler treatment is by adding directly to the silane polymer and then adding thereto the filler, antioxidant composition, and other additives if desired. This can be done in an internal mixer, such as a Banbury mixer or a Werner & Pfleiderer mixer. Alternatively, the silane may be added directly to the filler and dispersed therein, followed by the addition of the polymer and antioxidant composition. Any processing equipment known in the art that ensures intimate mixing of the essential ingredients can be used. however,
The silane must be evenly and well dispersed on the surface of the hydrated inorganic filler. It is clear that in addition to the essential ingredients of the compositions of the invention, other ingredients such as pigments, stabilizers can be present as desired, provided they do not interfere with cross-linking or impair the desired properties. be. Such materials are present in very small proportions, ranging from less than 10% of the polymer, and usually less than 5%. There are two reasons why the amounts of other ingredients are undesirable. The first reason is that the composition of the present invention itself already has excellent properties. Second, for example, significant amounts of other fillers only serve to disrupt the balance or properties. For the most preferred embodiment of the invention, the formation of insulation on conductors by extrusion, another component, a lubricant, such as a fatty acid soap or its metal derivative, is generally required. Such materials are also important in improving the strippability of the wire insulation thereby allowing the user to easily strip the insulation from the wire to make connections and make terminations. However, it is necessary to avoid soaps that interfere with cross-linking reactions (free radical mechanisms), such as zinc stearate (which reacts with organic peroxides). Acceptable soaps are alkaline earth metal fatty acid soaps. A preferred soap is calcium stearate. Additional representative examples of useful lubricants include alkaline earth metal and aluminum salts of stearic acid, oleic acid, palmitic acid and other fatty acids used in the art for this purpose; silicone oils; long chain Aliphatic amides; waxes, etc. A particularly preferred lubricant is 15
It is a mixture of ~35% lauric acid and 85-65% ethylene bisstearamide. The following examples are intended to illustrate certain aspects of the invention. A number of cross-linkable EVA polymer compositions were prepared and subjected to CSA varnish testing. Each of these samples contained the same copolymer, hydrated alumina, silane, and crosslinker in the same proportions. That is, as follows. Amount, phr(1) Ethylene-vinyl acetate copolymer (17% vinyl acetate; index 1.5) 100 Hydrated alumina 125 Silane [vinyl-tris(2-methoxyethoxy)silane] 2 Cross-linking agent [α, α′- Bis(t-butylperoxy)diisopropylbenzene] 4.25 (1) phr=pounds per 100 pounds of resin 17 samples were prepared. Each of these samples contained one or two other components in addition to those listed above.
It contained a seed antioxidant composition, and a lubricant. 4, including two thiodipropionic acid diesters, which are often used interchangeably in the art due to their very similar antioxidant properties.
A variety of commercially available antioxidants were investigated.
The other two antioxidants were amine type and phenolic type antioxidants. The two lubricants studied were also commercially available products. Silane, filler and other ingredients were added to the polymer and mixed together. Care was taken to control the temperature rise during mixing to avoid activating the peroxide before mixing was complete. After mixing, the polymer composition was extruded onto copper wire using a Brabender extruder and brought to the activation temperature of the peroxide by vulcanization with steam under high pressure. The compositions of these samples and the results of the CSA varnish tests are shown in the table below.

【table】

[Table] Sample No. 1 is US Patent No. 3832326 by North et al.
This is one specific example of the composition of No. 3,922,442. This sample did not pass the CSA varnish test. Six other samples also failed this test. Of the 7 samples containing DSTDP, 6 samples passed this test (Samples No. 3, 7, 8, 14 and 16). These 6
Out of 18 samples consisting of 2 DSTDP samples, only one sample showed deep cracks in the insulation. Each of the 15 samples containing polymerized quinoline antioxidant exhibited deep cracks (Samples Nos. 1, 2, 11, 12, and 13). All nine of the samples containing DLTDP antioxidant were similar (Samples No. 12, 15 and 17). Significantly, the only DSTDP sample that failed the test (Sample No. 11) also contained polymerized quinoline antioxidant, and all three samples exhibited deep cracking. These tests show that DSTDP is not effective with polymerized quinoline antioxidants. Also, DLTDP cannot be used as a substitute for DSTDP if passing the CSA varnish test is a requirement. From these tests, it was found that among the additives considered
It can be seen that DSTDP is the most significant contributor to passing the CSA varnish exam. Furthermore, while the best antioxidant combination was DSTDP plus the hydrocinnamate, the most effective systems were those containing this antioxidant system plus the moldwise lubricant. Samples of the latter system (Nos. 4, 14 and 16) showed only slight cracking, if any.

Claims (1)

[Scope of Claims] 1. The following components: (a) a copolymer of ethylene and a vinyl ester of a C ₂ -C ₆ aliphatic carboxylic acid, a C ₁ -C ₆ alkyl acrylate, or a C ₁ -C ₆ alkyl methacrylate; (b) 80 to 400 parts of hydrated inorganic filler per 100 parts of said polymer component; (c) 0.5 to 5 parts per 100 parts of said hydrated inorganic filler;
part of the alkoxysilane, and (d) at least 25% distearyl in an amount effective to cause the polymer composition to pass the CSA varnish test.
1. A cross-linkable polymer composition capable of passing the CSA varnish test, comprising: an antioxidant composition comprising 3,3'-thiodipropionate. 2. The composition of claim 1, wherein the copolymer is an ethylene-vinyl acetate copolymer. 3. The composition comprises 80 to 400 parts of a hydrated inorganic filler per 100 parts of the polymer component, 0.5 to 5 parts of alkoxysilane per 100 parts of the hydrated inorganic filler, and 0.1 to 5 parts per 100 parts of the polymer component. distearyl-
3. A composition according to claim 1 or claim 2, comprising 3,3'-thiodipropionate. 4. The composition according to any one of claims 1 to 3, wherein the antioxidant composition of component d further contains a sterically hindered phenol. 5. The composition of claim 4 in which 0.1 to 5 parts of sterically hindered phenol are present per 100 parts of polymer component. 6. The composition according to claim 4 or 5, wherein the sterically hindered phenol is tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methane. 7. The composition according to any one of claims 1 to 6, further comprising a lubricating effective amount of a lubricant consisting of lauric acid and ethylene-bis-stearamide. 8. A composition according to claim 7, wherein from 0.1 to 5 parts of a lubricant consisting of lauric acid and ethylene-bis-stearamide are present.