NO790816L - FLAME DELAYING POLYMER MATERIALS - Google Patents

Description

This invention relates to polymeric, fire-retardant materials with improved properties, which materials are particularly suitable for coating electrical conductors.

The industry is constantly seeking to find new fire-resistant polymeric materials to replace the existing products and/or to satisfy the demands of new areas of application. One of the most important areas where refractory polymeric materials are used are electrical applications for which good physical properties, insulation properties and refractory properties are sought. A particularly important application in this area is the use as insulation material in electrical wiring for cars. For many applications, this type of wiring also requires resistance to oil. Typical application areas include primary wiring, spark plug cables, ignition wiring and battery cables. Another important area of application is insulated wire suitable for use as a fusible link in automotive wiring harnesses. Good physical properties are of paramount importance in this application to minimize the occurrence of insulation breaks as a result of short circuits, as such insulation breaks can cause explosions.

Insulating materials currently used for such purposes in the automotive industry include "Hypalon", ethylene-propylene elastomers, chlorinated polyethylene, silicone elastomers, and flame retardant crosslinked polyolefin. However, these materials are unfortunately unsuitable for use e.g. as a fusible connection in cable networks, e.g. for cars, because they do not exhibit the right combination of fire-retardant properties, physical strength, resistance to oil, moisture, heat, petrol and solvents and resistance to insulation breakdown as a result of strong electrical overload. In addition, it is very important that the material can be easily processed, e.g. by extruding, into its intended form. The properties of these materials as electrical insulating materials in the automotive industry are described in detail in product brochures and the like, which are distributed by the manufacturers of these materials.

The reference books are full of explanations of the mechanisms behind fire suppression and of operational systems. Examples of such are "Flame Retardancy of Polymeric Materials", Vol. 1, by W.C. Kuryla and A.J. Papa, Marcel Dekker, Inc., N.Y., 1973, Chapter 1 and pages 171-181, and Lyons, "The Chemistry & Uses of Fire Retardants", John Wiley and Sons, Inc., 1970, pages 330-332.

A number of US patent documents illustrate the large variety of fire retardant additive combinations known in the art. US Patent No. 3,832,326 describes crosslinkable polymeric materials based on an ethylene-vinyl acetate copolymer, which preferably contains less than approx. 28% by weight vinyl acetate. The materials have improved resistance to moisture and heat, and improved fire-retardant properties and are particularly suitable for covering electrical cables. The materials are specially designed for a system of non-halogenated fire retardants. Another non-halogenated system is described in US Patent No. 3,741,929. US Patent No. 3,362,928 describes a thermosetting system based on a castable diallyl phthalate, a fire-retardant organic chlorine-containing compound, antimony oxide and hydrated aluminum oxide. The materials are used for the manufacture of electronic components and hard-type switches. US Patent No. 3,694,305 discloses an emulsion type adhesive for laminating different layers of a fire retardant flame barrier. US Patent No. 3,720,643 describes a fire retardant polymer material based on the addition of talc, chlorinated polyethylene and antimony trioxide to polypropylene, styrene -acrylonitrile copolymer or acrylonitrile-butadiene-styrene resins.

US Patent No. 3,936,403 relates to synthetic resin materials which are fireproof and have a hard surface, and which include an olefinic resin, vinyl chloride resins and aluminum trihydrate with a crystal structure such as gibbsite. Ethylene-vinyl acetate copolymers are not discussed, and the preferred resin is high density polyethylene, which, as shown below, cannot be extruded to form an overcoat on an electrical conductor. Furthermore, the mentioned vinyl chloride resin is polyvinyl chloride, which cannot be used in the materials according to the present invention either, because the coated wire does not pass the UL-FR-1 flame test.

It has now unexpectedly been found that fire-retardant polymer materials which have improved properties, and which are suitable as insulation for wires for use in cars, are obtained by using a vinyl acetate-ethylene copolymer, chlorinated polyethylene and hydrated aluminum oxide in appropriate proportions.

Typically, the polymeric fire retardant material contains a vinyl acetate-ethylene copolymer containing approx. 20 - 90% by weight vinyl acetate and, per 100 parts of the copolymer, approx. 10 - 50 parts chlorinated polyethylene and approx. 70 - 300 parts hydrated aluminum oxide. A preferred material contains approx. 10 - 35 parts chlorinated polyethylene and approx. 100 - 250 parts hydrated aluminum oxide. Particularly preferred is a material where the copolymer contains vinyl acetate in an amount of approx. 40 - 70% by weight.

Although this is not necessary to achieve the desired properties, it is advantageous to use antimony trioxide and/or silicon oxide to further improve the material's fire resistance and its formability respectively. Generally, both the antimony oxide and the silicon oxide can be used in an amount of approx. 10 - 50 parts per 100 parts of the copolymer, preferably in an amount of approx. 10 - 35 parts. A silane-based coupling agent, as described below, is necessary to produce a material that can be used as a covering for wires and cables.

Such polymeric fire-retardant materials are particularly useful as insulation in cables for cars, but they can also be used for other purposes where a unique combination of good properties is necessary, such as good formability, good physical properties, good electrical properties, good oil resistance, good resistance to moisture, petrol and solvents, as well as good fire resistance.

The polymer component of the present material is based on a vinyl acetate-ethylene copolymer. The copolymer contains approx. 20 - 90% by weight vinyl acetate (VA), preferably approx. 40 - 70% by weight, e.g. 50 - 65% by weight. The preferred copolymers have a distinctive combination of properties that depend mainly on the vinyl acetate content. When e.g. increasing the vinyl acetate content usually increases resistance to oil and solvents. A more detailed account of the preferred copolymer is given in the brochure "Vynathene R VAE Elastomers" published by the National Distillers and Chemical Corporation. Generally, the preferred copolymers have a density of about 0.960 - 1.05 g per cm 3, a melt flow rate at 125°C of approx. 0.1 - 20 g per 10 minutes of flow, a vinylacetate content of approx. 40 - 70% by weight and intrinsic viscosity of 0.70 - 1.10 for 0.15 g of polymer per 100 ml of tetrahydrofuran at 40°C. Three preferred copolymers, which are manufactured by National Distillers and Chemical Corporation are: (a) "VYNATHENE EY 904", a vinyl acetate-ethylene copolymer having a VA content between about 50% by weight and 54% by weight and a melt flow rate (MER) from approx. 0.5 to approx. 1.5 at 125°C, (b) "VYNATHENE EY 905", a vinyl acetate-ethylene copolymer with a VA content between approx. 50% by weight and 54% by weight and a melt flow rate from approx. 1.5 to 7.0 at 125°C, and (c) "VYNATHENE EY 907", a vinyl acetate-ethylene copolymer with a VA content from ca. 58% by weight to approx. 62% by weight and a melt flow rate of approx. 1.0 to approx. 2.2 at 125°C.

Although this is not necessary, in order to achieve a particular combination of properties, small amounts of other polymers or copolymers or mixtures thereof can be incorporated into the copolymers according to the invention, such as e.g. polyethylene, polypropylene, ethylene propylene elastomer, polybutylene, ethylene acrylate-co-. polymer, ethylene-vinyl chloride copolymer and the like. These can be present in quantities of up to approx. 25 parts or more, per 100 parts of the vinyl acetate-ethylene copolymer. It is preferable to use less than approx. 15 parts, e.g. 10 parts.

Chlorinated polyethylene (CPE) is a well-known material, and preferred materials are CPEX02242.46 and CPE 4814 manufactured by Dow Chemical Co. Other chlorinated polymers are chlorinated polypropylene, polyvinylidene chloride, chlorosulfonated polyethylene and the like. Other halogenated polymers are also useful, especially brominated polymers. Such polymers can be found in the above-mentioned book by W.C. Kuryla and A.J. Papa. A material containing polyvinyl chloride was found not to be applicable, because it does not satisfy the UL-FR-1 test for coated wire. CPE is preferred because of its efficiency.

The hydrated aluminum oxide, or aluminum trihydrate, is preferably added in a relatively small particle size of approx. 0.3 - 2/Am, although larger or smaller particle sizes can also be used. Preferred materials are "HYDRAL 710" and "P.G. Alumina" manufactured by Aluminum Co of America.

An important feature of the invention consists in combining CPE and hydrated aluminum oxide with the vinyl acetate-ethylene copolymer as indicated above, whereby a highly preferred material is obtained with an excellent combination of properties, including the property that the material satisfies the strict requirements of flame tests such as UL -FR-1.

It has unexpectedly turned out that the combination of the halogenated polymer and hydrated aluminum oxide gives the polymer material according to the invention a synergistic fire-retardant effect. Other known halogenated fire-retardant additives do not provide such an increase in fire resistance when combined with hydrated aluminum oxide, but on the contrary result in a reduction in the material's fire resistance. In the above-mentioned US patent document no. 3,694,305, the theory is put forward that the combination of a chlorinated paraffin, antimony oxide and hydrated aluminum oxide gives a faster synergistic fire-retardant effect. Although one does not wish to be bound by any particular theory, it is believed that the combination of the halogenated polymer and hydrated aluminum oxide produces a synergistic fire-retardant effect in that both materials work together to produce a very effective and persistent fire-retardant effect. This effect is particularly significant under the strict requirements for fire-retardant effect that are added in tests such as the UL-FR-1 test, and is achieved by means of the above-mentioned combinations of the halogenated polymer and hydrated aluminum oxide. Although the amount of halogenated polymer and hydrated aluminum oxide may vary within wide limits, as indicated above, it is preferred, with a view to achieving a further improved combination of properties, that large amounts of both components are not used. As shown below in the examples, increasing amounts of the halogenated polymer will therefore reduce the material's percentage elongation when the content of hydrated aluminum oxide is high. It is therefore important for certain applications to correlate the amount of halogenated polymer and hydrated aluminum oxide, and it is definitely preferred when the proportion of hydrated aluminum oxide is greater than ea. 150 parts per 100 parts resin, that the amount of halogenated polymer is not greater than approx. 15 parts.

Antimony trioxide is the preferred antimony compound, although many other antimony compounds are also suitable, as is well known in the art. Examples of such antimony compounds are antimony sulphide and sodium antimonite and the organic antimony compounds such as antimony butyrate and antimony caprylate.

The silicon oxide component can be any

of the well-known materials, and preferred silicon oxides include "Hi-Sil 233" and "Hi-Sil EP", both of which are manufactured by PPG Industries, Inc. The silicon oxide particle size is preferably from about 0.01 to 0.05 µm, although larger or smaller particle sizes can also be used.

The polymer materials according to the invention may also contain other components and additives, depending on the intended application area of the finished products and the necessary or desired properties. These additional components can e.g. include antioxidants, acid acceptors, preservatives, lubricants and processing aids, release agents, pigments or dyes, inorganic fillers, water fixing agents, coupling agents, etc.

The preferred antioxidants are the polyquinolines such as polytrimethyl-dihydroquinoline marketed under the trade names "Agerite Resin D" and "AgeriteMA" (higher molecular weight) by R.T. Vanderbilt Company, Inc. Other conventional antioxidants, which are known in the art e.g. to be useful in stabilizing low density polyethylene and ethylene copolymers, can also be used. The quantity used of the antioxidant is approx. 0.25 - 4% by weight calculated on the total weight of the material.

The preferred acid acceptor is tetrabasic lead fumarate, which is marketed by N.L. Industries, Inc. under the trademark "Lectro 78". Other acid acceptors such as magnesium oxide, lead monoxide and the like can also be used. The concentration is approx. 0.5 - 4% by weight of the material's total weight or approx. 1 - 3% of the total resin content.

Lubricants and processing aids such as stearic acid ("Hystrene 9718", supplied by Humko-Sheffield Chemicals Co.) and calcium stearate are preferred. Other such means well known in the art can also be used. Usually amounts of approx. 1 - 3 parts, preferably 1.5 —-2.5 parts, per 100 parts resin.

It is preferred to use a coupling agent when a material suitable for covering wires or cables is to be produced. Any coupling agent can be used in the materials, but it is important that this does not interfere with the cross-linking of the polymer or split during the polymer processing. It is preferred to use silanes of the type described in the above-mentioned US patent document No. 3,832,326, which is incorporated herein by reference. For example, "Silane A-172", manufactured by Union Carbide Co., gives excellent results. Quantities of approx. 0.2 - 4% by weight, preferably 0.2 - 2%, and most preferably 0.5 - 1.2% by weight, calculated on the total weight of the material.

An important feature of the invention consists in cross-linking the materials described above to produce their final product form. The cross-linking can be carried out by means of any known cross-linking technique, such as by chemical cross-linking, or by irradiation.

Curing agents which may be used include peroxides such as t-butyl perbenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butyl-peroxy)-hexane, 2,5-dimethyl-2,5-di (t-butyl-peroxy)-hexyn-3, 1,3,5-tris-[a,a-dimethyl-a-(t-butylperoxy)]-methylbenzene, a,a'-bis(t-butyl-peroxy )-diisopropylbenzene and N,butyl-4,4-bis-(t-butyl-peroxy)-valerate. These curing agents can be used alone or together with one or more polyfunctional monomers, such as triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, trimethylolpropane triacrylate, diallyl fumarate, pentaerythritol tetraacrylate, trimethylolpropane trimethacrylate, 1, 3-bu.tylene glycol dimethacrylate , allyl methacrylate, ethylene glycol dimethacrylate and 1,3-butylene glycol diacrylate. The preferred curing agents for use in the materials of the invention include "Vul-Cup 40 KE" alone

[40% a,a'-bis-(t-butylperoxy)-diisopropylbenzene on "Burgess KE", supplied by Hercules Inc.] and "Vul-Cup 40 KE" combined with the polyfunctional monomer triallyl isocyanurate (TAIC)] , which is supplied by Allied Chemical Corporation.

The quantity of peroxide hardener can be from approx. 1.0 to approx. 10 parts, and is preferably from 3.0 parts to approx. 6.0 parts per 100 parts copolymer.

The polyfunctional monomer used as an auxiliary curing agent together with the cross-linking peroxide can be used in amounts of from approx. 0.1 to approx. 3.0 parts per 100 parts of the copolymer. The preferred amount of auxiliary curing agent can be from approx. 0.5 to approx. 1.5 parts, and the most preferred amount approx. 1.0 part per 100 parts copolymer.

The materials according to the invention can be produced using known methods. Mixing operations are preferably carried out using an intensive mixer such as a Banbury mixer or a Werner&Pfeliderer type mixer. A preferred method involves first preparing a mixture of the resin components and the chlorinated polyethylene. Any other ingredients, apart from the cross-linking agents, can then be added and mixed into the material. If silicon oxide is used, it is preferred

to add the pre-hydrated alumina. After thorough mixing, the temperature is raised to approx. 121°C, and the mixture continues for approx. 1-2 minutes. The temperature is then reduced to below approx. 112.7°C, and the crosslinking agents are added. The mixing is continued until the material is homogeneous, which usually takes approx. 4-5 minutes. The portion can then be processed further in a two-roll mill or in an extruder.

The materials according to the invention will now be described in more detail in the following examples, which, however, are not intended to limit the invention. All parts and percentages are by weight.

Example I

The materials listed in Table 1 were prepared as described below in a Banbury type mixer.

In the production of material no. 1, the resin and CPE were mixed for approx. 3 minutes at 230 rpm. minute. "Hi-Sil 233", "Agerite" and antimony trioxide were added to the Banbury mixer and the mixture was continued approx. 3 minutes. The temperature was raised to approx. 121°C, and the mixture was continued at this temperature for approx. 1 - 2 minutes. The temperature was then lowered to below approx. 112.7°C, after which the stearic acid and "Lectro 78" were added, and the whole mixed in approx. 3 minutes. Then the indicated amount of "Vul-Cup 40 KE was added and the mixture was continued 1 about 4-5 minutes. The portion was then ground in a 6" x 12" 2-yal-sér rubber mill of the make "Thropp<:>' at'approx. 37.8°C and rolled out into a 10 - 15 mm thick creped plate, which was cut into cubes of size approx. 3.2 mm. Samples of coated wire were produced by extruding the material onto a 0.81 mm thick multi-stranded wire in a wall thickness of 0.76 mm using a 3/4" Brabender extruder, type PL-V340. Curing was carried out in a vulcanizing tube at 204.5°C for 6 minutes.The insulated wire was cooled by immersion in cold water for 2 minutes under pressure and then kept immersed in the water while slowly relieving the pressure over 10 minutes.

During the preparation of materials No. 2, 3 and 4, the resin, the hydrated aluminum oxide, the silane and "Agerite" were mixed approx. 5 minutes. The temperature was then raised to approx. 121°C, after which the same procedure was followed as for material no. 1, except that "Lectro 78" was omitted and in materials no.

2 and 3 were replaced with calcium stearate.

During the production of materials 5 and A, the resin and CPE were mixed for approx. 3 minutes at 230 revolutions per minute. "Hi-Sil 233", "Agerite" and the silane were added, and the mixture was continued approx. 3 minutes, after which the aluminum oxide and antimony trioxide were added and the mixture further continued for approx. 3 minutes. The temperature was then raised to approx. 121°C, after which the procedure used for material No. 1 was followed.

In the production of materials B and C, the resin and CPE were mixed for approx. 3 minutes at 230 rpm. minute. The aluminum oxide, "Agerite" and the silane were then added and mixing was continued for a further 5 minutes. The temperature was then raised to approx. 121°C, and the procedure used for material No. 1 was followed, except that instead of "Lectro 78" calcium stearate was used.

The cured materials were tested using the following standard methods, and the results are listed in Table 2 below:

Materials A, B and C were tested in the aged condition (70 hours at 125°C) and the results are listed below in Table 3. The volumetric swelling (%) was determined with ASTM i=£ 3 oil as prescribed in the specifications according to SAE J 878a for insulation forming a fusible joint, and ASTM Method D-471.

The volumetric swelling (%) was determined for materials no. 1, 3 and 4. The results were respectively 166%, 75.4% and 96.8%.

The results listed in tables 2 and 3 show the unexpected and synergistic effect achieved with the materials according to the invention. A comparison between materials 1, 2, 5 and A clearly shows how important it is for fire resistance to use chlorinated polyethylene in combination with hydrated aluminum oxide and to use the hydrated aluminum oxide in an amount of more than approx. parts per 100 parts copolymer. The material A is particularly preferred because of its generally good properties and its good machinability. A comparison between materials B and C shows the importance of using correlated amounts of chlorinated polyethylene and hydrated aluminum oxide to achieve an improved percentage elongation.

Example II

To further illustrate the invention, the following comparison materials were produced and tested according to the methods indicated in example I. The material A was produced again, and is here denoted A'. Material A' was then remanufactured, replacing the vinyl acetate-ethylene copolymer (VAE) with high density polyethylene (HDPE) ("Petrothene LB 830" manufactured by NationalDistillers and Chemical Corp.). This material is designated as material 6. The material A' was then manufactured again, (1) replacing CPE with polyvinyl chloride (material 7) and (2) replacing CPE with PVC softened with 25% by weight dioctylphthalate (material 8), - both with the same chlorine content, calculated on a weight basis. Material A' was then produced once more, in that

VAE was replaced with an ethylene-vinyl acetate copolymer ("Ultrathene UE 630" manufactured by National Distillers and Chemical Corp.) containing approx. 18% by weight vinyl acetate. This material is designated material 9. The results of the tests carried out on the materials in the unaged state were as follows:

As the test results clearly show, the material 6 containing HDPE and the material 7 containing PVC could not be extruded onto wire. Material 8, which contained plasticized PVC, failed the FR-1 flame test. Material 9, which contained an ethylene-vinyl acetate copolymer with only 18% VA, also failed the FR-1 flame test.

The material A", which did not contain the silane component, could not be extruded on wire and had an oxygen index of 34.9.

Although the invention refers to copolymers of vinyl acetate and ethylene containing more than approx. 20% by weight of vinyl acetate, the person skilled in the art will understand that the described combination of components is also applicable to other polymer systems and/or copolymer systems which give the same results as the preferred vinyl acetate-ethylene copolymers, and that such embodiments are therefore also included within the scope of the invention.

Claims (16)

1. Polymeric fire retardant material comprising a vinyl acetate-ethylene copolymer containing approx. 20 - 90% by weight vinyl acetate, and, per 100 parts of the copolymer, approx. 10 - 50 parts chlorinated polyethylene and approx. 70 - 300 parts hydrated aluminum oxide. 2. Material according to claim 1, characterized in that the copolymer contains 40 - 70% by weight of vinyl acetate. 3. Material according to claim 1 or 2, characterized in that it contains 10 - 35 parts of the chlorinated polyethylene and 100 - 250 parts of the hydrated aluminum oxide. 4. Material according to one of the claims - 1 - 3, characterized in that it further contains a silane component in an amount of approx. 0.2 - 4% by weight, calculated on the total weight of the material. 5. Material according to claim 4, characterized in that the amount of silane is 0.2 - 2% by weight. 6. Material according to claim 4 or 5, characterized in that it further contains approx. 10 - 50 parts antimony trioxide and/or approx. 10 - 50 parts silicon oxide per 100 parts of the copolymer. 7. Material according to one of claims 4-6, characterized in that it is cross-linked. 8. Electrical conductor coated with the material according to one of claims 4 - 7. 9. Method for the production of a polymeric, fire-retardant material, characterized in that a vinyl acetate-ethylene copolymer containing approx. 20 - 90% by weight vinyl acetate is mixed with approx. 10 - 50 parts chlorinated polyethylene and approx. 70 - 300 parts hydrated aluminum oxide per 100 parts of the copolymer. 10. Method according to claim 9, characterized in that a copolymer containing 40 - 70% by weight of vinyl acetate is used. 11. Method according to claim 9 or 10, characterized in that 10 - 35 parts of the chlorinated polyethylene and 100 - 250 parts of the hydrated aluminum oxide are used. 12. Method according to one of claims 9-11, characterized in that a silane component is further mixed in. an amount of approx. 0.2 - 4% by weight of the material. 13. Method according to claim 12, characterized in that the silane is used in an amount of 0.2 - 2% by weight. 14. Method according to claim 12 or 13, characterized in that approx. 10 - 50 parts antimony trioxide and/or approx. 10 - 50 parts silicon oxide per 100 parts of the copolymer. 15. Method according to one of claims 12-14, characterized in that a cross-linking agent is used. 16. Method according to one of claims 12-15, characterized in that the material is applied as a coating on an electrical conductor.