EP0377080B1 - Electrical conductor with polymeric insulation - Google Patents

Abstract

Process for joining a completely thermally cured polymer to itself or to another material by coating the polymer with an adhesive layer of a completely thermally cured organosiloxanimide adhesive which contains an organic peroxide, and curing the adhesive by heating in order to crosslink it. The polymer used may be a polyimide, a polyphenylene sulphide or a polyether ether ketone. A heat-resistant and solvent-resistant polymer-insulated wire is obtained.

Description

This invention relates to insulated electrical conductors, particularly those conductors that are insulated with polymers. Round cables as well as flat and coaxial cables are to be used as electrical conductors.

In the coating and insulation technology of electrical conductors, it is known that in order to produce satisfactory insulated circuits or installations, hard and solid coatings or insulations which are subject to high wear, bending stresses, high temperatures, aggressive environmental conditions and a chemical attack by liquids resist, are required.

bezeichnet, worin m zwei oder mehr, n 0 oder eine ganze Zahl, R der Rest einer ethylenisch ungesättigten Dicarbonsäure nach der Entfernung der Hydroxylgruppen und R1 der Rest von Isophthal-, Terephtal- oder gesättigten aliphatischen Säuren mit 4 bis 10 Kohlenstoffatomen darstellt, deren Hydroxylgruppen entfernt sind.Among the materials used to insulate conductors for use under such conditions are mixtures of solvent-soluble, thermosetting phenylmethylsiloxanes and organic polyamides disclosed in U.S. Patent 2,983,700. The siloxanes have 1.3 to 1.95 phenyl and methyl groups per silicon atom, up to half of the phenyl groups can be biphenyl groups and up to 10% of the organic groups can be tolyl, alkyl, ethyl or other groups. The siloxanes are soluble in aromatic, organic solvents or mixtures. The polyamide comes with

referred to, wherein m represents two or more, n 0 or an integer, R is the residue of an ethylenically unsaturated dicarboxylic acid after removal of the hydroxyl groups and R1 is the residue of isophthalic, terephthalic or saturated aliphatic acids having 4 to 10 carbon atoms, their hydroxyl groups are removed.

A wire is coated with this mixture and cured by removal of the solvent and by heating to form an insulating varnish coating on the wire.

in organischen Lösungsmitteln gelöst, wie in US-PS 3,325,450 dargelegt, und auf Metalle, beispielsweise in der Form von Drähten, aufgebracht. Das Lösungsmittel wurde verdampft und die Überzüge wurden erhitzt, um das Amid in den harten, widerstandsfähigen und gebrannten Imidüberzug zu zyklisieren. Von dem Amid, das in die Imidform zyklisiert werden sollte, konnten ebenfalls Filme gegossen werden, die in der Form von gewickelten Polyimid-Streifenfilmen auf Leitern verwendbar waren, wobei das Polyimid die Formel

aufwies, worin R ein bivalentes Kohlenwasserstoffradikal, R¹ ein monovalentes Kohlenwasserstoffradikal, ml 1 bis 1000, n 10 bis 10000 oder mehr bedeuten.Below were polyamides with the formula

dissolved in organic solvents as set forth in U.S. Patent 3,325,450 and applied to metals, for example in the form of wires. The solvent was evaporated and the coatings were heated to cyclize the amide into the hard, tough and fired imide coating. Films could also be cast from the amide to be cyclized into the imide form which could be used in the form of striped polyimide strip films on conductors, the polyimide having the formula

wherein R is a bivalent hydrocarbon radical, R¹ is a monovalent hydrocarbon radical, ml is 1 to 1000, n is 10 to 10,000 or more.

R is usually polyalkylene or polyarylene, and R¹ is, for example, methyl or phenyl.

Composite materials could be made by firmly joining two sheet material elements made of the same or different materials, e.g. glass, metals or polymers, by converting the organosilanamide block copolymers described in U.S. Patent 3,740,305 to the corresponding polyimides in order to to form firmly bonded materials. The organosilane imides were applied to the surfaces of the sheet members to be bonded, the solvent was removed, and the cyclization reaction was effected by heat.

Another way to achieve good properties with the siloxaneimide resins has been set forth in U.S. Patent 3,763,081 where unsaturated vinyl groups substituted on organosiloxanes have been crosslinked to a cured product by heat and oxygen or peroxide with unsaturated groups on bismaleimides by Condensation of maleic anhydride with p, p¹-methylenedianiline were prepared.

worin R ein monovalentes Kohlenwasserstoffradikal, üblicherweise Methyl, und n 0 bis 150 ist.Such organosiloxanes have the formula

wherein R is a monovalent hydrocarbon radical, usually methyl, and n is 0 to 150.

A much broader and wider variety of organosiloxaneimide block copolymers than those mentioned above has been provided by U.S. Patent 4,522,985; according to this publication, the norbornane and norbornene cores have been used extensively for both the siloxane and diamine regions of the starting materials. The end products, the organosiloxane imides, are rubbers that can be cured with hard peroxides to form hard elastomers.

Where tape wrap processes are used to build up layers on conductors in the manufacture of insulated electrical cables, the insulating and physical properties of polyimide, polyether ether ketone and polyphenylene sulfide have made the use of these materials desirable if they can be successfully bonded to themselves.

Curing under heat, for example to cyclize a polyamide into a polyimide directly on the cable, was not a good solution. It is now common to coat a fully cured polyimide tape with a thermoplastic adhesive material, such as a fluorinated ethylene-propylene copolymer. This works very well unless halogen-free insulation is required due to reduced toxicity when burned; it is desirable to remove the outer layer of the thermoplastic adhesive after processing, or to subject the cable to electromagnetic radiation, in which case a halogenated polymer does not work very well under such radiation and a halogenated material must be avoided.

The invention has for its object to provide an insulation material that has good insulating properties and good adhesiveness when it is applied to the material to be insulated. Furthermore, a method for insulating an electrical conductor is to be specified, by means of which the insulation material can be applied to the conductor with good adhesion.

Solutions to these problems are given in claims 1 to 21.

The insulation material according to the invention consists of a high temperature-resistant polymer which surrounds an electrical conductor. A completely heat-cured organosiloxaneimide adhesive is applied to this polymer, which surprisingly ensures a good polymer-polymer connection. The polymer is a polyimide, polyphenylene sulfide (PPS) or a polyether ether ketone (PEEK). The cables according to the invention are particularly suitable for use at high temperatures and under aggressive environmental conditions. The innovative composite material can be used both as primary insulation and as a jacket.

The organopolysiloxaneimide is dissolved in an organic solvent, possibly with organic peroxides and pigments, and the solution is applied to a layer of the fully cured polymer. The solvent is then evaporated and the polymer layer is wrapped around an electrical conductor with the adhesive on top. The polymer layer is preferably cut into a band shape and wound spirally around the electrical conductor. The conductor wrapped in the tape is first of all for a relatively short time heated to a higher temperature to seal the layers of polymer. It is then kept at a low temperature for an extended period of time to increase the cross-link curing reaction and to prevent problems such as tarnishing of metal conductors, which can occur at higher temperatures and longer heating times.

worin Q ein tetravalentes Radikal ist, das ausgewählt wird aus

worin D ausgewählt wird aus
-O-, -S-,

und -O R⁴-O-,
worin R⁴ ein bivalentes Radikal ist, das ausgewählt ist aus

und bivalenten organischen Radikalen der allgemeinen Formel

worin R¹ und R² Alkylene darstellen, für gewöhnlich -(CH₂)₃ -, oder R⁴, worin R Methyl, Phenyl, Tolyl oder eine Mischung von aliphatischen und aromatischen Radikalen darstellt, worin R³ Wasserstoff oder ein Alkylradikal mit 1 bis 8 C-Atomen darstellt, X aus bivalenten Radikalen -CR $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$

- , C_yH_2y-,-CO-,-SO₂-, -O-, und -S-, ausgewählt ist, wobei y 1 bis 5, k 1 bis 7, n 1 bis 7, m eine ganze Zahl größer als 1 und p 0 oder 1 sind.The preferred organopolysiloxaneimide adhesive is a fully cured material with the formula

where Q is a tetravalent radical selected from

where D is selected from
-O-, -S-,

and -O R⁴-O-,
wherein R⁴ is a bivalent radical selected from

and divalent organic radicals of the general formula

wherein R¹ and R² represent alkylenes, usually - (CH₂) ₃ -, or R⁴, wherein R represents methyl, phenyl, tolyl or a mixture of aliphatic and aromatic radicals, wherein R³ represents hydrogen or an alkyl radical with 1 to 8 carbon atoms , X from bivalent radicals -CR $\genfrac{}{}{0ex}{}{\text{3rd}}{\text{2nd}}$

-, C _y H _2y -, - CO -, - SO₂-, -O-, and -S-, is selected, where y 1 to 5, k 1 to 7, n 1 to 7, m is an integer greater than 1 and p are 0 or 1.

Since the polyimide siloxane is a thermoplastic, the chemical resistance and the heat resistance of the material are severely limited. To partially compensate for these disadvantages, it is necessary to chemically crosslink the matrix. The crosslinking reaction is preferably carried out in the presence of a peroxide. Benzoyl peroxides such as bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide or t-butyl peroxide are particularly suitable as peroxides. The presence of peroxide accelerates the crosslinking reaction and increases chemical resistance to solvents.

The crosslinking reaction is initiated by cleavage of the peroxide, as can be seen from the formula below.

The radicals formed in this way generate a polymer radical by splitting off hydrogen from the polymer chain. Two of the polymer radicals formed in this way can saturate to form a CC bond, as can be seen from the formula below.

In the presence of a coactivator, such as, for example, triallyl cyanurate, three-dimensional crosslinking can be achieved, which leads to a thermally more stable product which, by multiplying the number of crosslinking sites, also has better chemical resistance. In this case, the polymer radical reacts with an allyl group of the cyanurate. The formula is shown below.

Other peroxide radicals, polymer radicals or allyl residues of another cyanurate can attach to the radicals of the allyl groups of the cyanurate, which are linked to the main chain, and thus saturate one another. This leads to an increase in the number of networking points and thus to an increase in the degree of networking. In addition to these preferred crosslinking reactions, there can of course also be numerous other side reactions which overall lead to a spatially crosslinked, thermally stable and chemically resistant product.

The crosslinking is only started when the finished product is exposed to a higher temperature, which ensures that no pre-crosslinking takes place during the drying and further processing of the product. The reaction is only triggered when the product is held at 300 ° C for a period of 1 to 3 minutes. In order to equalize the crystallization areas in the microstructure of the material, the finished products are subjected to post-heating, which normally takes place at 200 ° C for 2 to 3 hours. Insulation produced using this method can be used for mechanical loads up to a permanent temperature of 150 ° C and for only electrical loads up to a permanent temperature of 170 ° C.

• (1)   (CH₃OCH₂CH₂O)₃ - Si - CH = CH₂
• (2)
  
• (3)   (C₂H₅O)₃ - Si - CH₂ - CH₂ - CH₂ - SCN
• (4)
  

A low dielectric constant is required to use the insulation material for flat or coaxial cables. To do this, the adhesive approach must be modified. This can be done, for example, by adding expanded glass spheres, preferably microspheres that are hollow on the inside, in addition to the mixture mentioned. To achieve better adhesion between the plastic matrix and the glass balls, a silane-based coupling agent is added. In particular, vinyl tris (2-methoxyethoxy) silane (1); 3,4 epoxybutyltriethoxysilane (2); 3-thiocyanatopropyltriethoxysilane (3) or 3-methacryloxypropyltriethoxysilane (4) can be used.

• (1) (CH₃OCH₂CH₂O) ₃ - Si - CH = CH₂
• (2)
  
• (3) (C₂H₅O) ₃ - Si - CH₂ - CH₂ - CH₂ - SCN
• (4)
  

beruht auf der Ausbildung einer monomolekularen Silanschicht auf der Oberfläche der Glaskugeln, wobei hier die funktionelle Gruppe y reagiert. Die verbliebene funktionelle Gruppe X kann chemisch mit der Kunststoffmatrix oder mit dem Vernetzer/Coaktivator-System reagieren.The amount of silane used in each case is approximately 0.1 to 0.8% of the weight of glass balls. The silanes that can be used have the following general formula y-Si-R'-X, where y and X represent the two different reactive centers. The functional group X is linked to an organic intermediate R 'with the four-bonded silicon atom. The functional group y is a removable group, in this case either a trimethoxy or a trieethoxysilyl group. The function of silanes as an adhesion promoter

is based on the formation of a monomolecular silane layer on the surface of the glass spheres, the functional group y reacting here. The remaining functional group X can react chemically with the plastic matrix or with the crosslinker / coactivator system.

In addition to the glass spheres, which reduce the dielectric constant of the insulation material to about 2.1 to 1.8, a halogen-free flame retardant can also be added. On the one hand, this leads to an improved flame resistance of the insulation material and, on the other hand, to a substantial increase in the viscosity of the coating material. The proportion of the flame retardant can be up to approx. 20 percent by weight. This also makes it possible to obtain a higher layer thickness of the adhesive application and thus to use the coated polymer layer, for example in the form of a film, for the production of ribbon cables. The thickness of the adhesive layer is preferably 50 to 100 »m. This enables the embedding of bare conductors or of fully insulated wires.

Example 1:

A roll of polyimide film (DuPont Kapton H-50) is coated with a 2.54 »m (0.0001 inch) thick layer of an organopolysiloxanimide adhesive which has been dissolved in methylene chloride to form a 5% solids solution surrender. 20% by weight of a green pigment in polyester, based on the organopolysiloxaneimide, was added to the solution of organopolysiloxaneimide and methylene chloride to color the film. The solvent is evaporated to a to produce dry film.

The roll is then cut into evenly wound bobbins with an approximately 1.83 mm (0.072 inch) wide band. The tape is wrapped around a 30 AWG silver plated copper conductor to give a 2.1 wrap construction with a 0.3048 mm (0.012 inch) end diameter. This wrapped structure is connected in an air oven at 300 ° C with a residence time of 50 seconds. The outer adhesive layer, which is not covered with a film layer, is washed off the assembly by passing the assembly through a methylene chloride bath to give a green, insulated wire assembly. Tests are carried out on this wire construction with regard to the dielectric in a moist environment, with regard to aging when heated and with regard to the resistance to solvents. The test procedure for dielectric in a humid environment is carried out according to the provisions of MIL-W-81822A, section 4.6.20; the heat resistance test procedure is in accordance with the provisions of MIL-W-81822A, section 4.6.22; and fluid resistance is in accordance with the provisions of MIL-W-8l822A, Section 4.6.25. The heat resistance of the construction using an organosiloxaneimide adhesive is greater than the heat resistance of a comparable polyester adhesive, but the solvent resistance to 1,1,1-trichloroethane is insufficient.

Example 2:

A roll of polyimide film (DuPont Kapton H-100) is covered with a 2.54 »m (0.0001 inch) thick layer coated with an organopolysiloxaneimide adhesive dissolved in methylene chloride to give a 5% solids solution. A red pigment containing chromium is added to the adhesive solution to color the tape. The solvent is evaporated to give a dry film.

Another tape is coated exactly as above, except that an organic peroxide (e.g. Luprox 500R dicumyl peroxide) is added in an amount of 10% by weight based on the organopolysiloxaneimide adhesive.

Both tapes are cut into evenly wound coils approximately 2.64 mm (0.104 inch) wide. The tapes are wrapped around a 30 AWG silver plated copper conductor to create a 3.2 wrap construction with a finished 0.4064 mm (0.016 inch) diameter. The wrapped superstructures are fired in an air oven with a temperature of 320 ° C and a residence time of 100 seconds. The outer layer of adhesive, which is not covered by the film, is washed off the assembly by passing the assembly through a methylene chloride bath. A red, insulated wire structure is obtained.

Samples from each setup are cured at 225 ° C for 3.5 hours. Physical test procedures are performed on both the cured sample and the uncured sample. Resistance to fluids is performed in accordance with the provisions of MIL-W-81822A, Section 4.6.25, except that methylene chloride is added to the list of test fluids and the test voltage is increased until a breakdown occurs. The results are summarized in the table below (KV = Kilovolt).

From the examples it can be seen that the adhesive is more resistant to some solvents than to other solvents. The curing of samples in the presence of peroxide accelerates the crosslinking and thus increases the solvent resistance of the adhesive to those solvents which more easily dissolve the adhesive, for example methylene chloride.

Example 3:

A roll of PEEK (polyether ether ketone) film is coated with a 0.00254 mm (0.0001 inch) thick layer of an organopolysiloxane imide adhesive dissolved in methylene chloride to form a 5% solids solution. to surrender. A chromium-containing red pigment is added at 25% by weight, based on the organopolysiloxanimide adhesive, in order to color the tape. The solvent is evaporated to give a 5.0 wrap construction with a final diameter of 0.508 mm (0.020 inch). The wrapped structure is heated in an air oven at 300 ° C with a residence time of 100 seconds. The outer layer of adhesive, which is not covered by a film layer, is washed off the assembly by passing it through a methylene chloride bath so that a red, insulated conductor assembly results.

The finished composite insulation material had a tensile strength of 175 (25000 psi) and an elongation of 110%. It also had good heat resistance and good electrical properties.

Example 4:

A polyphenylene sulfide film with a layer thickness of about 12 to 100 »m is coated with an adhesive solution. The adhesive solution, which is used as a coating material, contains organopolysiloxane imide as the plastic matrix, bis-2,4-dichlorobenzoyl peroxide as the crosslinker, triallyl cyanurate as the coactivator, and color pigments and methylene chloride as the solvent. The solids concentration is approximately 20 to 25% by weight, depending on the required layer thickness. The solvent is evaporated, the crosslinking reaction takes place at 300 ° C and a time of 1 to 3 minutes. The finished product is subjected to post-heating, which takes place at 200 ° C. for a period of 2 to 3 hours.

The end product is a primary insulation material for electrical parts, can be used mechanically for a permanent temperature of at least 150 ° C and electrically for a temperature of at least 170 ° C.

Methylene chloride proved to be the best solvent for the uncured organopolysiloxaneimide adhesive. The improved resistance to methylene chloride by means of an organopolysiloxane imide hardened with the help of peroxide thus eliminates a weak point in the use of this adhesive for the production of wires and cables.

Claims (21)

1. An insulated electric conductor having:

   (a) a core made of electroconductive metal;

   (b) an insulating material surrounding the core and made of a polymer selected from polyimide, polyphenylene sulfide or polyetheretherketone;

   (c) a completely thermoset organosiloxanimide adhesive which is applied to the polymer; and

   (d) a further layer of the polymer which is glued to the adhesive.
2. The insulated conductor of claim 1, characterized in that the adhesive is selected from adhesives which have the formula

   

   wherein Q is a tetravalent radical selected from

   

   wherein D is selected from
   -O-, -S-,

   

   et -O-R⁴-O-,
   wherein R⁴ is a bivalent radical selected from

   

   

   

   and

   

   wherein:
   R¹ and R² are alkylene, in particular -(CH₂)₃-, or R⁴, R is methyl, phenyl, tolyl or a mixture of aliphatic and aromatic radicals, R³ is hydrogen or an alkyl radical with 1-8 C atoms, X is selected from bivalent radicals
   -CR₂-, -C_yH_2y-, -CO-, -SO₂-, -O-, and -S-,
   wherein y is 1 to 5, k is 1 to 7, n is 1 to 7, m is an integral number greater than 1, and p is zero or 1.
3. The insulated conductor of claim 1 or 2, characterized in that R is -CH₃, R¹ is

   

   R² is -CH₂)₃-, R⁴ is

   

   X -C(CH)₃)₂-, Q

   

   wherein D is -O-R⁴-O-, p equals 1, k equals 5, n equals 4 and m is 4 to 8.
4. The insulated conductor of any of claims 1 to 3, characterized in that the adhesive has been cured in the presence of an organic peroxide.
5. The insulated conductor of claim 4, characterized in that the organic peroxide is benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide or t-butyl peroxide.
6. The insulated conductor of claim 4 or 5, characterized in that the adhesive has been cured in the presence of a coactivator.
7. The insulated conductor of claim 6, characterized in that the coactivator is a cyanurate.
8. The insulated conductor of claim 7, characterized in that the cyanurate is a triallyl cyanurate.
9. The insulated conductor of any of claims 1 to 8, characterized in that the adhesive is mixed with glass microballs which are hollow inside to lower the dielectric constant of the insulating material.
10. The insulated conductor of claim 10, characterized in that the adhesive contains a silane to increase adhesion with the glass microballs.
11. The insulated conductor of claim 11, characterized in that the silane is selected from vinyl tris-(2-methoxyethoxy)-silane, 3,4-epoxybutyltriethoxysilane, 3-thiocyanatopropyltriethoxysilane or 3-methacryloxypropyltriethoxysilane.
12. The insulated conductor of claim 10 or 11, characterized in that the quantity of silane is 0.1 to 0.8% of the weight of microballs.
13. The insulated conductor of any of claims 1 to 12, characterized in that the adhesive contains a flameproofing agent.
14. The insulated conductor of claim 13, characterized in that the flameproofing agent is present in a concentration up to about 20% by weight.
15. A method for insulating a conductor made of electro-conductive metal having the following method steps:

    (a) covering a polymer film with an adhesive layer comprising a completely thermoset organosiloxanimide in an organic solvent;

    (b) evaporating the solvent;

    (c) wrapping the conductor with the polymer film and the adhesive or embedding the conductor in the adhesive layer;

    (d) heating the wrapped conductor for connecting the layers.
16. The method of claim 16, characterized in that the solution of the completely thermoset organosiloxanimide in an organic solvent contains an organic peroxide, and after the heating for connecting the layers the conductor is held for a relatively long time at a temperature lower than the crosslinking temperature to carry out the spatial crosslinking of the organosiloxanimide.
17. A method for gluing a polymer used as insulating material in a cable, which is a polyimide, a polyphenylene sulfide or a polyetheretherketone, to itself or to another material by heating a connecting layer of completely thermoset organosiloxanimide adhesive which covers the polymer.
18. The method of claim 17, characterized in that the adhesive contains an organic peroxide.
19. The method of claim 18, characterized in that the organic peroxide is a benzoyl peroxide, for example bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide or t-butyl peroxide.
20. The method of claim 18 or 19, characterized in that a coactivator, preferably a cyanurate, is used additionally to the organic peroxide.
21. The method of claim 20, characterized in that the cyanurate used is a triallyl cyanurate.