COMPOSITIONS FOR AN INSULATION TAPE

Abstract

Compositions for fixing a non-conductive material to a reinforcing layer are provided. In one embodiment, the composition being used to fix a non-conductive material on a reinforcing layer including a novolac produced by condensation of a substituted or unsubstituted phenol with an aldehyde in the presence of a catalyst, and optionally other additives.

Claims

1. An article of manufacture, comprising: a reinforcement layer; an adhesive composition disposed on the reinforcement layer, the adhesive composition comprising: a) a novolac produced by condensation of a substituted or unsubstituted phenol with an aldehyde, where the molar mass of the novolac is from 250 to 1000 g/mol; b) a catalyst selected from the group consisting of boron(III) halides and/or amine complexes thereof, imidazoles, acetylacetonates, tin(IV) chloride, tertiary amines, tetramethylguanidine, and combinations thereof; and c) optionally other additives; and a nonconductive material disposed on the reinforcement layer and the adhesive composition.

2. The article of claim 1, wherein the composition comprises from 50 to 90% by weight of novolac, from 1 to 30% by weight of catalyst and from 0 to 49% by weight of other additives based on the entirety of all of the components of the composition.

3. The article of claim 1, wherein the composition comprises from 5 to 30% by weight of catalyst based on the weight of the novolac.

4. The article of claim 1, wherein the novolac has been produced by condensation of phenol and/or cresol with formaldehyde.

5. The article of claim 1, wherein the molar mass of the novolac is from 250 to 500 g/mol.

6. The article of claim 1, wherein the catalyst comprises an imidazole.

7. The article of claim 1, wherein the nonconductive material comprises mica.

8. The article of claim 1, wherein the reinforcement layer comprises a woven fabric, a knitted fabric, a nonwoven fabric or foil made of glass, rockwool, polyimide, polyester, or a combination thereof, and combinations thereof.

9. The article of claim 1, wherein the article comprises from 5% to 20% by weight of the adhesive.

10. The article of claim 1, wherein the article further comprises an electrical conductor.

11. The article of claim 10, wherein the article further comprises a resin based on epoxy resin.

12. The article of claim 10, wherein the resin based on epoxy resin impregnates the article.

13. The article of claim 1, wherein the article comprises a tape.

14. The article of claim 13, wherein the article comprises a mica tape.

15. The article of claim 10, wherein the electrical conductor comprises a medium-voltage devices, a high-voltage device, or both.

16. A process comprising: (I) providing an insulation tape comprising a nonconductive material and a reinforcement layer adhesive-bonded to one another by means of a composition, wherein the composition comprises: a) a novolac produced by condensation of a substituted or unsubstituted phenol with an aldehyde, where the molar mass of the novolac is from 250 to 1000 g/mol; b) a catalyst selected from the group consisting of boron(III) halides and/or amine complexes thereof, imidazoles, acetylacetonates, tin(IV) chloride, tertiary amines, tetramethylguanidine, and combinations thereof; and c) optionally other additives; (II) winding the insulation tape around an electrical conductor; and (III) impregnating the insulation tape wound around the conductor with a resin based on epoxy resin.

Description

[0006] It is therefore an object of the present invention to provide an insulation tape—preferably mica tape—that, in particular when used in the production of the insulation for medium- and high-voltage devices in the VPI process, avoids use of conventional hardeners, in particular carboxylic anhydrides.

[0007] Said object is achieved in the invention via a composition for the production of an insulation tape, where the composition serves for the fixing of a nonconductive material on a reinforcement layer, characterized in that the composition comprises [0008] a) a novolac produced by condensation of a substituted or unsubstituted phenol with an aldehyde, where the molar mass of the novolac is from 250 to 1000 g/mol, and [0009] b) a catalyst selected from the group of the boron(III) halides and/or amine complexes thereof, imidazoles, acetylacetonates, tin(IV) chloride and/or tertiary amines and/or tetramethylguanidine, and [0010] c) optionally other additives.

[0011] The composition of the invention is applied in conventional manner by means of spreading or doctoring, or through nozzles, to the reinforcement layer, i.e. the backing tape, preferably composed of a woven fabric, knitted fabric, nonwoven fabric or foil made of glass and/or rockwool and/or polyimide and/or polyester and/or quartz, as adhesive between the nonconductive material, preferably mica. This gives a composite made of mica paper coated with reinforcement layers on one or more sides and impregnated over its entire area by the composition of the invention. The insulation tape preferably comprises from 5 to 20% by weight of the adhesive of the invention, based on the entirety (backing tape, nonconductive material, adhesive).

[0012] By virtue of the careful selection of the components and of the resultant reactivity of the composition of the invention, said composite is stable in storage at room temperature, and can optionally be cut to size to give a desired tape width and stored as rolls of product. It is now possible to provide mica tapes with better stability in storage than the mica tapes described above based on epoxy resin with a catalyst component that initiates subsequent anhydride curing.

[0013] The mica tape comprising the composition of the invention can in particular be used to provide insulation for medium- and high-voltage devices which comprise epoxy resins as impregnation resin and advantageously are produced by the VPI process. During the impregnation procedure, the conductor around which mica tape has been wound is impregnated, by means of vacuum, by the impregnation resin which is based on epoxy resin and has been heated (at about 40-80° C.), where the mica tape comprises the composition of the invention. The novolac of the composition of the invention is introduced by way of the mica tape into the epoxy resin of the impregnation resin, and acts as co-hardener for the latter. The catalyst present in the mica tape serves to initiate the homopolymerization of the impregnation resin and to accelerate the curing procedure of all of the impregnated layers; it was thus possible to optimize the hardening time.

[0014] By virtue of the inventive composition of the mica tape, it was possible to keep the loss factor tan(δ) of the insulation layer, which states the loss of electrical energy resulting from conversion into heat, at an appropriate level, thus permitting achievement of adequate insulation properties. By virtue of the use of the composition of the invention in the mica tape, it was possible to omit use, in the epoxy impregnation resin, of anhydride hardeners that were hitherto conventional; this is desirable for reasons related to health and to the environment.

[0015] The novolacs used for the insulation-tape composition of the invention are known from the prior art. They are produced by condensation of a substituted or unsubstituted phenol with an aldehyde, where the molar mass of the resultant novolac is from 250 to 1000 g/mol (measured in accordance with DIN 55672-1): it is preferable that monocyclic substituted or unsubstituted phenols (e.g. phenol, cresols and/or p-tert-butylphenol) are reacted with aldehydes (preferably formaldehyde) under acidic conditions. These compounds are readily available. The catalysts most frequently used for the acidic condensation are oxalic acid, hydrochloric acid, p-toluenesulfonic acid, phosphoric acid and sulfuric acid. Typical molar ratios in the reaction mixture here are from 0.75 to 0.85 mol of formaldehyde to 1 mole of phenol (F/P=from 0.75 to 0.85). The condensation is terminated when a molar mass of from 250 to 1000 g/mol, preferably from 250 to 500 g/mol, has been reached, because it is thus possible to adjust the viscosity of the composition, which plays an important part in application to the backing tape, to an ideal value.

[0016] The novolacs used in the invention are obtainable commercially by way of example as Bakelite® PH 8505 (product of Hexion GmbH).

[0017] The composition of the invention moreover comprises a catalyst, preferably from 1 to 30% by weight, more preferably from 5 to 30% by weight, based on the entire novolac, selected from the group of the boron(III) halides and/or amine complexes thereof, imidazoles, acetylacetonates, tin(IV) chloride and/or tertiary amines and/or tetramethylguanidine. Preference is given to boron trifluoride complexes and boron trichloride complexes, and also amine borates, but particular preference is given to compounds from the group of the imidazoles, in particular 2-phenylimidazole. A requirement deriving from the process is that the catalyst present in the mica tape has an appropriate vapor pressure which on the one hand does not result in evolution of gas after the final processing of the mica tape and on the other hand allows migration during the VPI process into the layers saturated by the impregnation resin in order to accelerate thorough curing of the impregnated layers. This is ensured via careful selection of the catalysts.

[0018] The composition of the invention can optionally comprise, as further constituent, other additives such as processing aids (e.g. solvents, e.g. methyl ethyl ketone), coupling agents (e.g. silanes), or wetting agents. These additives have a favorable effect on the production and properties of the insulation tape.

[0019] The composition therefore advantageously comprises by way of example from 50 to 90% by weight of novolac, from 1 to 30% by weight of catalyst and from 0 to 49% by weight of other additives, based on the entirety of all of the components of the composition.

[0020] Production of insulation for a conductor requiring insulation is achieved by a process comprising the following steps: [0021] (I) provision of an insulation tape which comprises a nonconductive material and a reinforcement layer adhesive-bonded to one another by means of a composition, where the composition comprises [0022] a) a novolac produced by condensation of a substituted or unsubstituted phenol with an aldehyde, where the molar mass of the novolac is from 250 to 1000 g/mol, and [0023] b) a catalyst selected from the group of the boron(III) halides and/or amine complexes thereof, imidazoles, acetylacetonates, tin(IV) chloride and/or tertiary amines and/or tetramethylguanidine, and [0024] c) optionally other additives, [0025] (II) winding of the insulation tape around the electrical conductor and [0026] (III) use of a resin based on epoxy resin to impregnate the insulation tape wound around the conductor.

[0027] The impregnation resin based on epoxy resin is known from the prior art: the resin can be selected from the group of the polyepoxides based on bisphenol A and/or F and of advancement resins produced therefrom, based on epoxidized halogenated bisphenols and/or on epoxidized novolacs, and/or polyepoxyester based on phthalic acid or hexahydrophthalic acid, or based on terephthalic acid, or of epoxidized o- or p-aminophenols, or epoxidized polyaddition products made of dicyclopentadiene and phenol.

[0028] Examples of materials used as resin components are therefore epoxidized phenol novolacs (condensate of phenol and, for example, formaldehyde and/or glyoxal), epoxidized cresol novolacs, bisphenol-A-based polyepoxides (including, for example, product of bisphenol A and tetraglycidylmethylenediamine), epoxidized halogenated bisphenols (e.g. tetrabromobisphenol-A-based polyepoxides) and/or bisphenol-F-based polyepoxides, and/or epoxidized novolac and/or epoxy resins based on triglycidyl isocyanurates. The average molar mass of all of these resins is preferably from 200 to 4000 g/mol, and the epoxy equivalent is preferably from 100 to 2000 g/eq.

[0029] Examples of resin components that can be used are inter alia the following: polyepoxides based on bisphenol A (e.g. Epikote® 162 or 828) and/or bisphenol F (e.g. Epikote® 158 or 862), and also mixtures thereof, and cycloaliphatic epoxy resins (e.g. Epikote® 760 products obtainable from Hexion Inc.), and mixtures comprising reactive diluents (e.g. Heloxy® Modifier AQ).

[0030] The impregnation resin can also optionally comprise other components, e.g. wetting agents, which serve to control surface tension. It would also be possible to add other constituents having curing action, but it is preferable here to avoid use of anhydrides in the impregnation resin.

[0031] The impregnation in step (III) particularly preferably takes place in vacuo (VPI process), thus ensuring that the impregnation resin achieves almost complete impregnation of the composite made of the conductor around which, mica tape has been wound. The impregnation procedure is generally followed by hardening in a drying oven in the temperature range from 80° C. to 180° C., as required by the impregnation resin used.

[0032] The invention will be explained in more detail with reference to an embodiment:

[0033] 1. Production of the Mica Tape [0034] The adhesive component for production of the mica tape is first formulated as follows: [0035] 1000 g of the novolac (Bakelite® PH 8505) is heated to 60° C. and 150 g of 2-phenylimidazole are admixed therewith. [0036] The mixture is homogenized at 60° C. within a period of one hour. An 80% solution in methyl ethyl ketone is then produced at 60° C. and cooled to room temperature. The resultant adhesive is used to fix a layer of mica paper, thickness 100 μm, on a nonwoven glass fabric with layer weight 23 g/m.sup.2. To this end, 20 g/m.sup.2 of the adhesive are sprayed onto the nonwoven glass fabric and bonded to the mica paper, and the composite is dried at 70° C. in vacuo (10 mbar). [0037] The resultant mica tape is cooled to room temperature.

[0038] 2. Production of the Impregnation System in the VPI Process [0039] The mica tape produced as described above is cut to size to give sheets measuring 10×10 cm. Ten layers of the mica tape are placed in layers on top of one another to give a total layer thickness of about 2 mm and, at 40° C. and 5 mbar in a metal mold with two open sides, impregnated with an impregnation resin consisting of 250 g of EPIKOTE™ Resin 162, 750 g of EPIKOTE™ Resin 158 and 150 g of Heloxy™ Modifier AQ within a period of 60 minutes. A gauge pressure of 6 bar is used for continued impregnation for a further 60 minutes. [0040] The excess impregnation resin is discharged, and the metal mold is transferred to a curing oven. Curing takes place in two stages, firstly 3 hours at 90° C. and then 15 hours at 140° C.

[0041] 3. Insulation Properties [0042] The composite made of impregnation resin and adhesive leads to the following temperature-dependent loss factors (tan(δ)) after curing:

TABLE-US-00001 Temp. in ° C. tan(δ) 25 0.005 50 0.00715 75 0.0104 100 0.017 120 0.0522 140 0.2425 180 1.206 [0043] These are at a level comparable with those comprising anhydride hardeners in the impregnation resin, and the impregnation system of the invention therefore also provides the desired insulation properties.