AT519409A1

AT519409A1 - Use of vinyl ester resins for insulation of electrical equipment

Info

Publication number: AT519409A1
Application number: ATA557/2016A
Authority: AT
Original assignee: Dr Klaus Urban
Priority date: 2016-12-07
Filing date: 2016-12-07
Publication date: 2018-06-15

Abstract

The invention relates to the use of vinyl ester resins based on modified and unmodified epoxy resins for the insulation of electrical equipment.

Description

The application refers to the use of vinyl ester resins for the insulation of electrical equipment.

The insulation of electrical equipment utilising synthetic resins is common practice and thermosetting resins have proven especially suitable for such applications. Insulation Systems are provided in many forms and processed by several techniques and this invention relates to a novel insulation system that can be applied via the vacuum-pressure impregnation process [VPI process].

Current Systems utilised in VPI processing are generally cata-lysed epoxy Systems that are processed by incorporation of Catalyst [s] that will induce homo-polymerisation of the epoxy or by combination of the epoxy resin with anhydride cross-linker which is accelerated through latent or semi-latent curing agents that are incorporated in the System and/or the reinforcement material, in most cases glass fabric /mica paper tapes. These epoxy Systems each offer their own benefits and negative points. The Systems are used for the insulation of the wires or coils to insulate and/or fix and protect them. The VPI process is based on these electrical current carrying areas being wrapped with the reinforcement/ insulation [mica -glass fabric for example] and after the wrapping Operation is concluded the reinforcement is impregnated with the thermoset-ting System and this is where the VPI process can be applied.

The VPI process is broadly speaking based on the recipient component being housed in a suitable autoclave that be evacu-ated such that the component is conditioned and Consolidated in advance of the matrix resin being fed into the evacuated at a suitable viscosity to allow penetration into the reinforcement. The autoclave is then subjected to positive pressure [sometimes with additional heating to further reduce the viscosity of the matrix and allow greater penetration] and the matrix material penetrates and impregnates the reinforcement/ insulation ensuring an absence of voids.

The residual matrix material is removed from the autoclave back to the main storage reservoir which is optionally replen-ished with new or fresh matrix as required. Cooling may be applied to extend the shelf-life before the next application. The impregnated component [s] are then subjected to a pre-determined thermal cycle in order to eure the matrix resin and fix the insulated parts of the component and/or to embed the component in the insulating matrix.

This cyclic Operation and use of the matrix material to im-pregnate the reinforcement and return to the storage reservoir until further use can give rise to viscosity increase which in turn can limit the effectiveness of the matrix System to suc-cessfully impregnate the reinforcement which in turn can lead to electrical failures in the component on test or when in Service.

It is quite evident that the viscosity of the matrix resin is important and the matrix System must be low enough in viscosity to offer effective penetration at the process temperature and have sufficient bath stability to avoid increasing viscosity with repeated cycling. Whilst stability and low level of reactivity of the matrix System whilst housed for use is important, the matrix polymer has to eure when exposed to the eure schedule employed post impregnation. The matrix System conveys several attributes which may include electrical insu-lation, mechanical fixture, protection from the environment and other stresses and the properties must offer longevity to ensure the lifetime of the component in service.

Epoxy Systems have generally good properties to satisfy these requirements. The current Systems employed in VPI Processing are generally of two types. Formulated epoxy Systems utilised with catalysts to induce homo-polymerisation or epoxy anhy-dride combinations. The epoxy Systems that are homo-polymerised are generally single part Systems and tend to have higher viscosities than the epoxy-anhydride Systems which therefore requires elevated temperatures to allow for sufficient impregnation which in turn can reduce stability of the cycled material. Epoxy Systems that contain anhydrides generally have much lower viscosity making them more effective at impregnation at lower temperatures which in turn improves sta-bility. These can be multi-part Systems with epoxy and anhy-drides combined on site or supplied in a pre-blended form. Catalyst[s] are employed to accelerate eure response and in the case of the epoxy-anhydride based formulations the Systems generally offer low viscosity and subsequent impregnation with adequate shelf-life or stability. The catalyst[s] may be incorporated into the resin matrix and/or the reinforcement and historically it has been common practice to incorporate a catalyst [an example being zinc naphthenate] into the mica reinforcement tape.

Due to further understanding of the effect of Chemicals and development of regulatory requirements and restrictions there has been great concern over the use of anhydrides and some grades are already listed under the REACH regulations candi-date list for SVHC's substances of very high concern which in turn will restrict or preclude their use.

Therefore it becomes apparent that new and novel anhydride free products are required to satisfy the process and perform-ance characteristics of these Systems. The present invention provides such a matrix insulation System having suitable stor-age and Processing characteristics that are comparable/ fa-vourable to the conventional epoxy-anhydride Systems described previously when applied in vaeuum pressure impregnation proc-esses.

The present invention relates to the use of vinyl ester resin compositions that have been formulated with low viscosity, ex-cellent storage stability and excellent cured properties for the insulation of electrical equipment. The vinyl ester dass of resins have for some years now been recognized for their inherent Chemical resistance and mechanical performance but these materials are excellent insulators when processed cor-rectly. The resins are chemically the reaction products of ep-oxy resins and ethylenically unsaturated monocarboxylic acids. Typical vinyl ester resins now commercially available include the CURALINK (RTM) resins, marketed by Bitrez Ltd.

The vinyl esters are produced by reacting the epoxy resins and ethylenically unsaturated monocarboxylic acids to a desirable end point and then they can be diluted with diluents or fur-ther unsaturated materials that act as co-reactants during the process. This allows for the formulation of materials that are fluid enough to allow for ease of application and to permit good wetting and impregnation of reinforcements. Inclusion of stabilisers and latent catalysts in optionally the matrix and or the reinforcement allows for suitable eure of the compo-nents thereafter.

The polyepoxides used to prepare the vinyl ester resins com-prise those compounds containing at least one vicinal epoxy group. These polyepoxides may be saturated or unsaturated, a-liphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted if desired with non-interfering substituents such as halogen atoms, hydroxyl groups, ether radicals, and the li-ke. They may also be monomeric or polymeric. For clarity, many of the polyepoxides and particularly those of the polymeric type are described in terms of epoxy equivalent values. The polyepoxides used in the present process are preferably those having an epoxy equivalency greater than 1.0.

Preferred polyepoxides are the glycidyl polyethers of polyhy-dric phenols and polyhydric alcohols, especially the glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propane having an average molecular weight between about 300 and 3,000 g/mol and an epoxide equivalent weight between about 140 and 2,000 g/mol.

Other suitable epoxy compounds include those compounds derived from polyhydric phenols and having at least one vicinal epoxy group wherein the carbon-to-carbon bonds within the six-membered ring are saturated. Such epoxy resins may be obtained by at least two well-known techniques, i.e., by the hydrogena-tion of glycidyl polyethers of polyhydric phenols or by the reaction of hydrogenated polyhydric phenols with epichloro-hydrin in the presence of a suitable catalyst such as Lewis acids. i.e., boron trihalides and complexes thereof, and sub-sequent dehydrochlorination in an alkaline medium. The method of preparation forms no part of the present invention and the resulting saturated epoxy resins derived by either method are suitable in the present compositions.

In any event, the term "saturated epoxy resin", as used herein shall be deemed to mean the glycidyl ethers of polyhydric phe-nols wherein the aromatic ring structure of the phenols have been or are saturated.

Further preferred modified or unmodified epoxy resins are se-lected from carbonyl terminated butadiene acrylonitrile [CTBN] rubber or other toughened modified epoxy which may be obtained by the incorporation of thermoplastic and/ or core Shell material. Other preferred modified and unmodified epoxy resins are selected from halogenated epoxy resins. Particularly preferred are modified or unmodified epoxy resins which are selected from bisphenol A free epoxy resins.

The other component in the reaction comprises an organic car-boxylic acid which is unsaturated, aliphatic, cycloaliphatic or aromatic, and may be monocarboxylic or polycarboxylic. The preferred acids to be employed are the monocarboxylic acids, such as acrylic acid, methacrylic acid, and the like.

Particularly preferred acids to be utilized comprise the ethy-lenically unsaturated acids such as, for example, acrylic a-cid, methacrylic acid, crotonic acid, alpha-phenylacrylic a-cid, alpha-cyclohexylacrylic acid, maleic acid, alpha-chloromaleic acid, tetrahydrophthalic acid, itaconic acid fu-maric acid, cyanocrylic acid, methoxyacrylic acid, and the like .

Also particularly preferred are the partial esters of polycar-boxylic acids, and particularly the alkyl, alkenyl, cycloalkyl and cycloalkenyl esters of polycarboxylic acids such as, for example, allyl hydrogen maleate, butyl hydrogen maleate, allyl hydrogen phthalate, allyl hydrogen succinate, allyl hydrogen fumarate, butenyl hydrogen tetrahydrophthalate, cyclohexenyl hydrogen maleate, cyclohexyl hydrogen tetrahydrophthalate, and the like, and mixtures thereof.

Coming under special consideration, particularly because of the superior coating properties of the resulting unsaturated Polyesters, are the ethylenically unsaturated monocarboxylic acids and unsaturated partial esters, and especially the unsaturated aliphatic monocarboxylic acids containing 3 to 10 carbon atoms, and the alkenyl and alkenyl esters of al-kenedioic acids containing up to 12 carbon atoms.

The reaction of the polyepoxides with the unsaturated carbox-ylic acids to produce the vinyl esters is preferably carried out in the presence of an esterification catalyst such as ter-tiary amine, phosphine, phosphinic acid, sulfonic acid, or o-nium compound.

The preferred catalyst comprises the onium salts, and preferably those containing phosphorous, sulfur or nitrogen, such as, for example, the phosphonium, sulfonium and ammonium salts of inorganic acids. Examples of these include, among others, ben-zyltrimethylammonium sulfate, benzyltrimethylammonium nitrate, diphenyldimethylammonium Chloride, benzyltrimethylammonium Chloride, diphenyldimethylammonium nitrate, diphenylmethylsul-fonium Chloride, tricyclohexylsulfonium bromide, triphenyl methylphosphonium iodide, diethyldibutylphosphonium nitrate, trimethylsulfonium thiocyanate, triphenylsulfonium Chloride, dicyclohexyldiamylphosphonium iodide, benzyltrimethylammonium thiocyanate, and the like, and mixtures thereof.

Other suitable catalysts include the sulfonic acids such as para-toluene sulfonic acid and the strong mineral acids such as phosphonic acid.

The amount of the above-noted polyepoxide and acid to be used in the reaction may vary over a wide ränge. In general, these reactants are used in approximately chemically equivalent a-mounts. As used herein and in the appended Claims a Chemical equivalent amount of the polyepoxide refers to that amount needed to furnish one epoxy group per carboxyl group. Excess amounts of either reactant can be used. Preferred amounts ränge from about 0.5 to 2 equivalents of epoxide per equivalent of carboxylic acid.

The amount of the catalyst employed may also vary over a con-siderable ränge. In general, the amount of the catalyst will vary from about 0.05% to about 3% by weight, and more prefera-bly from 0.1% to 2% by weight of the reactants.

The reaction may be conducted in the presence or absence of solvents or diluents. In most cases, the reactants will be liquid and the reaction may be easily effected without the addi-tion of solvents or diluents. However, in some cases whether either or both reactants are solids or viscous liquids it may be desirable to add diluents to assist in effecting the reaction. Examples of such materials include the inert liquids, such as ketones, xylene, toluene, cyclohexane and the like.

Temperatures employed in the reaction will generally vary from about 50° C. to about 150° C. In most cases, the reactants will combine in the presence of the new catalysts at a very rapid rate and lower temperatures will be satisfactory. Par-ticularly preferred temperatures ränge from about 50° C. to 120° C.

The reaction will be preferably conducted under atmospheric pressure, but it may be advantageous in some cases to employ sub atmospheric or super atmospheric pressures.

The course of the reaction may be conveniently followed by de-termination of the acidity. The reaction is considered to be substantially complete when the acidity has been reduced to about 0.020 eq./ΙΟΟ g. or below.

The preparation may be effected in any suitable manner. The preferred method merely comprises adding the polyepoxide, a-cid, catalyst, and solvent or diluent, if desired, in any order and then applying the necessary heat to bring about the reaction. The reaction mixture may then be distilled or strip-ped to remove any of the necessary components, such as sol-vents, catalyst, excess reactants and the like.

These vinyl esters may be used neat or more likely blended with a compatible co-polymerizable monomer or other unsatu-rated material. Examples of such monomers include, among oth-ers, aromatic Compounds such as styrene, alpha-methylstyrene, dichlorostyrene, vinyl naphthalene, vinyl phenol and the like, unsaturated esters, such as acrylic and methacrylic esters, vinyl acetate, vinyl benzoate, vinyl chloroacetate, vinyl laurate, and the like, unsaturated acids, such as acrylic and al-pha-alkylacrylic acids, butenoic acid, allylbenzoic acid, vinyl benzoic acid, and the like, halides, such as vinyl Chloride, vinylidene Chloride, nitriles, such as acrylonitrile, methacrylontrile, diolefins, such as butadiene, isoprene, me-thylpentadiene, esters of polycarboxylic acids, such as dial-lyl phthalate, divinyl succinate, diallyl maleate, divinyl a-dipate, dichloroallyl tetrahydrophthalate, and the like, and mixtures thereof. Further multifunctional compounds may be incorporated to provide the desired viscosity and crosslink den-sity. Suitable difunctional ethylenically unsaturated compounds include, for example: di(meth)acrylates of diols and polyetherdiols, including glycols and polyglycols, such as propylene glycol and polypropylene glycols. Repeating units of glycols including di-, tri- and higher glycols can be used. Other suitable di(meth)acrylates include the di(meth)acrylate of 1,4-butanediol (e.g., SR 213), 1,3-butanediol, neopentyl-glycol, propoxylated neopentyl glycol, a diacrylate of a pro-poxylated neopentyl glycol, diethylene glycol hexanediol, dipropylene glycol, tripropylene glycol, triethylene glycol, polyethylene glycol, alkoxylated hexane diols, neopentylgly-col, tetraethylene glycol and the like, and di(meth)acrylates including alkoxylated aliphatic diacrylates

Exemplary suitable trifunctional ethylenically unsaturated compounds include (meth)acrylate esters of triols, for exam-ple: glycerol, trimethylol propane, pentaerythritol, neopentyl alcohol, and the like. Alkoxylated (meth)acrylates can also be used, for example propoxylated and ethoxylated (meth)acrylates such as ethoxylated trimethylol propane tri(meth)acrylates, propoxylated glyceryl tri(meth)acrylates, propoxylated pentaerythritol tri(meth)acrylates, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, and trifunctional acrylate esters.

Suitable tetra-functional ethylenically unsaturated compounds include, for example: alkoxylated (meth)acrylates obtained from tetraols, such as ethoxylated pentaerythritol tet-ra(meth)acrylates, and the like.

The low viscosity vinyl esters may be polymerized alone in combination with any of the above-noted unsaturated materials to form valuable polymeric products. When used in combination with the above components, the amount of the other component may vary over a wide ränge, but it is generally preferred to have at least 30% by weight of the vinyl ester present.

The polymerization of the above-noted vinyl esters or mixtures thereof with monomers may be accomplished by any suitable me-thod. The preferred method comprises heating the modified vinyl esters or mixtures thereof, in the presence of a free ra-dical yielding catalyst. Generally around 0.05 to about 2.5 phr of a catalyst is required. If lower amounts of catalyst are employed, then the eure may not be complete and greater concentrations can reduce storage stability. The catalyst is a free radial polymerization initiator, preferably high tempera-ture peroxides. Whilst most peroxides can be used the resul-tant shelf-life may be problematic and so dicumyl peroxide is preferred as it gives high temperature properties, a long pot life, and a good eure. Other peroxides which may be used in-clude di-tertiary butyl peroxide, benzoyl peroxide, benzoyl acetyl peroxide, dinaphthoyl peroxide, and benzoyl lauryl peroxide .

Other materials may also be added to the mixtures before or during polymerization, including plasticizers, coupling a-gents, flow agents, air release agents, stabilizers, extend-ers, resins as well as all types of colouring or pigments.

The vinyl ester resins may be applied in combination with o-ther agents selected among others from one or more accelera-tors, vinyl ester reactive flexibilizers with a number of re-active groups of more than 1, UV curing agents or temperature curing agents and the like to.

The invention will be described in more detail in the follow-ing examples which do not restrict the scope of the invention in any way, said scope being defined be the appended Claims. EXÄMPLE 1 A one litre reaction flask was provided with a stirring mecha-nism, a dropping funnel for the addition of reactants, and a thermometer for measuring the temperature within the flask. The base methacrylated epoxy resin CURALINK(RTM) 90-900 was blended in a ratio of 70 parts:30 parts by weight with Di Allyl Phthalate at a temperature of 50°C. The mixture was stirred continuously for 15 minutes to complete the dissolu-tion. To this uniform solution 1% dicumyl peroxide was added and stirred to dissolve.

The solution had a viscosity of less than 1500 mPas at 25°C and eure time at 140 °C of <10 minutes. This preparation was then used for fest purposes.

Storage stability

Example 1 was held without agitation at various temperatures

As can be seen from the above table the product shows out-standing stability even when exposed to 60°C for 60 days. Processing

Example 1 is suitable for processing via the Vacuum Pressure Impregnation [VPI] method which varies between one operator and another but essentially consists of the part[s] being im-pregnated at elevated temperatures. A catalyst can be incorporated in the Mica tape to provide localised targeted reaction and subsequent eure although pre-catalysed Systems are also employed.

Vacuum Pressure Impregnation process provides many benefits as it offers complete sealing of windings against moisture and Vibration providing greater mechanical strength and corona protection. This additional protection improves reliability and longevity of the equipment even in difficult working envi-ronments.

The process will vary slightly from operator to operator but will generally comprise of pre-heating of the component to re-move moisture with the time and temperature being determined by the operator. The unit will then generally be cooled before being placed in a vacuum tank and being subjected to a prede-termined period of being subjected to vacuum [generally be-tween 0.1 - 3 mm mercury] . The time and level of vacuum will be determined by the voltage, layers of mica tape and System such that it will allow correct impregnation.

The System is introduced whilst maintaining the desired level of vacuum and must completely cover the coils and is held in this state again for a period of time to allow impregnation. When this stage is complete the pressure is altered by break-ing vacuum with Nitrogen and the application of pressure [6 BarG] for a period of time which as a rule of thumb is twice that of the vacuum stage. This process and the times, tempera-tures and vacuum/pressure levels should be determined through experience and design.

Following the impregnation cycle the residual resin is pumped back to the storage tank. The impregnated component is drained for a short period of time then subjected to the eure process. Trial material processed using this technique

Example 1 has the ability to be cured with much shorter eure cycles than those generally attributed to epoxy Systems. A ramped eure schedule is recommended in most cases and eure will be dependent on mass penetration depths. Curing with high reactivity catalysis is also achievable and because these pro-duct types tend to rapidly transition from fluid to solid with limited viscosity increase they lend themselves to greater flow than conventional epoxy grades which tend to have a more linear viscosity build.

Example 1 was utilised for experimental evaluation and pro-vided the following results.

Properties Example 1: A high voltage bar insulated by a 2mm wall thickness insula-tion based on glass fabric/ mica tape was VPI impregnated and cured with vinyl ester based on di-functional epoxy resin with a molecular weight of 350-500 g/mol, diallyl phthalate di-luted, synthesis like in example 1 described.

The properties are as follows: 2mm wall thickness mica-glass fabric tape: fully impregnated to the copper bar

Glass transition point of insulation [measured by DSC]: 175°C CTI [Comparative tracking index] value: 600

Thermal rating dass IEC [International Electrochemical Commission] : 165°C

Dissipation factor in p.U. 155°C: 0.08 Example 2: A high voltage bar insulated by a 2mm wall thickness insula-tion based on glass-fabric / mica tape was VPI impregnated and cured with vinyl ester based on 3.6 functional epoxy phenol novolac with a molecular weight of 500-600 g/mol (CURALINK (RTM) 90-974), diallyl phthalate diluted

The properties are as follows: 2mm wall thickness mica-glass fabric tape: fully impregnated until the copper bar dass transition point of insulation [measured by DSC]: 190°C CTI value: 600

Thermal rating dass IEC: 182°C Dissipation factor in p.U. 155°C: 0,06

Example 3: A high voltage bar insulated by a 2mm wall thickness insulation based on glass fabric / mica tape was VPI impregnated and cured with vinyl ester based on 5.5 functional epoxy cresol novolac with a molecular weight of 1200-1300 g/mol, diallyl phthalate diluted

The properties are as follows: 2mm wall thickness mica-glass fabric tape: fully impregnated until the copper bar

Glass transition point of insulation [measured by DSC]: 220°C CTI value: 600

Thermal rating dass IEC: 189°C Dissipation factor in p.U. 155°C: 0.05

Claims

Patent Claims

1. Use of vinyl ester resins based on modified and unmodified epoxy resins for the insulation of electrical equipment.
2. Use according to claim 1, wherein the modified or unmodified epoxy resins are selected from carbonyl terminated butadiene acrylonitrile [CTBN] rubber modified epoxy or other toughened epoxy resin with thermoplastic substances and/or core-shell tougheners.
3. Use according to claim 1, wherein the modified or unmodified epoxy resins are selected from halogenated epoxy resins.
4. Use according to claim 1, wherein the modified or unmodified epoxy resins are selected from bisphenol A free epoxy resins .
5. Use according to claim 1 wherein the modified and unmodified epoxy resins are selected from a) monomeric or polymeric polyepoxides containing at least one vicinal epoxy group, which polyepoxides are saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and optionally substituted with halogen atoms, hydroxyl groups or ether radicals; or b) epoxy compounds derived from polyhydric phenols and having at least one vicinal epoxy group wherein the carbon-to-carbon bonds within the six-membered ring are saturated.
6. Use according to any of claims 1 to 5, wherein the vinyl ester resin is diluted in monomers.
7. Use according to any of claims 1 to 6, wherein the vinyl ester resin comprises one or more accelerators.
8. Use according to any of claims 1 to 7, wherein the vinyl ester resin comprises a vinyl ester reactive flexibilizer with a number of reactive groups of more than 1.
9. Use according to any of claims 1 to 8, wherein the vinyl ester resin comprises a UV curing agent.
10. Use according to claim 9, wherein the vinyl ester resin comprises one or more temperature curing agents.