How to avoid cracks in the sealing of sharp-edged inserts

Abstract

A method for encapsulating an insert with an encapsulating resin, the method comprising: a. applying a coating layer of a thermosetting material to a part or all of the surface of the insert; b. curing the coating layer obtained in step a; c. encapsulating the coated insert obtained in step b with an encapsulating resin;

Description

[Technical Field]

[0001] The present invention relates to a method for preventing cracks in the sealing of sharp-edged inserts, for example, inserts with a lower coefficient of thermal expansion (CTE) than the sealing material. The present invention also relates to a kit of materials for sealing sharp-edged inserts and articles resulting from the sealing. The method is based on applying a coating based on an elastic material between the insert and the sealing material. A typical application is the sealing of stators or rotors for electric engines or electrical devices. [Background technology]

[0002] It is known to seal sharp-edged inserts in electrical devices such as stators or rotors with a filled liquid resin system that is cast into the remaining void space between the coils or between the insert and the component housing. Sealing rigid materials, e.g., materials with low CTE and potentially sharp edges, with high glass transition temperature (Tg) materials often leads to cracking during thermal cycling. Patent document 1 teaches a method of avoiding cracks by using soft silicone rubber materials to seal high voltage instrument transformers, but the material disclosed in that document is too soft for the intended use in the present invention. Patent Document 2 discloses a curable composition comprising an epoxy resin and a specific extender mixture for direct overmolding onto components or parts of electrical or electronic components, such as switchgear. The curable composition is applied to the housing of the electrical or electronic component, such as the ceramic housing of a vacuum chamber for the switchgear. The specific sealing composition disclosed in the document cannot be used for this purpose because its glass transition temperature (Tg) is too low. Patent Document 3 discloses a curable composition containing a cationically polymerizable epoxy resin and a specific extender composition as an insulating material for electrical and electronic components, particularly as an encapsulating system for printed circuit boards. A mixture of different extenders makes it possible to adjust the CTE and reduce / avoid cracks, but the disclosed formulation is expensive for this intended use. Patent Document 4 teaches the application of two layers with different properties to provide a laminate with excellent abrasion and chemical resistance. The document is silent about providing improved crack-resistant sealing of sharp-edged inserts. US Patent No. 5,949,693 teaches a two-component polyurethane composition that has a long open time and can still be applied and cured to form a polymer with high mechanical strength. Those skilled in the art know that potential transformers are manufactured using a cushion / pad technique around the critical iron core to prevent crack formation during thermal changes. This technique is performed manually, is labor intensive, and therefore expensive, and is not adaptable to all geometries. The technical problem consisting of encapsulating a rigid material with a low CTE and potentially sharp edges with a high Tg material that should not crack during thermal cycling is solved by US Patent No. 6,223,999. This document teaches an epoxy system containing a mixture of micrometer and nanometer scale SiO2 particles that allows for high filler loadings that result in low CTE and therefore low stress. However, this method is not applicable to encapsulating materials with high Tg (eg, Tg>160°C), and has some disadvantages, such as high cost and complicated formulation. The technical problem of crack formation in encapsulating materials is multifactorial. Among the parameters that influence its appearance, we can mention: CTE, elongation at break, chemical shrinkage, toughness, thermal conductivity. Thus, there remains a need for a method of sealing rigid materials, especially those with sharp edges, with a high Tg material that will not crack during thermal cycling, at a cost that is compatible with the intended application and that is applicable on an industrial scale. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] DE3702782 [Patent Document 2] WO2010112272 [Patent Document 3] WO2016202608 [Patent Document 4] JP2020 011457A [Patent Document 5] US2013 / 0294921A1 [Patent Document 6] WO201620260 Summary of the Invention

[0004] The present invention is based on a method comprising applying a thin layer of a specific resin system onto an insert and curing the thin layer. A standard process for encapsulating devices, in particular electrical or electronic devices, by casting can then be carried out using the encapsulating resin, which is known from the prior art. Surprisingly, the presence of the coating layer leads to an improvement in the crack resistance of the known encapsulating resin.

[0005] A first object of the present invention resides in a method for sealing an insert, said method comprising at least: a. applying a coating layer of a thermosetting material to at least a portion of a surface of the insert; b. at least partially curing the coating layer obtained in step a; c. encapsulating the coated insert obtained in step b with an encapsulating resin; Including, The thermosetting material of the coating layer is selected from those having a tensile modulus, measured by method ISO 527, in the range of 50 MPa to 1000 MPa after curing, and an elongation at break, measured by method ISO 527, in the range of 20% to 500% after curing.

[0006] A second object of the present invention resides in a kit that can be used in a method for sealing an insert, comprising a first resin system and a second resin system, the kit comprising: thermosetting materials, which have a tensile modulus, determined according to ISO 527 method, in the range from 50 MPa to 1000 MPa after curing, and an elongation at break, determined according to ISO 527 method, in the range from 20% to 500%, after curing; Resin systems capable of sealing inserts, Includes:

[0007] A third object of the invention is a device consisting of a sealed insert, said device resulting from the implementation of the method defined above.

[0008] A fourth object of the present invention resides in the use, in a method as defined above, of a thermosetting material selected from those having a tensile modulus, measured according to method ISO 527, in the range of 50 MPa to 1000 MPa after curing, and those having an elongation at break, measured according to method ISO 527, in the range of 20% to 500% after curing, in order to avoid cracks in the sealing of the insert.

[0009] Another object of the present invention is a method for manufacturing an electrical and electronic insulating device, said method comprising at least one step consisting of carrying out the method for sealing an insert as disclosed above and in detail below.

[0010] According to a preferred embodiment, the thermosetting material of the coating layer is selected from those having a viscosity in the range of 0.1 Pa·s to 10 Pa·s at 25°C, measured by method ISO 3219.

[0011] According to a preferred embodiment, the thermosetting material of the coating layer is selected from polyurea-based, polyurethane-based, and polyepoxy-based materials, preferably polyurea-based.

[0012] According to a preferred embodiment, the thermosetting material of the coating layer is a two-component thermosetting system, comprising at least: Component (A), selected from diisocyanate or polyisocyanate components or mixtures thereof; component (B), selected from amines having at least two primary amine groups; Includes:

[0013] According to a preferred embodiment, component (A) is selected from: MDI, TDI, IPDI, HMDI, or the corresponding uretdione homopolymers, or prepolymers with polyols, or mixtures thereof.

[0014] According to a preferred embodiment, component (B) is selected from: jeffamine, polyamidoamine, aliphatic polyamine, cycloaliphatic polyamine, or aromatic amine.

[0015] According to a preferred embodiment, a coating layer of thermosetting material is applied to the insert with a thickness in the range of 0.05 mm to 1 mm.

[0016] According to a preferred embodiment, in step b of the method for sealing the insert, the coating layer is cured at a temperature in the range of 15°C to 60°C.

[0017] According to a preferred embodiment, the insert has a CTE, specified according to ISO 11359-2, in the range of 5 to 30 ppm / K.

[0018] According to a preferred embodiment, the insert is selected from: - objects with at least one geometric angle between 1° and 120°; or - Objects with at least one radius <3mm.

[0019] According to a preferred embodiment, the insert is selected from a rotor or stator of an electric machine such as a motor or generator, a (power) electronic component, a battery, a switch ring of an electric motor, a switch gear, a printed circuit board, a bushing, a transformer, a dry-type transformer, a potential transformer, a metal insert embedded in the structural material of an insulator. DETAILED DESCRIPTION OF THE INVENTION

[0020] Unless otherwise defined herein, technical terms used in connection with this disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0021] All patents, published patent applications, and non-patent publications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this disclosure pertains. All patents, published patent applications, and non-patent publications referenced anywhere in this application are expressly incorporated by reference in their entirety herein to the same extent as if each individual patent or publication was specifically and individually indicated to be incorporated by reference to the extent not inconsistent with this disclosure.

[0022] All of the compositions and / or methods disclosed herein can be made or executed without undue experimentation in light of the present disclosure. While the compositions and methods of the present disclosure have been described in terms of preferred embodiments, it will be apparent to those skilled in the art that modifications can be applied to the compositions and / or methods described herein, and in the steps or sequence of steps of the methods, without departing from the concept, spirit, and scope of the present disclosure. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the present disclosure.

[0023] As used in accordance with the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

[0024] The use of the words "a" or "an," when used in conjunction with the terms "comprising," "including," "having," or "containing" (or variations of such terms), can mean "one," but is also consistent with the meanings "one or more," "at least one," and "one or more than one."

[0025] Use of the term "or" is used to mean "and / or," unless expressly stated to refer only to alternatives and only where the alternatives are mutually exclusive.

[0026] Throughout this disclosure, the term "about" is used to indicate that a value includes the inherent variation of error of a quantification device, mechanism, or method, or includes the inherent variation that exists between the subject(s) being measured. By way of example, and not limitation, when the term "about" is used, the specified value to which the term refers can vary by plus or minus 10%, or 9%, or 8%, or 7%, or 6%, or 5%, or 4%, or 3%, or 2%, or 1%, or one or more fractions therebetween.

[0027] The use of "at least one" is to be interpreted as including one as well as any amount greater than one, including, but not limited to, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term "at least one" can extend up to 100 or 1000 or more, depending on the term to which it refers. Also, the amount 100 / 1000 should not be interpreted as a limit, as lower or higher limits can also produce satisfactory results.

[0028] As used herein, the words "comprising" (and any of its forms, e.g., "comprise" and "comprises"), "having" (and any of its forms, e.g., "have" and "has"), "including" (and any of its forms, e.g., "includes" and "include"), or "containing" (and any of its forms, e.g., "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0029] The phrases "or combinations thereof" and "and combinations thereof," when used herein, refer to all permutations and combinations of the items listed preceding the term. For example, "A, B, C, or combinations thereof" is intended to include at least one of the following: A, B, C, AB, AC, BC, or ABC, and, if order is important in the particular situation, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, combinations including repeats of one or more items or terms, e.g., BB, AAA, CC, AABB, AACC, ABCCCC, CBBAAA, CABBB, etc., are expressly included. As one of ordinary skill in the art will appreciate, there is typically no limit to the number of items or terms in any combination unless otherwise clear from the context. In the same spirit, the terms "or combinations thereof" and "and combinations thereof," when used in conjunction with the phrase "selected from" or "selected from the group consisting of," refer to all permutations and combinations of the items listed preceding that phrase.

[0030] Phrases such as "in one embodiment," "in an embodiment," "according to one embodiment," and the like generally mean that the particular feature, structure, or characteristic that follows the phrase is included in at least one embodiment of the present disclosure, and may be included in more than one embodiment of the present disclosure. Importantly, such phrases are open-ended and do not necessarily refer to the same embodiment, but rather, of course, can refer to one or more prior and / or subsequent embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0031] As used herein, the term "ambient temperature" refers to the temperature of the surrounding working environment (e.g., the temperature of the space, building, or room in which the curable system is used or manufactured), and does not include any temperature changes induced by chemical reactions. Ambient temperature is typically from about 10°C to about 30°C, more specifically about 25°C. The term "ambient temperature" is used interchangeably herein with "room temperature."

[0032] The term "consisting essentially of," when followed by one or more features, means that the process or material of the invention may contain elements or steps in addition to those explicitly recited that do not materially affect the nature and characteristics of the invention.

[0033] The phrase "consisting of X to Y" is inclusive unless otherwise specified. This phrase means that the target range includes values ​​X and Y, as well as all values ​​from X to Y.

[0034] Throughout the description and claims of this specification, the terms "comprise" and "contain," as well as variations of these terms (e.g., "comprising" and "comprises"), mean "including, but not limited to," and do not exclude other moieties, additives, elements, integers, or steps. Moreover, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification should be interpreted as contemplating the plural as well as the singular, unless the context otherwise requires.

[0035] When upper and lower limits are stated for a property, e.g., the concentration of a component, a range of values ​​defined by combining any of the upper limits with any of the lower limits can also be implied.

[0036] insert: The method according to the invention is applied to the sealing of inserts, for example inserts that have a lower CTE than the sealing material.

[0037] The CTE of a material is measured according to ISO 11359-2.

[0038] For example, the insert is characterized by a CTE in the range of 5 ppm / K to 30 ppm / K, preferably 5 ppm / K to 25 ppm / K, and more preferably 10 ppm / K to 17 ppm / K.

[0039] In the present invention, an insert is an object made of a rigid material, such as an object essentially made of metal (mainly steel and aluminum). The rigidity of a material is measured by the tensile modulus of the material, which can be measured in accordance with DIN EN ISO 6892-1.

[0040] For example, the insert is made of a material selected from those having a tensile modulus in the range of 70 to 250 GPa, preferably 130 to 220 GPa.

[0041] The method according to the invention is applicable to inserts with any kind of shape, preferably the method according to the invention is applied to sealing inserts with sharp edges.

[0042] "Sharp edge insert" in the context of the present invention means: - objects with at least one geometric angle between 1° and 120°; or - Objects with at least one radius <3mm.

[0043] Figure 1a illustrates an object with a radius of 2 mm (1) and an angle of 90° (2).

[0044] Figure 1b illustrates an object with a radius of 1 mm (3) and an angle of 100° (4).

[0045] The function of the insert can be of various nature, but is generally selected from electrical and electronic components. The present invention has particular application to inserts that are part of equipment that is subjected to thermal cycling during normal function.

[0046] Thermocycling in the context of the present invention means subjecting the insert to a temperature difference of at least 50° C., preferably at least 120° C., and better still at least 190° C. Such a temperature difference is applied for a period of time ranging from 5 minutes to 10 hours.

[0047] For example, the inserts may be selected from rotors or stators of machines such as motors or generators, (power) electronic components, batteries, switch rings of electric motors, switchgear (gas insulated and vacuum type), printed circuit boards, bushings, transformers, dry type transformers, potential transformers, metal inserts embedded in the structural material of insulators.

[0048] Coating layer: The present invention relies on applying a coating layer of material, preferably as a liquid material, to the surface of the insert, which is at least partially cured after application in order to form a solid layer on the insert surface prior to application of the sealing material.

[0049] The present invention relies on applying a coating layer of a resilient material to the surface of the insert.

[0050] The cured coating layer must be highly flexible and compatible with the sealing system. Preferably, the material of the coating layer is selected so that it is capable of chemically crosslinking with the sealing system when the sealing system cures.

[0051] The coating material must have a viscosity sufficient to allow the application of a uniform layer of sufficient thickness. For example, the coating material is selected to have a viscosity, before curing, at ambient temperature in the range of 0.1 Pa·s to 10 Pa·s, preferably 0.2 Pa·s to 5 Pa·s. Viscosity is measured by method ISO 3219.

[0052] The cured coating material must be sufficiently resilient to avoid crack formation in the encapsulant during and after thermal cycling.

[0053] For example, the cured coating material is selected from those having a tensile modulus in the range of 50 MPa to 1000 MPa, preferably 80 MPa to 400 MPa.

[0054] Tensile modulus is measured by method ISO 527.

[0055] For example, the cured coating material is selected from those having an elongation at break in the range of 20% to 500%, preferably 40% to 250%, and even more preferably 50% to 200%.

[0056] The elongation at break is determined by method ISO 527 on a sample 1 mm thick.

[0057] Advantageously, the coating is based on a material consisting of a two-component thermosetting system.

[0058] "Two-component thermoset system" means a composition that includes two components as a two-pack system (or kit) designed to be mixed in situ to form a coating immediately prior to curing.

[0059] When the two components are mixed / blended together and cured, they can form a hardened solid coating by forming chemical bonds called crosslinks between the two components. The viscosity of the coating material is evaluated after mixing the two components but before curing.

[0060] For example, the coating material can be selected from polyurea, polyepoxy, or polyurethane systems, provided that the coating material has suitable physicochemical properties, particularly viscosity, tensile modulus, and elongation at break, in the ranges described above.

[0061] Preferably, the coating material is based on, or preferably consists of, a polyurea system.

[0062] Preferably, the coating material is based on a curable two-component resin system comprising component (A) and component (B), Component (A) is an isocyanate component consisting of one or more diisocyanates or one or more polyisocyanate components, or a mixture thereof; Component (B) is an amine component consisting of an amine having at least two primary amine groups.

[0063] Polyisocyanate components (A) useful in producing polyurea coatings according to the present invention are well known in the art and are organic compounds having two or more isocyanate groups per molecule. The isocyanate component (A) can be aromatic, cycloaliphatic, or aliphatic, and can be monomeric or oligomeric compounds.

[0064] Advantageously, the polyisocyanate component has an NCO functionality of 2 or greater, preferably in the range of 2-3.

[0065] Isocyanate "functionality" is the number of reactive NCO groups per isocyanate molecule or polymeric isocyanate molecule. For example, most polyisocyanates, especially MDI-type polyisocyanate compounds, contain a blend of monomeric and polymeric MDI, and the isocyanate functionality is the average functionality across the different molecular and polymeric species.

[0066] As used herein, "MDI" refers to methylene diphenyl diisocyanate, also known as diphenylmethane diisocyanate, and its isomers. MDI exists as one of three isomers (4,4'MDI, 2,4'MDI, and 2,2'MDI) or as a mixture of two or more of these isomers. Unless otherwise specified, "MDI" can also refer to and include polymeric MDI. Polymeric MDI is a compound having a chain of three or more benzene rings connected to each other by methylene bridges, with an isocyanate group attached to each benzene ring.

[0067] Suitable polyisocyanate components (A) that can be used in the coating according to the invention are, for example, dodecane-1,12-diisocyanate, 2-ethyltetramethylene-1,4-diisocyanate, 2-methylpentamethylene-1,5-diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate (HMDI), cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), hexahydrotoluene-2,4-diisocyanate, hexahydrotoluene-2,5-diisocyanate, dicyclohexane The isocyanate may be selected from the group consisting of xylmethane-2,2'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI), diphenylmethane-2,2'-diisocyanate (2,2'-MDI), diphenylmethane-4,4'-diisocyanate (4,4'-MDI), diphenylmethane-2,4'-diisocyanate (2,4'-MDI), polyphenylpolymethylene polyisocyanate (crude MDI), and mixtures thereof.

[0068] Commercially available diisocyanates often contain dimeric (uretdione), trimeric (triazine), and oligomeric compounds, or prepolymers with polyols. In coatings according to the present invention, such mixtures of monomers and oligomers can be used without separation or purification of by-products.

[0069] Amine components (B) useful in producing polyurea coatings according to the present invention are well known in the art and are organic compounds containing two or more primary amine groups per molecule. Amine components (B) can be aromatic, cycloaliphatic, or aliphatic, and can be monomeric or oligomeric compounds.

[0070] In principle, any amine that is liquid at ambient temperature can be used, such as jeffamine, polyamidoamines, aliphatic polyamines, cycloaliphatic polyamines such as isophorone diamine, or aromatic amines, such as dimethylthiotoluene diamine, diethyltoluene diamine, etc.

[0071] Those skilled in the art will know how to select components (A) and (B) and their ratios to provide a polyurea system having the required physicochemical properties, in particular viscosity before cure, and tensile modulus and elongation at break after cure, in the ranges described above.

[0072] Sealing resin: The encapsulating resins are curable materials known from the prior art for the same and similar applications.

[0073] The present invention finds application of particular interest where the cured encapsulating resin is a rigid material, for example a resin system selected from those having a tensile modulus after curing in the range of 5 GPa to 20 GPa, preferably 10 GPa to 16 GPa.

[0074] For example, the resin system is selected from those having a breaking elongation after curing in the range of 0.1% to 5%, preferably 0.4% to 2%.

[0075] The present invention finds applications of particular interest when the cured encapsulation resin has a low coefficient of thermal expansion (CTE), i.e., a CTE of 27 ppm / K or less, more preferably less than 20 ppm / K, at T < Tg.

[0076] The viscosity of the resin system is an important parameter regarding the processability of the resin system. Preferably, the resin system before curing has a viscosity in the range of 4 Pas to 30 Pas at 60 °C. The viscosity is measured according to method ISO 3219.

[0077] The present invention finds applications of particular interest when the cured encapsulation resin is of a high glass transition temperature system, e.g., a system with Tg > 140 °C, preferably Tg > 180 °C.

[0078] The Tg of the encapsulation resin can be evaluated according to method ISO 11359-2. Preferably, the resin system is selected from those having good long-term thermal degradation stability (grade H according to IEC 60216).

[0079] Preferably, the resin system is selected from those having very good thermal cycle crack resistance (SCT < -100 °C). The method for measuring thermal cycle crack resistance is described in EP 1 165 688 B1 (page 9).

[0080] The encapsulation resin can be based on any material known in the prior art for this application, such as two-component epoxy systems, polyurethanes, polyisocyanurates, etc.

[0081] For illustrative purposes, some examples of resin systems that can be used as the encapsulation system in the present invention are shown in detail below. However, this illustration should not be considered as limiting the scope of the present invention.

[0082] According to a first embodiment, the encapsulation resin is a curable two-component resin system comprising (a) a resin part containing at least one epoxy resin, and (b) a hardener moiety having an amine, or an anhydride or isocyanate functional group.

[0083] Alternatively, the encapsulating resin can be a single component system, such as that described in WO2016 / 202608 A1.

[0084] According to a first embodiment, the curable two-component resin system may further comprise inorganic fillers and / or fillers such as metal powders, which are well known to those skilled in the art.

[0085] According to a first example of this embodiment, the encapsulating resin may be based on a curable two-component resin system including an epoxy resin and an acid anhydride, such as the Araldite® CW 30386 / Aradur® HW 30387 system, which is commercially available from Huntsman.

[0086] According to a second example of this first embodiment, the encapsulating resin may be based on a curable two-component resin system comprising an epoxy resin and an isocyanate. In particular, the reactive resin mixture may include: a) polyfunctional isocyanates, b) an epoxy resin composition comprising predominantly compounds A' based on glycidyl ethers of aliphatic and / or cycloaliphatic alcohols having at least two alcohol functional groups or compounds B' based on glycidyl esters of aliphatic and / or cycloaliphatic carbonic acids having at least two carboxylic acid functional groups, c) Curing accelerator. According to a preferred embodiment of this example, the epoxy resin composition comprises (predominantly) butanediol diglycidyl ether, hexanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, hexahydrophthalic acid diglycidyl ester, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, or mixtures thereof.

[0087] According to a preferred embodiment of this example, the equivalent ratio of isocyanate groups of component (a)—the polyfunctional isocyanate—to epoxide groups of component (b)—the epoxy resin—is 10:1 to 1:1, preferably 5:1 to 3:1.

[0088] Furthermore, the polyfunctional isocyanate is preferably selected from the group comprising cycloaliphatic polyisocyanates, aromatic polyisocyanates, and mixtures thereof.

[0089] In a particularly preferred embodiment of this example, the polyfunctional isocyanate is selected from the group comprising diphenylmethane-2,4- or -4,4'-diisocyanate; polyphenylenepolymethylene polyisocyanate; diphenylmethane diisocyanate having carbodiimide or uretonimide groups; modified polyisocyanates having allophanate, urethane, biuret, and / or uretdione groups; isocyanate-based prepolymers obtained by reacting an excess of the above polyisocyanates with polyols; and mixtures thereof.

[0090] In an advantageous embodiment of this example, the curing accelerator is based on a boron trichloride amine complex, which complex is preferably selected from the group comprising boron trichloride dimethyloctylamine complex, boron trichloride trimethylamine complex, boron trichloride benzyldimethylamine complex, boron trichloride tributylamine complex, and mixtures thereof.

[0091] According to a preferred embodiment of this example, the hardening accelerator is present in an amount of 0.01 to 5% by weight, preferably 0.05 to 2.5% by weight, based on the total weight of the mixture.

[0092] According to a third example of this first embodiment, the curable two-component resin system, as disclosed in application EP20216430.7, may comprise: (a) a resin portion comprising at least one cycloaliphatic epoxy resin; and (b) a hardener portion comprising: (i) at least one alicyclic acid anhydride; and (ii) a block copolymer comprising a polysiloxane block and an organic block.

[0093] In one embodiment of this example, the organic block in the block copolymer is a polyester block, such as one based on caprolactone or other lactone, or a polycarbonate block. Non-limiting examples of suitable block copolymers include polycaprolactone-polysiloxane block copolymers, polylactic acid-polysiloxane block copolymers, and polypropylene carbonate-polysiloxane block copolymers. The polysiloxane block is, for example, a polydimethylsiloxane block or a polymethylethylsiloxane block. In one specific embodiment, the block copolymer is a polycaprolactone-polysiloxane block copolymer, such as Genioperl® W35 (Wacker Chemie AG, Munich, Germany).

[0094] In one embodiment of this example, the resin portion (a) and hardener portion (b) of the two-component resin system are present in a stoichiometric ratio of resin portion to hardener portion ±15 mol %. The cycloaliphatic epoxy resin can be selected from the group consisting of, for example, bis(epoxycyclohexyl)methyl carboxylate, bis(2,3-epoxycyclopentyl)ether, 1,2-bis(2,3-epoxycyclopentyl)ethane, vinylcyclohexene dioxide, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6'-ethylcyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, dicyclopentadiene dioxide, dipentene dioxide, 1,2,5,6-diepoxycyclooctane, 1,2,7,8-diepoxyoctane, 1,3-butadiene diepoxide, 3-ethyl-3-oxetanemethanol, and combinations thereof. In another embodiment, the cycloaliphatic epoxy resin is a non-glycidyl epoxy resin. In yet another embodiment, the cycloaliphatic epoxy resin is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.

[0095] In one embodiment, the alicyclic acid anhydride is an unsaturated compound. In a preferred embodiment, the alicyclic acid anhydride contains 9 to 10 carbon atoms. The alicyclic acid anhydride can be selected from the group consisting of, for example, methyltetrahydrophthalic anhydride (MTHPA), himic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA), hexahydromethylphthalic anhydride, tetrahydrophthalic anhydride, methylphthalic anhydride, naphthalic anhydride, dodecenylsuccinic anhydride, and succinic anhydride derivatives. In one specific embodiment, the alicyclic acid anhydride is methyltetrahydrophthalic anhydride (MTHPA), himic anhydride, or methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA).

[0096] According to another embodiment, the encapsulating resin is a single component system, such as a cationically polymerizable epoxy resin combined with a specific extender mixture, as disclosed in WO2016 / 202608.

[0097] In particular, according to this embodiment, the curable resin system comprises: (a) a cationically polymerizable epoxy resin; (b) an initiator for cationic polymerization; and (c) a microparticle bulking agent; and (d) Nanoparticle bulking agent.

[0098] Method process: The present invention relates to a method for sealing an insert. The present invention also relates to a method for manufacturing the sealed insert. The present invention further relates to a method for manufacturing electrical and electronic insulating equipment. The method according to the present invention comprises: a. applying a first layer of coating material to the insert; and b. at least partially curing the coating layer obtained in step a; and c. Encapsulating the coated insert obtained in step b with an encapsulating resin having a higher thermal expansion coefficient than the insert material.

[0099] Advantageously, in step a, the coating is applied to the surface of the insert with a thickness of 0.05 mm to 1 mm, preferably 0.1 mm to 0.5 mm. The coating is applied especially when sharp edges are present. The coating does not necessarily have to be of equal thickness over the entire surface of the insert, but preferably the coating layer, if applied, has a regular thickness over the entire surface of the insert. Preferably, the coating layer is applied to the entire surface of the insert that is to be sealed.

[0100] The coating layer can be applied by any method known to those skilled in the art, such as spraying, dipping, brushing, spin coating, etc. Mechanically applicable methods are preferred.

[0101] The coating layer is at least partially cured in step b, for example, at a temperature of 15°C to 60°C.

[0102] Advantageously, in step b, the resin is cured at ambient temperature for a period of 1 to 24 hours, preferably 2 to 16 hours, more preferably 4 to 12 hours.

[0103] In step c, the coated, partially cured insert obtained in step b is encapsulated with an encapsulating resin in a known manner. Briefly, the components of the encapsulating resin system, optionally with one or more inorganic fillers or metal powders, are mixed and applied to the insert. Application to the insert can be by, for example, dipping, trickle infiltration, vacuum pressure impregnation, and / or casting. The encapsulating resin system is then cured according to a standard curing schedule depending on the composition of the resin system.

[0104] Device: The method disclosed above results in a device consisting of three parts: an insert, a coating layer covering part or all of the surface of the insert, and an encapsulating resin. Advantageously, there is no direct contact between the surface of the insert and the encapsulating resin, with the coating layer interposed between the insert and the encapsulating resin. The device can be used in electrical and electronic applications.

[0105] use: The invention derives from the combined effect of inserting a coating system with elastic properties between the insert and the encapsulation resin, which results in the absence of cracks in the encapsulation resin after thermal cycling, which can be identified by visual inspection.

[0106] When applied directly to the surface of the insert, the sealing system alone generally suffers from cracking during thermal cycling tests. The coating alone does not appear to provide sufficient stiffness at elevated temperatures, making it unusable as a casting system.

[0107] The method according to the invention is useful not only for electric motor applications, but also for crack-critical MV-Power applications, such as certain bushings or switchgear or potential transformers, which today employ cost-critical casting systems. Using the method according to the invention, the encapsulation of inserts for such applications can be achieved using cheaper, less demanding casting systems. [Brief explanation of the drawings]

[0108] [Figure 1A] 1 is a diagram showing angles corresponding to sharp edge inserts. [Figure 1B] 1 is a diagram showing angles corresponding to sharp edge inserts. [Figure 2] 1 is a drawing showing cube inserts in a cylindrical mold as used in Example Series 1. [Figure 3] 1 is a drawing showing a diamond insert in a cylindrical shape as used in Example Series 2. [Example]

[0109] Experimental section: In the following examples, contents and percentages are given in units of weight unless otherwise stated.

[0110] I-Raw materials Polyisocyanates: - Rencast 6429A, supplied by Huntsman, which is a blend of primarily aliphatic and TDI-based isocyanates

[0111] Polyamines: - Rencast 5425B, supplied by Huntsman, is a liquid aromatic amine-based hardener. - Rencast 5427B, supplied by Huntsman, is a liquid aromatic amine-based hardener.

[0112] Sealing resin: - Araldite® CW 30386, supplied by Huntsman, which is a high Tg epoxy resin based on cycloaliphatic epoxy resin and inorganic extenders - Aradur® HW 30387, supplied by Huntsman, which is a hardener formulated mainly with acid anhydrides and extenders

[0113] II-Method Viscosity measurement: The compositions are subjected to a Rheomat viscometer and the viscosity is measured according to ISO 3219.

[0114] Tensile modulus Tensile modulus was determined according to ISO 527 at 23°C, with a sample thickness of 1 mm and curing at 23°C for 24 hours followed by 80°C for 4 hours.

[0115] Breaking elongation The elongation at break was determined according to ISO 527 at 23°C, with a specimen thickness of 1 mm and curing at 23°C for 24 hours followed by 80°C for 4 hours.

[0116] Glass transition temperature The glass transition temperature Tg was determined according to ISO 6721 / 94.

[0117] Linear thermal expansion coefficient The CTE shall be specified in accordance with ISO 11359-2.

[0118] Chemical Shrinkage Chemical shrinkage is determined in accordance with ISO 2579.

[0119] Preparation of polyurea coating system: The polyurea system is prepared by mixing the polyisocyanate and polyamine in a predetermined ratio at room temperature.

[0120] The compositions and their properties are reported in Table 1 below.

[0121] [Table 1]

[0122] Preparation of encapsulating resin The sealing system consisted of a mixture of CW 30386 / HW 30387 in a 100 / 130 weight ratio.

[0123] The mixture was introduced into a mold under vacuum at 90° C. and cured in an oven at 120° C. for 20 minutes and at 190° C. for 3 hours. After this process, all test specimens were demolded from the cylindrical aluminum housing.

[0124] The properties of the mixture are as follows:

[0125] [Table 2]

[0126] Molds and inserts -Molds and Inserts Series 1: A representative aluminum mold and first series of inserts were used, which are illustrated in Figure 2.

[0127] The mold consists of a cylindrical housing (2.1) made of aluminum and 50 mm in diameter. The insert is an aluminum cube (2.2) with a radius (2.3) of 0.2 mm.

[0128] -Molds and Inserts Series 2: The same aluminum mold and a second series of inserts were used, which are illustrated in Figure 3.

[0129] The mold consists of a cylindrical housing (3.1) made of aluminum and 50 mm in diameter. The insert (3.2) is a diamond-shaped aluminum insert with rounded corners and radii of 2 mm (3.3) and 15 mm (3.4).

[0130] Preparation of sealed inserts For each mold and insert series 1 and 2, the following test specimens were prepared: Six specimens were sealed without any coating (control). Six test specimens were coated with a thin layer (0.2 mm) of the coating composition of Example 1, cured, and then cast with an encapsulating resin system. Six test specimens were coated with a thin layer (0.2 mm) of the coating composition of Example 2, allowed to cure, and then the sealing system was cast. The coating was applied to the inserts with a brush to a thickness of 0.2 mm and allowed to cure at 23°C for 24 hours.

[0131] A sealing system consisting of a mixture of the mixtures disclosed above was introduced into a mold at 90°C under vacuum and cured in an oven in two stages: stage 1 / 120°C for 20 minutes and stage 2 / 190°C for 3 hours.

[0132] After this step, all test specimens were released from the cylindrical aluminum housings. Comparative examples correspond to using the same sealing system with the same casting and curing conditions as the examples, but without applying a coating before casting. Comparative examples are reported as "Control."

[0133] III-Tests and Results 1-Crack resistance test test: The samples are evaluated by visual inspection: the presence of cracks in the sealing system is visually detected and recorded.

[0134] result: Tests were performed on 3 x 6 specimens of mold and insert series 1. The results are as follows: Five samples according to Inventive Example 1 and four samples according to Inventive Example 2 show no signs of cracking.

[0135] All of the control samples cracked after demolding.

[0136] 2-Heat shock test test: To see the benefit of the new method, all parts (coated and uncoated) were subjected to heat shock, starting at 20°C and decreasing to -50°C over 7 hours, followed by stepwise heat shocks at 20°C, 10°C, 0°C, -10°C, -20°C, -30°C, -40°C, and -50°C for 1 hour each.

[0137] The operator records the number of cracked samples in each group at each temperature.

[0138] result: Tests were performed on 3 x 6 specimens of mold and insert series 1. The results are as follows: The results of the test are reported in Table 3 below:

[0139] [Table 3]

[0140] All control samples (uncoated specimens) were cracked prior to testing.

[0141] Five out of six specimens of Example 1 did not show any cracks after testing.

[0142] Four out of six specimens of Example 1 did not show any cracks after testing. One specimen cracked at -50°C.

[0143] 3-Heat resistance test: This test was carried out on another set of specimens (Mold and Insert Series 2) containing inserts of different shapes corresponding to FIG.

[0144] After casting and demolding, the samples were exposed to 150°C for 50 minutes and then transferred directly to another chamber at -40°C where they remained for 50 minutes to allow the temperature within the specimen to stabilize.

[0145] result: Testing was performed on 3 x 6 specimens of mold and insert series 2. The results are summarized in Table 4 below, which reports the number of samples (out of 6) that showed cracks after a certain number of temperature cycles. After 300 cycles, none of the coated specimens had cracked, while all specimens that were not coated before casting (controls) had cracked after a maximum of 10 cycles.

[0146] [Table 4]

Claims

1. A method for sealing an insert, comprising at least the following: a. applying a coating layer of a thermosetting material to at least a portion of a surface of the insert; b. at least partially curing the coating layer obtained in step a; c. encapsulating the coated insert obtained in step b with an encapsulating resin; Including, the thermosetting material of the coating layer is selected from those having a tensile modulus after curing in the range of 50 MPa to 1000 MPa, as measured by method ISO 527, and an elongation at break after curing in the range of 20% to 500%, as measured by ISO 527; The method.

2. 2. The method according to claim 1, wherein the thermosetting material of the coating layer is selected from those having a viscosity measured in accordance with ISO 3219 in the range of 0.1 Pa·s to 10 Pa·s at 25°C.

3. 10. The method according to any one of the preceding claims, wherein the thermosetting material of the coating layer is selected from polyurea-, polyurethane- and polyepoxy-based materials, preferably polyurea-based materials.

4. The thermosetting material of the coating layer comprises at least: Component (A) selected from diisocyanate or polyisocyanate components or mixtures thereof; Component (B) selected from amines having at least two primary amine groups 10. The method of any one of the preceding claims, wherein the curing agent is a two-component thermosetting system comprising:

5. 5. The method of claim 4, wherein component (A) is selected from MDI, TDI, IPDI, HMDI, or the corresponding uretdione homopolymers, or prepolymers with polyols, or mixtures thereof.

6. 6. The method of claim 4 or claim 5, wherein component (B) is selected from jeffamine, polyamidoamine, aliphatic polyamine, cycloaliphatic polyamine, or aromatic amine.

7. 10. A method according to any one of the preceding claims, wherein the coating layer of thermosetting material is applied onto the insert to a thickness in the range of 0.05 mm to 1 mm.

8. 10. The method according to any one of the preceding claims, wherein in step b, the coating layer is cured at a temperature in the range of 15°C to 60°C.

9. 9. An insert sealing kit for use in the method according to any one of claims 1 to 8, comprising: thermosetting materials selected from those having a tensile modulus, measured by method ISO 527, in the range of 50 MPa to 1000 MPa after curing, and an elongation at break, measured by ISO 527, in the range of 20% to 500% after curing; a resin system capable of encapsulating said insert; The kit comprises:

10. A device consisting of a sealed insert, said device resulting from the implementation of a method according to any one of claims 1 to 8.

11. 11. The apparatus of claim 10, wherein the insert has a CTE in the range of 5 ppm / K to 30 ppm / K, the CTE being specified in accordance with ISO 11359-2.

12. The insert comprises: - objects with at least one geometric angle (2;4) between 1° and 120°, or - objects with at least one radius (1;3) < 3 mm 12. The device according to claim 10 or claim 11, wherein the device is selected from:

13. 13. The device according to any one of claims 10 to 12, wherein the insert is selected from a rotor or stator of an electric machine such as a motor or generator, a (power) electronic component, a battery, a switch ring of an electric motor, a switch gear, a printed circuit board, a bushing, a transformer, a dry-type transformer, a potential transformer, a metal insert embedded in the structural material of an insulator.

14. 9. Use of a thermosetting material in the method according to any one of claims 1 to 8 for avoiding cracks in the seal of an insert, wherein the thermosetting material is selected from those having a tensile modulus, measured according to ISO 527, in the range of 50 MPa to 1000 MPa after curing, and those having an elongation at break, measured according to ISO 527, in the range of 20% to 500% after curing.

15. A method for manufacturing an electrical and electronic insulating device, said method comprising at least one step consisting of carrying out the method for sealing an insert according to any one of claims 1 to 8.

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