Method for avoiding cracks in packaging of sharp-edge inserts

Abstract

The invention relates to a method for packaging a plug-in by using packaging resin, which comprises the following steps: a, coating a thermosetting material coating on part or all of the surface of the plug-in, b, curing the coating formed in the step a, and c, packaging the coated plug-in generated in the step b by using the packaging resin.

Description

Technical Field

[0001] The present invention relates to a method for avoiding cracks in the encapsulation of edge - sharp inserts, such as inserts with a coefficient of thermal expansion (CTE) lower than that of the encapsulation material. The present invention also relates to a material kit for encapsulating edge - sharp inserts and an article produced by said encapsulation. The method is based on applying an elastomer - based coating between the insert and the encapsulation material. Typical applications are the encapsulation of stators or rotors of electric motors or devices. Background Art

[0002] It is known to encapsulate edge - sharp inserts in electrical appliances such as stators or rotors by casting a filled liquid resin system in the voids left between the coils or inserts and the part housing. Encapsulating hard materials (such as materials with a low CTE) and materials with potentially sharp edges with materials having a high glass transition temperature (Tg) usually causes cracks during thermal cycling.

[0003] DE3702782 teaches a method for avoiding cracks by applying a flexible silicone rubber material to encapsulate a high - voltage instrument transformer. The materials disclosed in this document are too soft for the target use of the present invention.

[0004] WO2010112272 discloses a curable composition comprising an epoxy resin and a specific filler mixture for direct molding of components or parts of electrical or electronic components (such as switchgear). The curable composition is used for the housing of electrical or electronic components, such as the ceramic housing of a switchgear vacuum chamber. The special encapsulation composition disclosed in this document cannot be used for the target use due to its too - low glass transition temperature (Tg).

[0005] WO2016202608 teaches a curable composition comprising a cationically polymerizable epoxy resin and a specific filler composition, which is used as an insulating material for electrical and electronic components, especially as an encapsulation system for printed circuit boards. The mixture of different fillers allows adjusting the CTE to reduce / avoid cracks, but the disclosed formulation is too expensive for the target use.

[0006] JP 2020 011457 A teaches applying two layers with different properties to provide a laminate with excellent wear resistance and chemical resistance. This document does not mention the encapsulation of edge - sharp inserts with improved crack resistance.

[0007] US 2013 / 0294921 A1 teaches a two - component polyurethane composition having a long open time but still capable of bonding and curing to form a polymer with high mechanical strength.

[0008] It is known to skilled professionals that instrument transformers are produced by applying a buffering / filling technique around the critical iron core to prevent cracking during thermal change processes. This technique is manually implemented, labor-intensive, thus costly, and cannot be applied to any shape.

[0009] WO201620260 solves this technical problem by encapsulating a hard material with a low CTE and possibly having sharp edges with a high Tg material that does not cause cracks during the thermal cycling process. This document teaches an epoxy resin system containing a mixture of micron and nanoscale SiO 2 particle mixtures, allowing a high filler loading, thus resulting in a low CTE and low stress.

[0010] However, the said method is not applicable to encapsulating materials with a high Tg (e.g., Tg > 160 °C), and has disadvantages such as high cost and complex formulation.

[0011] The technical problem of crack formation in encapsulating materials is multi-factorial. Among the parameters affecting crack generation, there can be mentioned CTE, elongation at break, chemical shrinkage, toughness, thermal conductivity.

[0012] Therefore, there is still a need for a method of encapsulating hard materials, especially materials with sharp edges, with a high Tg material that does not cause cracks during the thermal cycling process, which is applicable on an industrial scale and has a cost compatible with the target use. Summary of the Invention

[0013] The present invention is based on a method including coating and curing a thin layer of a specific resin system on a plug-in. Then, a standard encapsulation method can be implemented using an encapsulating resin through a casting device (especially for electrical or electronic devices), and the encapsulating resin is known in the prior art. Surprisingly, the presence of the said coating results in improved crack resistance of this known encapsulating resin.

[0014] A first object of the present invention is a method for encapsulating a plug-in, which at least includes:

[0015] a. Coating a layer of a thermosetting material on at least part of the surface of the plug-in,

[0016] b. At least partially curing the coating formed in step a,

[0017] c. Encapsulating the coated plug-in produced in step b with an encapsulating resin,

[0018] wherein the thermosetting material of the coating is selected from materials having a tensile modulus of 50 - 1000 MPa and an elongation at break of 20 - 500% after curing, wherein the tensile modulus is measured according to method ISO 527, and the elongation at break is measured according to method ISO 527.

[0019] A second object of the present invention is a kit comprising a first resin system and a second resin system, which can be used in a method for encapsulating a plug-in, and the kit comprises:

[0020] · A thermosetting material selected from materials having a tensile modulus of 50 - 1000 MPa after curing and an elongation at break of 20 - 500% after curing, wherein the tensile modulus is measured according to method ISO 527, and the elongation at break is measured according to method ISO 527.

[0021] · A resin system capable of encapsulating the plug-in.

[0022] A third object of the present invention is a device composed of an encapsulated plug-in, and the device is formed by implementing the method defined above.

[0023] A fourth object of the present invention is the use of a thermosetting material selected from materials having a tensile modulus of 50 - 1000 MPa after curing and an elongation at break of 20 - 500% after curing in the method defined above, for avoiding cracks in plug-in encapsulation, wherein the tensile modulus is measured according to method ISO 527, and the elongation at break is measured according to method ISO 527.

[0024] Another object of the present invention is a method for preparing electrical and electronic insulation devices, wherein the method comprises at least one step of implementing the method for encapsulating a plug-in as disclosed above and described in detail below.

[0025] According to an advantageous embodiment, the thermosetting material of the coating is selected from materials having a viscosity of 0.1 - 10 Pa·s at 25°C, wherein the viscosity is measured according to method ISO 3219.

[0026] According to an advantageous embodiment, the thermosetting material of the coating is selected from polyurea, polyurethane and polyepoxy resin systems, preferably a polyurea system.

[0027] According to an advantageous embodiment, the thermosetting material of the coating is a two-component thermosetting system comprising at least the following:

[0028] Component (A), selected from diisocyanate or polyisocyanate components or mixtures thereof

[0029] Component (B), selected from amines having at least 2 primary amine groups.

[0030] According to an advantageous embodiment, component (A) is selected from: MDI, TDI, IPDI, HMDI or the corresponding uretdione homopolymers, or prepolymers with polyols, or mixtures thereof.

[0031] According to an advantageous embodiment, component (B) is selected from: polyetheramines (jeffamines), polyamides, aliphatic polyamines, cycloaliphatic polyamines or aromatic amines.

[0032] According to an advantageous embodiment, the thermosetting material coating is applied to the insert with a thickness of 0.05 - 1 mm.

[0033] According to an advantageous embodiment, in step b of the method for encapsulating the insert, the coating is cured at a temperature of 15 - 60 °C.

[0034] According to an advantageous embodiment, the CTE of the insert is 5 - 30 ppm / K, and the CTE is measured according to ISO 11359 - 2.

[0035] According to an advantageous embodiment, the inserts are selected from:

[0036] - an object having at least one geometric angle between 1 - 120°, or

[0037] - an object having at least one radius < 3 mm.

[0038] According to an advantageous embodiment, the inserts are selected from rotors or stators of electrical devices such as electric motors or generators, (power)-electronic components, batteries, switch rings of electric motors, switchgear, printed circuit boards, bushings, transformers, dry-type transformers, instrument transformers, and metal inserts embedded in insulating structural materials. Detailed Description

[0039] Unless otherwise defined herein, technical terms applied in connection with the present invention should have the meanings commonly understood by those of ordinary skill in the art. Additionally, unless the context otherwise requires, singular terms should include plurals, and plural terms should also include singulars.

[0040] All patents, published patent applications, and non-patent disclosures mentioned in this specification indicate the technical level of those skilled in the art to which the present invention pertains. All patents, published patent applications, and non-patent disclosures referred to in any part of this application are hereby incorporated by reference in their entirety to the same extent as if each patent or published document was specifically and individually indicated herein, to the extent that they do not conflict with the present invention.

[0041] All of the compositions and / or methods disclosed herein can be made and executed according to the present invention without undue experimentation. Although the compositions and methods of the present invention have been described from the perspective of preferred embodiments, it will be apparent to those of ordinary skill in the art that various changes can be made to the compositions and / or methods and the steps or the order of steps of the methods described herein without departing from the concept, spirit, and scope of the present invention. It is believed that all such obvious equivalent substitutions and modifications for those skilled in the art are within the spirit, scope, and concept of the present invention.

[0042] As used in the present invention, unless otherwise indicated, the following terms should be understood to have the following meanings.

[0043] When used in combination with the terms "comprising", "including", "having", or "containing" (or variants of these terms), the indefinite article can mean "one", but also has the same meaning as "one or more", "at least one", and "one or more".

[0044] Unless clearly indicated to refer only to alternatives or that the alternatives are mutually exclusive, the term "or" means "and / or".

[0045] In this disclosure, the term "about" is used to indicate that the stated value includes the inherent error variations of the measuring equipment, machinery, or method, or the inherent variations present within the target to be measured. For example, but not by way of limitation, when the term "about" is used, the value being referred to can vary between ±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.

[0046] The use of "at least one" should be understood to include one and any quantity greater than one, including but not limited to 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. Depending on the term to which it refers, the term "at least one" can extend up to 100 or 1000 or more. Additionally, the quantities of 100 / 1000 are not considered limiting, as lower or higher bounds can also produce satisfactory results.

[0047] As used herein, the terms "comprising", "having", "including", or "containing" are either closed or open and do not exclude additional, unrecited elements or method steps.

[0048] As used herein, the terms "or combinations thereof" and "and combinations thereof" refer to all permutations and combinations of the items listed before such terms. 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 also includes BA, CA, CB, CBA, BCA, ACB, BAC, or CAB if order is important in a particular context. Continuing with this example, it is clearly included that repeated combinations of one or more items or terms are included, such as BB, AAA, CC, AABB, AACC, ABCCCC, CBBAAA, CABBB, and so on. One of ordinary skill in the art will understand that, unless the context clearly dictates otherwise, there is generally no limit to the number of items in any combination. Similarly, when used in conjunction with the terms "selected from" or "selected from the group consisting of", the terms "or combinations thereof" and "and combinations thereof" refer to all permutations and combinations of the items listed before such terms.

[0049] The terms "in one embodiment", "in embodiments", "according to one embodiment", etc. generally mean that the particular feature, structure, or characteristic after such term is included in at least one embodiment of the present invention, and may also be included in multiple embodiments of the present invention. Importantly, such terms are non-limiting and do not necessarily refer to the same embodiment, but may of course refer to one or more of the preceding and / or following embodiments. For example, in the appended claims, any of the claimed embodiments may be applied in any combination.

[0050] As used herein, the term "ambient temperature" refers to the temperature surrounding the working environment (e.g., the temperature of the location, building, or room where a curable system is applied or generated), excluding any temperature changes caused by a chemical reaction. The ambient temperature is generally about 10 - 30 °C, and more specifically about 25 °C. In this document, the term "ambient temperature" is used interchangeably with "room temperature".

[0051] The term "consisting essentially of" followed by one or more features means that in addition to the components or steps explicitly listed, components or steps that do not materially affect the nature and characteristics of the present invention may also be included in the methods or materials of the present invention.

[0052] Unless otherwise clearly stated, the expression "comprised between X and Y" includes the boundaries. This expression means that the target range includes the X and Y values and all values from X to Y.

[0053] Throughout the description and claims of this specification, the terms "comprising" and "containing" and variations thereof, such as gerunds and present tenses, mean "including but not limited to" and do not exclude other parts, additives, components, wholes or steps. Additionally, unless the context requires otherwise, the singular includes the plural, especially in the case of using indefinite articles, and this specification should be understood to include both plural and singular, unless the context requires otherwise.

[0054] When upper and lower limits are cited for a certain property, for example, for the concentration of a certain component, a numerical range defined by any combination of any upper limit and any lower limit is simultaneously implied.

[0055] Plugin :

[0056] The method of the present invention is applicable to the encapsulation of inserts, such as inserts with a CTE lower than that of the encapsulation material.

[0057] The CTE of the material is measured according to ISO 11359-2.

[0058] For example, the insert is characterized in that its CTE is 5 - 30 ppm / K, preferably 5 - 25 ppm / K and more preferably 10 - 17 ppm / K.

[0059] In the present invention, the insert is an object made of a hard material, such as an object made substantially of metal (mainly steel and aluminum). The hardness of the material is measured by its tensile modulus, and the tensile modulus can be measured according to DIN EN ISO 6892-1.

[0060] For example, the insert is made of a material selected from those materials having a tensile modulus of 70 - 250 GPa, preferably 130 - 220 GPa.

[0061] The method of the present invention is applicable to inserts having all types of shapes, and the method of the present invention is preferably applicable to the encapsulation of inserts with sharp edges.

[0062] "Insert with sharp edges" in the context of the present invention means:

[0063] - an object having at least one geometric angle between 1 - 120°, or

[0064] - an object having at least one radius < 3 mm.

[0065] Figure 1a depicts an object having a radius of 2 mm (1) and an angle of 90° (2).

[0066] Figure 1b depicts an object having a radius of 1 mm (3) and an angle of 100° (4).

[0067] The functions of the plug-in can be diverse, but are usually selected from electrical and electronic components. The present invention is particularly applicable to plug-ins as components of a device, where the plug-in is subjected to thermal cycling during normal operation.

[0068] In the context of the present invention, thermal cycling means subjecting the plug-in to a temperature difference of 50 °C or higher, preferably 120 °C or higher, more preferably 190 °C or higher. These temperature differences apply for a duration of 5 minutes to 10 hours.

[0069] For example, the plug-in can be selected from rotors or stators of electrical devices such as electric motors or generators, (power)-electronic components, batteries, switching rings of electric motors, switching devices (gas-insulated and vacuum types), printed circuit boards, bushings, transformers, dry-type transformers, instrument transformers, metal plug-ins embedded in insulating structural materials.

[0070] Coating :

[0071] The present invention relies on coating the surface of the plug-in with a material coating, preferably a liquid material, which at least partially cures after coating to form a solid layer on the surface of the plug-in before applying the encapsulating material.

[0072] The present invention relies on coating the surface of the plug-in with a coating based on an elastic material.

[0073] The cured coating should have high flexibility and should also be compatible with the encapsulation system. The material of the coating is preferably selected such that the coating can chemically crosslink with the encapsulation system when the encapsulation system cures.

[0074] The coating material should have a satisfactory viscosity to allow the application of a uniform layer of sufficient thickness. For example, the coating material is selected from materials having a viscosity of 0.1 - 10 Pa·s at ambient temperature before curing, preferably 0.2 - 5 Pa·s. The viscosity is measured according to method ISO3219.

[0075] The cured coating material should have sufficient elasticity to avoid the formation of cracks in the encapsulating material during and after thermal cycling.

[0076] For example, the cured coating material is selected from materials having a tensile modulus of 50 - 1000 MPa, preferably 80 - 400 MPa.

[0077] The tensile modulus is measured according to method ISO 527.

[0078] For example, the cured coating material is selected from materials having an elongation at break of 20 - 500%, preferably 40 - 250%, even more preferably 50 - 200%.

[0079] The elongation at break is measured according to method ISO 527 on a sample with a thickness of 1 mm.

[0080] Advantageously, the coating is based on a material consisting of a two-component thermosetting system.

[0081] "Two-component thermosetting system" refers to a composition containing two components as a two-pack system (or kit), designed to mix the two components immediately before curing to form a coating.

[0082] When the two components are mixed / blended together and cured, they can form a cured solid coating by forming chemical bonds called crosslinks between the two components. After mixing the two components and before curing, the viscosity of the coating material is evaluated.

[0083] For example, the coating material can be selected from polyurea systems, polyepoxy resin systems or polyurethane systems, provided that it has suitable physicochemical properties within the above ranges, especially viscosity, tensile modulus and elongation at break.

[0084] The coating material is preferably based on a polyurea system, or preferably consists of a polyurea system.

[0085] The coating material is preferably based on a curable two-part resin system containing component (A) and component (B), wherein:

[0086] · Component (A) is an isocyanate component, which consists of one or more diisocyanates or one or more polyisocyanate components or a mixture thereof,

[0087] · Component (B) is an amine component, which consists of an amine having at least 2 primary amine groups.

[0088] The polyisocyanate component (A) used for producing a polyurea coating according to the present invention is well-known in the art and is an organic compound containing two or more isocyanate groups per molecule. The isocyanate component (A) can be aromatic, cycloaliphatic or aliphatic, and can also be a monomer or an oligomer.

[0089] The NCO functionality of the polyisocyanate component is advantageously greater than or equal to 2, preferably 2-3.

[0090] Isocyanate "functionality" is the number of reactive NCO groups per molecule in an isocyanate molecule or a polymeric isocyanate. 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 of different molecules and polymeric substances.

[0091] 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 isomers. Unless otherwise specifically stated, "MDI" may also refer to and include polymeric MDI. Polymeric MDI is a compound having a chain in which three or more benzene rings are interconnected by methylene bridges, with isocyanate groups attached to each benzene ring.

[0092] Suitable polyisocyanate components (A) that can be used in the coatings of the present invention can be selected, for example, from 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, dicyclohexylmethane-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), polyphenyl polymethylene polyisocyanate (crude MDI), and mixtures thereof.

[0093] Commercially available diisocyanates typically contain dimers (uretdiones), trimers (triazines), and oligomers, or prepolymers with polyols. In the coatings of the present invention, these mixtures of monomers and oligomers can be used without separating by-products or purification.

[0094] The amine component (B) used in accordance with the present invention for producing polyurea coatings is well-known in the art and is an organic compound containing two or more primary amine groups per molecule. The amine component (B) can be an aromatic, cycloaliphatic, or aliphatic compound and can also be a monomer or an oligomer.

[0095] In principle, any amine that is liquid at ambient temperature can be applied, such as polyetheramines (jeffamines), polyamides, aliphatic polyamines, cycloaliphatic polyamines such as isophorone diamine, or aromatic amines such as dimethylthiotoluenediamine, diethyltoluenediamine.

[0096] A skilled professional knows how to select the group components (A), component (B), and their ratios to provide a polyurea system having the desired physicochemical properties within the above ranges, particularly the viscosity before curing and the tensile modulus and elongation at break after curing.

[0097] Encapsulation Resin :

[0098] The encapsulating resin is a curable material known in the prior art for the same or similar uses.

[0099] The present invention is particularly applicable when the cured encapsulating resin is a hard material. For example, the resin system is selected from those having a tensile modulus after curing of 5 - 20 GPa, preferably 10 - 16 GPa.

[0100] For example, the resin system is selected from those having an elongation at break after curing of 0.1 - 5%, preferably 0.4 - 2%.

[0101] The present invention is particularly applicable when the cured encapsulating resin has a small coefficient of thermal expansion (CTE), i.e., CTE is less than or equal to 27 ppm / K, more preferably less than 20 ppm / K at T < Tg.

[0102] The viscosity of the resin system is an important parameter for the processability of the resin system. Preferably, the viscosity of the resin system before curing at 60 °C is preferably 4 - 30 Pas. The viscosity is measured according to method ISO 3219.

[0103] The present invention is particularly applicable when the cured encapsulating resin is a high glass transition temperature system, such as a system with Tg > 140 °C, preferably Tg > 180 °C.

[0104] The Tg of the encapsulating resin can be evaluated according to method ISO 11359 - 2. The resin system is preferably selected from those having good long - term thermal aging stability (class H of IEC 60216).

[0105] The resin system is preferably selected from those having very good resistance to thermal cycling cracking (SCT < - 100 °C). The method for measuring the resistance to thermal cycling cracking is described in EP1165688 B1 (page 9).

[0106] The encapsulating resin can be based on any material known in the prior art for this use, such as two - component epoxy resin systems, polyurethanes, polyisocyanurates.

[0107] For illustration, some embodiments of the resin system that can be used as the encapsulating system in the present invention are described in detail below. However, these descriptions should not be regarded as limiting the scope of the present invention.

[0108] According to the first embodiment, the encapsulating resin is a curable two - part resin system, comprising

[0109] (a) a resin part, comprising at least one epoxy resin, and

[0110] (b) a hardener part, comprising amine, acid anhydride or isocyanate functional groups.

[0111] Alternatively, the encapsulating resin may be a one - component system, such as that described in WO2016 / 202608A1.

[0112] According to the first embodiment, the curable two - part resin system may further include fillers, such as inorganic fillers and / or metal powders. Such fillers are well - known to those skilled in the art.

[0113] According to the first example of this embodiment, the encapsulating resin may be based on a curable two - part resin system comprising an epoxy resin and an acid anhydride, such as CW 30386 / HW 30387 system, which is commercially available from Huntsman.

[0114] According to the second example of this embodiment, the encapsulating resin may be based on a curable two - part resin system comprising an epoxy resin and an isocyanate. In particular, the reactive resin mixture may comprise:

[0115] a) a polyfunctional isocyanate,

[0116] b) an epoxy resin composition mainly comprising a compound A' based on a glycidyl ether of an aliphatic and / or cycloaliphatic alcohol having at least 2 alcohol functional groups, or a compound B' based on a glycidyl ester of an aliphatic and / or cycloaliphatic carbonic acid having at least 2 carboxylic acid functional groups,

[0117] c) a curing accelerator.

[0118] According to a preferred embodiment of this example, the epoxy resin composition (mainly) comprises 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 a mixture thereof.

[0119] According to a preferred embodiment of this example, the equivalent ratio of the isocyanate groups of component (a) - polyfunctional isocyanate to the epoxy groups of component (b) - epoxy resin is from 10:1 to 1:1, preferably from 5:1 to 3:1.

[0120] In addition, the polyfunctional isocyanate is preferably selected from cycloaliphatic polyisocyanates, aromatic polyisocyanates, and mixtures thereof.

[0121] In a particularly preferred embodiment of this example, the polyfunctional isocyanate is selected from: diphenylmethane-2,4- or -4,4'-diisocyanate; polyphenylene polymethylene polyisocyanate; diphenylmethane diisocyanate containing a carbodiimide group or a uretonimine group; a modified polyisocyanate containing a urethane group, an ethyl carbamate group, a biuret group and / or a uretdione group; an isocyanate group prepolymer obtained by reacting an excess of the above polyisocyanate with a polyol; and mixtures thereof.

[0122] In a preferred embodiment of this example, the curing accelerator is based on a boron trichloride-amine complex and is preferably selected from boron trichloride-dimethyloctylamine complex, boron trichloride-trimethylamine complex, boron trichloride-benzyl dimethylamine complex, boron trichloride-tributylamine complex and mixtures thereof.

[0123] According to a preferred embodiment of this example, based on the total weight of the mixture, the curing accelerator is present in an amount of 0.01-5 wt%, preferably 0.05-2.5 wt%.

[0124] According to a third embodiment of this first embodiment, the curable two-part resin system may comprise:

[0125] (a) a resin part comprising at least one alicyclic epoxy resin, and

[0126] (b) a hardener part comprising (i) at least one alicyclic anhydride and (ii) a block copolymer comprising a polysiloxane block and an organic block, as described in application EP20216430.7.

[0127] In one embodiment of this example, the organic block in the block copolymer is a polyester block, such as a polyester block based on caprolactone or other lactones, or a polycarbonate block. Non-limiting examples of suitable block copolymers include polycaprolactone-polysiloxane block copolymers, polylactic acid-polysiloxane block copolymers and poly(propylene carbonate)-polysiloxane block copolymers. The polysiloxane block is, for example, a polydimethylsiloxane block or a polymethylethylsiloxane block. In a specific embodiment, the block copolymer is a polycaprolactone-polysiloxane block copolymer such as W35 (Wacker Chemie AG, Munich, Germany).

[0128] In one embodiment of this example, the resin part (a) and the hardener part (b) of the two-part resin system are present in a stoichiometric ratio of resin part to hardener part ±15 mol%.

[0129] Alicyclic epoxy resins can, for example, be selected from bis(epoxycyclohexyl)-methyl carboxylate, bis(2,3-epoxycyclopentyl) ether, 1,2-bis(2,3-epoxycyclopentyl) ethane, vinylcyclohexene dioxide, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6'-ethylcyclohexane carboxylate, 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-oxetane methanol, and their combinations. In another embodiment, the alicyclic epoxy resin is a non-glycidyl epoxy resin. In another embodiment, the alicyclic epoxy resin is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate.

[0130] In one embodiment, the alicyclic anhydride is an unsaturated compound. In a preferred embodiment, the alicyclic anhydride contains 9 - 10 carbons. Alicyclic anhydrides can, for example, be selected from methyltetrahydrophthalic anhydride (MTHPA), nadic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA), hexahydro-methylphthalic anhydride, tetrahydrophthalic anhydride, methylphthalic anhydride, naphthalenedicarboxylic anhydride, dodecenyl succinic anhydride, and derivatives of succinic anhydride. In a particular embodiment, the alicyclic anhydride is methyltetrahydrophthalic anhydride (MTHPA), nadic anhydride, or methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA).

[0131] According to another embodiment, the encapsulating resin is a one-component system, such as a cationically polymerizable epoxy resin combined with a specific filler mixture, as described in WO2016 / 202608.

[0132] In particular, according to this embodiment, the curable resin system includes:

[0133] (a) A cationically polymerizable epoxy resin,

[0134] (b) A cationic polymerization initiator,

[0135] (c) Particulate fillers, and

[0136] (d) Nanoparticle fillers.

[0137] Method Steps:

[0138] The present invention relates to a method for encapsulating inserts.

[0139] The present invention also relates to a method for producing encapsulated inserts.

[0140] The present invention also relates to a method for preparing electrical and electronic insulation devices.

[0141] The method of the present invention comprises:

[0142] a. applying a first coating material onto the plug-in, and then,

[0143] b. at least partially curing the coating obtained in step a, and

[0144] c. encapsulating the coated plug-in obtained in step b with a potting resin having a coefficient of thermal expansion higher than that of the plug-in material.

[0145] Advantageously, in step a, a coating with a thickness of 0.05 - 1 mm, preferably 0.1 - 0.5 mm, is applied onto the surface of the plug-in. The coating is particularly suitable for places with sharp edges. The coating does not have to have an equal thickness on all surfaces of the plug-in, but preferably has a regular thickness on the entire surface of the plug-in on which it is applied. The coating is preferably applied onto the entire surface of the plug-in to be encapsulated.

[0146] The application of the coating can be achieved by any method known to those skilled in the art, such as spraying, dipping, painting, spin coating. Preferably, it is a method that can be mechanically implemented.

[0147] In step b, the coating is at least partially cured, for example, at a temperature of 15 - 60 °C.

[0148] In step b, the resin is advantageously cured at ambient temperature for 1 - 24 hours, preferably 2 - 16 hours, more preferably 4 - 12 hours.

[0149] In step c, the coated and partially cured plug-in obtained in step b is encapsulated with a potting resin in a known manner. Briefly, the components of the potting resin system are mixed, optionally mixed with one or more mineral fillers or metal powders, and applied onto the plug-in. The plug-in is coated, for example, by dipping, trickle impregnation, vacuum pressure impregnation, and / or casting. Then, according to the composition of this resin system, the potting resin system is cured according to a standard curing procedure.

[0150] Equipment:

[0151] The method disclosed above produces a device composed of three parts: a plug-in, a coating covering part or all of the surface of the plug-in, and a potting resin. Advantageously, there is no direct contact between the surface of the plug-in and the potting resin, and the coating is inserted between the plug-in and the potting resin. The device can be used for electrical and electronic applications.

[0152] Usage:

[0153] The present invention stems from the combination of a coating system with elastic properties inserted between the plug-in and the encapsulating resin, thereby achieving the combined effect that the encapsulating resin has no cracks after thermal cycling. Cracks are identified by visual inspection.

[0154] When directly coated onto the surface of the plug-in, the encapsulating system itself usually shows cracks during the thermal cycling test. The coating itself cannot be used as a casting system because it cannot provide a sufficiently high hardness at high temperatures.

[0155] The method of the present invention is applicable not only to electric vehicle applications but also to MV-electric applications where cracks are critical (such as certain bushings, switchgear, or instrument transformers), which currently use expensive toughened casting systems. By applying the method of the present invention, the encapsulation of plug-ins for such applications can be implemented with a cheaper non-toughened casting system.

[0156] Drawings:

[0157] Figure 1A is a schematic diagram corresponding to the corner of a sharp plug-in.

[0158] Figure 1B is a schematic diagram corresponding to the corner of a sharp plug-in.

[0159] Figure 2 is a schematic diagram of a cubic plug-in in the cylindrical mold applied in Example Sequence 1.

[0160] Figure 3 is a schematic diagram of a rhombic plug-in in the cylindrical mold applied in Example Sequence 2.

[0161] Experimental part:

[0162] In the following examples, unless otherwise specified, contents and percentages are given in mass units.

[0163] I - Raw Materials

[0164] Polyisocyanate :

[0165] - Rencast 6429A provided by Huntsman, which is based on a blend of aliphatic and TDI-based isocyanates.

[0166] Polyamine :

[0167] - Rencast 5425B provided by Huntsman, which is a formulated hardener based on liquid aromatic amines

[0168] - Rencast 5427B provided by Huntsman, which is a formulated hardener based on liquid aromatic amines

[0169] Encapsulation Resin :

[0170] - Provided by Huntsman CW 30386, which is a high Tg epoxy resin based on alicyclic epoxy resin and inorganic fillers

[0171] - Provided by Huntsman HW 30387, which is a formulated hardener based on anhydride and fillers

[0172] II - Method

[0173] Viscosity Measurement:

[0174] The composition was subjected to a Rheomat viscometer. Viscosity was measured according to ISO 3219.

[0175] Tensile Modulus

[0176] Tensile modulus was measured according to ISO 527 at 23°C, with a sample thickness of 1 mm, cured at 23°C for 24 hours and then at 80°C for 4 hours.

[0177] Elongation at Break

[0178] Elongation at break was measured according to ISO 527 at 23°C, with a sample thickness of 1 mm, cured at 23°C for 24 hours and then at 80°C for 4 hours.

[0179] Glass Transition Temperature

[0180] The glass transition temperature Tg is measured according to ISO 6721 / 94.

[0181] Coefficient of Linear Thermal Expansion

[0182] CTE is measured according to ISO 11359-2.

[0183] Chemical Shrinkage

[0184] Chemical shrinkage is measured according to ISO 2579.

[0185] Preparation of Polyurea Coating System:

[0186] The polyurea system is prepared by mixing polyisocyanate and polyamine in the specified proportions at room temperature. The compositions and their characteristics are shown in Table 1 below

[0187] Table 1: Composition of Examples

[0188]

[0189] Preparation of Encapsulation Resin

[0190] The encapsulation system consists of a CW 30386 / HW 30387 mixture with a weight mixing ratio of 100 / 130.

[0191] The mixture was introduced into the 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 step, all the samples were demolded from the cylindrical aluminum shell.

[0192] The properties of the mixture are as follows:

[0193] Table 1: Characteristics of the encapsulation resin system

[0194]

[0195] Molds and Plugins

[0196] - Molds and Plugins Series 1:

[0197] A representative aluminum mold and a first series of inserts have been applied. They are shown in Figure 2 .

[0198] The mold consists of an aluminum cylindrical shell (2.1) with a diameter of 50 mm. The insert is an aluminum cube (2.2) with a radius (2.3) of 0.2 mm.

[0199] - Molds and Plugins Series 2:

[0200] The same aluminum mold and a second series of inserts have been applied. They are shown in Figure 3 .

[0201] The mold consists of an aluminum cylindrical shell (3.1) with a diameter of 50 mm. The insert (3.2) is an aluminum rhombus with a rounded corner radius (3.3) of 2 mm and (3.4) of 15 mm.

[0202] Preparation of Encapsulated Plugins

[0203] For each mold and insert series 1 and 2, the following samples were prepared:

[0204] 6 samples were encapsulated without coating (control example).

[0205] 6 samples were coated with a thin layer (0.2 mm) of the coating composition of Example 1 and cured before casting the encapsulation resin system.

[0206] 6 samples were coated with a thin layer (0.2 mm) of the coating composition of Example 2 and cured before casting the encapsulation resin system.

[0207] The coating was applied to the inserts with a brush at a thickness of 0.2 mm and cured at 23 °C for 24 hours.

[0208] The encapsulation system consisting of the mixture disclosed above was introduced into the mold under vacuum at 90 °C and cured in two steps in an oven: step 1 / cured at 120 °C for 20 minutes, step 2 / cured at 190 °C for 3 hours.

[0209] After this step, all samples were demolded from the cylindrical aluminum cases.

[0210] The comparative example corresponded to applying the same encapsulation system under the same casting and curing conditions as in the examples, but without applying the coating before casting. The comparative example was recorded as "Comparative Example".

[0211] III - Tests and Results

[0212] 1 - Anti - Crack Test

[0213] Test:

[0214] The samples were evaluated by visual inspection. The presence of cracks in the encapsulation system was visually inspected and recorded.

[0215] Result:

[0216] The tests were carried out on 3x6 samples of the mold and insert series 1. The results were as follows:

[0217] Five samples of Example 1 of the present invention and four samples of Example 2 of the present invention did not show signs of cracks.

[0218] The comparative (control) samples all cracked after demolding.

[0219] 2 - Thermal Shock Test

[0220] Test:

[0221] To see the benefits of the new method, all parts (coated and uncoated) were subjected to thermal shock, starting from 20 °C and dropping to -50 °C within 7 hours, in steps of 1 hour at 20 °C, 10 °C, 0 °C, -10 °C, -20 °C, -30 °C, -40 °C, -50 °C.

[0222] The operator recorded the number of cracked samples at each temperature in each group.

[0223] Result:

[0224] The tests were carried out on 3x6 samples of the mold and insert series 1. The results were as follows.

[0225] The test results are shown in Table 3 below:

[0226] Table 3: Thermal Shock Test

[0227] Comparative Example Example 1 Example 2 Room Temperature 6 1 2 0℃ 6 1 2 -10℃ 6 1 2 -20℃ 6 1 2 -30℃ 6 1 2 -40℃ 6 1 2 -50℃ 6 1 3

[0228] All the comparative samples (uncoated samples) were cracked before the test.

[0229] After the test, 5 out of 6 samples of Example 1 did not show any cracks.

[0230] After the test, 4 out of 6 samples of Example 2 did not show any cracks, and 1 sample cracked at -50°C

[0231] 3 - Heat Resistance Test :

[0232] This test has been carried out on another set of samples, which includes inserts of different shapes corresponding to Figure 3 (molds and insert series 2).

[0233] After casting and demolding, the samples were exposed to 150°C for 50 minutes, and then directly moved to another chamber at -40°C, where they stayed for 50 minutes to stabilize the temperature inside the samples.

[0234] Result:

[0235] This test was carried out on 3x6 samples of molds and insert series 2. The results are summarized in Table 4 below. In Table 4, the number of samples that cracked after a certain number of thermal cycles (a total of 6 test samples) was recorded. After 300 cycles, none of the coated samples cracked, while all the samples that were not coated before casting (comparative examples) cracked after at most 10 cycles.

[0236] Table 4 Thermal Cycle Test

[0237] Number of Cycles Comparative Example Example 1 Example 2 0 5 0 0 1 5 0 0 10 6 0 0 25 6 0 0 50 6 0 0 100 6 0 0 200 6 0 0 300 6 0 0

Claims

1. A method for encapsulating a plug-in, the method at least comprises: a. Coating a layer of thermosetting material on at least part of the surface of the plug-in, b. Curing at least part of the coating formed in step a, c. Encapsulating the coated plug-in produced in step b with an encapsulating resin. Wherein the thermosetting material of the coating is selected from materials having a tensile modulus of 50 - 1000 MPa after curing and an elongation at break of 20 - 500% after curing, wherein the tensile modulus is measured according to method ISO 527, and the elongation at break is measured according to method ISO 527.

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

3. The method of any one of the preceding claims, wherein the thermosetting material of the coating is selected from polyurea, polyurethane and polyepoxy resin systems, preferably a polyurea system.

4. The method of any one of the preceding claims, wherein the thermosetting material of the coating is a two-component thermosetting system comprising at least the following: · Component (A), selected from diisocyanates or polyisocyanate components or mixtures thereof · Component (B), selected from amines having at least 2 primary amine groups.

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. The method of claim 4 or 5, wherein component (B) is selected from: polyetheramines (jeffamines), polyamides, aliphatic polyamines, cycloaliphatic polyamines or aromatic amines.

7. The method of any one of the preceding claims, wherein the thermosetting material coating is applied to the plug-in with a thickness of 0.05 - 1 mm.

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

9. A kit for encapsulating a plug-in in the method of any one of claims 1 - 8, the kit comprising: · Thermosetting material, selected from materials having a tensile modulus of 50 - 1000 MPa after curing and an elongation at break of 20 - 500% after curing, wherein the tensile modulus is measured according to method ISO 527, and the elongation at break is measured according to method ISO 527, · A resin system capable of encapsulating the plug-in.

10. An apparatus composed of encapsulated plug-ins, the apparatus being formed by implementing the method of any one of claims 1 - 8.

11. The apparatus of claim 10, wherein the CTE of the plug-in is 5 - 30 ppm / K, and the CTE is measured according to ISO 11359 - 2.

12. The apparatus of claim 10 or 11, wherein the plug-in is selected from: - An object having at least one geometric angle (2; 4) between 1 - 120°, or - An object having at least one radius (1; 3) < 3 mm.

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

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

15. A method for producing an electrical and electronic insulation device, wherein the method comprises at least one step of implementing the method for encapsulating an insert as claimed in any one of claims 1-8.

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