WO2015104064A1

WO2015104064A1 - Electromagnetic radiation transparent polymer mould and method for manufacturing the same

Info

Publication number: WO2015104064A1
Application number: PCT/EP2014/050496
Authority: WO
Inventors: Patrick Meier; Jan Van Loon; Spiros Tzavalas; Willi Gerig; Xavier Kornmann; Marco Schneider
Original assignee: Abb Research Ltd.
Priority date: 2014-01-13
Filing date: 2014-01-13
Publication date: 2015-07-16

Abstract

The present invention relates to a mould comprising an electromagnetic radiation transparent polymer resin and to a method for manufacturing a mould for moulding electrical devices from electromagnetic radiation curable polymer compositions. Further, the present invention refers to a process for producing electrical devices as well as to the use of the claimed mould to over mould electrical devices for low-, medium- and high voltage components with insulating material.

Description

ELECTROMAGNETIC RADIATION TRANSPARENT

POLYMER MOULD AND METHOD FOR MANUFACTURING THE SAME

FIELD OF INVENTION

[001] The present invention relates to a mould comprising an electromagnetic radiation transparent polymer resin and to a method for manufacturing a mould for moulding electrical devices from electromagnetic radiation curable polymer compositions. Further, the present invention refers to a process for producing electrical devices as well as to the use of the claimed mould to over mould electrical devices for low-, medium- and high voltage components with insulating material.

STATE OF THE ART

[002] Electromagnetic radiation curing of polymers, such as ultraviolet (UV) light curing, has been known for many years and its chemistry is well understood and established, particularly in the field of printing and coatings. For instance, the basic principle of the UV-light curing chemistry is the following: Reactive polymer precursors are mixed with a light sensitive photoinitiator and subsequently irradiated with a suitable UV-light source. The UV-light activates the photoinitiator and a polymerisation process between the precursor molecules is initiated. Depending on the nature of the precursor(s) and photoinitiator, as well as on the geometry of the device to be cured, the curing takes a few seconds (for coatings, printings) up to several minutes (for three dimensional devices). Typical polymer types to be used for UV-light curing are epoxies, acrylates and silicones. The main advantage of UV-light curing is the fast curing process. Compared to conventional curing principles such as thermal-, or humidity curing or "curing" by evaporation of volatile solvents, UV-light curing is about a factor 5 to 50 faster. Furthermore, in comparison to thermal curing, there is no need of thermal heat sources (e.g. ovens) and the compensation of pressure built-up due to thermal expansion is reduced. [003] Most applications concerning UV-light curing are located in the coating and printing industries. This is due to the fact that the polymer precursor can be applied as a thin layer (typically 10 μιη to 500 μιη) to a substrate and then cured by irradiation. A mould is not required at all.

[004] However, when using UV-light curing technology for producing complex three dimensional devices in a precise shape, a suitable UV-light transparent mould is required.

[005] The conventional approach is the use of quartz (glass) moulds, e.g. as described in WO 2007/065766 Al. Quartz moulds have been described to manufacture UV-light curable devices. Quartz exhibits the benefit to be UV-light stable and UV-light transparent. However, quartz is very brittle and the cost and complexity of manufacturing quartz moulds is high (comparable to steel moulds for thermal curing). Therefore, quartz moulds are not suitable for the manufacturing of big and complex shaped devices on an industrial level.

[006] Another approach for producing complex three dimensional devices is based on the use of thermoformed moulds, e.g. known from WO 2012/170008 Al. These thermoformed moulds can be manufactured by heating up UV-transparent plates, e.g. PMMA plates, forming these plates on a positive mould and mounting together two mould halves using a frame. This thermoforming moulding concept has been successfully proven to work with UV-light curing silicones by manufacturing different prototypes of devices (e.g. vacuum interrupters, fuse cut-out insulators, stress cone).

[007] However, the above described thermoforming moulding technology shows several drawbacks. In particular, thermoformed moulds feature reduced mechanical stiffness and suffer from decreased geometrical precision concerning the UV-light curable devices produced. [008] More specifically, since the mould consists of a thin three dimensional polymer plate or sheet (e.g. PMMA sheet), it is pressure-sensitive. If the filling pressure is too high, the mould starts to bend and leak, and during demoulding, excessive shear forces can damage the mould. This particularly concerns complex mould shapes as well as big dimension moulds. Further, due to the thermoforming moulding technology, it is not possible to provide mould geometries equal to 90° angles between the two half-moulds. This causes inevitable thick flashes at the mould lines which have to be removed manually from every cast part. These drawbacks are in the nature of the thermoforming moulding technology and can be minimized to a certain degree, but never completely avoided.

[009] In view of the above, there is a need for electromagnetic radiation transparent and stable moulds, such as UV-light transparent and UV-light stable moulds that can be used for producing complex shaped articles (three dimensional devices) such as electrical insulators on an industrial level and in high geometrical precision, which moulds are comparatively cheap while at the same time exhibit sufficient mechanical stiffness.

BRIEF DESCRIPTION OF THE INVENTION

[0010] As a result of intensive studies conducted taking the above described problems into consideration, the present inventors were surprised to find that by i) providing a positive model for an electrical device, ii) placing the positive model in a container, iii) adding an electromagnetic radiation transparent polymer resin to the container, iv) curing the electromagnetic radiation transparent polymer resin, v) removing the positive model from the cured electromagnetic radiation transparent polymer resin, and vi) providing a connection for attaching an injection hose, an electromagnetic radiation transparent mould for moulding an electrical device is provided which, compared to quartz glass moulds and thermoformed moulds, integrates all the advantages of the earlier concepts and eliminates all of their drawbacks. [0011] Producing the claimed moulds and using them for producing radiation cured devices widens the use of radiation curing technology such as UV-curing technology for a variety of products, combining fast curing, complex geometries and high injection pressures at the same time, while keeping the mould cost at a low level.

[0012] Further, the claimed moulding technology can be particularly used to manufacture electrical devices such as insulators and any other polymer encapsulated devices, e.g. for fuse cutouts, hollow core insulators, MV and HV sensors, cable accessories as for instance HV stress cones and HV cable joints, MV and HV surge arresters and silicone vacuum interrupters.

[0013] The basic concept of the present invention is to manufacture an electromagnetic radiation transparent mould directly in its final shape, by casting it around its positive shape (see Figure 1) using specific electromagnetic radiation transparent polymer resins such as UV-light transparent polymer resins. After having manufactured the mould, it can be used to embed electrical parts with electromagnetic radiation curable compositions by employing resin injection technology (e.g. APG).

[0014] Therefore, in an embodiment, a method for manufacturing a mould for moulding an electrical device from electromagnetic radiation curable polymer compositions is provided, said method comprises the steps of i) providing a positive model for an electrical device, ii) placing the positive model in a container, iii) adding an electromagnetic radiation transparent polymer resin to the container, iv) curing the electromagnetic radiation transparent polymer resin, v) removing the positive model from the cured electromagnetic radiation transparent polymer resin, and vi) providing a connection for attaching an injection hose.

[0015] In another embodiment, a mould for moulding electromagnetic radiation curable polymer compositions is provided, said mould comprises an electromagnetic radiation transparent polymer resin which is curable at room temperature.

[0016] In a further embodiment, a process for producing an electrical device is provided, said process comprises the steps of a) injecting an electromagnetic radiation curable polymer composition to a mould according to the present invention, b) applying pressure, c) curing the electromagnetic radiation curable polymer composition with electromagnetic radiation to obtain an electromagnetic radiation cured polymer composition, and d) removing the electromagnetic radiation cured polymer composition from the mould.

[0017] Another embodiment refers to the use of a mould according to the present invention to over mould electrical devices for low-, medium- and high voltage components with insulating material.

[0018] In principle, electromagnetic radiation (EMR) is characterized by the frequency or wavelength of its wave. According to the present invention, EMR comprises radio waves, microwaves, infrared (IR) radiation, visible light, ultraviolet (UV) radiation, X-rays and gamma rays. Preferably, EMR is selected from the group consisting of UV, IR and microwave. UV radiation is defined as electromagnetic radiation having wavelengths ranging from 100 nm and 400 nm. This range of wavelengths corresponds to a frequency range of 3 PHz to 750 THz. IR radiation is defined as electromagnetic radiation having wavelengths ranging from 700 nanometers (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of 430 THz to 300 GHz. Microwaves are defined as electromagnetic radiation having wavelengths ranging from one millimeter to one meter, corresponding to a frequency range of between 300 GHz and 300 MHz.

[0019] Further embodiments, aspects, advantages and features of the present invention are described in the dependent claims, the description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The details will be described in the following with reference to the figures.

Figure 1 shows the principle of the mould concept according to the present invention. Dark grey: positive shape of the mould, equals to geometry of the final part to be manufactured. Bright grey: UV-light transparent mould. Figure 2 shows a casting of UV-light transparent mould according to the present invention. Dark grey: ground plate, positive model, and frame. Bright grey: resulting UV-light transparent mould.

Figure 3 shows a possible setup, where the UV-light source is movable in x-, y- and z- direction while the mould (not shown) turns around its symmetrical axis (indicated by the rotation arrow around the device produced by the mould).

DETAILED DESCRIPTION OF THE INVENTION

[0021] Reference will now be made in detail to various aspects of the invention and embodiments. Each aspect is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment or aspect can be used on or in conjunction with any other embodiment or aspect to yield yet a further embodiment or aspect. It is intended that the present disclosure includes any such combinations and variations.

[0022] The following embodiments and aspects of embodiments refer to UV-light as exemplary electromagnetic radiation. However, it is possible to adapt all embodiments and aspects described for UV-light below to any other wavelength range such as IR and microwave by suitable choice of parameters and materials.

[0023] According to an embodiment, the invention relates to a method for manufacturing a mould for moulding an electrical device from UV-light curable polymer resins, said method comprises the steps of i) providing a positive model for an electrical device, ii) placing the positive model in a container, iii) adding a UV-light transparent polymer resin to the container, iv) curing the UV-light transparent polymer resin, v) removing the positive model from the cured UV-light transparent polymer resin, and vi) providing a connection for attaching an injection hose. Preferably, steps i), ii), iii), iv), v) and vi) are carried out in the order given.

[0024] According to an aspect, step i), i.e. providing a positive model for an electrical device comprises the step of producing a positive model by milling said model from a three dimensional block or by three dimensional printing. In a preferred aspect, the three dimensional block is selected from the group consisting of a metal block, wood block and a polymer block. Preferably said metal block is a steel or aluminum block. Preferably said polymer block is a PU-styling block. According to a preferred aspect, the positive model used in step i) is a three dimensional body. Preferably, but not necessarily, the three dimensional body has at least one symmetrical axis. Preferably, the positive model used in step i) is an exact duplicate of the device to be produced by the mould according to the present invention. Alternatively, the positive model used in step i) has the dimension of a fragment (portion) of the device to be produced by the mould according to the present invention. Preferably, the dimension of the fragment extends from one of the two sides of any symmetrical plane going through the symmetrical axis of the device to the outer surface of the device to be produced. Still preferably, the ratio between the volume of the fragment and the volume of the device to be produced by the mould according to the present invention is between 1:5 and 1: 1, preferably 1:2.

[0025] According to an alternative aspect, step i) comprises the step of providing an already existing prototype of the device to be produced as positive model.

[0026] According to an aspect, step i) further comprises a step of applying a finishing to the positive model (i.e. on the positive model's surface). Preferably, applying a finishing is carried out by spraying varnish to the surface of the positive model.

[0027] Still, according to an aspect, step i) further comprises a step of treating the positive model with an anti-sticking agent. Preferably, the anti-sticking agent is at least one selected from the group consisting of silicone release agents, fluorinated anti- sticking agents and natural greases, or any combination thereof. Preferred fluorinated anti-sticking agents are flouropolymers. Preferred flouropolymers are at least one selected from the group consisting of PTFE, FEP and ETFE, or any combination thereof.

[0028] According to an aspect, step ii), i.e. placing the positive model for the electrical device in a container comprises setting the positive model to any place on the bottom of the container, preferably in the center of the container. This means that in case the positive model has the dimension of only a fragment of the device to be produced, the positive model is placed to any place on the bottom of the container. In a preferred aspect, step ii) further comprises fixing the positive model on the bottom of the container. This can be done by appropriate fixing means, such as screws or threaded bars. In case the positive model is an exact duplicate of the device to be produced, it is placed by threaded bars into the container, preferably in the center of the container, in such way that it has no contact to any of the container forming plains (i.e. side walls). According to a preferred aspect, placing the positive model for the electrical device in a container means placing the positive model on the bottom plate of the container such that the positive model contacts none of the four rectangular side walls.

[0029] According to a further aspect, the container used in step ii) is made of anti- sticking material. Preferably, the anti-sticking material is selected from fluoropolymers and/or non-polar hydrocarbon based polymers. Particularly preferred fluoropolymers are at least one selected from the group consisting of PTFE, FEP and ETFE, or any combination thereof. Particularly preferred non-polar hydrocarbon based polymers are polypropylene (PP) and/or polyethylene (PE). Still according to an aspect, the container used in step ii) has any appropriate shape, and preferably has a cross-section which is rectangular. Preferably, the container used in step ii) is a box having a rectangular bottom plate and four rectangular side walls. Preferably, the container used in step ii) has the form of a cuboid. Preferably, the cuboid has at least one opening. Still preferably, the opening of the cuboid extends over one of the six cuboid faces. An exemplary container is shown in Figure 2. The shape of the container helps to obtain a most suitable geometry of the desired mould (e.g. for material saving, weight savings, improved UV-light penetration).

[0030] Preferably, step ii) further comprises placing light guides in the container. According to a preferred aspect, placing the light guides in the container comprises setting the light guides to any position in the container. The light guides can be fixed to the desired position in the container by appropriate fixing means, such as metal rods or any fixating means which attach the light guides to the container walls. Preferably the fixating means are made of UV-light transparent materials, such as PMMA, epoxy resins, polyurethane resins or glass. The light guides serve to guide the UV-light to areas where a direct UV-light irradiation by the UV-lamp is difficult or not possible. Suitable light guides to be used in the present invention comprise glass fibre optics or light scattering Plexiglas (e.g. Endlighten from Evonik).

[0031] According to an aspect, step iii), i.e. adding a UV-light transparent polymer resin to the container comprises pouring a UV-light transparent polymer resin into the container until at least a part of the positive model is embedded in the UV-light transparent polymer resin. Preferably, the whole positive model is embedded in the UV- light transparent polymer resin. This is, in particular, the case if the positive model used in step i) has the dimension of a fragment of the device to be produced and the dimension of that fragment extends from one of the two sides of any symmetrical plane going through the symmetrical axis of the device and the outer surface of the device to be produced.

[0032] Alternatively, only a part of the positive model is embedded in the UV-light transparent polymer resin. Preferably, only 50% of the positive model's surface is embedded in the UV-light transparent polymer resin. This is, in particular, the case if the positive model used in step i) is an exact duplicate of the device to be produced by the mould according to the present invention. In this case, the UV-light transparent polymer resin, which is covering only 50% of the positive model is then cured. Curing is preferably performed as described in step iv) below. After curing, an anti-sticking agent described above is applied on the cured polymer surface. After that, additional UV-light transparent polymer resin is poured over it until the whole positive model is embedded in the UV-light transparent polymer resin.

[0033] According to a preferred aspect, the UV-light transparent polymer resin used in the present invention is a polymer with a UV-transparency of at least 30%, preferably of at least 60%, preferably of at least 80%, and preferably of at least 90%. For example with 60% UV-transparency in a wavelength range of the UV- activation- spectrum of the material of about 360 nm to 380 nm. Preferably, the UV-light transparent polymer resin is a polymer which is curable at room temperature. Still according to a preferred aspect, the UV-light transparent polymer resin is UV-light stable. Preferably, the UV-light transparent polymer resin is at least one selected from the group consisting of polyurethane (PUR) resin, epoxy resin and vinyl ester resin, or any combination thereof. Most preferred UV-light transparent polymer resins are cycloaliphatic epoxy resins and room temperature curing polyurethane resins.

[0034] According to an aspect, step iv), i.e. curing the UV-light transparent polymer resin comprises amine curing, anhydride curing, cationic curing or radical curing. In case the UV-light transparent polymer resin is an epoxy resin, amine curing or cationic curing is preferably carried out.

[0035] According to an aspect, step v), i.e. removing the positive model from the cured UV-light transparent polymer resin comprises separating the positive model from the cured UV-light transparent polymer resin, preferably by mechanical means. Alternatively, separation of the positive model from the cured UV-light transparent polymer resin is carried out by melting the positive model.

[0036] According to a further aspect, step vi), i.e. providing a connection for attaching an injection hose comprises milling a tubular opening into the cured UV-light transparent polymer resin in the desired dimensions at any position in the cured UV- light transparent polymer resin which is found appropriate. To this tubular opening, an injection hose can be attached to the UV-light transparent mould. After having carried out steps i) to vi), a mould is provided which is further described in the following.

[0037] According to an embodiment, the present invention refers to a mould for moulding UV-light curable polymer compositions. Preferably, said mould is producible by a method according to the present invention. Further, the mould is preferably UV- light transparent. Still preferably, the mould is both UV-light transparent and UV-light stable. According to an aspect, the mould according to the present invention comprises at least one solid three dimensional body and a cavity. Preferably, the solid three dimensional body of the mould is such that it is possible to place an imaginary sphere (ball) of 1 cm diameter (preferably 1.5 cm diameter) fully within the dimensional body. Preferably said cavity has the exact dimensions of the electrical device to be produced, or alternatively, has the dimension of only a fragment of the electrical device to be produced. According to a preferred aspect, the mould comprises at least one mould part (mould element). In other words, the mould comprises one mould part, two or a plurality of mould parts. Preferably, the mould is a two-part or a multi-part mould. Still preferably, the two-part mould comprises two identical mould parts. According to a preferred aspect, each mould part of the mould according to the present invention comprises a UV-light transparent polymer resin. Preferably, all mould parts comprise the same UV-light transparent polymer resin. According to another aspect, the mould parts of the mould according to the present invention are made of a UV-light transparent polymer resin. Preferably, the UV-light transparent polymer resin is a polymer with a UV-transparency of at least 30%, preferably of at least 60%, preferably of at least 80%, and preferably of at least 90%. For example with 60% UV-transparency in a wavelength range of the UV-activation-spectrum of the material of about 360 nm to 380 nm. Preferably, the UV-light transparent polymer resin is a polymer which is curable at room temperature. Still according to a preferred aspect, the UV-light transparent polymer resin is UV-light stable. Preferably, the UV-light transparent polymer resin is at least one selected from the group consisting of polyurethane (PUR) resin, epoxy resin and vinyl ester resin, or any combination thereof. Most preferred UV-light transparent polymer resins are cycloaliphatic epoxy resins and room temperature curing polyurethane resins. Preferably, the mould according to the present invention comprises light guides as specified in the present description. Still preferably, the mould according to the present invention comprises at least one tubular opening. To this tubular opening, an injection hose can be attached. According to a further aspect, at least five faces of the mould according to the present invention form a cuboid having an irregular sixth face. Preferably, the irregular sixth face of the cuboid has the form of at least a portion of the outer surface of the positive model.

[0038] Still, according to a further embodiment, the present invention refers to a process for producing an electrical device, said process comprises the steps of a) injecting a UV-light curable polymer composition to a mould according to the present invention, b) applying pressure, c) curing the UV-light curable polymer composition with UV-light to obtain a UV-light cured polymer composition and, d) removing the UV-light cured polymer composition from the mould.

[0039] According to an aspect, electrical devices produced by the process according to the present invention are insulators, such as fuse cutouts or hollow core insulators, MV and HV sensors, cable accessories, such as HV stress cones or HV cable joints, MV and HV surge arresters and silicone vacuum interrupters, or combinations thereof.

[0040] According to an aspect, the mould used in step a) is a mould as described above. Preferably, the mould is a two-part or a multiple part mould. Still preferably, the mould used in step a) is a two-part mould. Fixing of the two parts of the mould can be done by clamps or by a press as used for traditional APG-molding. To avoid resin leakage, the mold can be sealed by a sealing.

[0041] Preferably, the UV-light curable polymer composition used in step a) comprises a UV-light curable silicone resin composition. UV-light curable silicone resin composition preferably include high temperature vulcanizing silicone rubber (HTV-SR) compositions and room temperature vulcanizing silicone rubber (RTV- SR) compositions, including liquid silicone rubber (LSR) compositions. In the case of RTV-SR and LSR compositions, the curable silicone rubber composition is generally composed of two components, namely a first component comprising at least one polysiloxane having alkenyl groups, such as vinyl groups, incorporated in the molecule, and a second component comprising at least one polysiloxane having SiH-groups incorporated in the molecule. These two components are mixed, filled into a mould and cured in the presence of a catalyst, e.g. a UV sensitive cross-linking catalyst. The UV- curable polymer composition may further contain fillers, sensitizers and/or photoinitiators such as compounds derived from anthracene, xanthonone, anthrachinone. Such compounds and their use as sensitizers and/or photoinitiators are known in the art and are commercially available.

[0042] According to an aspect, in step b), pressure (post-pressure) is applied to the liquid UV-light curable polymer composition in the mold in order to eliminate trapped air bubbles. This is achieved by increasing the default filling pressure in the filling hose by factor 1.5 to 3.0. This leads to nearly bubble free electrical parts produced by the claimed mould.

[0043] According to an aspect, in step c), no heating is applied. According to a preferred aspect, step c) is performed using at least one UV-light source. Alternatively, step c) is performed using at least one light source in the infrared or microwave range. As a light source for curing with UV-light, any light source can be used. Such UV-light sources are commercially available. The wavelength generally is within the range of 180 nm to 700 nm, preferably within the range of 190 nm to 500 nm, preferably within the range of 300 nm to 400 nm, and preferably at about 360 nm to 400 nm. UV-light sources to produce UV-light, which can be used according to the present invention, are for example xenon lamps, mercury lamps and mercury lamps doped with iron or gallium, black-light lamps, excimer lasers and UV-LED lamps. The UV-light source may be provided for example by an arcing UV-lamp, or by a microwave powered UV-lamp or by an LED UV-lamp. The major advantage of LED UV-lamp over the two other types of UV-lamps is the fact that an LED UV-lamp irradiates only within a narrow wavelength band of about 10-30nm which can be optimized for the used UV-sensitive cross-linking catalyst. Additionally, an LED UV- lamp does not emit radiation in the infrared range. In this way, a significantly lower amount of heat is generated during UV-irradiation. Therefore, LED UV-lamps are preferred to work with transparent (organic) moulds.

[0044] Preferred is a light source based on the UV-LED technique, particularly in the form of the Semiconductor Light Matrix (SLM), as closed packed LEDs. Such a light source is simple to install, is safe to use and energy efficient, and has a long service life with practically no maintenance costs. UV-LED sources further have a high UV-light intensity and give good curing results, for example when comparing cure depth versus distance of the UV-light source and irradiation time, for UV-curing UV-LSR compositions. UV-LED sources generally give better results than conventional halogen UV-sources, as the UV-intensity of UV-LED sources is generally higher than the UV- intensity of conventional halogen UV-sources. An example for a commercially available UV-lamp is the Phoseon water cooled UV-LED RX StarFire Max, with wavelength of 365 nm and 395 nm with a stated output of 2 W/cm 2 or 4 W/cm 2. Still, according to a preferred aspect, the UV-light sources fit with the mould transparency and activation wavelength of the resin. Preferred UV-light sources used in step c) are arcing UV-lamps, microwave powered UV-lamps or LED UV-lamps.

[0045] According to an aspect, in step c), the mould and/or the UV-light source rotate. For instance, the mould can rotate around its symmetrical axis. The UV-light source can rotate in x-, y- and z-direction. Preferably, the UV-light source moves around the mould in a specific distance thereto. This distance is usually in the range of 1 cm to 5 cm, preferably 2 cm to 4 cm. In principle, the distance between the mould and the UV-light source depends on the geometry of the mould and the available setup for curing. Also, it depends on how warm the mould gets by the emitted IR radiation of the UV-source. If this radiation becomes too hot, the mold can be damaged. Generally, the shorter the distance, the stronger the UV energy going into the material to be cured.

[0046] A possible setup indicating the mobility of both the mould and the UV-light source is shown in Figure 3, where the UV-light source is movable along x-, y- and z- direction while the mould (not shown) turns around its symmetrical axis. The rotation of the mould is indicated by the rotation arrow around the device which is produced by the mould according to the present invention.

[0047] According to a further aspect step d), i.e. removing the UV-cured polymer composition from the mould, comprises the step of opening the mould. Preferably opening is carried out by a pneumatic system. This leads to the beneficial effect that the mould is not damaged and can be reused for several times.

[0048] According to a further embodiment, the present invention refers to the use of a mould according to the present invention to over mould electrical devices for low-, medium- and high voltage components with insulating material. According to the present invention, the expression "over mould" means embedding any kind of "core" with the UV-light curable polymer composition. The "core" can contain any electric or mechanical functional device or a mechanical reinforcement, such as a rod or hollow cylinder. Preferably, the insulating material is the UV-light curable polymer composition as defined in the present invention. Further, the present invention refers to the use of a mould according to the present invention to produce an electrical device as described above.

[0049] The present invention shall be described in more detail in the following Examples.

EXAMPLES

[0050] In the following paragraph, the method for manufacturing a mould for moulding an electrical device from UV-light curable polymer composition is described step by step and in chronological order.

[0051] Manufacture of full scale positive model

[0052] To manufacture the UV-light transparent mould, a positive model which is representing the shape of the final device, is produced, e.g. the final shape of a silicone embedded vacuum interrupter or the fuse cut-out insulator. This model could be produced by milling from a metal block (steel, aluminium). However, the milling from a solid metal block is time consuming and costly. Therefore, the full scale model is produced by the following established technologies, i.e. three dimensional printing, milling from wood, milling from special polymer block material (e.g. PU-styling-plate). Alternatively, an already existing prototype of the final device can be used as the positive model too.

[0053] All these technologies enable cost effective and fast production of a full scale model. When required, the surface quality can be further improved by applying a finishing by varnish spraying on the top.

[0054] Manufacture of UV-light transparent mould [0055] The positive model is then treated with an anti-sticking agent and put into a container which is open on the top (see Figure 2). In this example, the container is made by PTFE material. However, the container can also be made by other anti-sicking material. In this example, the cross-section of the container is rectangular.

[0056] After that, a UV-light transparent polymer resin is poured into the container until the whole positive model is embedded. Preferably, a room temperature curing resin, e.g. a UV-light transparent PUR resin is used so as to avoid thermal shrinkage during the cross-linking process of the resin. However, also UV-light transparent epoxy resins, amine or anhydride cured, or UV-light transparent cycloaliphatic epoxy resin, cationic cured can be used.

[0057] After curing, and removing of the positive, a ready to be used, UV-light transparent mould is achieved. The only thing to be supplemented on the mould is a connection for attaching an injection hose. This is achieved by milling a suitable tubular opening with the desired dimensions.

[0058] As an additional feature, the mould can be equipped with light guides that are directly casted into the mould. The light guides can consist for example glass fibre optics or light scattering Plexiglas Endlighten from Evonik.

[0059] Moulding of an electrical device

[0060] The described mould can be used as a commercial 2-part (or multiple part)- metal mould for moulding any kind of electrical device with a UV-light curing composition, preferably a UV-light curing silicone resin. This can happen by employing traditional APG-equipment as used for epoxy or silicone injection process. However, since the curing does not need any heating, there will be no or only minor thermally induced expansion forces that have to be compensated. Therefore also simpler and less costly equipment can be used, that does not need high clamping forces for pressure compensation, e.g. quick release, thread insert (embedded in negative epoxy mould) and screw, bar clamp.

[0061] After the injection of the UV-light curing composition, a post-pressure can be applied in order to eliminate trapped air bubbles. Then, the composition can be cured, using any kind of UV-light sources that fit with the mould transparency- and activation wavelength of the composition to be cured. In the present example, an LED UV-lamp was used. However, also other types of lamps can be used such as microwave powered UV- lamp or arcing lamp.

[0062] The lamps can be installed to fit best with the given mould geometry, and, if technical possible, the mould or lamp can be rotated around. Embedded light guides, as described above, can be used to guide the UV-light also to shaded areas.

[0063] After curing, the mould can be opened easily by a pneumatic system, without damaging the mould so that it can be used numerous times.

[0064] Results

[0065] The moulding method according to the present invention stands out with superior properties, and leads to moulds which are particularly useful to produce electrical devices for low-, medium- and high voltage components with insulating material. In comparison with the known methods of manufacturing UV-light transparent moulds and moulding thereby electrical devices with UV-light curing compositions, the method for manufacturing a mould for moulding UV-light curable polymer composition according to the present invention results in UV-light transparency moulds having high geometrical precision, similar to metal moulds. Further, the claimed method produced is simple, cost-effective and is open for various manufacturing methods to make the negative shape of the mould. Additionally, the mould according to the present invention is mechanical stable, exhibits superior endurance and is suitable for polymer injection under pressure. Further, in the manufacture of the inventive mould into the final shape, there is no need of any post machining. Still further, demoulding of cast part is very simple since the mould can be fixed on a pneumatic demoulding tool. The cast parts have only small flashes (mould lines) which is comparable to APG technology.

[0066] Advantageously, a post-pressure can be applied after the injection process to eliminate catch air bubbles from the composition. This leads to nearly bubble free electrical parts produced by the claimed mould. Moreover, due to the high stability of the claimed mould, also high viscose material can be used, allowing also the adding of fillers.

Claims

WHAT IS CLAIMED IS:

1. Method for manufacturing a mould for moulding an electrical device from an electromagnetic radiation curable polymer composition, comprising the steps of

i) providing a positive model for the electrical device,

ii) placing the positive model in a container,

iii) adding an electromagnetic radiation transparent polymer resin to the container,

iv) curing the electromagnetic radiation transparent polymer resin,

v) removing the positive model from the cured electromagnetic radiation transparent polymer resin, and

vi) providing a connection for attaching an injection hose.

2. Method according to claim 1, wherein the electromagnetic radiation curable polymer composition is selected from the group consisting of UV-light curable polymer composition, IR-light curable polymer composition and microwave curable polymer composition.

3. Method according to claim 1 or 2, wherein the electromagnetic radiation transparent polymer resin is selected from the group consisting of UV-light transparent polymer resin, IR-light transparent polymer resin and microwave transparent polymer resin.

4. Method according to any one of the preceding claims, wherein step i) comprises the step of producing the positive model by milling from a three dimensional block or by three dimensional printing.

5. Method according to claim 4, wherein the three dimensional block is selected from the group consisting of a metal block, wood block and a polymer block.

6. Method according to any one of claims 1 to 3, wherein step i) comprises the step of providing an already existing prototype to be used as positive model.

7. Method according to any one of the preceding claims, wherein step i) further comprises a step of applying a finishing to the positive model, wherein applying a finishing is preferably carried out by varnish spraying on the top of the positive model.

8. Method according to any one of the preceding claims, wherein step i) further comprises the step of treating the positive model with an anti-sticking agent.

9. Method according to claim 8, wherein the anti-sticking agent is selected from the group consisting of silicone release agents, fluorinated anti-sticking agents and natural greases.

10. Method according to any one of the preceding claims, wherein the container in step ii) is made of anti-sticking material, preferably of fluoropolymers or non-polar hydrocarbon based polymers.

11. Method according to any one of the preceding claims, wherein step iii) comprises pouring an electromagnetic radiation transparent polymer resin into the container until the whole positive model is embedded.

12. Method according to claim 3, wherein the electromagnetic radiation transparent polymer resin is a UV-light transparent polymer resin selected from the group consisting of UV-light transparent polyurethane (PUR) resin, UV-light transparent epoxy resin and UV-light transparent vinyl ester resin.

13. Method according to any one of the preceding claims, wherein step vi) comprises milling a tubular opening into the cured electromagnetic radiation transparent polymer resin.

14. Mould for moulding electromagnetic radiation curable polymer compositions, comprising an electromagnetic radiation transparent polymer resin which is curable at room temperature.

15. Mould according to claim 14, wherein the electromagnetic radiation transparent polymer resin is a UV-light transparent polymer resin selected from the group consisting of UV-light transparent polyurethane (PUR) resin, UV-light transparent epoxy resin and UV-light transparent vinyl ester resin.

16. Mould producible by a method according to claims 1-13.

17. Process for producing an electrical device, comprising the steps of a) injecting an electromagnetic radiation curable polymer composition to a mould as defined in anyone of claims 14 to 16,

b) applying pressure,

c) curing the electromagnetic radiation curable polymer composition with electromagnetic radiation to obtain an electromagnetic radiation cured polymer composition,

d) removing the electromagnetic radiation cured polymer composition from the mould.

18. Process according to claim 17, wherein in step c), no heating is applied.

19. Process according to claims 17 and 18, further comprising the step of manufacturing the mould as defined in a method according to claims 1 to 13.

20. Use of a mould according to anyone of claims 14 to 16 to over mould electrical devices for low-, medium- and high voltage components with insulating material.