WO2017024531A1 - Pressboard laminate, and electrical device comprising the same - Google Patents

Pressboard laminate, and electrical device comprising the same Download PDF

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Publication number
WO2017024531A1
WO2017024531A1 PCT/CN2015/086674 CN2015086674W WO2017024531A1 WO 2017024531 A1 WO2017024531 A1 WO 2017024531A1 CN 2015086674 W CN2015086674 W CN 2015086674W WO 2017024531 A1 WO2017024531 A1 WO 2017024531A1
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WO
WIPO (PCT)
Prior art keywords
electrically insulating
pressboards
hot melt
pressboard
melt adhesive
Prior art date
Application number
PCT/CN2015/086674
Other languages
French (fr)
Inventor
Yang Wang
Jens Rocks
Jiansheng Chen
Lars Schmidt
Elson MONTIBON
Original Assignee
Abb Schweiz Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Schweiz Ag filed Critical Abb Schweiz Ag
Priority to PCT/CN2015/086674 priority Critical patent/WO2017024531A1/en
Publication of WO2017024531A1 publication Critical patent/WO2017024531A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/48—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials
    • H01B3/52—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials wood; paper; press board
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
    • B27N3/04—Manufacture of substantially flat articles, e.g. boards, from particles or fibres from fibres

Definitions

  • the present invention relates to an electrically insulating pressboard laminate comprising a hot melt adhesive film with one or more through holes, and a method for manufacturing the electrically insulating pressboard laminate.
  • the present invention also relates to the use of the electrically insulating pressboard laminate in an electrical device for insulation.
  • the present invention further relates to an electrical device comprising the electrically insulating pressboard laminate, and a method for manufacturing the electrical device.
  • Electrically insulating pressboard laminates have an important role in electrical devices, such as transformers, generators, motors, instrument transformers, capacitors, and so on.
  • electrically insulating pressboard laminates There are two conventional solutions to make an electrically insulating pressboard laminate. One is to bond adjacent pressboards with polyester glue. The other one is to bond adjacent pressboards with water-based casein glue. It has been found that the polyester glue method can provide high mechanical strength but moderate insulation performance, and the casein glue method is good at insulation performance but weak at mechanical strength.
  • the present invention relates to an electrically insulating pressboard laminate, comprising at least two electrically insulating pressboards laminated on each other, and a hot melt adhesive film with one or more through holes, wherein the hot melt adhesive film is arranged between at least two adjacent pressboards of the at least two electrically insulating pressboards, and wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50% of the surface.
  • the present invention relates to a method for manufacturing an electrically insulating pressboard laminate, comprising the steps of
  • step d) cooling and pressing the laminated pressboards obtained from step c) to bond the at least two adjacent pressboards together, thereby providing the electrically insulating pressboard laminate.
  • the present invention relates to the use of the electrically insulating pressboard laminate according to the first aspect of the present invention in an electrical device for insulation.
  • the present invention relates to an electrical device comprising the electrically insulating pressboard laminate according to the first aspect of the present invention.
  • the present invention relates to a method for manufacturing an electrical device, comprising the steps of manufacturing an electrically insulating pressboard laminate by the method according to the second aspect of the present invention and incorporating the electrically insulating pressboard laminate into the electrical device.
  • the hot melt adhesive film with one or more through holes as a bonding layer to provide an electrically insulating pressboard laminate, at least one or more of the following advantages can be achieved:
  • the manufacturing process is simplified due to the use of a pre-shaped hot melt adhesive film as a bonding layer, as compared with the conventional process by applying the polyester glue or water-based casein glue;
  • the hot melt adhesive film has a reduced moisture content, especially as compared with the water-based casein glue
  • the terms ′′about′′ and ′′approximately′′ denote an interval of accuracy that a person skilled in the art will understand to still ensure the technical effect of the feature in question.
  • the term typically indicates a deviation from the indicated numerical value of ⁇ 20 %, preferably ⁇ 15 %, more preferably ⁇ 10 %, and even more preferably ⁇ 5 % or even ⁇ 1 %.
  • the term ′′comprising′′ is not limiting.
  • the term ′′consisting of′′ is considered to be a preferred embodiment of the term ′′comprising′′ . If hereinafter a group is defined to comprise at least a certain number of embodiments, this is meant to also encompass a group which preferably consists of these embodiments only.
  • the term “electrically insulating pressboard” refers to any electrically insulating material in the form of a sheet or a board, whether laminated or unlaminated.
  • the electrically insulating pressboard may be made from cellulose and/or other polymers including but not limited to polyamide, polyester, polyolefin, acrylic, polyacrylonitrile, polyphenylene sulfide, polysulfonamide, and any combination thereof.
  • the electrically insulating pressboard may be made from cellulose pulp, polyamide fibers, polyester fibers, polyolefin fibers, acrylic fibers, polyacrylonitrile fibers, polyphenylene sulfide fibers, polysulfonamide fibers, or any combination thereof.
  • Figeholm and Pucaro from ABB company are typical commercially available cellulose electrically insulating pressboards.
  • Nomex from Dupont and Thermal shield from 3M are typical commercially available polymeric electrically insulating pressboards.
  • the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50%, at most 40%, at most 30%, at most 25%, at most 20%, at most 15%, or even at most 10% of the surface.
  • the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at least 0.5%, at least 1%, at least 2%, at least 3%, at least 4%, or even at least 5% of the surface.
  • the one or more through holes take up 1% to 20% of the surface of the hot melt adhesive film. In another specific embodiment, the one or more through holes take up 2% to 15% of the surface of the hot melt adhesive film. These ranges would provide the best balance of the mechanical strength and the insulation performance of the resulting laminate.
  • the one or more through holes may have various cross sectional shapes.
  • the one or more through holes are each independently of a cross sectional shape selected from circle, square, rectangle, triangle, trapezoid, polygon, irregular shape and combinations thereof.
  • the one or more through holes are each independently of a cross sectional shape selected from circle, square, rectangle and triangle, especially from a viewpoint of facilitating the production and/or ensuring the even distribution of the through holes.
  • the cross-sectional area of the one or more through holes may depend on the size of the pressboard laminate or the hot melt adhesive film.
  • the one or more through holes may each independently have a cross-sectional area of at most 10000mm 2 , 8000mm 2 , 6000mm 2 , 5000mm 2 , 4000mm 2 , 3000mm 2 , 2000mm 2 , 1000mm 2 , 500mm 2 , or even 100mm 2 .
  • the one or more through holes may each independently have a cross-sectional area of at least 0.05mm 2 , 0.1mm 2 , 0.5mm 2 , 0.8mm 2 , 1mm 2 , 5mm 2 , 10mm 2 , 20mm 2 , 50mm 2 , or even 80mm 2 .
  • the one or more through holes each independently has a cross-sectional area of 0.05mm 2 to 10000mm 2 .
  • the one or more through holes each independently has a cross-sectional area of 0.1mm 2 to 5000mm 2 .
  • the one or more through holes each independently has a cross-sectional area of 1mm 2 to 1000mm 2 .
  • the one or more through holes are distributed evenly along the surface of hot melt adhesive film to provide the resulting electrically insulating pressboard laminate with an even bonding strength, mechanical strength or dielectric strength along the bonding surface of adjacent pressboards.
  • the one or more through holes may be distributed in a certain pattern along the surface of hot melt adhesive film to provide the resulting electrically insulating pressboard laminate with a desired distribution of the bonding strength, mechanical strength or dielectric strength along the bonding surface of adjacent pressboards.
  • the one or more through holes may be distributed randomly or irregularly along the surface of hot melt adhesive film, provided that no significant adverse impact is exerted on the hot melt adhesive film or the electrically insulating pressboard laminate comprising the same.
  • the thickness of the hot melt adhesive film may vary with the area of the surface of the hot melt adhesive film and/or with the cross-sectional area of the one or more through holes, so as to provide an efficient bonding.
  • the hot melt adhesive film may have a thickness of at most 800 ⁇ m, 500 ⁇ m, 300 ⁇ m, 200 ⁇ m, 150 ⁇ m, or even 100 ⁇ m.
  • the hot melt adhesive film may have a thickness of at least 0.1 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 10 ⁇ m, 50 ⁇ m, or even 80 ⁇ m.
  • the hot melt adhesive film has a thickness of 0.1-500 ⁇ m. In another specific embodiment, the hot melt adhesive film has a thickness of 1-200 ⁇ m. In a further specific embodiment, the hot melt adhesive film has a thickness of 50-150 ⁇ m.
  • the hot melt adhesive film may be made from any material which is suitable for forming a hot melt adhesive film and for use in the desired applications.
  • the materials which have good insulation oil compatibility and heat resistance may be preferred.
  • the hot melt adhesive film is made from a material selected from the group consisting of polyesters, polyether sulfones, polyamides, polyethylene-vinyl acetates, thermoplastic polyurethanes, reactive or non-reactive polyurethanes, styrene-butadiene-styrene copolymers, polyolefins, hot melt silicones, polyvinyl acetals, polyvinyl alcohols, ethylene-acrylate copolymers, polyvinyl acetates, acrylic acid polymers, epoxy resins, butyl rubbers, phenolics, starches, and copolymers or blends thereof.
  • the hot melt adhesive film is made from a material selected from the group consisting of polyether sulfones, thermoplastic polyurethanes, polyethylene terephthalate, polyamides, and combinations thereof.
  • step d) cooling and pressing the laminated pressboards obtained from step c) to bond the at least two adjacent pressboards together, thereby providing the electrically insulating pressboard laminate.
  • step c) The purpose of step c) is to melt the hot melt adhesive film so as to provide a melt of the hot melt adhesive film which can adhere to the surfaces of the adjacent pressboards contacting the melt of the hot melt adhesive film. Therefore, the temperature in step c) should be higher than the melt point of the hot melt adhesive film. From an economical viewpoint, the temperature in step c) may be 1-100°C, 5-50°C or 10-30°C higher than the melt point of the hot melt adhesive film. According to an embodiment of the present invention, step c) comprises heating the laminated pressboards to a temperature of 50-250°C, 70-200°C, 90-180°C, or even 100-150°C. The temperature in step c) may be raised to the desired temperature in one step, or in successive steps.
  • step c) comprises heating the laminated pressboards to a temperature of 50-250°C in one step or in two steps.
  • step c) may comprise heating the laminated pressboards to a temperature ranging from 50°C to 250°C in one step and this temperature may be maintained for a desired period till the hot melt adhesive film is completely melt.
  • step c) may comprise heating the laminated pressboards to a temperature ranging from 50°C to 100°C, for example, 80°C, and then heating to a temperature ranging from 100°C to 250°C, for example, 120°C or 150°C, to melt the hot melt adhesive film thoroughly.
  • the specific temperature or temperature combination may depend on the property of the hot melt adhesive film, and aims at enabling the hot melt adhesive film to efficiently adhere to the surfaces of the adjacent pressboards which contact the melt of the hot melt adhesive film.
  • step c) of the present method may be conducted at a pressure of no more than 50 MPa, 40 MPa, 30 MPa, 20 MPa, or even 10 MPa.
  • step c) of the present method may be conducted at a pressure of no less than 0.1 MPa, 0.5 MPa, 1 MPa, 4 MPa, or even 8 MPa.
  • step c) is conducted at a pressure of 0.1-50 MPa, 0.5-30 MPa, 1-10 MPa, or 2-6 MPa.
  • step c) of the present method may last no more than 240 mins, 200 mins, 150 mins, 100 mins, 60 mins, or 30 mins. According to an embodiment of the present invention, step c) of the present method may last no less than 1 mins, 5 mins, 10 mins, 15 mins, 20 mins, or 25 mins. In a specific embodiment, step c) lasts 1-240mins, 5-60 mins, or 10-30 mins.
  • step d) The purpose of step d) is to cool and solidify the melt of the hot melt adhesive film so as to bond the adjacent pressboards which sandwich the hot melt adhesive film therebetween together. Therefore, the temperature in step d) should be lower than the melt point of the hot melt adhesive film.
  • step d) comprises cooling the laminated pressboards obtained from step c) to less than 50°C, 40°C, 30°C, 20°C, or even 10°C.
  • step d) of the present method may be conducted at a pressure of no more than 50 MPa, 40 MPa, 30 MPa, 20 MPa, or even 10 MPa.
  • step d) of the present method may be conducted at a pressure of no less than 0.1 MPa, 0.5 MPa, 1 MPa, 4 MPa, or even 8 MPa.
  • step d) is conducted at a pressure of 0.1-50 MPa, 0.5-30 MPa, 1-10 MPa, or 2-6 MPa.
  • step d) of the present method may last no more than 60 mins, 50 mins, 40 mins, 30 mins, 20 mins, or 10 mins. According to an embodiment of the present invention, step d) of the present method may last no less than 1 mins, 2 mins, 3 mins, 5 mins, 7 mins, or 8 mins. In a specific embodiment, step d) lasts 5-60 mins, 8-30 mins or 10-20 mins.
  • the method of the present invention may be practiced in combination with a conventional bonding technology in the art, such as the polyester glue method and the water-based casein glue method as discussed above.
  • a conventional bonding technology such as the polyester glue method and the water-based casein glue method as discussed above.
  • at least another two adjacent pressboards are bonded together in a manner other than via a hot melt adhesive film.
  • the electrically insulating pressboard laminate comprises at least three electrically insulating pressboards laminated on each other, which can be named as the first pressboard, the second pressboard, the third pressboard and so on from the top to the bottom, wherein the first pressboard and the second pressboard may be bonded together via a hot melt adhesive film according to the present invention, and the second pressboards and the third pressboard may be bonded together via a conventional polyester glue or water-based casein glue.
  • Those skilled in the art could determine the best mode of practicing the present invention, whether alone or in combination with other bonding technology, so as to maximize the benefit of the present invention or meet the specific requirement under certain conditions.
  • an electrical device comprising the electrically insulating pressboard laminate according to the present invention.
  • the electrical device may be selected from a transformer, a generator, a motor, an instrument transformer, a capacitor, a switchgear, and combinations thereof.
  • the electrically insulating pressboard laminate may be in the form of a spacer, barrier, strip or press ring.
  • the electrical device is an oil filled transformer.
  • the machine direction (MD) of the pressboards or laminates was determined prior to machining the pressboards or laminates to smaller sizes for bonding and performance evaluation. During the machining process, the length direction is kept along the MD direction. Before the bonding process, all the pressboards or laminates were dried according to IEC 60763-2. Two pressboards were bonded by a hot melt adhesive film or casein glue to provide a pressboard laminate. After the bonding was conducted, samples were left for 24 h in an ambient condition before subsequent tests.
  • the performance of the pressboard laminates obtained was evaluated in terms of shear strength, flexural strength, dielectric strength, and oil absorbance.
  • the shear strength test was conducted according to ISO 4587 at a shear rate of 5 mm/min.
  • the flexural strength test was conducted according to ISO 178, by a three-point bending test at a flexural rate of 5 mm/min.
  • the dielectric strength test was conducted according to IEC 60243 by AC power with a voltage ramping speed of 0.5 kV/s.
  • the oil absorbance test was conducted according to IEC 60763.
  • the oil used was 45#transformer oil.
  • Two cellulose pressboards were bonded with various types of hot melt adhesive films without through holes by the following procedures: sandwiching a hot melt adhesive film between two cellulose pressboards to provide laminated pressboards, heating and pressing the laminated pressboards at a heating temperature and a heat pressing pressure for a heat pressing time as shown in Table 1 to melt the hot melt adhesive film; and then cooling and pressing the laminated pressboards at 25°C at 2 MPa for 20 min to fix the final sample.
  • the pressboard laminates obtained by the present process also exhibit good and balanced mechanical property and dielectric property, as shown in Table 4.
  • Shear test is employed to evaluate the bonding strength of the adhesive film. It can be seen that all the pressboard laminates obtained according to the present invention show higher or equivalent shear strength than those obtained by the conventional method of using water-based casein glue.
  • Dielectric strength shows the insulation performance of the obtained pressboard laminates. It can be seen from Table 4 that all the pressboard laminates obtained according to the present invention show higher dielectric strength than those obtained by the conventional method of using water-based casein glue.
  • the present invention makes it possible to provide electrically insulating pressboard laminates with improved and balanced mechanical property and insulation performance.

Abstract

An electrically insulating pressboard laminate comprises at least two electrically insulating pressboards laminated on each other and a hot melt adhesive film with one or more through holes. The hot melt adhesive film is arranged between at least two adjacent pressboards of the at least two electrically insulating pressboards. The hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％of the surface.

Description

PRESSBOARD LAMINATE， AND ELECTRICAL DEVICE COMPRISING THE SAME Field of the Invention
The present invention relates to an electrically insulating pressboard laminate comprising a hot melt adhesive film with one or more through holes， and a method for manufacturing the electrically insulating pressboard laminate. The present invention also relates to the use of the electrically insulating pressboard laminate in an electrical device for insulation. The present invention further relates to an electrical device comprising the electrically insulating pressboard laminate， and a method for manufacturing the electrical device.
Background of the Invention
Electrically insulating pressboard laminates have an important role in electrical devices， such as transformers， generators， motors， instrument transformers， capacitors， and so on. There are two conventional solutions to make an electrically insulating pressboard laminate. One is to bond adjacent pressboards with polyester glue. The other one is to bond adjacent pressboards with water-based casein glue. It has been found that the polyester glue method can provide high mechanical strength but moderate insulation performance， and the casein glue method is good at insulation performance but weak at mechanical strength.
Many attempts have been made to improve the property of the polyester glue or casein glue so as to improve and balance the mechanical strength and the insulation performance of the resulting pressboard laminate. However， few progresses have been reported to show a satisfactory improvement in terms of balancing the mechanical strength and the insulation performance till now.
Therefore， there is still a need to provide an electrically insulating pressboard laminate with improved and balanced mechanical strength and insulation performance.
Summary of the Invention
In a first aspect， the present invention relates to an electrically insulating pressboard laminate， comprising at least two electrically insulating pressboards laminated on each other， and a hot melt adhesive film with one or more through holes， wherein the hot  melt adhesive film is arranged between at least two adjacent pressboards of the at least two electrically insulating pressboards， and wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％ of the surface.
In a second aspect， the present invention relates to a method for manufacturing an electrically insulating pressboard laminate， comprising the steps of
a) providing at least two electrically insulating pressboards， and a hot melt adhesive film with one or more through holes， wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％ of the surface；
b) laminating the at least two electrically insulating pressboards on each other， with the hot melt adhesive film being sandwiched between at least two adjacent pressboards of the at least two electrically insulating pressboards， to provide laminated pressboards；
c) heating and pressing the laminated pressboards to melt the hot melt adhesive film；
d) cooling and pressing the laminated pressboards obtained from step c) to bond the at least two adjacent pressboards together， thereby providing the electrically insulating pressboard laminate.
In a third aspect， the present invention relates to the use of the electrically insulating pressboard laminate according to the first aspect of the present invention in an electrical device for insulation.
In a fourth aspect， the present invention relates to an electrical device comprising the electrically insulating pressboard laminate according to the first aspect of the present invention.
In a fifth aspect， the present invention relates to a method for manufacturing an electrical device， comprising the steps of manufacturing an electrically insulating pressboard laminate by the method according to the second aspect of the present invention and incorporating the electrically insulating pressboard laminate into the electrical device.
By using the hot melt adhesive film with one or more through holes as a bonding layer to provide an electrically insulating pressboard laminate， at least one or more of the following advantages can be achieved：
a) the manufacturing process is simplified due to the use of a pre-shaped hot melt  adhesive film as a bonding layer， as compared with the conventional process by applying the polyester glue or water-based casein glue；
b) the hot melt adhesive film has a reduced moisture content， especially as compared with the water-based casein glue；
c) the oil permeability is improved due to the presence of the through holes in the hot melt adhesive film； and
d) the resulting laminate shows both good mechanical strength and improved dielectric strength.
Detailed Description of the Invention
Although the present invention will be described with respect to particular embodiments， this description is not to be construed in a limiting sense.
As used in this specification and in the appended claims， the singular forms of ″a″ and ″an″ also include the respective plurals unless the context clearly dictates otherwise.
In the context of the present invention， the terms ″about″ and ″approximately″ denote an interval of accuracy that a person skilled in the art will understand to still ensure the technical effect of the feature in question. The term typically indicates a deviation from the indicated numerical value of ±20 ％， preferably ±15 ％， more preferably ±10 ％， and even more preferably ±5 ％ or even ±1 ％.
It is to be understood that the term ″comprising″ is not limiting. For the purposes of the present invention the term ″consisting of″ is considered to be a preferred embodiment of the term ″comprising″ . If hereinafter a group is defined to comprise at least a certain number of embodiments， this is meant to also encompass a group which preferably consists of these embodiments only.
Furthermore， the terms ″first″ ， ″second″ ， ″third″ or ″a) ″ ， ″b) ″ ， ″c) ″ ， ″d) ″ etc. and the like in the description and in the claims， are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
In case the terms ″first″ ， ″second″ ， ″third″ or ″ (a) ″ ， ″ (b) ″ ， ″ (c) ″ ， ″ (d) ″ etc. relate to steps of a method or use there is no time or time interval coherence between the steps， i.e. the steps may be carried out simultaneously or there may be time intervals of seconds， minutes， hours， days， weeks， months or even years between such steps， unless otherwise indicated in the application as set forth herein above or below.
It is an object of the present invention to provide a novel and improved electrically insulating pressboard laminate， comprising at least two electrically insulating pressboards laminated on each other， and a hot melt adhesive film with one or more through holes， wherein the hot melt adhesive film is arranged between at least two adjacent pressboards of the at least two electrically insulating pressboards， and wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％ of the surface.
As used herein， the term “electrically insulating pressboard” refers to any electrically insulating material in the form of a sheet or a board， whether laminated or unlaminated. The electrically insulating pressboard may be made from cellulose and/or other polymers including but not limited to polyamide， polyester， polyolefin， acrylic， polyacrylonitrile， polyphenylene sulfide， polysulfonamide， and any combination thereof. For example， the electrically insulating pressboard may be made from cellulose pulp， polyamide fibers， polyester fibers， polyolefin fibers， acrylic fibers， polyacrylonitrile fibers， polyphenylene sulfide fibers， polysulfonamide fibers， or any combination thereof. Figeholm and Pucaro from ABB company are typical commercially available cellulose electrically insulating pressboards. Nomex from Dupont and Thermal shield from 3M are typical commercially available polymeric electrically insulating pressboards.
Without being bound to any theory， it is believed that the mechanical strength would be adversely impacted if the through holes take too much of the surface of the hot melt adhesive film. Therefore， according to an embodiment of the present invention， the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％， at most 40％， at most 30％， at most 25％， at most 20％， at most 15％， or even at most 10％ of the surface.
It is also believed that the presence of the through holes is favorable to the oil permeability of the hot melt adhesive film and even the resulting laminate， and thereby would favorably impact the insulation performance of the resulting laminate. Therefore， according to an embodiment of the present invention， the hot melt adhesive  film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at least 0.5％， at least 1％， at least 2％， at least 3％， at least 4％， or even at least 5％ of the surface.
In a specific embodiment， the one or more through holes take up 1％ to 20％ of the surface of the hot melt adhesive film. In another specific embodiment， the one or more through holes take up 2％ to 15％ of the surface of the hot melt adhesive film. These ranges would provide the best balance of the mechanical strength and the insulation performance of the resulting laminate.
The one or more through holes may have various cross sectional shapes. According to an embodiment of the present invention， the one or more through holes are each independently of a cross sectional shape selected from circle， square， rectangle， triangle， trapezoid， polygon， irregular shape and combinations thereof. In a specific embodiment， the one or more through holes are each independently of a cross sectional shape selected from circle， square， rectangle and triangle， especially from a viewpoint of facilitating the production and/or ensuring the even distribution of the through holes.
As for the cross-sectional area of the one or more through holes， it may depend on the size of the pressboard laminate or the hot melt adhesive film. According to an embodiment of the present invention， the one or more through holes may each independently have a cross-sectional area of at most 10000mm2， 8000mm2， 6000mm2， 5000mm2， 4000mm2， 3000mm2， 2000mm2， 1000mm2， 500mm2， or even 100mm2. According to an embodiment of the present invention， the one or more through holes may each independently have a cross-sectional area of at least 0.05mm2， 0.1mm2， 0.5mm2， 0.8mm2， 1mm2， 5mm2， 10mm2， 20mm2， 50mm2， or even 80mm2. In a specific embodiment， the one or more through holes each independently has a cross-sectional area of 0.05mm2 to 10000mm2. In another specific embodiment， the one or more through holes each independently has a cross-sectional area of 0.1mm2 to 5000mm2. In a further specific embodiment， the one or more through holes each independently has a cross-sectional area of 1mm2 to 1000mm2.
Preferably， the one or more through holes are distributed evenly along the surface of hot melt adhesive film to provide the resulting electrically insulating pressboard laminate with an even bonding strength， mechanical strength or dielectric strength along the bonding surface of adjacent pressboards. Alternatively， the one or more  through holes may be distributed in a certain pattern along the surface of hot melt adhesive film to provide the resulting electrically insulating pressboard laminate with a desired distribution of the bonding strength， mechanical strength or dielectric strength along the bonding surface of adjacent pressboards. Further alternatively， the one or more through holes may be distributed randomly or irregularly along the surface of hot melt adhesive film， provided that no significant adverse impact is exerted on the hot melt adhesive film or the electrically insulating pressboard laminate comprising the same.
There is no specific restriction about the thickness of the hot melt adhesive film. The thickness of the hot melt adhesive film may vary with the area of the surface of the hot melt adhesive film and/or with the cross-sectional area of the one or more through holes， so as to provide an efficient bonding. According to an embodiment of the present invention， the hot melt adhesive film may have a thickness of at most 800 μm， 500 μm， 300 μm， 200 μm， 150 μm， or even 100 μm. According to an embodiment of the present invention， the hot melt adhesive film may have a thickness of at least 0.1 μm， 0.5 μm， 1 μm， 10 μm， 50 μm， or even 80 μm. In a specific embodiment， the hot melt adhesive film has a thickness of 0.1-500 μm. In another specific embodiment， the hot melt adhesive film has a thickness of 1-200 μm. In a further specific embodiment， the hot melt adhesive film has a thickness of 50-150 μm.
The hot melt adhesive film may be made from any material which is suitable for forming a hot melt adhesive film and for use in the desired applications. In the case that the resulting pressboard laminate works together with an insulation oil， the materials which have good insulation oil compatibility and heat resistance may be preferred. According to an embodiment of the present application， the hot melt adhesive film is made from a material selected from the group consisting of polyesters， polyether sulfones， polyamides， polyethylene-vinyl acetates， thermoplastic polyurethanes， reactive or non-reactive polyurethanes， styrene-butadiene-styrene copolymers， polyolefins， hot melt silicones， polyvinyl acetals， polyvinyl alcohols， ethylene-acrylate copolymers， polyvinyl acetates， acrylic acid polymers， epoxy resins， butyl rubbers， phenolics， starches， and copolymers or blends thereof. In a specific embodiment， the hot melt adhesive film is made from a material selected from the group consisting of polyether sulfones， thermoplastic polyurethanes， polyethylene terephthalate， polyamides， and combinations thereof.
It is another object of the present invention to provide a novel and improved method for  manufacturing an electrically insulating pressboard laminate， comprising the steps of
a) providing at least two electrically insulating pressboards， and a hot melt adhesive film with one or more through holes， wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％ of the surface；
b) laminating the at least two electrically insulating pressboards on each other， with the hot melt adhesive film being sandwiched between at least two adjacent pressboards of the at least two electrically insulating pressboards， to provide laminated pressboards；
c) heating and pressing the laminated pressboards to melt the hot melt adhesive film；
d) cooling and pressing the laminated pressboards obtained from step c) to bond the at least two adjacent pressboards together， thereby providing the electrically insulating pressboard laminate.
The purpose of step c) is to melt the hot melt adhesive film so as to provide a melt of the hot melt adhesive film which can adhere to the surfaces of the adjacent pressboards contacting the melt of the hot melt adhesive film. Therefore， the temperature in step c) should be higher than the melt point of the hot melt adhesive film. From an economical viewpoint， the temperature in step c) may be 1-100℃， 5-50℃ or 10-30℃ higher than the melt point of the hot melt adhesive film. According to an embodiment of the present invention， step c) comprises heating the laminated pressboards to a temperature of 50-250℃， 70-200℃， 90-180℃， or even 100-150℃. The temperature in step c) may be raised to the desired temperature in one step， or in successive steps. In a specific embodiment， step c) comprises heating the laminated pressboards to a temperature of 50-250℃ in one step or in two steps. For example， step c) may comprise heating the laminated pressboards to a temperature ranging from 50℃ to 250℃ in one step and this temperature may be maintained for a desired period till the hot melt adhesive film is completely melt. Alternatively， step c) may comprise heating the laminated pressboards to a temperature ranging from 50℃ to 100℃， for example， 80℃， and then heating to a temperature ranging from 100℃ to 250℃， for example， 120℃ or 150℃， to melt the hot melt adhesive film thoroughly. The specific temperature or temperature combination may depend on the property of the hot melt adhesive film， and aims at enabling the hot melt adhesive film to efficiently adhere to the surfaces of the adjacent pressboards which contact the melt of the hot melt adhesive film.
According to an embodiment of the present invention， step c) of the present method may be conducted at a pressure of no more than 50 MPa， 40 MPa， 30 MPa， 20 MPa， or  even 10 MPa. According to an embodiment of the present invention， step c) of the present method may be conducted at a pressure of no less than 0.1 MPa， 0.5 MPa， 1 MPa， 4 MPa， or even 8 MPa. In a specific embodiment， step c) is conducted at a pressure of 0.1-50 MPa， 0.5-30 MPa， 1-10 MPa， or 2-6 MPa.
According to an embodiment of the present invention， step c) of the present method may last no more than 240 mins， 200 mins， 150 mins， 100 mins， 60 mins， or 30 mins. According to an embodiment of the present invention， step c) of the present method may last no less than 1 mins， 5 mins， 10 mins， 15 mins， 20 mins， or 25 mins. In a specific embodiment， step c) lasts 1-240mins， 5-60 mins， or 10-30 mins.
The purpose of step d) is to cool and solidify the melt of the hot melt adhesive film so as to bond the adjacent pressboards which sandwich the hot melt adhesive film therebetween together. Therefore， the temperature in step d) should be lower than the melt point of the hot melt adhesive film. According to an embodiment of the present invention， step d) comprises cooling the laminated pressboards obtained from step c) to less than 50℃， 40℃， 30℃， 20℃， or even 10℃.
According to an embodiment of the present invention， step d) of the present method may be conducted at a pressure of no more than 50 MPa， 40 MPa， 30 MPa， 20 MPa， or even 10 MPa. According to an embodiment of the present invention， step d) of the present method may be conducted at a pressure of no less than 0.1 MPa， 0.5 MPa， 1 MPa， 4 MPa， or even 8 MPa. In a specific embodiment， step d) is conducted at a pressure of 0.1-50 MPa， 0.5-30 MPa， 1-10 MPa， or 2-6 MPa.
According to an embodiment of the present invention， step d) of the present method may last no more than 60 mins， 50 mins， 40 mins， 30 mins， 20 mins， or 10 mins. According to an embodiment of the present invention， step d) of the present method may last no less than 1 mins， 2 mins， 3 mins， 5 mins， 7 mins， or 8 mins. In a specific embodiment， step d) lasts 5-60 mins， 8-30 mins or 10-20 mins.
The method of the present invention may be practiced in combination with a conventional bonding technology in the art， such as the polyester glue method and the water-based casein glue method as discussed above. According to an embodiment of the present invention， at least another two adjacent pressboards are bonded together in a manner other than via a hot melt adhesive film.
For example， in a specific embodiment， the electrically insulating pressboard laminate comprises at least three electrically insulating pressboards laminated on each other， which can be named as the first pressboard， the second pressboard， the third pressboard and so on from the top to the bottom， wherein the first pressboard and the second pressboard may be bonded together via a hot melt adhesive film according to the present invention， and the second pressboards and the third pressboard may be bonded together via a conventional polyester glue or water-based casein glue. Those skilled in the art could determine the best mode of practicing the present invention， whether alone or in combination with other bonding technology， so as to maximize the benefit of the present invention or meet the specific requirement under certain conditions.
It is a further object of the present invention to provide the use of the electrically insulating pressboard laminate as described herein in an electrical device for insulation.
According to an embodiment of the present invention， an electrical device comprising the electrically insulating pressboard laminate according to the present invention is provided. The electrical device may be selected from a transformer， a generator， a motor， an instrument transformer， a capacitor， a switchgear， and combinations thereof. The electrically insulating pressboard laminate may be in the form of a spacer， barrier， strip or press ring. In a specific embodiment， the electrical device is an oil filled transformer.
It is also an object of the present invention to provide a method for manufacturing an electrical device， comprising the steps of manufacturing an electrically insulating pressboard laminate as described herein and incorporating the electrically insulating pressboard laminate into the electrical device.
Examples
The present invention will be further clarified by the following examples， which are intended to be purely exemplary of the invention. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention as disclosed herein.
Materials
The following materials were used in the examples.
Figure PCTCN2015086674-appb-000001
General procedure
The machine direction (MD) of the pressboards or laminates was determined prior to machining the pressboards or laminates to smaller sizes for bonding and performance evaluation. During the machining process， the length direction is kept along the MD direction. Before the bonding process， all the pressboards or laminates were dried according to IEC 60763-2. Two pressboards were bonded by a hot melt adhesive film or casein glue to provide a pressboard laminate. After the bonding was conducted， samples were left for 24 h in an ambient condition before subsequent tests.
Test methods
The performance of the pressboard laminates obtained was evaluated in terms of shear strength， flexural strength， dielectric strength， and oil absorbance.
The shear strength test was conducted according to ISO 4587 at a shear rate of 5 mm/min.
The flexural strength test was conducted according to ISO 178， by a three-point bending test at a flexural rate of 5 mm/min.
The dielectric strength test was conducted according to IEC 60243 by AC power with a voltage ramping speed of 0.5 kV/s.
The oil absorbance test was conducted according to IEC 60763. The oil used was 45#transformer oil.
Comparative Example 1
Two cellulose pressboards were bonded with casein glue by pressing to each other at 2 MPa at room temperature (about 25℃) for 3h to finish the bonding.
Comparative Example 2
Two Nomex pressboards were bonded with casein glue by pressing to each other at 2 MPa at room temperature (about 25℃) for 3h to finish the bonding.
Examples 1-4
Two cellulose pressboards were bonded with various types of hot melt adhesive films without through holes by the following procedures： sandwiching a hot melt adhesive film between two cellulose pressboards to provide laminated pressboards， heating and pressing the laminated pressboards at a heating temperature and a heat pressing pressure for a heat pressing time as shown in Table 1 to melt the hot melt adhesive film； and then cooling and pressing the laminated pressboards at 25℃ at 2 MPa for 20 min to fix the final sample.
Table 1. Hot Melt Adhesive Films and Corresponding Heat Pressing Conditions for Example 1-4
Figure PCTCN2015086674-appb-000002
Examples 5-14
Through holes were drilled in the hot melt adhesive films to provide a series of hot melt adhesive films with through holes， which were then used to bond two cellulose pressboards by following almost the same procedures as described for Examples 1-4. The details of the hot melt adhesive films with through holes and the corresponding heat pressing conditions， including the heating temperature， the heat pressing pressure and the heat pressing time， are shown in Table 2.
Table 2. Hot Melt Adhesive Films and Corresponding Heat Pressing Conditions for Example 5-14
Figure PCTCN2015086674-appb-000003
Examples 15-19
The same procedures as described for Examples 5-14 were followed， expect that the cellulose pressboards were replaced with Nomex pressboards. The details of the hot melt adhesive films with through holes and the corresponding heat pressing conditions， including the heating temperature， the heat pressing pressure and the heat pressing time， are shown in Table 3.
Table 3. Hot Melt Adhesive Films and Corresponding Heat Pressing Conditions for Example 15-19
Figure PCTCN2015086674-appb-000004
Test results
It can be seen that the whole process of the present invention can be finished in 35 min to 140min to provide a pressboard laminate， while the conventional processes (Comparative Fxamples 1 and 2) requires 3 hours. Therefore， it is a great advantage of the present invention to shorten the processing time and thereby improve the productivity.
The pressboard laminates obtained by the present process also exhibit good and balanced mechanical property and dielectric property， as shown in Table 4.
Table 4. Properties of the obtained pressboard laminates
Figure PCTCN2015086674-appb-000005
Figure PCTCN2015086674-appb-000006
Shear test is employed to evaluate the bonding strength of the adhesive film. It can be seen that all the pressboard laminates obtained according to the present invention show higher or equivalent shear strength than those obtained by the conventional method of using water-based casein glue.
In the case of transformer application， it is known that the load force is perpendicular to the pressboard plane-direction， so flexural property is also important in determining the lifetime of the pressboard laminate. It can be seen from Table 4 that all the pressboard laminates obtained according to the present invention show better or equivalent flexural strength than those obtained by the conventional method of using water-based casein glue.
Dielectric strength shows the insulation performance of the obtained pressboard laminates. It can be seen from Table 4 that all the pressboard laminates obtained according to the present invention show higher dielectric strength than those obtained by the conventional method of using water-based casein glue.
In the oil absorbance test， 24h oil absorbance rate for each of the examples was evaluated. It can be seen from Table 4 that the hole on adhesive film has positive effect on oil absorbance performance.
To sum up， as compared with the conventional casein glue method for manufacturing electrically insulating pressboard laminates， the present invention makes it possible to provide electrically insulating pressboard laminates with improved and balanced mechanical property and insulation performance.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention， and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Although claims have been formulated in this application to particular combinations of features， it should be understood that the scope of the present disclosure also includes any novel features or any novel combinations of features disclosed herein either explicitly or implicitly or any generalization thereof， whether or not it relates to the same invention as presently claimed in any claim. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of features during the prosecution of the present application or of any further application derived therefrom.

Claims (19)

  1. An electrically insulating pressboard laminate， comprising at least two electrically insulating pressboards laminated on each other， and a hot melt adhesive film with one or more through holes， wherein the hot melt adhesive film is arranged between at least two adjacent pressboards of the at least two electrically insulating pressboards， and wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％of the surface.
  2. The electrically insulating pressboard laminate according to claim 1， wherein one or more through holes take up 1％to 20％of the surface.
  3. The electrically insulating pressboard laminate according to claim 1 or 2， wherein the one or more through holes are each independently of a cross sectional shape selected from circle， square， rectangle， triangle， trapezoid， polygon， irregular shape and combinations thereof.
  4. The electrically insulating pressboard laminate according to any one of claims 1-3， wherein the one or more through holes each independently has a cross-sectional area of at most 10000mm2.
  5. The electrically insulating pressboard laminate according to any one of claims 1-4， wherein the hot melt adhesive film has a thickness of 0.1-500 μm.
  6. The electrically insulating pressboard laminate according to any one of claims 1-5， wherein the hot melt adhesive film is made from a material selected from the group consisting of polyesters， polyether sulfones， polyamides， polyethylene-vinyl acetates， thermoplastic polyurethanes， reactive or non-reactive polyurethanes， styrene-butadiene-styrene copolymers， polyolefins， hot melt silicones， polyvinyl acetals， polyvinyl alcohols， ethylene-acrylate copolymers， polyvinyl acetates， acrylic acid polymers， epoxy resins， butyl rubbers， phenolics， starches， and copolymers or blends thereof.
  7. The electrically insulating pressboard laminate according to any one of claims 1-6， wherein the hot melt adhesive film is made from a material selected from the group consisting of polyether sulfones， thermoplastic polyurethanes， polyethylene terephthalate， and polyamides.
  8. The electrically insulating pressboard laminate according to any one of claims 1-7， wherein the electrically insulating pressboard is made from cellulose， polyamide， polyester， polyolefin， acrylic， polyacrylonitrile， polyphenylene sulfide， polysulfonamide， or any combination thereof.
  9. A method for manufacturing an electrically insulating pressboard laminate， comprising the steps of
    a) providing at least two electrically insulating pressboards， and a hot melt adhesive film with one or more through holes， wherein the hot melt adhesive film has a surface to be adhered to the insulating pressboard and the one or more through holes take up at most 50％of the surface；
    b) laminating the at least two electrically insulating pressboards on each other， with the hot melt adhesive film being sandwiched between at least two adjacent pressboards of the at least two electrically insulating pressboards， to provide laminated pressboards；
    c) heating and pressing the laminated pressboards to melt the hot melt adhesive film；
    d) cooling and pressing the laminated pressboards obtained from step c) to bond the at least two adjacent pressboards together， thereby providing the electrically insulating pressboard laminate.
  10. The method according to claim 9， wherein step c) comprises heating the laminated pressboards to a temperature of 50-250℃ in one step or in two steps.
  11. The method according to claim 9 or 10， wherein step c) is conducted at a pressure of 0.1-50 MPa for 1-240 mins.
  12. The method according to any one of claims 9-11， wherein step d) comprises cooling the laminated pressboards obtained from step c) to less than 50℃.
  13. The method according to any one of claims 9-12， wherein step d) is conducted at a pressure of 0.1-50 MPa for 5-60 mins.
  14. The method according to any one of claims 9-13， wherein at least another two adjacent pressboards are bonded together in a manner other than via a hot melt adhesive film.
  15. The use of the electrically insulating pressboard laminate according to any one of  claims 1-8 in an electrical device for insulation.
  16. An electrical device comprising the electrically insulating pressboard laminate according to any one of claims 1-8.
  17. The electrical device of claim 16， wherein the electrical device is selected from a transformer， a generator， a motor， an instrument transformer， a capacitor， a switchgear， and combinations thereof.
  18. The electrical device of claim 16 or 17， wherein the electrically insulating pressboard laminate is in the form of a spacer， barrier， strip or press ring for insulation in a transformer.
  19. A method for manufacturing an electrical device， comprising the steps of manufacturing an electrically insulating pressboard laminate by the method according to any one of claims 9-14 and incorporating the electrically insulating pressboard laminate into the electrical device.
PCT/CN2015/086674 2015-08-11 2015-08-11 Pressboard laminate, and electrical device comprising the same WO2017024531A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108777283A (en) * 2018-05-31 2018-11-09 上海工程技术大学 A kind of high temperature resistant PSA/PAN/PSA composite lithium battery membranes and preparation method thereof
US20230121933A1 (en) * 2020-03-17 2023-04-20 Hitachi Energy Switzerland Ag Mfc in pressboards for hv devices

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JPS6048842B2 (en) * 1978-07-07 1985-10-29 昭和電線電纜株式会社 Laminated paper for electrical insulation
US4820570A (en) * 1982-03-19 1989-04-11 Fujikura Ltd. Laminated insulation
CN201122445Y (en) * 2007-10-23 2008-09-24 苏州巨峰绝缘材料有限公司 Three-layer insulation composite material
CN104066887A (en) * 2012-01-20 2014-09-24 Abb技术有限公司 Cellulose based electrically insulating material

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Publication number Priority date Publication date Assignee Title
JPS6048842B2 (en) * 1978-07-07 1985-10-29 昭和電線電纜株式会社 Laminated paper for electrical insulation
US4820570A (en) * 1982-03-19 1989-04-11 Fujikura Ltd. Laminated insulation
CN201122445Y (en) * 2007-10-23 2008-09-24 苏州巨峰绝缘材料有限公司 Three-layer insulation composite material
CN104066887A (en) * 2012-01-20 2014-09-24 Abb技术有限公司 Cellulose based electrically insulating material

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108777283A (en) * 2018-05-31 2018-11-09 上海工程技术大学 A kind of high temperature resistant PSA/PAN/PSA composite lithium battery membranes and preparation method thereof
US20230121933A1 (en) * 2020-03-17 2023-04-20 Hitachi Energy Switzerland Ag Mfc in pressboards for hv devices
US11769608B2 (en) * 2020-03-17 2023-09-26 Hitachi Energy Switzerland Ag MFC in pressboards for HV devices

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