WO2014131245A1

WO2014131245A1 - Electrically insulating composite material and electrical device comprising the same

Info

Publication number: WO2014131245A1
Application number: PCT/CN2013/075262
Authority: WO
Inventors: Jiansheng Chen; Chau-Hon HO; Jens Rocks; Sufeng Zhang; Lars Schmidt; Yong Feng; Delun MENG; Zhaoxia SUN
Original assignee: Abb Technology Ltd
Priority date: 2013-03-01
Filing date: 2013-05-07
Publication date: 2014-09-04
Also published as: EP2962313A1; US20150354144A1; EP2962313A4

Abstract

The present invention relates to an electrical device in the form of a paper or a pressboard, wherein the electrically insulating composite material is obtained through post-treating by electron beam irradiation treatment, gamma irradiation treatment or x-ray irradiation treatment.

Description

ELECTRICALLY INSULATING COMPOSITE MATERIAL AND

ELECTRICAL DEVICE COMPRISING THE SAME

Technical Field The present invention relates to an electrically insulating composite material in the form of a paper or a pressboard, wherein the electrically insulating composite material is obtained through post-treating by irradiation treatment.

Backgr ound

Insulation of oil-filled distribution and power transformers may be made from cellulose, polymer paper and pressboard. The cellulose papers or pressboards are mainly used in transformers with relatively lower thermal stability requirements, and polymer papers or pressboards are mainly for transformers with relatively higher thermal stability requirements. Nomex from Dupont and Thermal shield from 3M are typical commercially available polymer papers or pressboards. Generally speaking, cellulose papers or pressboards are more extensively used than polymer ones. The major reason is that the cost of cellulose paper and pressboard is much lower than those made of polymer. However, the use of cellulose papers or pressboards at high temperature is limited by the low thermal stability of cellulosic materials. On the other hand, it is unsatisfactory to use the polymer paper or pressboard due to its relatively high cost. Furthermore, for some uses, it is necessary that the paper or pressboard not only have a suitably high thermal stability, but also possess enhanced mechanical property, so that the paper or the pressboard can provide better electrical insulation performance.

In the past, many attempts have been made to improve the property of the papers or the pressboards and most of them are focused on the selecting of different polymers and different processing methods. Irradiation treatment, such as electron beam irradiation treatment, gamma irradiation treatment and x-ray irradiation treatment, is an effective method to increase the crosslinking density of some polymer materials, thus enhance the mechanical property of the polymers. Few works have been reported related to irradiation treatment in the application of electrically insulating paper or pressboard until now.

US 6 824 728 B2 relates to a process for crosslinking polyacrylate compositions, wherein, by selective irradiation of the pressure- sensitive adhesive composition with electron beams, the polymer is cured only in certain structures and, as a result, structured pressure- sensitive adhesive compositions can be prepared.

US 3 707 692 discloses a method of increasing the dimensional stability of cellulosic material by impregnating the cellulose with a composition including a cellulose swelling agent and a compound capable of crosslinking with the cellulose molecules. The crosslinking takes place at elevated temperatures in the absence of an acidic catalyst and the crosslinked cellulosic materials are useful as insulators in electrical apparatus.

There is still a need to provide an electrically insulating composite material in the form of a paper or a pressboard with improved performance, such as higher thermal stability and better mechanical property. Summary

According to the present invention, an electrically insulating composite material in the form of a paper or a pressboard is provided, wherein the electrically insulating composite material is obtained through post-treating by irradiation treatment.

One aspect of the present invention relates to an irradiation treatment for post-treating, wherein the irradiation treatment for post-treating is electron beam irradiation treatment, gamma irradiation treatment, x-ray irradiation treatment or combinations thereof. According to one embodiment of the present invention, the electron beam irradiation, gamma irradiation or x-ray irradiation is under ambient air atmosphere or with the injection of inert gas. According to another embodiment of the present invention, the dose for the electron beam irradiation, gamma irradiation or x-ray irradiation is from 30 kGy to 300kGy and preferably 50 kGy to 200 kGy.

According to another aspect of the present invention, it relates to an electrically insulating composite material, wherein the composite material is composed of fiber and fibrid. According to one embodiment of the present invention, the said fiber comprises at least one of the following fibers: polyethylene terephthalate fiber, polyethylene naphthalate fiber, polytrimethylene terephthalate fiber, polybutylene terephthalate fiber, polyacrylonitrile fiber, poly (metaphenylene isophthamide) fiber, poly(paraphenylene terephthalamide) fiber, polysulfonamide fiber, polyphenylene sulphide fiber, polyphenylene oxide fiber, polyethersulfone fiber, polyetheretherketone fiber, polyetherimide fiber, and cellulose fiber. According to another embodiment of the present invention, the said fibrid comprises at least one of the following fibrids: polyacrylonitrile fibrid, polyethylene terephthalate fibrid, polyethylene naphthalate fibrid, polytrimethylene terephthalate fibrid, polybutylene terephthalate fibrid, poly (metaphenylene isophthamide) fibrid, and polysulfonamide fibrid.

According to one embodiment of the present invention, the fiber in the electrically insulating composite material is present in an amount of 5 wt% to 95 wt% and the fibrid is present in an amount of 5 wt% to 95 wt%, base on the total weight of the electrically insulating composite material.

According to one embodiment of the present invention, the electrically insulating composite material is in the form of a paper or a pressboard.

Another aspect of the present invention relates to an electrical device comprising the above electrically insulating composite material, such as an electrical transformer or an electrical motor.

The inventors have found unexpectedly that, by post-treated with electron beam irradiation gamma irradiation or x-ray irradiation, it is possible to provide an electrical device, especially high voltage insulating device, with improved mechanical property and thermal stability. Specifically, the electrically insulation composite material displays significant different performance after such irradiation treatment. For example, for the electrically insulation composite material composed by polyacrylonitrile fibrid and polyethylene terephthalate fiber (Example 1), the 5% decomposition temperature is increased from 323 °C to 339 °C , the tensile strength is increased from about 100 MPa to about 115 MPa and the compressibility is lowered from 3.5% to 3.1% after electron beam irradiation treatment. Brief Description of the Drawings

Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic flow chart of an embodiment of a method according to the present invention.

Detailed Description

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Preferably, the pressboard according to the present invention has a thickness of higher than 0.9 mm. More preferably, the thickness of the pressboard is 1-12 mm, and most preferably 1-8 mm. A paper of the present invention has a thickness of less than 0.9 mm, preferably less than 0.8 mm, and more preferably is between 0.05 to 0.5 mm.

An important factor to impact the mechanical property and thermal stability of the polymer material is the crosslinking degree. Crosslinking is the term used to denote the reaction in which a large number of linear or branched macromolecules, which initially are still soluble, become linked together to form three-dimensional polymeric networks (crosslinked polymers, network polymers) which are insoluble and now only swellable. Crosslinking is possible as a result of the formation of covalent and noncovalent (coordinative, ionic physical, saltlike) bonds. Crosslinking can be carried out during the actual construction of the macromolecules and/or by reaction on performed (pre)polymers which generally contain functional groups.

Generally speaking, the crosslinking of the polymers can be initiated by heat or irradiation. Due to the relatively poor thermal stability of some electrically insulation composite material, irradiation treatment should be a better method to conduct the crosslinking. Irradiation treatments usually include ultraviolet light (UV) irradiation, electron beam (EB) irradiation, gamma irradiation and x-ray irradiation treatment. In particularly, UV crosslinking is a very simple process requiring only a simple coating used with a few low-pressure Hg lamps. UV crosslinking functions very well for polymer compositions with low film thickness. The EB, gamma irradiation and x-ray irradiation technologies are more expensive in terms of apparatus but tolerate the crosslinking of greater film thicknesses and faster web speeds.

One aspect of the present invention relates to an irradiation treatment for post-treating, wherein the irradiation treatment for post-treating is electron beam irradiation treatment, gamma irradiation treatment, x-ray irradiation treatment or combinations thereof. According to one embodiment of the present invention, the electron beam irradiation, gamma irradiation or x-ray irradiation is under ambient air atmosphere or with the injection of inert gas. It is believed that the post-treating by electron beam irradiation, gamma irradiation or x-ray irradiation could increases the crosslinking density in the electrically insulation composite material and also could induce the material degradation, with appropriate irradiation post treatment to balance the crosslinking reaction and degradation reaction, we can enhance the thermal stability and mechanical property of the electrically insulation composite material. According to the present invention, the thermal stability of the electrically insulation composite material is evaluated by 5% decomposition temperature, which is known to the skilled in the art and is commonly used in this field. For example, for the electrically insulation composite material composed by polyacrylonitrile fibrid and polyethylene terephthalate fiber (Example 1), the volume increase of the pressboard after EB irradiation is only 35%, much lower than the corresponding pressboard without EB irradiation (50%), indicating the increased crosslinking density. Furthermore, after such EB irradiation treatment, the 5% decomposition temperature of the pressboard is increased from 323 °C to 339 °C , the tensile strength of the pressboard is increased from about 100 MPa to about 115 MPa and the compressibility of the pressboard is lowered from 3.5% to 3.1%, implying the improved mechanical property.

According to another aspect of the present invention, it is related to an electrically insulating composite material, wherein the composite material is composed of fiber and fibrid. The fiber may be a polymer fiber. The polymer fiber for paper and pressboard preparation is a short fiber which is generally made of normal continuous fiber with regular diameter. The short polymer fiber could be treated by further beating to develop their sheetmaking properties. The said fibrid may be a polymer fibrid. The polymer fibrid, a type of fibrous particle used for binding, is with irregular shape and made from polymer solution.

According to one embodiment of the present invention, the said fiber comprises at least one of the following fibers: polyethylene terephthalate fiber, polyethylene naphthalate fiber, polytrimethylene terephthalate fiber, polybutylene terephthalate fiber, polyacrylonitrile fiber, poly (metaphenylene isophthamide) fiber, poly(paraphenylene terephthalamide) fiber, polysulfonamide fiber, polyphenylene sulphide fiber, polyphenylene oxide fiber, polyethersulfone fiber, polyetheretherketone fiber, polyetherimide fiber, cellulose fiber or the combinations thereof. According to one embodiment of the present invention, the said fibrid comprises at least one of the following fib rids: polyacrylonitrile fibrid, polyethylene terephthalate fibrid, polyethylene naphthalate fibrid, polytrimethylene terephthalate fibrid, polybutylene terephthalate fibrid, poly (metaphenylene isophthamide) fibrid, polysulfonamide fibrid, or combinations thereof.

According to one embodiment of the present invention, the fiber in the electrically insulating composite material is present in an amount of 5 wt to 95 wt and preferably 20 wt to 60 wt . According to another embodiment of the present invention, the fibrid is present in an amount of 5 wt to 95 wt , and preferably 40 wt to 80 wt , based on the total weight of the electrically insulating composite material.

After extensive research, the present inventors have found that specific dose under a temperature within a certain range achieves a great balance in producing an electrically insulating composite material without destruction degradation to the final material, which possesses unexpected comprehensive properties, such as mechanical strength and thermal stability. According to one embodiment of the present invention, the suitable dose for the electron beam irradiation, gamma irradiation and x-ray irradiation is from 30 kGy to 300 kGy. In order to achieve better crosslinking, the dose can be further optimized. According to some embodiments of the present invention, the dose for EB, gamma irradiation or x-ray irradiation is preferred to be 50 kGy to 200 kGy. Particularly, for the pressboard made from polyethylene terephthalate fibrid and polyethylene terephthalate fiber, the preferred dose for EB irradiation is about 200 kGy (Example 2). More particularly, for the pressboard made from polyacrylonitrile fibrid and cellulose fiber, the preferred dose for EB irradiation is about 100 kGy (Example 4). The composite material is electrically insulating and is suitable for use as insulation material in an electrical device. The composite material may be, for example, used as electrical insulation in an electrical device, such as in a power transformer, whereby the composite material may be a high voltage insulation material.

As mentioned above, the electrically insulating composite material may have especially beneficial electrically insulating properties in an oily environment. Thus, the electrically insulating composite material may be at least partly soaked in oil.

The present invention further provides an electrical device comprising the electrically insulating composite material according to the present invention. The electrical device may be any electrical device which comprises electrical insulation, e.g. an electrical transformer or a conductor of electricity or an electrical motor, which may especially benefit from the composite material, such as with improved mechanical properties, less time is needed for insulation height adjustment during transformer fabrication and the total insulation thickness can be reduced. Especially, the electrical device according to the present invention is an electrical transformer.

The electrically insulating composite material may be in the form of a paper, spacer, barrier, strip or press ring for insulation in or of an electrical device, such as a conductor of electricity, an electrical transformer. The electrically insulating composite material has electrically insulating properties which may be useful in any electrical device, such as for insulating an electricity conduit, but the electrically insulating composite material may be especially advantageous in an oily environment, such as in an electrical transformer. Specifically, the electrically insulating composite material may be used for making electrically insulating spacers in a transformer winding. An improved electrical device is obtained by using the electrically insulating composite material in accordance with the present invention. In particular, the electrically insulation composite material displays improved mechanical properties, such as an improved compressibility.

Fig 1 is a schematic flow chart of an embodiment of a method 1 which is the-state-of-the-art method for insulation paper and pressboard preparation. Fibrids are provided, see 2, and fibers are also provided, see 3. The fibrids and fibers are then mixed with each other, see 4. A paper press, multi-daylight hot press of the like, is then used for pressing the mixture to provide a pressboard or a presspaper or the like of the composite material discussed herein, see 5. The pressing also comprises heating, see 6, and drying the mixture, see 7, as well as pressing the mixture to the pressboard, see 8. The pressboard was then cooled, see 9. The cooled pressboard may then be cut into desired insulation parts, for example, for use in a transformer or any other electrical device. For instance, a spacer, barrier, strip or press ring for insulation of an electrical transformer can be produced from the composite material from this invention.

Examples An electrically insulation composite material in the form of a paper or a pressboard, which is first produced according to the-state-of-the-art method as shown in Fig 1, is obtained through post-treating by irradiation treatment. The properties of the electrically insulation composite material are tested according to the IEC (International Electrotechnical Commission) standard 60641-2. Example 1

A pressboard was made according to the process in Fig 1. The solid materials used in the making of this pressboard were 60 weight percent of polyacrylonitrile fibrid (Shanghai Labon Technical Fiber Co., Ltd)and 40 weight percent of polyethylene terephthalate fiber (Woongjin Chemical Co., Ltd). This pressboard had a basic weight of 2420 g/m , a thickness of 2 mm and a density of 1.21 g/cm³. An electron beam source of 1.5 MeV was used for the post-treating of the pressboard and the irradiation was carried out at room temperature under ambient air. The pressboard samples were placed in an open steel tray on a conveyer band which passed the electron beam scan horn with a speed of 3m/min and in 6 turns. In each turn the pressboard samples were irradiated with 25 kGy and total dose of 150 kGy was applied on the samples. Swelling measurements for the comparison of the network density in pressboard were performed on the basis of these described in "Cross-Linking-Effect on Physical Properties of Polymers" (Nielsen, L. E., Journal of Macromolecular Science, Part C, 1969, 3, 69-103). In this test, the volume change of the pressboard is measured after immersing in a solvent at a certain temperature for a certain duration. For each swelling measurement, 3 specimens per pressboard with and without irradiation treatment of approximately 25*15*2mm were cut and measured with an accuracy of 0.05mm. The specimens were immersed in lOOmL of m-cresol at 70°C for 24 hours. The specimens were removed from the solvent thereafter, shortly cooled to room temperature and the dimensions were remeasured. The increase in volume after swelling of the pressboard without irradiation treatment is about 50% and that of the pressboard with irradiation treatment is about 35%.

The 5% decomposition temperature of the untreated pressboard determined by thermogravimetry analyzer (TGA) in air atmosphere is about 323°C and that of the treated pressboard is 339 °C. The tensile strength of the untreated pressboard is about 100 MPa and that of the treated pressboard is about 115MPa; the compressibility of the untreated pressboard is about 3.5% that of the treated pressboard is about 3.1%.

Another test was carried out as described in Example except that the pressboard was irradiated with an irradiation dose of 300 kGy in air, the result showed that the properties of the treated pressboard were quite similar to those of the untreated pressboard. It is assumed that the higher irradiation dose in air could induce the higher degree of degradation of pressboard. Another test was carried out as describe in Example except that the pressboard was irradiated with an irradiation dose of 150 kGy in nitrogen atmosphere, the result showed that the properties of the treated pressboard is a little better than the properties of the treated pressboard with an irradiation dose of 150 kGy in air, we assume that the nitrogen atmosphere can avoid some competing oxidation processes during the irradiation treatment which is beneficial to the final material properties.

Example 2 A pressboard was made according to the process in Fig 1. The solid materials used in the making of this pressboard were 60 weight percent of polyethylene terephthalate fibrid (Shanghai Labon Technical Fiber Co., Ltd) and 40 weight percent of polyethylene terephthalate fiber. This pressboard had a basic weight of 1160 g/m , a thickness of 1 mm and a density of 1.16 g/cm³. An electron beam source of 1.5 MeV was used for the post-treating of the pressboard and the irradiation was carried out at room temperature under ambient air. The pressboard samples were place in an open steel tray on a conveyer band which passed the electron beam scan horn with a speed of 3m/min and in 8 turns. In each turn the pressboard samples were irradiated with 25 kGy and total dose of 200 kGy was applied on the samples. For each swelling measurement, 3 specimens per pressboard with and without irradiation treatment of approximately 25*15*lmm were cut and measured with an accuracy of 0.05mm. The specimens were immersed in lOOmL of m-cresol at 70°C for 24 hours. The specimens were removed from the solvent thereafter, shortly cooled to room temperature and the dimensions were remeasured. The increase in volume after swelling of the pressboard without irradiation treatment is about 48% and that of the pressboard with irradiation treatment is about 32%. When the specimens were immersed in lOOmL of m-cresol at 90°C for 14 hours, the increase in volume after swelling of the pressboard without irradiation treatment is about 86% and that of the pressboard with irradiation treatment is about 54%.

The 5% decomposition temperature of the untreated pressboard determined by thermogravimetry analyzer (TGA) in air atmosphere is about 360°C and that of the treated pressboard is 377 °C. The tensile strength of the untreated pressboard is about 80 MPa and that of the treated pressboard is about 90 MPa; the compressibility of the untreated pressboard is about 3.4% that of the treated pressboard is about 3.0%.

Example 3 A pressboard was made according to the process in Fig 1. The solid materials used in the making of this pressboard were 60 weight percent of polyacrylonitrile fibrid, 10 weight percent of poly (metaphenylene isophthamide) fiber (Yantai Tayho Advanced Materials Co., Ltd) and

30 weight of polyethylene naphthalate fiber. This pressboard had a basic weight of 1120 g/m , a thickness of 1 mm and a density of 1.12 g/cm³.

A gamma irradiation source of 1.5 MeV was used for the post-treating of the pressboard and the irradiation was carried out at room temperature under ambient air. The pressboard samples were placed in an open steel tray on a conveyer band which passed the gamma irradiation scan horn with a speed of 2m/min and in 8 turns. In each turn the pressboard samples were irradiated with 25 kGy and total dose of 200 kGy was applied on the samples.

For each swelling measurement, 3 specimens per pressboard with and without irradiation treatment of approximately 25*15*lmm were cut and measured with an accuracy of 0.05mm. The specimens were immersed in lOOmL of m-cresol at 70°C for 24 hours. The specimens were removed from the solvent thereafter, shortly cooled to room temperature and the dimensions were remeasured. The increase in volume after swelling of the pressboard without irradiation treatment is about 60% and that of the pressboard with irradiation treatment is about 50%. The 5% decomposition temperature of the untreated pressboard determined by thermogravimetry analyzer (TGA) in air atmosphere is about 370°C and that of the treated pressboard is 380 °C. The tensile strength of the untreated pressboard is about 100 MPa and that of the treated pressboard is about l lOMPa; the compressibility of the untreated pressboard is about 3.2% that of the treated pressboard is about 2.9%. Example 4

A pressboard was made according to the process in Fig 1. The solid materials used in the making of this pressboard were 20 weight percent of polyacrylonitrile fibrid and 80 weight percent of cellulose fiber. This pressboard had a basic weight of 1140 g/m , a thickness of 1 mm and a density of 1.14 g/cm . An electron beam source of 1.5 MeV was used for the post-treating of the pressboard and the irradiation was carried out at room temperature under ambient air. The pressboard samples were placed in an open steel tray on a conveyer band which passed the electron beam scan horn with a speed of 3m/min and in 4 turns. In each turn the pressboard samples were irradiated with 25 kGy and total dose of 100 kGy was applied on the samples. The 5% decomposition temperature of the untreated pressboard determined by

thermogravimetry analyzer (TGA) in air atmosphere is about 316°C and that of the treated pressboard is 325 °C. The tensile strength of the untreated pressboard is about 105 MPa and that of the treated pressboard is about 115MPa; the compressibility of the untreated pressboard is about 4.2% that of the treated pressboard is about 3.9%.

Claims

WHAT IS CLAIMED IS:

1. An electrical insulating composite material in the form of a paper or a pressboard, wherein the electrically insulating composite material is obtained through post-treating by irradiation treatment.

2. The electrically insulating composite material of claim 1, wherein the irradiation treatment for post-treating is electron beam irradiation treatment, gamma irradiation treatment, x-ray irradiation or combinations thereof.

3. The electrically insulating composite material of claim 1 or 2, wherein the electron beam irradiation treatment, gamma irradiation treatment and x-ray irradiation is under ambient air or with the injection of inert gas.

4. The electrically insulating composite material of any one of claims 1-3, wherein the dose for the electron beam irradiation, gamma irradiation or x-ray irradiation is from 30 kGy to 300 kGy and preferably 50 kGy to 200 kGy.

5. The electrically insulating composite material of claim 1 , wherein the electrically insulating composite material is composed of fiber and fibrid.

6. The electrically insulating composite material of claim 5, wherein the said fiber comprises at least one of the following fibers: polyethylene terephthalate fiber, polyethylene naphthalate fiber, polytrimethylene terephthalate fiber, polybutylene terephthalate fiber, polyacrylonitrile fiber, poly (metaphenylene isophthamide) fiber, poly(paraphenylene terephthalamide) fiber, polysulfonamide fiber, polyphenylene sulphide fiber, polyphenylene oxide fiber, polyethersulfone fiber, polyetheretherketone fiber, polyetherimide fiber, and cellulose fiber.

7. The electrically insulating composite material of claim 5, wherein the said fibrid comprises at least one of the following fibrids: polyacrylonitrile fibrid, polyethylene terephthalate fibrid, polyethylene naphthalate fibrid, polytrimethylene terephthalate fibrid, polybutylene terephthalate fibrid, poly (metaphenylene isophthamide) fibrid, and polysulfonamide fibrid.

8. The electrically insulating composite material of claim 5, wherein the fiber is present in an amount of 5wt to 95wt and the fibrid is present in an amount of 5wt to 95 wt , based on the total weight of the electrically insulating composite material.

9. An electrical device comprising the electrically insulating composite material according to any one of claims 1 to 8.

10. The electrical device of claim 9, wherein the said device is an electrical transformer or an electrical motor.

11. The electrical device of claim 9 or 10, wherein the electrically insulating composite material is in the form of a spacer, barrier, strip, a paper wrapped conductor or press ring for insulation.