MXPA05002636A

MXPA05002636A - High temperature paper containing aramid component.

Info

Publication number: MXPA05002636A
Application number: MXPA05002636A
Authority: MX
Inventors: Homan B Kinsley Jr
Original assignee: Fibermark Inc
Priority date: 2002-09-10
Filing date: 2003-09-10
Publication date: 2005-11-17
Also published as: AU2003270503A1; EP1558808A1; JP2006519318A; CA2498579A1; EP1558808A4; WO2004025024A1; US20040140072A1

Abstract

Provided is a paper structure comprised of cellulose pulp fiber, a polymeric binder, and an aramid component comprised of aramid fiber and/or fibrid. The paper structure can also comprise multiple layers of different composition, but at least one layer must comprise the aramid component and polymeric binder.

Description

HIGH TEMPERATURE RESISTANT PAPER CONTAINING A ARAMIDA COMPONENT FIELD OF THE INVENTION The present invention is concerned with high temperature resistant papers and in particular high temperature resistant papers comprising an aramid component. Such high temperature resistant papers may comprise a single layer or multiple layers.

BACKGROUND OF THE INVENTION A high temperature resistant E board is used in transformers and performs two functions. First, the E board provides electrical insulation. This prevents the coils in the transformer from short-circuiting. Second, the board provides mechanical strength. When there is a large passage of current through the transformer, there is a force on the layers of the coil to move the board, which is stuck to the coils. The gluing of the board to the coil prevents the various coils from being connected to the socket. Each coil acts like a solenoid and tries to move. It is the E board that prevents this plug connection. Improving the mechanical strength of the E board would help avoid problems with the coils that are connected to the plug. Having a reinforced E-board to reinforce the Ref: 162615 paper would help provide the necessary mechanical strength. However, the paper would have to be manufactured in a more efficient and effective way. There is also interest in increasing the temperature resistance of the E board for use in transformers, in such a way that a less expensive transformer could be designed. By reducing the diameters of the wires in a transformer, the coils would become smaller. Smaller coils require smaller cores and smaller metal containers. The smaller containers retain less oil and this means that less copper for the wire, steel for the cores and oil for the insulation are necessary. However, due to the thinner wire, the transformer would have more electrical resistance and would operate at a higher temperature. Thus, board E would exhibit improved thermal resistance before such a transformer would be practical. A role that exhibits such improved thermal resistance, as well as improved mechanical strength, would allow the industry to design transformers that can recognize the economic benefits and performance benefits discussed above. Thus, it is an object of the present invention to provide a paper structure exhibiting improved thermal resistance.

Still another object of the present invention is to provide a paper structure exhibiting improved mechanical strength. Still another object of the present invention is to provide a high temperature resistant paper suitable for use in transformers. These and other objects of the present invention will become apparent to those skilled in the art upon review of the following description and the claims appended hereto.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, a paper structure consisting of an aramid component is provided. The paper structure comprises a fiber and / or aramid fibride, a polymeric binder, such as polyvinyl alcohol and cellulose pulp fiber. In a preferred embodiment, the paper structure consists of two outer layers and at least one inner layer. The two outer layers preferably consist of substantially cellulose pulp fiber (wood). The inner layer consists of cellulose pulp fiber, the fiber and / or aramid fiber and a polymeric binder. In a preferred embodiment, the structure comprises at least three internal layers, all consisting of cellulose fiber pulp, the aramid component and a polymeric binder. The resulting paper structure provides a rather useful role as E-board in transformers due to its improved thermal resistance. In addition, the aramid fiber also helps to reinforce the paper to avoid problems in the plug connection of the coils.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The paper structure of the present invention is quite useful as a high temperature resistant E board. The paper exhibits improved thermal resistance as well as good mechanical strength. Good thermal resistance would allow the use of paper in a transformer with coils of smaller size since it would allow the coils to operate at a higher temperature. In addition, the paper is also reinforced in such a way that when it is stuck to the coils, it would prevent the various coils from being connected to the plug. In actual use in a transformer, the paper is coated with an adhesive such as an epoxy adhesive thermally bonded to the wire coil surface. It is attached to the coils which allows the board to prevent the various coils from being connected to the socket. The mechanical strength of the paper structure of the present invention, including its aramid component in combination with the polymeric binder, allows the board E to act efficiently and effectively while preventing the coils from being connected to the socket. The paper structure of the present invention comprises a polymeric binder, an aramid component that can be an aramid fiber, a fibride or a combination thereof, together with cellulosic pulp fiber. The aramid fiber can be any commercially available polyaramide fiber, such as that under the trademark NOMEX®. In general, the fiber is about 0.635 cm (1/4 inch) in length and has about a denier of 2. The fibrid is a small irregularly formed piece of aramid polymer that is much larger in two dimensions than in the Third dimension. It's like a microscopic shaped corn flake. The large dimensions are of the order of 5 to 25 microns, while the third and smaller dimension is approximately 0.01 to 1 micron. In the paper structure, the amount of cellulosic wood pulp fiber generally ranges from 50 to 80% by weight, while the amount of aramid component generally ranges from about 5 to 25% by weight. The amount of polymeric binder, preferably polyvinyl alcohol, generally ranges from about 10 to 25% by weight. The aramid component, from 5 to 25% by weight, can consist of only aramid fiber, aramid fiber or preferably a combination of the two. When a combination is used, it is preferable that about 60/40 wt.% Fiber / fibrate be used. When the aramid fibrid is present, the amount of polymeric binder can be reduced since the fibrid can also function as a binder for the fabric. For this reason, it is preferred that some aramid fibride be present. It performs a double function and can reduce the amount of aramid fiber and binder needed. A smaller amount of another synthetic fiber could also be present. Such a synthetic fiber can be for example a polyester or nylon fiber. The paper structure of the present invention can comprise a single layer or multiple layers. When a single layer is employed, the paper structure contains the cellulose pulp fiber, aramid component and polymeric binder as discussed above. Multiple layers of such combinations may also be employed, wherein the amounts of each component of a particular layer may change. Alternatively, a veiled structure can also be used. In such a veiled structure, the two outer layers consist of substantially wood pulp fiber, preferably without any polymeric binder, while the inner layers, either one or more comprise the pulp fiber components of cellulosic wood, component of aramid and polymeric binder. A smaller amount of synthetic fiber, such as polyester or nylon fiber, may be present in the outer cellulosic pulp fiber layers. When multiple layers are used, it is preferred to make the paper structure using a cylinder machine, as is known in the art, with at least three different cylinders. Different compositions of raw materials can be fed to each of the cylinders, which correspond to a particular layer of the paper structure. In a preferred embodiment, the paper structure consists of 5 different layers. The two outer layers consist substantially of cellulose pulp fiber, preferably wood. The three internal layers all consist of cellulose pulp fiber, aramid component and a polymeric binder. Optionally, the internal layers may be of different compositions. For example, they may contain different relative amounts of the cellulose pulp fiber, aramid component and polymeric binder, since different raw material compositions may be fed to the various corresponding cylinders to manufacture the various layers. Also, it may be desirable to have only one layer containing the aramid component and the polymeric binder. The remaining layers would then consist mainly of cellulosic pulp fibers or the relative amounts of fiber / fibride within the aramid component can be changed. In another embodiment, the paper structure comprises two outer layers consisting substantially of cellulosic pulp fiber and the inner layer consisting of the aramid component and polymeric binder. The presence of the aramid component and the polymeric binder together is important in at least one inner layer of the paper structure. The remaining layers may differ in composition, as long as the two outer layers do not contain the polymeric binder. The preferred polymeric binder is polyvinyl alcohol, but other polymeric binders such as acrylics may also be used. It can be added in the form of a synthetic fiber or as a dry powder. If the binder is added as fiber, it is important that the fiber has the appropriate chemical characteristics. Polyvinyl alcohol fiber is available with a wide range of water solubilization temperatures. The temperature at which the polymer becomes soluble depends on the properties of the polymer such as the degree of polymerization, degree of hydrolysis and crystallinity. This solubilization temperature can fluctuate from about 60 ° C to over 100 ° C. It is important to match or match this solubilization temperature with the papermaking process. To be more effective, polyvinyl alcohol fiber should behave as a binder as long as it is in fiber form. It should not be allowed to dissolve fully. The strongest bond or bond occurs when the surface of the fiber begins to dissolve. Then in the drying, the polyvinyl alcohol fiber will stick to all the other fibers, both synthetic and natural with which it is put in contact. This means that a polyvinyl alcohol fiber with a low solubilization temperature should be used with a low to medium basis weight paper (approximately 25 to 120 pounds / 3000 square feet) that is commonly run at high machine speeds. Due to the higher machine speed and lower sheet mass, evaporation will cool the paper. It will dry before it becomes very hot. It is likely that the maximum temperature that the paper reaches is less than 70 ° C. With high basis weight papers (200 pounds / 3000 square feet and higher) a polyvinyl alcohol fiber with a higher solubilization temperature can be used. These papers are commonly run at slower machine speeds in such a way that the temperature of the sheet is much higher. When the powder form of the polyvinyl alcohol binder is used, the polymer must be fully hydrolyzed (99% or higher) and the polymer must be ground to a particle size of 100 mesh or smaller. The powder can be added to the wood fiber before refining it or it can be added to the system after refining. It is important that the polymer powder is allowed to swell after it is added to the papermaking system. The swelling time depends on the temperature of the water. Cold water (0-14 ° C) requires a swelling period of approximately one hour. Warm water (40-50 ° C) will swell the particles in about 20 minutes. It is essential that the process water used either with polyvinyl alcohol fibers or powder is not at a temperature of more than 60 ° C, since the hot water will dissolve the polymer and most of the binding characteristics will be lost. It is advantageous to use a steam shower with the powder form of the polyvinyl alcohol binder. This shower will reach the paper before the dryer section. The steam shower is particularly useful with low weight basis papers. It will heat the sheet while it is still wet, allowing the exterior of the swollen polymer particles to begin to dissolve. In the preparation of the "veiled" embodiment of the present invention, a cylinder machine, as is well known in the art, can be employed and is preferably employed. The cylinder machine allows the creation of different layers using compositions of different raw materials as discussed above, thus allowing the paper structure to be adapted as necessary within the present invention. The process for manufacturing a veiled paper structure comprises feeding a raw material composition consisting substantially of wood pulp fiber to the cylinders corresponding to the outer layers. Thus, the two outer layers of the resulting paper structure substantially comprise cellulose pulp fibers, preferably wood. A smaller amount of synthetic fibers may be included in the raw material compositions. A cylinder corresponding to the inner layer is then fed with a raw material solution consisting of cellulosic pulp fiber, the selected aramid component, whether fiber, fibride or a mixture thereof and a polymeric binder. Thus, the inner layer of the paper structure consists of cellulose pulp fiber, aramid component and polymeric binder. The resulting paper structure is such that only the inner layer contains the polymeric binder, while the outer layers do not and thus potential bonding problems are avoided when the paper structure is dried, preferably in drying cans and the polymeric binder It is activated due to the high temperature. In the activation of the polymeric binder, the binder acts to bind the aramid component together with the wood pulp fiber and since it is on the inner layer it will not cause sticking problems. The paper structure of the present invention, either single-ply or multi-ply, provides a rather useful paper as a high-temperature resistant paper for transformers, the paper exhibits improved thermal resistance, as well as excellent mechanical strength to perform all the necessary functions of a transformer E board. While the invention has been described with preferred embodiments, it will be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications will be considered to be within the spirit and scope of the claims appended hereto. It is noted that, in relation to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A paper structure characterized in that it consists of cellulose pulp fiber, a polymeric binder and an aramid component consisting of an aramid fiber and / or aramid fibrida. 2. A paper structure characterized in that it comprises two outer layers and at least one inner layer, the two outer layers consist of substantially cellulosic pulp fiber and the inner layer consists of the paper structure according to claim 1. 3. The paper structure according to claim 1, characterized in that the polymeric binder consists of polyvinyl alcohol. 4. The paper structure according to claim 1, characterized in that the aramid component consists of a mixture of aramid fiber and aramid fiber. 5. The paper structure according to claim 2, characterized in that the polymeric binder consists of polyvinyl alcohol. 6. The paper structure according to claim 2, characterized in that the aramid component consists of a mixture of aramid fiber and aramid fiber. The paper structure according to claim 2, characterized in that the outer layers also comprise a smaller amount of synthetic fiber. A paper structure characterized in that it comprises two outer layers consisting of substantially cellulosic pulp fiber and at least two internal layers consisting of cellulosic pulp, a polymeric binder and an aramid component consisting of aramid fiber and / or fibrid of aramid. A process for manufacturing the paper structure according to claim 1, characterized in that it comprises using a cylinder machine with at least three different cylinders, the process comprises feeding a composition of raw material consisting substantially of cellulose pulp fiber. to the cylinders corresponding to the outer layers, such that the two outer layers of the resulting paper structure consist of substantially cellulosic pulp fibers and the other cylinder is fed with a raw material solution consisting of cellulosic pulp fiber, Aramid fiber, aramid fiber and a polymeric binder, such that the inner layer of the paper structure consists of cellulose pulp fiber, aramid fiber, aramid fiber and polymeric binder. 10. The process according to claim 9, characterized in that five cylinders are used, the cylinders correspond to the outer layers of the paper structure which is fed with raw material solutions consisting substantially of cellulose pulp fiber and the three cylinders Inmates are fed solutions consisting of cellulose pulp fiber, aramid fiber, aramid fibridate and a polymeric binder. 11. The process according to claim 9, characterized in that the polymer binder in the raw material solution fed to the cylinder corresponding to the inner layer consists of polyvinyl alcohol. 12. A high temperature resistant transformer paper characterized in that it consists of the paper structure according to claim 1. 13. A high temperature resistant transformer paper characterized in that it comprises the paper structure according to claim 2. 14 A high-temperature resistant transformer paper characterized in that it comprises the paper structure according to claim 3. 15. A transformer characterized in that it comprises the paper according to claim 1. 16. A transformer characterized in that it comprises the compliance paper. with claim 2. 17. A transformer characterized in that it comprises the paper according to claim 4. 18. A transformer characterized in that it comprises the paper according to claim 8.