Patent Application
20100000697
1. Field of the Invention
The invention relates to a dryer fabric for a condensation drying apparatus, as well as to a machine to produce and/or process web material, such as paper, cardboard or tissue, including a condensation drying apparatus.
2. Description of the Related Art
In a condensation drying apparatus of a paper machine, moisture is removed from the web material that is being produced whereby the web material is heated from one side, and cooled from the other side. Heating causes the moisture contained in the web material to evaporate. The vapor emerges from the web material and condenses outside the web material due to the cooling. In order to achieve this, the web material is in contact on one side with a very finely structured dryer fabric which is permeable to the liquid or liquid vapor emerging from the web material. On the backside of this finely structured dryer fabric which is facing away from the web material, a coarsely structured dryer fabric is provided whose primary function is the absorption or storage of the liquid vapor, or the condensed liquid. On the backside, in other words on the side of the coarsely structured dryer fabric which faces away from the finely structured dryer fabric a heat sink is provided, for example in the embodiment of a locally cooled, liquid-impermeable fabric. The other side of the web material is in contact with a heat source, for example a heated liquid-impermeable fabric or a drying cylinder which is heated in the area of its roll surface area over which the web material is carried. Generally speaking, an arrangement is therefore provided wherein three or even four fabrics are utilized. The routing of the individual fabrics in an arrangement of this type is oftentimes very expensive and therefore also often subject to malfunction.
It is further suggested in the current state of the art to use one single dryer fabric instead of a coarse and a fine structured dryer fabric, whereby for example a woven structure serves as the base structure and where the web material contact side is provided by a nonwoven fibrous structure.
Condensation drying apparatuses are oftentimes located immediately after the press section or at the beginning of the drying section. The paper or cardboard web is still relatively moist in this location and can therefore be easily formed. On the one hand this has the advantage that the side of the web that is in contact with the smooth surface area of the heated drying cylinder is glazed very well and on the other hand has the disadvantage that the structure of the dryer fabric in the form of undesirable markings or impressions are very easily embossed into the other side of the paper web, especially with graphic papers. This applies especially if additional pressure is exerted upon the web through the cooling medium via the dryer fabric which is in contact with the web.
No satisfactory results with regard to the smoothness and dry content of the paper or cardboard web that is processed in this manner are achieved when using either two dryer fabrics—that is one fine and one coarse dryer fabric—or when using one dryer fabric consisting of a woven structure and a fibrous nonwoven structure. This is especially true when producing graphic papers, since the dryer fabrics which are known from the state of the art cannot absorb sufficient water in order to increase the dry content of the paper web, or have a tendency to mark the still relatively moist and therefore susceptible web.
None of the known condensation drying apparatuses combine a sufficiently smooth web material contact side with a sufficiently high water absorption volume. Especially for the production of fine graphic papers no dryer fabrics are known with which graphic papers without markings can be produced. Even the dryer fabrics suggested in DE 10 2006 039 102 which have a fibrous nonwoven web material contact side are not suitable for the production of demanding graphic papers, for example copying paper.
The current invention provides a fabric for a condensation drying apparatus, as well as a paper or cardboard machine, including a condensation drying apparatus with which in particular graphic papers can be produced efficiently and free or markings.
According to a first aspect the invention presents a dryer fabric for a condensation drying apparatus in a machine which produces and/or processes a web material, such as paper, cardboard or tissue. The dryer fabric hereby has a base structure which essentially provides the dimensional stability of the fabric and which consists of polyester and/or PCTA and/or PCT and/or PEEK and/or PPS and/or thread material which includes PA with high temperature stability. The dryer fabric further includes a fibrous nonwoven layer located on the base structure, which essentially provides the water absorption capacity of the fabric and which provides the dryer fabric with a web material contact side on its outside, facing away from the base structure. The fibrous nonwovens layer includes a first polymer material located at least in the area of the outside. In addition the fibrous nonwovens layer is compressed and smoothed in the area of the outside which provides the web material contact side by hot-calendering above the melting temperature of the first polymer material.
The conception of the invention consists in the provision of a dryer fabric having a porous fibrous nonwovens layer which, on the one hand has a smooth and therefore mark-free web material contact side and, on the other hand has a sufficiently high water absorption capacity and which is further suitable for utilization in a condensation drying apparatus with regard to thermal stability and dimensional stability.
Because the fibrous nonwovens layer has a first polymer material at least in the area of its outside which was first melted and then again solidified through hot-calendering, that is through the effect of temperature and pressure and subsequent cooling, a dryer fabric is provided that has a web material contact surface which is smooth and hence free of markings.
Because the dryer fabric also has a fibrous nonwovens layer positioned between the base structure and the web material contact side, a dryer fabric having a sufficiently high water absorption capacity is provided.
Because the base structure providing the dimensional stability of the fabric is formed from polyester and/or PCTA and/or PCT and/or PEEK and/or PPS and/or thread material including PA with high temperature stability a dryer fabric is provided which—even at high temperature and high surrounding moisture—has a good dimensional stability in its machine direction and in its machine cross direction.
In the current example highly temperature stable polyamides are for example PA46 or PA6/6T or PA MXD6 (Para) or PA 6-T-6-I or PA 9-T.
Possible polyester materials are for example PET, PBT or PTT.
The fibrous nonwoven layer is preferably formed completely by the first polymer material.
In this instance it is for example conceivable that the fibrous nonwoven layer with the smoothed and compressed outside was produced whereby an untreated fibrous nonwoven fabric consisting of fibers from the first polymer material was provided which was hot-calendered in the area of an outside at a temperature above the melting temperature of the first polymer material, and was subsequently cooled to a temperature below the melting point of the first polymer material. Hereby at least the fibers located in the area of the outside were melted at least partially and were partially reshaped and/or conglutinated due to the influence of pressure, thereby producing a compressed and smoothed outside of the nonwoven fibrous layer.
An additional embodiment of the invention also provides that the nonwoven fibrous layer is formed by the first polymer material and at least a second polymer material with a higher melting temperature than the first polymer material and that in the area of the outside which represents the web material contact side, the nonwoven fibrous layer is compressed and smoothed through hot-calendering above the melting temperature of the first polymer material and below the melting temperature of the at least one second polymer material.
It is especially conceivable in this context that the at least one second polymer material is in the form of fibers.
In this instance the first polymer material and the second fibrous polymer material are blended with each other during hot calendering, at least in the area of the outside representing the web material contact side. This means that in the area of the outside of the fibrous nonwoven layer, fibers formed from the second polymer material are embedded at least in sections into the first polymer material and are conglutinated and/or bonded with each other by way of same, after solidification of the first polymer material. In this case accordingly, the first polymer material and the second fibrous polymer material form a porous composite structure, at least in the area of the outside providing the web material contact side.
In the case of the aforementioned fibrous nonwoven layers their porosity increases preferably from the outside representing the web material contact side, in direction of the base structure, whereby the dryer fabric preferably has a water absorption capacity of 100-150 kg per hour per m2 in order to be able to function optimally as dryer fabric in a condensation drying apparatus. The dryer fabric is water and water vapor permeable and has a permeability of preferably 1 to 200 cfm, especially preferred of 10 to 95 cfm.
Especially in the production of graphic papers it is advantageous if the outside of the dryer fabric which provides the web material contact side has a coarseness RZ of less than 2.4 μm. In the manufacture of the inventive fabric coarseness RZ in the range of 0.1 μm to 20 μm, especially 0.6 μm to 6 μm according to DIN EN ISO 4287, DIN EN ISO 4288 is generally achieved. The last mentioned coarseness can be achieved especially easily when the outside of the fibrous nonwovens layer is cooled to below the melting temperature of the polymer of the filler material, while the outside is carried under pressure over a smooth surface.
The second polymer material is preferred in the form of fibers in the fibrous nonwovens layer, whereby the first polymer material prior to its being melted is present in particle form, and is located especially between the fibrous material. It is conceivable here, that the particle shaped filler material is supplied into the fibrous nonwoven material in the area of the outside of the fibrous nonwoven material and is subsequently melted during hot-calendering, whereby the higher melting polymer fibers are embedded into the first polymer material in the area of the outside of the nonwovens layer and are conglutinated with it.
In addition it is conceivable that the fibrous nonwoven layer is formed by a fiber blend, whereby a part of the fibers consist of the first polymer material and another part of the fibers consist of the second polymer material.
An additional embodiment of the invention provides that the fibrous nonwoven layer includes Bi-component fibers or consists of these, whereby prior to hot-calendering the first polymer material exists as one component and the second polymer material as second component of the BI-component fibers.
In this context it is for example conceivable that the fibrous nonwoven layer was produced with the smoothed and compressed outside whereby an untreated fibrous nonwoven fabric was provided which includes Bi-component fibers at least on its outside that provides the web material contact side, or which consists entirely of the Bi-component fibers. Here, the first component of the Bi-component fibers is formed by the first polymer, as the second component of the Bi-component fibers is formed by the second polymer. To produce the fibrous nonwoven layer with the compressed and smoothed outside the untreated fibrous nonwoven material is hot-calendered at a temperature above the melting point of the first polymer material and below that of the second polymer material, and is subsequently cooled to a temperature below the melting temperature of the first polymer material 7. In this way a smoothed and porous composite structure is formed from the second fibrous poly material and the first polymer material in the outside area whereby the polymer fibers are embedded, at least in sections into the first polymer material. Subject to the temperature utilized during hot-calendering and the reaction time during hot-calendering an area is created between the outside and the base structure which is formed by the Bi-component fibers which are not melted.
The Bi-component fibers may for example exist as core-cover fibers or as side-side fibers. In the case of the cover-core fibers the first polymer material preferably forms the cover and the second polymer material preferably the core.
The first polymer material may be a thermoplast, especially a co-polyamide. The co-polyamide may be composed from at least two different monomers from the group caprolactam, lauriclactam, dicarbon acids with 4-12 C-atoms, terephthalic acid, isophthalic acid, dimeric acid with C-atoms, linear alpha-omega-diamines with 2-12 C-atoms and 2-methylpentamethylendiamine.
The aforementioned first polymers have a melting temperature, for example of 110° C. or higher.
The first polymer may however also be a duromer melamine resin, which may be in the form, for example, of a nonwoven structure or part of such a structure.
Because of its characteristic—for example a very high disintegration temperature of approx. 400° C. or higher, a very good dimensional stability under increased temperature, a “non-combustibility”, a very good chemical stability—melamine resin is very suitable for utilization in a dryer fabric for a condensation drying apparatus in a web material producing and/or processing machine.
Such a nonwoven structure consisting of, or containing melamine resin can be produced for example through a melt-spinning process with subsequent cross linkage, whereby for example filament diameters in the range of 1-18 μm and surface dimensions of the nonwoven material in the range of 35-250 g/m2 can be produced without problems. Therefore, there are practically no limits in the formation of the nonwoven structure.
A nonwoven structure containing melamine resin can be bonded with other textile layers without problem by known textile bonding processes, for example needle bonding.
Furthermore, the second polymer material may be a thermoplast, especially a polyamide. The polyamide may be from the group polyamide 6, polyamide 46, polyamide 66, polyamide 12, polyamide 11, polyamide 6T/66, polyamide 6T/6, polyamide 6T/61 or polyamide 12T.
In this context it must be noted that subject to the calendering temperature, the reaction time during calendering and the force of the pressure effect during calendering the first polymer material is more or less substantially melted and reshaped, thereby allowing targeted adjustment of the compression and smoothness of the fibrous nonwoven layer in the area of its outside which represents the web material contact side.
One possible embodiment of the invention provides that the outside is carried over a heated smooth surface during hot-calendering.
To increase the smoothness of the outside of the fibrous nonwoven layer which provides the web material contact side it can also be advantageous if, during cooling from a temperature above the melting temperature to a temperature below the melting temperature of the first polymer material, the outside is carried under pressure over a smooth surface. The topography of the outside of the fibrous nonwoven layer is hereby fixed in the condition it was while being carried over the cooling surface, whereby the smoothness of the outside of the material layer is determined or at least substantially influenced by the smoothness of the surface during cooling.
The base structure may be composed of a woven structure, a laid thread structure, or knitted fabric structure.
It is conceivable that between the fibrous nonwoven layer which provides the web material contact side and the base structure at least one fibrous nonwoven layer is arranged whose fiber forming polymer material has a higher melting temperature than the first polymer material.
In addition it is possible that on the side of the base structure facing away from the web material contact side at least one fibrous nonwoven layer is arranged whose fiber forming polymer material has a higher melting temperature than the first polymer material and whose other outside which faces away from the base structure provides a machine contact side of the dryer fabric.
According to a second aspect of the invention a machine is suggested for the production and/or processing of web material, such as paper, cardboard or tissue, including a condensation drying apparatus with at least one heatable drying cylinder whose surface area in the area of a contact is wrapped by the web material, one dryer fabric, as well as by a water and steam impermeable sealing belt, and including a cooling medium whose temperature is lower than the temperature of the surface area of the drying cylinder, whereby in the area of contact one side of the web material is in contact with the surface area of the drying cylinder and the other side of the web material is in contact with the web material contact side of the dryer fabric, while the machine contact side of the dryer fabric is in contact with one side of the sealing belt whose other side is treated with the cooling medium.
In the inventive machine a pressure hood which is open toward the sealing belt is advantageously arranged over the sealing belt which, in interaction with the sealing belt provides an enclosed chamber in which the especially pressurized cooling medium is located.
By this way the web material can be treated with pressure via the sealing belt, whereby the pressurized cooling medium exerts pressure upon the web material.
The cooling medium may be a liquid or a gas. A liquid-gas mixture is also conceivable as a cooling medium.
The inventive dryer fabric is utilized especially advantageously in the condensation drying apparatus if the web material runs into the condensation drying apparatus at a dry content in the range of 50-80%, since the paper is still easily formable and therefore susceptible to markings caused by the clothing in this dry content range.
Preferably, the web material running through the condensation drying apparatus especially at the aforementioned dry content is not only dried in this apparatus, but also glazed.
It is conceivable that the condensation drying apparatus viewed in direction of web travel is located after the press section and before the first conventional dryer group of the drying section, whereby especially the web material is fed into the condensation drying apparatus at a dry content of approx. 50-60%. It is also conceivable that the condensation drying apparatus viewed in direction of web travel is located after the first conventional dryer group of the drying section, whereby especially the web material is fed into the condensation drying apparatus at a dry content of approx. 70-80%.
In order to achieve a uniform smoothness of the paper or cardboard web on both sides a preferred embodiment of the invention provides that the condensation drying apparatus viewed in direction of web travel includes a second heatable drying cylinder located after the first heatable drying cylinder whose surface in a contact area is wrapped by the web material, a second dryer fabric which is designed as a felt covered drying wire as well as by a second water and steam impermeable sealing belt; and a cooling medium whose temperature is less than the temperature of the surface area of the second drying cylinder whereby in the contact area the other side of the web material is in contact with the surface area of the second drying cylinder and the one side of the web material is in contact with the web material contact side of the second dryer fabric or respectively with one side of the felt covered drying wire, while the machine contact side of the second dryer fabric is in contact with one side of the second sealing belt whose other side is treated with the cooling medium.
Since the paper or cardboard web in some cases is clearly less susceptible to marking already after running around the first drying cylinder, than was the case prior to running around the first drying cylinder it is no longer necessary in some configurations, depending upon the paper quality, to use an inventive dryer fabric as the dryer fabric which is carried over the second drying cylinder. Instead, a felt covered drying wire may for example be utilized.
In the currently known condensation drying apparatus a metal belt is often used as the sealing belt. However, other water and steam impermeable belts with sufficiently good heat conductivity, for example polymer belts with metal particles can also conceivably be used.
The web material is preferable a graphic paper, especially copy paper or news print.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
In the current example the first polymer material 7 is a thermoplast, especially a co-polyamide. In the current example the second polymer material 8 is a thermoplast, especially a polyamide.
In the current example the first and the second polymer materials 7, 8 are arranged throughout the entire fibrous nonwoven layer 5. In the outside area 6 which represents the web material contact side, the nonwoven fibrous layer 5 is compressed and smoothed through hot-calendering at a temperature higher than the melting temperature of the first polymer material 7 and below the melting temperature of the second polymer material 8.
In actual terms this means that the fibrous nonwoven layer 5 with the smoothed and compressed outside 6 was produced in that an untreated nonwoven fabric was provided which is formed by Bi-component fibers 9 in which a first component—for example the cover 10—is formed by the first polymer and a second component—for example the core 11—of the Bi-component fibers 9 is formed by the second polymer material 8. This untreated fibrous nonwoven fabric was hot-calendered at a temperature higher than the melting temperature of the first and lower than the melting temperature of the second polymer material. This means that the first polymer material was melted, the second polymer material was not melted and subsequently reduced to a temperature below the melting temperature of the first polymer material 7.
In the fibrous nonwoven layer 5 produced according to the process described above, the first polymer material 7 forms a discontinuous polymer layer 13, at least in the area of the outside 6, into which the second polymer material 8 which exists in the form of fibers 12 is embedded, at least in sections. In an area where the first polymer material 7 was not melted, the first and the second polymer material 7, 8 still exist as Bi-component fibers 9.
Alternatively to the embodiment illustrated in
In the existing example, the porosity of the fibrous nonwoven layer 5 increases from the outside 6 which provides the web material contact side in the direction of the base structure 2.
In the current example the first polymer material 7 is a thermoplast, especially a co-polyamide.
In the outside area 106 which represents the web material contact side, the nonwoven fibrous layer 105 is compressed and smoothed through hot-calendering at a temperature higher than the melting temperature of the first polymer material 107.
In actual terms this means that the fibrous nonwoven layer 105 with the smoothed and compressed outside 106 was produced whereby an untreated nonwoven fabric was provided which is formed by fibers 109 from the first polymer material 107. This untreated fibrous nonwoven fabric was hot-calendered at a temperature higher than the melting temperature of the first polymer material 107. This means that the first polymer material 107 was melted, at least in the area of the outside 106, and subsequently cooled to a temperature below the melting temperature of the first polymer material 7. The first polymer material is thereby melted, at least in the area of the outside 106 and reshaped, at least partially, from a thread-type material 109 to a discontinuous polymer layer 113.
In the fibrous nonwoven layer 105 produced according to the process described above, the first polymer material 107 forms a discontinuous polymer layer 113, at least in the area of the outside 106. In an area where the first polymer material 107 was not melted, the first polymer material 107 still exists in the form of fibers 109.
The dryer fabrics 1, 101 shown in
The coarseness RZ of the web material contact side 6, 106 of the dryer fabrics 1, 101 shown in
The condensation drying apparatus 30 includes at least one heatable drying cylinder 31 whose surface area 32 in a contact area B-C is wrapped by the web material, for example paper 33, one dryer fabric 1, 103 as described in
The condensation drying apparatus 30 further includes a cooling medium 35 whose temperature is lower than the temperature of the surface area 32 of the drying cylinder 31.
In the contact area B-C one side of the web material 33 is in direct contact with the surface area 32 of the drying cylinder 31 and the other side of the web material 33 is in direct contact with the web material contact side 6, 106 of the dryer fabric 1, 101, while the machine contact side of the dryer fabric 1, 101 is in direct contact with one side of the sealing belt 34 whose other side is treated with the cooling medium 35. Hereby the web material 33 is heated on the one hand, resulting in liquid from the web material 33 to evaporate and getting into the dryer fabric 1, 101. On the other hand, the sealing belt 34 is cooled by the cooling medium 35.
Through heating of the web material 33 by way of the direct contact to the surface area 32 of the heated drying cylinder 3Ion the one hand, and the cooling on the other side on the other hand, liquid contained in the web material 33 is evaporated and absorbed in the dryer fabric 1, 101. Due to the contact of the dryer fabric 1, 101 with the side of the sealing belt 34 which is cooled by way of the cooling medium 35 the liquid vapor condenses in this boundary area between the dryer fabric 1, 101 and the sealing belt 34 so that it can be removed from the web material 33, and said web material exits the condensation drying apparatus 30 with a clearly reduced moisture content.
As can be seen from the depiction in
In the current example the condensation drying apparatus 30 is located in a location in the machine where the web material 33 runs into the condensation drying apparatus 30 at a dry content in the range of 50-80%. Due to the pressure treatment and influence of heat in the condensation drying apparatus 30, the web material 33 is dried and glazed in the condensation drying apparatus 30.
It is for example conceivable that the condensation apparatus 30 is located after the press section, viewed in direction of web travel L, whereby the web material 33 is fed into the condensation drying apparatus 30 particularly at a dry content of approximately 50-60%.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 040 065.3 | Jul 2008 | DE | national |
| 10 2009 001 259.1 | Mar 2009 | DE | national |
